The growth hormone clamp technique: inhibition of growth hormone release by growth hormone occurs independently of free fatty acids.
It has been suggested that growth hormone (GH) can inhibit its own release: in fact it has repeatedly been shown that an acute methionyl-GH (met-GH) infusion blocks the GH response to GH-releasing hormone (GHRH). However, met-GH infusions are accompanied by a significant increase of free fatty acids (FFA), which can block GH release. The aim of this study was to evaluate whether the inhibition of GH response to GHRH also occurs when lipolysis is pharmacologically blocked. Therefore, six normal subjects received GHRH, 50 micrograms intravenously (IV), after a 4-hour saline infusion and a 4-hour met-GH infusion (80 ng/kg/min, yielding a constant GH level of 33.6 +/- 4.63 micrograms/L), and GH release was evaluated during the following 2 hours. To prevent lipolysis, all subjects received on both occasions acipimox, an antilipolytic agent, 500 mg during the 6 hours before IV GHRH. GHRH induced a clear GH release during saline infusion (46.6 +/- 2.70 micrograms/L) and a scanty GH release during met-GH infusion (9.3 +/- 1.52 micrograms/L; P less than .01). Plasma levels of FFA, somatostatin, insulin-like growth factor I (IGF-I), and glucagon and serum insulin levels were unaffected, while blood glucose levels slightly decreased during saline infusion, but not during GH infusion. These data confirm that met-GH inhibits GHRH-induced GH release, and demonstrate that this inhibition is not mediated by FFA levels.
Istituto Scientifico San Raffaele, Milano, Italy.
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D000328:Adult; D005230:Fatty Acids, Nonesterified / Q000097:blood*; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D013006:Growth Hormone / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism* / Q000494:pharmacology; D006728:Hormones / Q000494:pharmacology; D019382:Human Growth Hormone; D006801:Humans; D007262:Infusions, Intravenous; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008066:Lipolysis / Q000187:drug effects*; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology*; D011863:Radioimmunoassay
D005230:Fatty Acids, Nonesterified; D006728:Hormones; D019382:Human Growth Hormone; D007987:Gonadotropin-Releasing Hormone; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D009638:Norepinephrine