Growth hormone acutely stimulates forearm muscle protein synthesis in normal humans

Abstract

The short-term effects of growth hormone (GH) on skeletal muscle protein synthesis and degradation in normal humans are unknown. We studied seven postabsorptive healthy men (age 18-23 yr) who received GH (0.014 micrograms.kg-1.min-1) via intrabrachial artery infusion for 6 h. The effects of GH on forearm amino acid and glucose balances and on forearm amino acid kinetics [( 3H]Phe and [14C]Leu) were determined after 3 and 6 h of the GH infusion. Forearm deep vein GH rose to 35 +/- 6 ng/ml in response to GH, whereas systemic levels of GH, insulin, and insulin-like growth factor I (IGF-I) were unchanged. Forearm glucose uptake did not change during the study. After 6 h, GH suppressed forearm net release (3 vs. 6 h) of Phe (P less than 0.05), Leu (P less than 0.01), total branched-chain amino acids (P less than 0.025), and essential neutral amino acids (0.05 less than P less than 0.1). The effect on the net balance of Phe and Leu was due to an increase in the tissue uptake for Phe (71%, P less than 0.05) and Leu (37%, P less than 0.005) in the absence of any significant change in release of Phe or Leu from tissue. In the absence of any change in systemic GH, IGF-I, or insulin, these findings suggest that locally infused GH stimulates skeletal muscle protein synthesis. These findings have important physiological implications for both the role of daily GH pulses and the mechanisms through which GH can promote protein anabolism.

Effects of recombinant human growth hormone on muscle protein turnover in malnourished hemodialysis patients.

“…The mechanism(s) by which rhGH mediates its anabolic effects on muscle is (are) not yet completely understood. rhGH causes net anabolism in humans through an increase in protein synthesis both in the whole body (32) and in muscle (33,34). rhGH infused acutely into the brachial artery stimulates protein synthesis (35).…”

Somatotropin-induced protein anabolism in hindquarters and portal-drained viscera of growing pigs

“…Most research in ST-deficient (2,19,37), as well as normal, mature animals and humans (1,7,18,24,25,35) suggests that ST treatment increases protein deposition by stimulating whole body and muscle protein synthesis. For example, acute ST infusion in adult humans increases limb protein synthesis (24,25), although differing results have also been reported (11).…”

“…For example, acute ST infusion in adult humans increases limb protein synthesis (24,25), although differing results have also been reported (11). Chronic ST treatment in cattle increases amino acid uptake by the hindquarter (4) and protein synthesis in skeletal muscle (18).…”

Cardiac Effects of Growth Hormone in Physiology and in Heart Failure

“…Fryburg et al directly infused IGF-I into the brachial artery in order to avoid as much as possible the intervention of systemic mechanisms [18,19]. Forearm blood flow markedly rose.…”

“…If we look at the wall stress data measured in a recent study, they confirm the expectations. Wall stress is decreased in acromegaly and increased in GHD [18]. Systolic wall stress is a measure of afterload and therefore it plays a preeminent role in cardiac performance, as anticipated by the force-velocity relation [25].…”