Differential regulation of preovulatory luteinizing hormone and follicle-stimulating hormone release by opioids in the proestrous rat

We have investigated the role of mu- and kappa -opioid receptors in the cen tral control of preovulatory LH and FSH release in the proestrous rat. Anim als were anesthetized with chloral hydrate at 14:00 h on proestrus day. Fol lowing femoral artery cannulation, they were mounted in a stereotaxic appar atus. Morphine and U-50488H (benzene-acetamide methane sulphonate) were inf used intracerebroventricularly either alone or in combination with naloxone and MR1452, respectively. Controls received sterile saline alone. Blood sa mples were obtained at hourly intervals between 15:00 h and 17:00 h. Plasma LH and FSH levels were measured by radio immunoassay. Morphine did not sig nificantly change plasma LH levels at 15 00 h and 16:00 h sampling interval s. A significant increase was observed at 17:00 h compared to the controls (p<0.05). U-50488H significantly increased LH levels at 16:00 h and 17:00 I t (p<0.05). The co-administration of naloxone and MR1452 with mu- and kappa -agonist had no significant effect on LH levels at any sampling interval. In all groups, LH levels showed a linear rise over the sampling period betw een 15:00 h and 17:00 h. None of the treatments significantly altered plasm a FSH levels which however, declined towards the end of the afternoon surge . In conclusion, we suggest that the secretion of LH and FSH is differentia lly regulated by mu- and kappa -opioid receptors. It is thought that in all groups chloral hydrate interfered with the LH surge secretory systems.