Phorbol 12-myristate 13-acetate induces prolactin secretion from rat anterior pituitary gland by the activation of protein kinase-C.

The purpose of this study was to characterize the action of phorbol 12-myristate 13-acetate (PMA), a tumor-promoting agent, on rat anterior pituitary gland, focusing the attention on prolactin secretion. PMA elicited a significant increase in prolactin secretion without affecting phosphatidylinositol turnover, considered as an early post-receptor event controlling PRL secretion. However incubation of anterior pituitary glands with PMA caused a loss of protein kinase-C activity in cytoplasm concomitant with an increased enzyme activity in the membrane. The action of PMA on prolactin secretion seems to be mainly dependent from the redistribution and activation of protein kinase-C. In fact, the phorbol ester did not affect pituitary cAMP and cGMP metabolism either in basal conditions or after theophylline.