Role of pulsatile growth hormone (GH) secretion in the regulation of lipolysis in fasting humans

The increase in growth hormone (GH) secretion during a prolonged fast stimulates lipolytic rate, thereby augmenting the mobilization of endogenous energy at a time when fuel availability is very low. To identify the specific component of GH secretory pattern responsible for the stimulation of lipolytic rate during fasting in humans. We measured lipolytic rate (using stable isotope dilution technique) after an overnight fast in 15 young, healthy, non-obese subjects (11 men and 4 women), and again on four separate occasions after a 59 h fast. These four prolonged fasting trials differed only by the contents of an infusion solution provided throughout the 59 h fasting period. Subjects were infused either with normal saline ("Control"; n = 15) or with graded doses of a GH Releasing Hormone Receptor Antagonist (GHRHa):10 μg/kg/h ("High"; n = 15), 1 μg /kg/h ("Medium"; n = 8), or 0.5 μg /kg/h ("Low"; n = 6). As expected, the 59 h fast completely suppressed plasma insulin levels and markedly increased endogenous GH concentrations (12 h vs 59 h Fast; p = 0.0044). Administration of GHRHa induced dose-dependent reduction in GH concentrations in response to the 59 h fast (p