Aim: To determine the effects of opioids on serum oxytocin levels and neurohypophyseal noradrenaline concentrations in the late pregnant rats.

Material and Methods: The � and κ opioid agonists and antagonists (50 �g/kg/10ml saline) were intracerebroventricularly infused to the pregnant rats. Saline (10�l) was administered to control group. All rats were decapitated 20 minutes later and serum oxytocin levels were analysed by radioimmunoassay. The neurohypophysis tissues were removed and noradrenaline concentrations were detected by liquid chromatography. The results were statistically analysed with one way ANOVA.

Results: There was no significant difference in � agonist and κ antagonist groups when compared to control group. A significant decrease occurred in κ agonist group (p<0.05) and there was a significant increase in m antagonist group (p<0.01). There was no significant difference between the groups with respect to noradrenaline and its’ metabolite concentrations in the neurohypophysis.

Conclusion: There may be an endogenous � opioid restriction on oxytocin neurons in late pregnant rats and the neurohypophyseal noradrenergic transmission is not involved in this restriction.