[Effects of kappa-opiate receptor antagonist MR-2266-BS on ACTH and prolactin release]

The effect of intravenous injection of different doses of MR-2266-BS, a selective antagonist of kappa-opiate receptor, on plasma adrenocorticotropin (ACTH) and prolactin (PRL) in conscious male rats bearing an intrajugular cannulae was assessed. The results revealed that the MR-2266-BS of 3 mg/kg completely blocked the restraint stress-induced increase in plasma ACTH levels, and further elevated plasma PRL levels in these animals, while there were no effects on the resting levels of ACTH and PRL. MR-2266-BS of 6 mg/kg significantly increased the resting levels of plasma ACTH and also further elevated the restraint stress-induced increase of plasma ACTH and PRL. The present data suggest that kappa-opiate receptor and its endogenous ligand may be involved in the regulation of the resting and restraint stress-induced release of ACTH, and their action appears to be both stimulatory and inhibitory. Furthermore, kappa-opiate receptor and its endogenous ligand may only inhibit the stress-induced release of PRL.