Neurotransmitter Regulation of Growth Hormone and ACTH in the Rhesus Monkey: Effects of Biogenic Amines

Abstract

In an attempt to clarify the role of central neurotransmitters in GH and ACTH regulation, chair-adapted unanesthetized adult male rhesus monkeys with chronic indwelling intraatrial cannulae were given 30 min infusions of various agonists known to affect central amines, and plasma samples were withdrawn for GH and cortisol determinations. Infusion of acid-saline vehicle alone had no significant effect on plasma GH or cortisol (P < 0.05). L-Dihydroxyphenylalanine (L-Dopa) (4.5 and 45 mg/kg), but not apomorphine (7/Ag/kg), a specific dopaminergic agonist, produced significant elevations of GH. Both noradrenergic (clonidine HC1, 1.5, 15, and 150 /xg/kg, and D, L-threodihydroxyphenylserine (D, L-threodops) 90 mg/kg) and serotoninergic (5-hydroxy-L-tryptophan (5-HTP), 45 mg/kg) agonists induced significant GH responses. These findings suggest that GH is regulated in the rhesus monkey by noradrenergic and serotoninergic neurons, whereas participation of dopaminergic neurons has not been established. Significant cortisol responses were only observed following infusion of 5-HTP (45 mg/kg). Dopaminergic and noradrenergic agonists not only failed to alter resting cortisol levels but also did not affect the cortisol response to 5-HTP. In the rhesusmonkey serotoninergic mechanisms appear to be responsible for the regulation of resting cortisol levels. A catecholamine inhibitory mechanism was not demonstrated in this species. © 1976 by The Endocrine Society.