GROWTH HORMONE (GH) RESPONSES TO ARGININE AND L‐DOPA ALONE AND AFTER GHRH PRETREATMENT

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Abstract
In order to investigate the mechanisms by which arginine and L‐dopa cause GH release in humans we measured the GH response to GHRH 1–44 (200 μg i.v.), arginine (30 g i.v. over 30 min) and L‐dopa (500 mg orally) administered alone and 120 minutes following pretreatment with GHRH 1–44 (200 μg i.v.) in normal male subjects. Prior GHRH administration abolished the GH response to subsequent GHRH. Arginine infusion induced a rise in GH levels maximal at 45 min. Following GHRH pretreatment the GH response to arginine was enhanced, with peak values of 19.3 ± 6.4 vs 53.3 ± 16.5 mU/l (mean + SEM) respectively (P < 0.02). L‐dopa alone induced a rise in GH levels maximal at 90 min (17.6 ± 7.4 mU/l, mean ± SEM) but this rise was abolished by pretreatment with GHRH.