meccanismo secrezione insulina

[**ACHILLES**82**]

Achilles, i muscoli si fanno in palestra, non all'universita'.Mi raccomando eh?

tu hai gli occhi della tigre io ho gli occhi di un oni quando mi alleno..........l oni è un demone giapponese...........ho piu palle in palestra io che 200 iscritti a questo forum........questo però è stato un male..........
mannaggia a mentzer eheh

[**ACHILLES**82**]

....senza insulina nn assimili?....il corpo nn è stupido...gli aminoacidi alzano l'insulina e questo basta per il loro uptake e sintesi proteica (insulina senza aminoacidi= no sintesi proteica solo inibizione della proteolisi )...
..i ketoni e quindi indirettamente i grassi alzano l'insulina, questo è essenziale per evitare l'acidosi metabolica diabetica...

mangi solo protidi e grassi? assimili ciò che dvi assimilare...se devi riparare tessuti,aumenterà il ricambio proteico...se la glicemia è bassa aumenterà la Guconeogenesi dagli amino e/o glicerolo...e così via....
..i ragionamenti rendiamoli semplici, altrimenti arriveremo a conclusioni irreali come quella che hai fatto prima :"Senza insulina è dura che i nutrienti passino nei tessuti volevo quindi capire se pasti solo proteici bastano a produrre insulina quanto per farsi assimilare nei tessuti muscolari"

Allora ho letto che alcuni aminoacidi in particolare i ramificati stimolano l insulina !

Cio che chiedo io è se in momenti come è il post allenamento o la mattina mangiando solo proteine magari 40-50 grammi è possibile assimilarle e attraverso la gluconeogenesi ristoccare anche le riserve di glicogeno ?

Se i soli aminoacidi permettono rilascio di insulina e lo stoccaggio del glicogeno sia epatico che musccolare sono a posto ! dato che cosi la sintesi proteica puo avere atto !

Ho sentito anche parlare di un effetto alba che consiste in un innalzamento della glicemia al mattino dovuto alle ore di digiuno........se questo fosse vero sarebbe una stronzata mangiare carbo al mattino.......

thanks scusate l approssimazione tecnica ma da veri esperti penso che saprete decriptarmi il problema a un linguaggio piu vicino al mio

[marco78]

Allora ho letto che alcuni aminoacidi in particolare i ramificati stimolano l insulina !

Cio che chiedo io è se in momenti come è il post allenamento o la mattina mangiando solo proteine magari 40-50 grammi è possibile assimilarle e attraverso la gluconeogenesi ristoccare anche le riserve di glicogeno ?

Se i soli aminoacidi permettono rilascio di insulina e lo stoccaggio del glicogeno sia epatico che musccolare sono a posto ! dato che cosi la sintesi proteica puo avere atto !

Ho sentito anche parlare di un effetto alba che consiste in un innalzamento della glicemia al mattino dovuto alle ore di digiuno........se questo fosse vero sarebbe una stronzata mangiare carbo al mattino.......

thanks scusate l approssimazione tecnica ma da veri esperti penso che saprete decriptarmi il problema a un linguaggio piu vicino al mio

Ti ho scritto che nel primo post che la leucina ha la capacità di innalzare l'insulina (ed è uno dei tre BCAA).

Se le proteine sono in eccesso rispetto ai tuoi bisogni attuali vengono trasformate in glucosio e/o acidi grassi. Quindi cambia poco.

Mi spiace ma l'insulina è uno degli ormoni più anabolici che esistano... senza, aumentare di peso è difficile per alcuni soggetti. Poi che anche chi cresce anche solo respirando.

[max_power]

Mi spiace ma l'insulina è uno degli ormoni più anabolici che esistano... senza, aumentare di peso è difficile per alcuni soggetti. Poi che anche chi cresce anche solo respirando.

A me non dispiace

[Christian Troy]

parlando di insulina e dei suoi benefici secondo voi è troppo sbilanciato il mio prenanna?
25gr effettivi di pro (60% caseina 40% siero) + 10gr lecitina di soia...
secondo voi dovrei aggiungervi una piccola porzione di carbo? tipo 250ml di latte di soia (3,3gr carbo per 100gr, di cui 2,8 zuccheri), oppure meglio latte ps hd? o sono inutili i carbo nel pre-nanna?

[ct-7b]

Ti ho scritto che nel primo post che la leucina ha la capacità di innalzare l'insulina (ed è uno dei tre BCAA).

Se le proteine sono in eccesso rispetto ai tuoi bisogni attuali vengono trasformate in glucosio e/o acidi grassi. Quindi cambia poco.

Mi spiace ma l'insulina è uno degli ormoni più anabolici che esistano... senza, aumentare di peso è difficile per alcuni soggetti. Poi che anche chi cresce anche solo respirando.

1: Am J Physiol Endocrinol Metab. 2006 May 16; [Epub ahead of print] Links
Mechanism of Insulin's Anabolic Effect on Muscle - Measurements of Muscle Protein Synthesis and Breakdown Using Aminoacyl tRNA and Other Surrogate Measures.Chow LS, Albright RC, Bigelow ML, Toffolo G, Cobelli C, Nair KS.
Division of Endocrinology, Nutrition and Metabolism, Mayo Clinic College of Medicine, Rochester, Minnesota, United States.

Despite being an anabolic hormone in skeletal muscle, insulin's anti-catabolic mechanism in humans remains controversial with contradictory reports showing either stimulation protein synthesis (PS) or inhibition protein breakdown (PB) by insulin. Earlier measurements of muscle PS and PB in humans have relied on different surrogate measures of amino acyl tRNA and intracellular pool. We report insulin's effect on muscle protein turnover using amino acyl-tRNA as the precursor of PS and PB is calculated by mass balance of tracee amino acid (AA). We compared the results calculated from various surrogate measures. To determine the physiological role of insulin on muscle protein metabolism we infused tracers of leucine and phenylalanine into 18 healthy subjects and after a three hours, 10 subjects received a four hour femoral arterial infusion of insulin (0.125 mU/kg/min) while eight subjects continued with saline. Tracer to tracee ratios of leucine, phenylalanine and ketoisocaproate were measured in the arterial and venous plasma, muscle tissue fluid and AA-tRNA to calculate muscle PB and PS. Insulin infusion, unlike saline, significantly reduced the efflux of leucine and phenylalanine from muscle bed based on various surrogate measures which agreed with those based on leucyl-tRNA (-28%) indicating a reduction in muscle PB (P<0.02) without any significant effect on muscle PS. In conclusion, using amino-acyl tRNA as the precursor pool, it is demonstrated that in healthy humans in the postabsorptive state, insulin does not stimulate muscle protein synthesis and confirmed that insulin achieves muscle protein anabolism by inhibition of muscle protein breakdown.

PMID: 16705065 [PubMed - as supplied by publisher]


Exercise Effects on Muscle Insulin Signaling and Action
Invited Review: Role of insulin in translational control of protein synthesis in skeletal muscle by amino acids or exercise
Scot R. Kimball1, Peter A. Farrell2, and Leonard S. Jefferson1

1 Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey 17033; and 2 Noll Physiology Research Center, The Pennsylvania State University, University Park, Pennsylvania 16802

Protein synthesis in skeletal muscle is modulated in response to a variety of stimuli. Two stimuli receiving a great deal of recent attention are increased amino acid availability and exercise. Both of these effectors stimulate protein synthesis in part through activation of translation initiation. However, the full response of translation initiation and protein synthesis to either effector is not observed in the absence of a minimal concentration of insulin. The combination of insulin and either increased amino acid availability or endurance exercise stimulates translation initiation and protein synthesis in part through activation of the ribosomal protein S6 protein kinase S6K1 as well as through enhanced association of eukaryotic initiation factor eIF4G with eIF4E, an event that promotes binding of mRNA to the ribosome. In contrast, insulin in combination with resistance exercise stimulates translation initiation and protein synthesis through enhanced activity of a guanine nucleotide exchange protein referred to as eIF2B. In both cases, the amount of insulin required for the effects is low, and a concentration of the hormone that approximates that observed in fasting animals is sufficient for maximal stimulation. This review summarizes the results of a number of recent studies that have helped to establish our present understanding of the interactions of insulin, amino acids, and exercise in the regulation of protein synthesis in skeletal muscle.


Bird SP, Tarpenning KM, Marino FE.
Eur J Appl Physiol. 2006 May;97(2):225-38. Epub 2006 Mar 24.

Independent and combined effects of liquid carbohydrate/essential amino acid ingestion on hormonal and muscular adaptations following resistance training in untrained men.

This investigation examined chronic alteration of the acute hormonal response associated with liquid carbohydrate (CHO) and/or essential amino acid (EAA) ingestion on hormonal and muscular adaptations following resistance training. Thirty-two untrained young men performed 12 weeks of resistance training twice a week, consuming ~675 ml of either, a 6% CHO solution, 6 g EAA mixture, combined CHO + EAA supplement or placebo (PLA). Blood samples were obtained pre- and post-exercise (week 0, 4, 8, and 12), for determination of glucose, insulin, and cortisol. 3-Methylhistidine
excretion and muscle fibre cross-sectional area (fCSA) were determined pre- and post-training. Post-exercise cortisol increased (P<0.05) during each training phase for PLA. No change was displayed by EAA; CHO and CHO + EAA demonstrated post-exercise decreases (P<0.05). All groups displayed reduced pre-exercise cortisol at week 12 compared to week 0 (P<0.05). Post-exercise insulin concentrations showed no change for PLA; increases were observed for the treatment groups (P<0.05), which remained greater for CHO and CHO + EAA (P<0.001) than PLA. EAA and CHO ingestion attenuated 3-methylhistidine excretion 48 h following the exercise bout. CHO + EAA resulted in a 26% decrease (P<0.01), while PLA displayed a 52% increase (P<0.01). fCSA increased across groups for type I, IIa, and IIb fibres (P<0.05), with CHO + EAA displaying the greatest gains in fCSA relative to PLA (P<0.05). These data indicate that CHO + EAA ingestion enhances muscle anabolism following resistance training to a greater extent than either CHO or EAA consumed independently. The synergistic effect of CHO + EAA ingestion maximises the anabolic response presumably by attenuating the post-exercise rise in protein degradation.


Tu affermi che l'insulina sia anabolica....io ti dico che l'insulina è solamente anticatabolica e senza 2 fattori fondamentali, forse 3, nn avremo alcuna neosintesi proteica....i 3 fattori sono:
1)stimolo esterno alla riparazione/crescita tissutale
2)disponibilità di aminoacidi essenziali
3)favorevole quadro ormonale

nel secondo studio si fa menzione che il livello di insulina per ottenere una "corretta" sintesi proteica in rapporto allo stimolo nn serve che sia alto......quindi lasciamo stare la fissa dei carboidrati ad alto IG e GL nel post wo....
...nn facciamo altro che dare un bel pò di nutrimento all'adipe, specialmente se siamo in ipercalorica....

[ct-7b]

Allora ho letto che alcuni aminoacidi in particolare i ramificati stimolano l insulina !

Cio che chiedo io è se in momenti come è il post allenamento o la mattina mangiando solo proteine magari 40-50 grammi è possibile assimilarle e attraverso la gluconeogenesi ristoccare anche le riserve di glicogeno ?

Se i soli aminoacidi permettono rilascio di insulina e lo stoccaggio del glicogeno sia epatico che musccolare sono a posto ! dato che cosi la sintesi proteica puo avere atto !

..no...gli aminoacidi nn alzano la glicemia...via GNG si va a stoccare glicogeno prevalentemente nell'epatocito...la glicemia si alza o cmqw torna nella norma in seguito allo stimolo del glucagone...
...le proteine aumentano la tolleranza al glucosio, ciò sta a significare che tendono ad abbassare la glicemia aumentando il rilascio di insulina....un bene per i diabetici, un male per gli atleti....il ruilascio di glucagone avviene in seguito per riportare la glicemia stabile...
....per ricaricare le riserve muscolari di glicogeno dovresti assumere quantitativi spropositati di proteine poichè la conversione dei ketoacidi in glucosio richiede abbastanza energia...e ti ripeto, le proteine nn alzano la glicemia...
...ciò che cmq tu affermi è errato, nn hai bisogno del glicogeno per avviare la sintesi proteica, ti serve solo che la proteolisi sia inibita...ciò lo puoi ottenere in 4 modi:
1)assunzione di una buona quantità di cho insieme ai protidi
2)assunzione di una buona quantità di grassi insieme ai protidi
3)un connubio dei primi 2 punti.
4)assunzione di una grande quantità di proteine per far si che la glicemia venga riportata nella norma dal metabolismo delle sole proteine esogene...

[marco78]

Effect of insulin and plasma amino acid concentrations on leucine metabolism in man. Role of substrate availability on estimates of whole body protein synthesis.

Castellino P, Luzi L, Simonson DC, Haymond M, DeFronzo RA.

Division of Endocrinology/Diabetes, Yale University School of Medicine, New Haven, Connecticut 06510.

We examined the effect of insulin and plasma amino acid concentrations on leucine kinetics in 15 healthy volunteers (age 22 +/- 2 yr) using the euglycemic insulin clamp technique and an infusion of [1-14C]leucine. Four different experimental conditions were examined: (a) study one, high insulin with reduced plasma amino acid concentrations; (b) study two, high insulin with maintenance of basal plasma amino acid concentrations; (c) study three, high insulin with elevated plasma amino acid concentrations; and (d) study four, basal insulin with elevated plasma amino acid concentrations. Data were analyzed using both the plasma leucine and alpha-ketoisocaproate (the alpha-ketoacid of leucine) specific activities. In study one total leucine flux, leucine oxidation, and nonoxidative leucine disposal (an index of whole body protein synthesis) all decreased (P less than 0.01) regardless of the isotope model utilized. In study two leucine flux did not change, while leucine oxidation increased (P less than 0.01) and nonoxidative leucine disposal was maintained at the basal rate; endogenous leucine flux (an index of whole body protein degradation) decreased (P less than 0.01). In study three total leucine flux, leucine oxidation, and nonoxidative leucine disposal all increased significantly (P less than 0.01). In study four total leucine flux, leucine oxidation, and nonoxidative leucine disposal all increased (P less than 0.001), while endogenous leucine flux decreased (P less than 0.001). We conclude that: (a) hyperinsulinemia alone decreases plasma leucine concentration and inhibits endogenous leucine flux (protein breakdown), leucine oxidation, and nonoxidative leucine disposal (protein synthesis); (b) hyperaminoacidemia, whether in combination with hyperinsulinemia or with maintained basal insulin levels decreases endogenous leucine flux and stimulates both leucine oxidation and nonoxidative leucine disposal.

Differential effects of hyperinsulinemia and hyperaminoacidemia on leucine-carbon metabolism in vivo. Evidence for distinct mechanisms in regulation of net amino acid deposition.

Tessari P, Inchiostro S, Biolo G, Trevisan R, Fantin G, Marescotti MC, Iori E, Tiengo A, Crepaldi G.

The effects of physiologic hyperinsulinemia and hyperaminoacidemia, alone or in combination, on leucine kinetics in vivo were studied in postabsorptive healthy subjects with primed-constant infusions of L-[4,5-3H]leucine and [1-14C]alpha-ketoisocaproate (KIC) under euglycemic conditions. Hyperinsulinemia (approximately 100 microU/ml) decreased (P less than 0.05 vs. baseline) steady state Leucine + KIC rates of appearance (Ra) from proteolysis, KIC (approximately leucine-carbon) oxidation, and nonoxidized leucine-carbon flux (leucine----protein). Hyperaminoacidemia (plasma leucine, 210 mumol/liter), with either basal hormone replacement or combined to hyperinsulinemia, resulted in comparable increases in leucine + KIC Ra, KIC oxidation, and leucine----protein (P less than 0.05 vs. baseline). However, endogenous leucine + KIC Ra was suppressed only with the combined infusion. Therefore, on the basis of leucine kinetic data, hyperinsulinemia and hyperaminoacidemia stimulated net protein anabolism in vivo by different mechanisms. Hyperinsulinemia decreased proteolysis but did not stimulate leucine----protein. Hyperaminoacidemia per se stimulated leucine----protein but did not suppress endogenous proteolysis. When combined, they had a cumulative effect on net leucine deposition into body protein.



Allora Antò, come vedi anche dagli studi postati, l'insulina stimolerebbe anche la sintesi proteica (anche se nel secondo si capisce poco).

Ma cmq anche se avesse SOLO un'azione di bloccare la proteolisi, la sua azione sarebbe cmq anabolica. Perchè anabolismo può derivare anche da una sintesi uguale e da minore catabolismo.

E poi cmq qualunque libro di biochimica apri si capisce che l'attività della gran parte degli enzimi è modificata tramite la fosforilazione, dal rapporto glucagone/insulina, naturalmente si parla anche degli enzimi lipogenetici, perciò sono dell'opinione che se si aumentano i muscoli aumenta anche il grasso assieme.

Per non parlare poi dell'azione che l'insulina esercita sull'IGF1...

[marco78]

Achille cmq ho trovato nei meandri del pc questo articolo.... penso che ti sia utile.

Understanding Insulin

by Eric Cressey


All too often, we overlook the important underlying anatomy and physiology upon which solid training and nutrition recommendations are based. In rushing to get to the "meat and potatoes" (the program or ultimate recommendations) of an article, we fail to truly question and understand the basis for why we do what we do. Take, for example, post-workout nutrition. Ever wonder why you can suck up ridiculous amounts of high-carb foods after you train? In the Rugged mission statement, we promised to make you think; the following article should do just that. And, if it doesn't, you can at least gain an appreciation for one facet of an Exercise Science graduate student's course of study. Without further ado, I present "the insulin response to exercise: carbohydrate, fat, and protein metabolism implications."

Introduction

Insulin is well recognized as a powerful hormone capable of diverse metabolic effects in a variety of scenarios. Perhaps the most noteworthy of these scenarios is exercise, the stress of which presents significant metabolic demands. The response of insulin to these demands has far-reaching implications in terms of carbohydrate, fat, and protein metabolism.

Insulin: Broad Roles in Carbohydrate, Fat, and Protein Metabolism
Insulin exerts its most pronounced effects on carbohydrate metabolism at the skeletal muscle and hepatic levels. The hormone facilitates uptake of glucose into skeletal muscle and the liver, thus promoting glycogenesis. Simultaneously, it inhibits hepatic glucose release (glycogenolysis) and production (gluconeogenesis) (1). Insulin appears to demonstrate its most immediate and powerful influence in suppressing glycogenolysis, as more insulin is required to inhibit gluconeogenesis than glycogenolysis in non-diabetic subjects (2).
Insulin also plays crucial roles in fat metabolism, regulating both lipolysis and lipogenesis. Lipolysis, the hydrolysis of triglycerides, is a requisite step in fat oxidation, as it liberates fatty acids for transport to mitochondria for oxidation (3). Numerous studies have demonstrated that insulin markedly blunts lipolysis at rest (3-5). Likewise, via facilitation of glucose uptake in liver and adipose tissue, insulin stimulates lipogenesis as well. Glycolytic conversion of glucose to acetyl-CoA is the precursor to fatty acid synthesis (1,6).
In terms of protein metabolism, insulin's foremost role is inhibition of protein breakdown. Although the hormone does play a role in promoting protein synthesis, this effect is largely dependent on amino acid availability (7-9). Some studies have noted that insulin elevations without concurrent increases in amino acid availability actually decrease protein synthesis as a result of low plasma amino acid concentrations (10,11). Conversely, dietary amino acids exert their most prominent effect on optimizing protein synthesis rather than reducing protein breakdown (7,8,12).



Hormonal Regulation of Blood Glucose: Carbohydrate, Fat, and Protein Metabolism
Maintenance of plasma glucose concentrations is of paramount importance to optimal functioning of muscles and the central nervous system. Blood glucose regulation involves interactions of carbohydrate, fat, and protein metabolism; these interactions are even more readily apparent during exercise. While insulin is certainly a powerful modulator of plasma glucose levels, one must also consider several other hormones that exert the opposite physiological effects as insulin. Knowledge of these hormones - glucagon, growth hormone, cortisol, and the catecholamines epinephrine and norepinephrine - is an important prerequisite to comprehending the insulin response to exercise.

Glucagon responds to the same stimuli as insulin, but has the exact opposite effects on blood glucose concentrations. These effects are, on the whole, catabolic and anti-anabolic. They include stimulation of glycogenolysis, gluconeogenesis, and protein degradation with concurrent inhibition of protein synthesis (13,14). Some studies have noted that glucagon has a stimulatory effect on lipolysis in human adipose tissue in vitro, and pharmacological interventions to induce dramatic hyperglucagonemia have proven sufficient to stimulate lipolysis (15-17). However, there is insufficient evidence to suggest that normal human hyperglucagonemia can directly induce lipolysis in vivo (18,19). While hypoglycemia is the most potent stimuli for glucagon release from the pancreas, high concentrations of insulin during hypoglycemia can suppress the glucagon response (20).

Growth hormone serves as a counter-regulatory hormone to insulin in carbohydrate and fat metabolism, but works synergistically with insulin in establishing an anabolic protein metabolism environment (21). Growth hormone's insulin-antagonistic effects include increased lipolysis, decreased tissue glucose uptake, and enhanced hepatic gluconeogenesis (22-24). Meanwhile, growth hormone has an anabolic effect via enhanced protein synthesis and retention (25-31).

Cortisol opposes insulin action in several regards. This glucocorticoid is likely most well known for its catabolic properties, which include stimulation of lipolysis in adipose tissue, protein degradation (the hormone also inhibits protein synthesis), and hepatic gluconeogenesis (32-35). Additionally, in terms of insulin resistance, cortisol not only directly inhibits glucose entry to cells, but also delays insulin action via a post-insulin receptor block (33,36).
The catecholamines epinephrine and norepinephrine work in opposition to insulin in the regulation of the plasma glucose concentration. Epinephrine provides a strong stimulus to hepatic glucose mobilization via glycogenolysis and gluconeogenesis (37), although there is a lower threshold for glycogenolysis to occur (38). The catecholamines also stimulate lipolysis in adipose tissue (33,39) and interfere with glucose clearance by insulin (40). While the catecholamines have a catabolic effect on both liver and skeletal muscle glycogen, there is considerable evidence that they have anti-catabolic effects on muscle protein (41-43).
Thyroxine is a less recognized regulator of plasma glucose concentrations. While the hormone itself has no direct effect on substrate mobilization at rest or during exercise, it does serve a permissive role for the hormones that are directly involved in plasma glucose regulation. Thyroxine acts by either increasing receptor quantity at the target tissues or by increasing receptor affinity for the aforementioned hormones; during exercise, these effects are more pronounced, as there is an increase in free thyroxine concentrations (33). Hypothyroidism (and the related thyroxine deficiency) has been shown to interfere with fuel mobilization (33).

Clearly, a discussion of insulin must include attention to several glucoregulatory hormones, each of which has significant implications in carbohydrate, fat, and protein metabolism. Figure 1 summarizes the roles of those hormones with a direct effect on fuel metabolism in the liver, skeletal muscle, and adipose tissue.
Figure 1: Effects of Glucoregulatory Hormones in Various Tissues

Hormone
Liver
Skeletal Muscle
Adipose Tissue
Insulin
(+)Glucose Uptake
(+)Glycogenesis
(-)Glycogenolysis
(-)Gluconeogenesis
(+)Glucose Uptake
(+)Glycogenesis
(-)Glycogenolysis
(-)Proteolysis
(+)Protein Synthesis
(+)Glucose uptake
(+)Lipogenesis
(-)Lipolysis
Glucagon
(+)Glycogenolysis
(+)Gluconeogenesis
(-)Glucose Uptake
(-)Glycogenesis
(+)Proteolysis
(-)Protein Synthesis
(+)Lipolysis (?)
(-)Lipogenesis
(-)Glucose Uptake
Growth Hormone
(-)Glucose Uptake
(-)Glycogenesis
(+)Gluconeogenesis
(-)Proteolysis
(+)Protein Synthesis
(+)Lipolysis
(-)Lipogenesis
(-)Glucose Uptake
Cortisol
(+)Gluconeogenesis
(-)Glucose Uptake
(+)Proteolysis
(-)Protein Synthesis
(-)Glucose Uptake
(+)Lipolysis
Catecholamines
(+)Glycogenolysis
(+)Gluconeogenesis
(-)Glucose Uptake
(-)Glycogenesis
(-)Proteolysis
(-)Glucose Uptake
(-)Glycogenesis
(+)Lipolysis
(-)Glucose Uptake

Glucoregulatory Hormone Response to Exercise

Insulin is the only glucoregulatory hormone that decreases with exercise under normal physiologic conditions (33). Galbo et al. (1975) found that insulin decreased both during prolonged treadmill running at 76%VO2max and with incremental treadmill exercise at 47% and 77% VO2max (no significant difference was noted at 100% VO2max) (44). Numerous other studies have observed similar decreases (45-47); these decreases are more prominent in longer duration exercise at lower intensities than in short duration, high intensity exercise (47).

As a hormone working in direct opposition to insulin, glucagon increases in response to exercise. This effect has been demonstrated in both incremental (44) and prolonged (44,45) endurance exercise. In the aforementioned study by Galbo et al. (1975), the investigators found that glucagon increased more in the longer duration scenario (threefold increase over the resting value) than in incremental exercise (an increase of 35% from rest to VO2max) (44). Others have also noted that glucagon's effects are clearly more prominent in longer duration scenarios (48).

Describing plasma growth hormone changes during exercise proves to be a complex task, as numerous physical, psychological, chemical, and exercise modality (both aerobic and resistance training) factors. In a broad sense, plasma growth hormone concentrations increase as exercise intensity increases; plasma GH may increase 25-fold over resting concentrations at VO2max (49). In fact, recent research by Wideman et al. (2003) noted a linear relationship between GH secretion and exercise intensity (50). Bunt et al. (1986) found that plasma GH increased by 500-600% in both runners and non-runners (runners had a higher response) during one hour of treadmill running at 60% VO2max, implying a duration effect for GH secretion as well (33,51). The growth hormone response to resistance training is a product of the work-rest intervals, loads, and volume utilized, with one minute rest periods, 10-repetition maximums, and high volumes proving most beneficial in enhancing GH secretion (50,52).

Cortisol increases in response to exercise are related to intensity and duration. A study by Davies and Few (1973) demonstrated the presence of an intensity threshold that must be reached for cortisol increases to occur. In separate exercise sessions, subjects were tested for 60 minutes at 40%, 60%, 80%, and 100% VO2max. Plasma cortisol actually decreased at 40% VO2max over the course of the test, whereas cortisol increased whenever the intensity exceeded 60% VO2max (33). Apparently, light exercise facilitates plasma cortisol removal to the point that it exceeds secretion by the adrenal cortex in response to exercise. At greater intensities, secretion predominated over removal, which had increased even more (33). There also appears to be a duration threshold; Bonen (1973) observed that urinary excretion of cortisol did not change with 10 minutes of exercise at 76% VO2max. However, when the duration increased to 30 minutes, this excretion value doubled (53), likely due to a lag time in the hypothalamic-pituitary-adrenal axis between ACTH and cortisol secretion (54).

Numerous studies have found that epinephrine and norepinephrine secretions increase as exercise intensity increases (55-58). However, Kraemer et al. (1985) found that graded exercise did not increase plasma epinephrine above baseline at 54% VO2 max, implying an intensity threshold for catecholamine secretion (59). Several investigators have observed increasing plasma catecholamine concentrations as exercise duration increased (60,61). Galbo et al. (1975) demonstrated that intensity is more influential than duration in the catecholamine response to exercise, as plasma epinephrine increased steadily with prolonged treadmill exercise to exhaustion at 76% VO2 max, but graded exercise in the same subjects at 44, 77, and 100% of VO2 max yielded greater increases (55).

Glucose Uptake and Transport during Exercise

During exercise, muscle glucose uptake may increase 30-50 fold over resting values (62). There is only a limited supply of muscle glycogen, and it can virtually be depleted with just one hour of exercise at 70-75% VO2max (63); therefore, it is of no surprise that muscle glucose uptake increases so dramatically. Given insulin's key role in promoting glucose uptake in skeletal muscle, it seems counterintuitive that the hormone would actually decrease with exercise. However, numerous physiological factors interact to ensure that plasma glucose is maintained while skeletal muscles receive adequate fuel for the continuation of exercise.

First, and perhaps most logically, muscular contractions promote blood flow to skeletal muscles. With blood flow comes more glucose and insulin, so in spite of the fact that insulin is actually decreasing, there is still more opportunity for glucose uptake than at rest (33,64). Meanwhile, a gradient for more rapid glucose diffusion into the cell via increased membrane permeability is created because the muscles are utilizing glucose at a faster rate (64,65). Like insulin, exercise also leads to glucose transporter changes at the sarcolemmal level. In both scenarios, membrane transport capability increases due to translocation of insulin-stimulated GLUT4 transporters to the sarcolemma and transverse tubules from intracellular sites (65-69).

Kennedy et al. (1999) demonstrated that 45-60 minutes of bicycling at 60-75% VO2max resulted in acute mean increases of 71-74% in sarcolemmal GLUT4 content in both normal and type 2 diabetic subjects (70). Others have verified this increase in plasma membrane GLUT4 content with exercise (71-73). The mechanism by which muscle contraction facilitates GLUT4 translocation to the plasma membrane is yet to be definitively elucidated; however, the most likely answer is high intramuscular calcium concentrations during exercise. More specifically, protein kinase C (PKC) is an intermediary that is dependent on calcium; PKC downregulation has been associated with reduced contraction-induced glucose transport (33,73). Potential autocrine and paracrine effects on contraction-stimulated glucose transport have also been suggested (73). Figure 2 depicts a scheme of the potential factors influencing GLUT4 translocation in skeletal muscle.
Figure 2: GLUT4 Translocation in Skeletal Muscle
[IMG]file:///C:/DOCUME%7E1/user/IMPOST%7E1/Temp/msohtml1/01/clip_image002.jpg[/IMG]
Hayashi et al. Am J Physiol 1997.


For the sake of this discussion, it is important to note that insulin and muscular contraction facilitate glucose transport via different pathways, as Yeh et al. (1995) noted that it is possible to inhibit insulin action without inhibiting that of muscle contractions (74). Brozinick et al. (1992) validated this assertion with the observation that contraction-induced facilitated glucose transport is normal in insulin resistant muscle (75). GLUT4 and GLUT1 are two key glucose transporters found in skeletal muscle. Unlike GLUT4, which is responsive to insulin action, GLUT1 exerts its effects on glucose transport independent of insulin stimulation (69).

Henriksen et al. (1990) observed that GLUT4 protein concentration is closely associated with maximal glucose transport capability; it logically follows that the overall quantity of glucose transporters (both GLUT4 and GLUT1) in the plasma membrane during exercise is proportional to muscle GLUT4 content (76). However, there is evidence to suggest that GLUT4 transporters are more associated with fast-twitch oxidative-glycolytic fibers, while GLUT1 transporters are associated with slow-twitch oxidative fibers. Additionally, there is evidence to suggest that GLUT1 transporter increases are achieved through several weeks of endurance training, whereas GLUT4 transporters are more responsive to individual exercise bouts (77). Therefore, variations in fiber-type may interfere with this assumption (78).

Summarily, with more glucose transporters (both insulin-stimulated and non-insulin-stimulated) present due to both chronic and acute exercise adaptations, less insulin is necessary to have the same physiological effect. On a related note, Ivy (1997) asserted that increased concentrations of enzymes responsible for the phosphorylation, storage, and oxidation of glucose are also responsible for the improved insulin action (68).

Conclusions: Bringing it all Together

At first glance, it seems counterintuitive for insulin to decrease during exercise, a time when muscle glucose uptake increases rapidly. Upon further review, though, one can recognize that numerous hormonal and intracellular factors interact with this decrease to maintain plasma glucose concentrations, facilitate muscle glucose uptake, and effect appropriate changes in carbohydrate, fat, and protein metabolism.

As exercise progresses, skeletal muscle glycogen depletion occurs and the muscles must look to plasma glucose as a fuel source. Assuming no provision of exogenous carbohydrate during exercise, plasma glucose must come from hepatic gluconeogenesis or glycogenolysis. These physiological occurrences are stimulated by the presence of the glucagon, epinephrine, and norepinephrine at the onset of exercise, and growth hormone and cortisol as exercise duration increases (33). As counterregulators to insulin, these five hormones can only be present in sufficient quantities to elicit the desirable effects on plasma glucose maintenance if the plasma insulin concentration is low.

While the counterregulatory hormones take care of maintaining plasma glucose, there must be additional physiological adaptations to promote muscle glucose uptake in spite of the decrease in plasma insulin concentrations that occur with exercise. These exercise-induced physiological adaptations include increased skeletal muscle blood flow (and, in turn, glucose and insulin delivery), increased membrane permeability to glucose, translocation of GLUT4 proteins to the sarcolemma and transverse tubules, and increased cellular concentrations of key enzymes involved in glucose utilization. While both insulin and exercise favorably influence glucose uptake, they do so by different pathways. Nonetheless, the positive effects of acute and chronic exercise on insulin action and both insulin-dependent and non-insulin-dependent glucose transporters are undeniable.

It is important to also note that glucagon, growth hormone, cortisol, and the catecholamines have effects that extend beyond plasma glucose regulation. All five hormones promote lipolysis, and thus serve as powerful regulators of fat metabolism (which is also dependent on insulin-related lipogenesis). This increased lipolysis favors the increased reliance on free fatty acids with longer durations, lower intensities, and situations of muscle glycogen depletion (79-82). Likewise, some of these hormones - glucagon, the catecholamines, and most notably, cortisol - continue to oppose insulin in protein metabolism by promoting proteolysis and inhibiting protein synthesis. Meanwhile, growth hormone works synergistically with insulin (and amino acids) to achieve an anabolic effect of elevated protein synthesis and decreased protein breakdown.
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[Theycallmechobo]

Sembrava assodato che i carbo alto i.g. post w.o fossero ferfetti...invece..,qui ogni volta si dice tutto e poi ilsuo contrario.

[**ACHILLES**82**]

Sembrava assodato che i carbo alto i.g. post w.o fossero ferfetti...invece..,qui ogni volta si dice tutto e poi ilsuo contrario.

Adesso mi leggo per bene tutti gli articoli ma...............l insulina da quanto ricordo esercita la sua funzione nello spazzare il glucosio nel sangue nei tessuti.........

A noi nel post workout interessa che le pro assunte vengano sbattute all interno dei muscoli......se riuscissimo senza carboidrati riusciremmo a mantenere alto anche il gh.......otterremmo due piccioni con una fava....

[marco78]

Achille ragionando in termini "empirici": i pro odierni hanno 15-20 kg in più proprio grazie all'insulina.

[**ACHILLES**82**]

Achille ragionando in termini "empirici": i pro odierni hanno 15-20 kg in più proprio grazie all'insulina.

Marco mi trovi d accordo.....ma l insulina esogena è una manna perchè causa ipoglicemia.......

Quindi prendere insulina esogena da due vantaggi:
1)ipoglicemia quindi alti livelli di gh endogeno
2)permeabilità tissutale ai macronutr...


L allenamento causa elevati aumenti di gh.......se ti spari 50 g di glucosio.......cala drasticamente.....è qua il dilemma........in zone come la mattina la sera e il p.w. non ho chiaro cosa fare coi carbo.........negli altri momenti secondo me sono assumibili perchè cmq gli innalzamenti di gh notturni e p.w. sono temporanei dato che il corpo per la sua omeostasi poi riporta tutto a posto........ma mangiare carbo in momenti sbagliati potrebbe ridurre l anabolismo

[marco78]

Achille io cmq non penserei al GH prodotto dall'allenamento... onestamente credo che a livello muscolare possa fare ZERO.

Per fare qualcosa ci vogliono quantità molto alte (esogene).

[**ACHILLES**82**]

..no...gli aminoacidi nn alzano la glicemia...via GNG si va a stoccare glicogeno prevalentemente nell'epatocito...la glicemia si alza o cmqw torna nella norma in seguito allo stimolo del glucagone...
...le proteine aumentano la tolleranza al glucosio, ciò sta a significare che tendono ad abbassare la glicemia aumentando il rilascio di insulina....un bene per i diabetici, un male per gli atleti....il ruilascio di glucagone avviene in seguito per riportare la glicemia stabile...
....per ricaricare le riserve muscolari di glicogeno dovresti assumere quantitativi spropositati di proteine poichè la conversione dei ketoacidi in glucosio richiede abbastanza energia...e ti ripeto, le proteine nn alzano la glicemia...
...ciò che cmq tu affermi è errato, nn hai bisogno del glicogeno per avviare la sintesi proteica, ti serve solo che la proteolisi sia inibita...ciò lo puoi ottenere in 4 modi:
1)assunzione di una buona quantità di cho insieme ai protidi
2)assunzione di una buona quantità di grassi insieme ai protidi
3)un connubio dei primi 2 punti.
4)assunzione di una grande quantità di proteine per far si che la glicemia venga riportata nella norma dal metabolismo delle sole proteine esogene...

ok so che gli aminoacidi non alzano la glicemia.......indirettamente se non mangi carbo e ne assumi parecchi è il glucagone che alza la glicemia......

Quindi nel p.w. se mi sparo 60 grammi di proteine di cui 20 ramificati riesco anche a ricaricare il glicogeno muscolare ?

Voglio capire proprio questo io.....se nel p.w. mangiando sole proteine in qnt maggiore si ha un effetto benefico buono quanto mangiare meno proteine e cho