Further evidence for a significant participation of the melanocortin 4 receptor in the preovulatory prolactin surge in the rat

We previously reported that the melanocortin 4 receptor may play a signific ant role in mediating the preovulatory surges of luteinizing hormone and pr olactin in the rat. In order to confirm this previous finding, in the prese nt study we examined and compared the effects of intracerebroventricular ad ministrations of 1.0 nmol of MT II (a non-selective melanocortin 3 and 4 re ceptor agonist) and 10 nmol of gamma (1)-melanocytestimulating hormone (a s elective melanocortin 3 receptor agonist) on luteinizing hormone and prolac tin surges in starved, gonadal steroid-primed ovariectomized female rats, w hich is a model deprived of inherent surges of the two hormones. MT II sign ificantly recovered the surge of prolactin, but not of luteinizing hormone (although a tendency to increase was seen), and gamma (1)-melanocyte-stimul ating hormone was without effect on both hormones. This study corroborated our previous report through a different and direct approach that the melano cortin 4 receptor, but not the melanocortin 3 receptor, plays a significant role in mediating the preovulatory prolactin surge in the rat. (C) 2001 El sevier Science Inc.