Acute effects of nalmefene on LH, prolactin, and testosterone in male rhesus monkeys

The effects of the long-acting opioid antagonist, nalmefene [17-N-cycloprop ylmethyl-3,14-beta-dihydrox-4,5-alpha-epoxy-6-methylene morphinan hydrochlo ride] on LH, T, and prolactin release in rhesus monkeys are unknown. The ac ute effects of nalmefene (0.01 and 0.10 mg/kg, IV) or placebo on LH, PRL, a nd T were studied, and samples were collected at 10-min intervals for 360 m in to permit cluster analysis of pulsatile release patterns. LH increased s ignificantly within 30 min after nalmefene, and remained significantly abov e baseline levels for 50 to 60 min (p < 0.05). Testosterone increased signi ficantly within 70 to 80 min after nalmefene, and remained significantly ab ove baseline for 60 min (p < 0.05). Although nalmefene antagonizes opioid a gonists for 6-8 h, inhibitory feedback by testosterone appeared to limit th e duration of its antagonism of endogenous opioid inhibition of LHRH and st imulation of LH. Nalmefene did not change LH or PRL pulse frequency or ampl itude significantly in comparison to placebo administration. (C) 2000 Elsev ier Science Inc.