Stimulation of release of growth hormone from the anterior pituitary by α-melanocyte-stimulating hormone: a possible mechanism for induction of pseudopregnancy in the rat

Abstract

ABSTRACT In hypophysectomized rats on day 1 of dioestrus, as well as on day 4 of pseudopregnancy, α-MSH (continuous infusion of 1 μg/h) failed to maintain serum concentrations of progesterone. On the other hand, α-MSH did not modify the increase induced by ACTH (1 μg/μl as an infusion plus two additional daily injections of 30 μg/μl), prolactin (200 μg/0·2 ml at 12-h intervals) or GH (300 μg/0·2 ml twice daily) on serum concentrations of progesterone in such rats. However, in intact rats α-MSH caused a significant rise in serum concentrations of GH on day 1 and day 2 of dioestrus. Continuous infusion of α-MSH produced an increase in serum concentrations of GH at 12.00 and 14.00 h on day 1 of dioestrus and at 07.00 h on day 2. It is therefore suggested that α-MSH may exert its effect by facilitating the secretion of GH, which in turn may induce the release of progesterone. J. Endocr. (1988) 118, 465–470