Effect of nitric oxide on basal and TRH-or metoclopramide-stimulated prolactin release in normal men

In order to establish whether nitric oxide (NO) is involved in the regulati on of basal and/or TRH- or metoclopramide (MCP)-stimulated PRL secretion, n ormal male subjects were treated i.v. with the NO-synthase (NOS) inhibitor N-nitro-L-arginine methyl ester (L-NAME) (40 mg/kg injected plus 50 mg/kg i nfused over 60 min) in basal conditions (N.7 subjects) or just before the P RL releasing hormone TRH (20 or 200 mu g iv) (N.7 subjects) or the antidopa minergic agent MCP (1 or 10 mg iv) (N.7 subjects). In control experiments, subjects received normal saline instead of L-NAME. The administration of L- NAME modified neither the basal secretion of PRL, nor the PRL release induc ed by TRH (20 or 200 mu g) or MCP (1 or 10 mg), These data suggest that in humans, NO is not involved in the control of PRL release at the anterior pi tuitary level.