The growth hormone clamp technique: inhibition of growth hormone release by growth hormone occurs independently of free fatty acids

Metabolic effects of graded glucagon infusions in man: inhibition of glucagon, insulin, and somatostatin response to arginine

Insulin inhibits its own release (autofeedback), and growth hormone (GH) inhibits the GH response to a variety of stimuli. The aim of this study was to evaluate whether glucagon (G) can modify pancreatic G (IRG) release in humans. Seven healthy men received intravenous (i.v.) arginine (30 g in 30 minutes) 240 minutes after the beginning of a 0.9% NaCI saline infusion and a 2.5-, 4.0-, and 8.0-ng/kg.min-1 porcine G infusion, with each infusion lasting 360 minutes. All G infusions yielded stable and dose-related plasma IRG levels, and the 4.0- and 8.0-ng/kg.min-1 G infusions decreased plasma free fatty acids (FFA) and blood glycerol and beta-OH-butyrate levels and elicited insulin (IRI) release, and the 8.0-ng/kg.min-1 G infusion elicited GH release and increased blood glucose (BG) levels; somatostatin (SRIF) levels were not affected by G infusions. At 240 minutes, plasma IRG levels were higher during G infusion than during saline infusion, whereas serum IRI and BG levels had returned to preinfusion levels. At this point, G infusions decreased the integrated (240 to 300 minutes) IRG, IRI, BG, and SRIF responses, but not the GH response to arginine. These data indicate that prolonged G infusions decrease the IRG response to arginine; in addition, G decreases plasma FFA levels, and higher G doses stimulate IRI release and exert a self-limited hyperglycemic effect. The fact that the IRI response to arginine was decreased by G could be due to a refractoriness of beta cells to subsequent stimuli; the decreased SRIF response to arginine is likely due to G itself or to a decrease of plasma FFA levels.

Plasma free fatty acids and serum insulin in subjects feeding at 12-hour intervals; effects of methionyl growth hormone and of acipimox, an inhibitor of lipolysis

In normal men, plasma free fatty acids (FFA) are influenced by feeding and by fasting; in addition, iv infusions of methionyl growth hormone (met-GH), so far performed during morning hours, induce an FFA rise that can be blocked by acipimox (ACX), a nicotinic acid analogue. The aims of the present study were to evaluate, in the absence of food interferences, the following aspects: i) Fasting FFA, glycerol, and insulin (IRI) in the morning and in the evening, and their response to met-GH ii) The effect of ACX and of a sustained release ACX formulation (ACX-SR) on fasting and met-GH induced lipolysis and on IRI levels. In a double blind study, 6 normal men received 50% cal at 09:30 h and 50% at 21:30 h; during placebo administrations FFA, glycerol, and IRI levels were lower at 06:30 h than at 18:30 h, and an iv met-GH infusion (160 ng/kg/min lasting 180 min) had a similar effect on FFA and on glycerol at 06:30 h and at 18:30 h. ACX-SR, administered at 21:30 h and 09:30 h, lowered FFA and glycerol in the morning as well as in the evening, and prevented met-GH induced lipolysis in the morning, but not in the evening.(ABSTRACT TRUNCATED AT 250 WORDS)