Effect of lipids on growth hormone secretion in humans

Abstract

A B S T R A C T To determine the effect of elevations of plasma lipids on growth hormone secretion in humans, paired insulin hypoglycemia tests and paired arginine infusion tests were performed on eight and six normal female volunteers respectively. On 1 of the 2 test days for each growth hormone stimulus, subjects were given 60 g corn oil (Lipomul) 3 hr before testing followed by intravenous heparin (5000 U) at the time of insulin or arginine administration.Lipomul plus heparin administration inhibited both insulin-and arginine-induced plasma HGH elevations with almost complete suppression of the response to arginine. The plasma HGH (human growth hormone) inhibition was associated with elevation in plasma triglycerides and inhibition of plasma FFA (free fatty acid) depression after insulin or arginine. Neither the hypoglycemic response to insulin nor the blood glucose and plasma immunoreactive-insulin responses to arginine were altered by Lipomul plus heparin administration.In four additional subjects in whom Lipomul was given without heparin, the elevated plasma triglyceride values were not associated with suppression of arginineinduced plasma HGH elevations. In the same four subjects, heparin administration without Lipomul neither suppressed arginine-induced plasma HGH elevations nor prevented the depression in plasma FFA after arginine as much as when Lipomul plus heparin had been given. These latter observations suggest that the elevation in plasma FFA was responsible for suppression of growth hormone secretion by Lipomul plus heparin. These studies indicate a possible role of plasma FFA in regulation of growth hormone secretion. INTRODUCTIONGrowth hormone plays an important role in intermediary metabolism. Its administration results in hyperglycemia,

Studies on the relationship between plasma free fatty acids and growth hormone secretion in man

“…These results confirm the reports of Irie et al (3) that NA-induced FFA depression is followed by an increase of HGH with a lag period of about 2 hr and of Blackard et al (6) that elevation of FFA inhibits hypoglycemia-induced HGH release. The mechanism of this relationship has not been elucidated.…”

“…Here again apparently FFA and glucose are not interchangeable in their influence on HGH release. The relationship between FFA and other stimuli of HGH secretion may be different since arginine-induced HGH release is abolished by FFA elevation (6). Whether higher BS levels than those attained in our experiments-which were roughly equivalent to those reported by Tsushima et al (4) are more effective to suppress the HGH response to FFA depression, remains to be investigated.…”

“…That both methods proved effective to inhibit HGH release provides evidence that in fact elevation of FFA and not constituents of the lipid mixture, heparin, or NE were responsible for the inhibition. Blackard et al have shown, that neither triglycerides nor ketone bodies can account for the suppressive effect of lipids on GH release (5,6). NE has predominantly alpha adrenergic stimulatory activity (27) and HGH secretion is enhanced by stimulation of alpha adrenergic receptors (28,29).…”

“…Lipid infusion just before the expected HGH increase prevented the HGH response to FFA depression. HGH rise during insulin hypoglycemia (32.2± 6.5 ng/ml) was significantly inhibited by prior FFA elevation whether achieved by lipid infusion (maximum HGH rise 11.4±1.6 ng/ml) or by NE infusion (maximum HGH rise 19.0±6.2 ng/ml).…”

Somatotropic responses to soy protein alone and as part of a meal.

“…With respect to the role of fat intake as part of a meal, increasing plasma concentrations of free fatty acids (FFAs), but not triglycerides, as a result of fat ingestion may also have been involved in the suppression of the GH-promoting effect of soy protein during meal ingestion, since FFAs have suggested to suppress GH secretion (13,14).…”