Human relaxin increases cyclic AMP levels in cultured anterior pituitary cells

Although relaxin acts at several abdominal sites and mammary tissue associated with pregnancy and parturition, the scope of target tissues and the signals conveying the relaxin message into the cell are poorly defined. We found that human relaxin rapidly elevates the cyclic AMP content of cultured rat anterior pituitary cells. This is a graded response (EC50 0.3 nM relaxin) that can be blocked by anti-relaxin antibodies or the hormones somatostatin and dopamine. Furthermore, other hormones with some sequence homology to relaxin, such as insulin and insulin-like growth factor-I, have no such action. We conclude that the anterior pituitary may be a target tissue for relaxin and that cyclic AMP may act as an intracellular messenger for relaxin in these cells.