Predominant involvement of mu-rather than delta- or kappa-opiate receptors in LH secretion.

Opiate alkaloids and opioid peptides have been shown to suppress plasma LH and FSH levels via a naloxone sensitive mechanism in several species including man. Three subtypes of opiate receptors have been characterized: mu, delta and kappa. The present study was designed to investigate their role in gonadotropin release. Three highly selective opioid ligands, DAGO, MRZ and DTE12 (a dimeric tetrapeptide enkephalin), were injected intraventricularly into chronically ovariectomized rats. Injection of the mu-agonist at doses of 1 and 10 nmol produced a significant suppression of LH secretion, while the delta- and kappa-agonists had no significant effect. Thus, the mu-receptor seems to be the primary opiate receptor involved in the regulation of LH secretion. None of the opiate agonists employed had an effect on FSH secretion.