THE EFFECT OF NALMEFENE ON PULSATILE SECRETION OF LUTEINIZING-HORMONEAND PROLACTIN IN MEN

Luteinizing hormone (LH) and prolactin are released in pulses which ar e relatively synchronous in the luteal phase of the menstrual cycle in women. The concordance of LH and prolactin pulses in normal men has n ot been reported. The objectives of this study were firstly to determi ne whether LH and prolactin pulses are synchronous in men, and secondl y to examine the effects of naloxone and a new orally active opiate an tagonist, nalmefene, on LH and prolactin release in men. Three groups of normal male subjects received saline infusion (control n = 5), nalo xone infusion (2 mg/h; n = 5) or nalmefene (10 mg p.o.; n = 6). Blood samples were collected every 15 min for 2 h before and 6 h after study medication for determination of LH, prolactin and testosterone by rad ioimmunoassay. Both naloxone and nalmefene resulted in a significant i ncrease in LH pulse frequency and in mean serum LH and testosterone co ncentrations with no change in LH pulse amplitude, prolactin pulse fre quency or amplitude. In controls, 61% of LH pulses were synchronous wi th prolactin pulses. There was a decrease in concomitance of LH and pr olactin pulses with naloxone (48%) and nalmefene (24%; P < 0.025) admi nistration. In contrast, 52% of prolactin pulses were concomitant with LH pulses in controls, while naloxone (100%) but not nalmefene (67%) resulted in a significant (P < 0.01) increase in pulse synchrony. The difference observed between naloxone and nalmefene on prolactin - LH p ulse synchrony is probably due to differential opioid receptor activit y at the pituitary and hypothalamic level. Nalmefene may prove to be u seful for exploring the complex neuroendocrine control of LH and prola ctin secretion in the human.