Effect of delta-opioid receptor agonist deltorphin on circulating concentrations of luteinizing hormone and follicle stimulating hormone in healthy fertile women

There is evidence that endogenous opioid peptides exert an inhibitoryeffect on pituitary luteinizing hormone (LH) secretion both in animals andin humans, by interacting with mu-opioid receptors. However, a role fordelta-opioid receptors in the regulation of gonadotrophin releasing hormone(GnRH) secretion has recently been suggested. In the present study, weevaluated the effect of the highly selective delta-opioid receptor agonistdeltorphin on the LH and follicle stimulating hormone (FSH) responses tonaloxone in six healthy fertile women during the luteal phase of themenstrual cycle. Deltorphin infusion alone (7 microg/kg/min for 60 min) didnot significantly change the basal serum concentrations of LH in this groupof women. The intravenous (i.v.) bolus administration of naloxone (15 mg)induced a significant (P < 0.001) increase in serum LH concentrations(from a mean basal value of 4.24+/-1.10 IU/l to a peak of 13.27+/-1.8IU/l). The LH response to naloxone was significantly (P < 0.001) bluntedby preinfusion of deltorphin (13.27+/- 1.80 IU/l versus 4.80+/-1.18 IU/l).No significant changes in FSH concentrations were observed duringdeltorphin, naloxone or deltorphin plus naloxone administration. These dataindicate that activation of delta-opioid receptors can reducenaloxone-induced LH release, suggesting a possible role of delta receptorsin opioidergic modulation of LH secretion in women.