Influence of prolactin on the processes of protein and/or peptide secretion in mouse and rat pinealocytes. An in vitro study.

In cultured mouse pinealocytes prolactin stimulates protein/peptide secretion, characterized by the formation of granular vesicles (GV), in the presence of noradrenaline. Prolactin also stimulates this secretion in rat pinealocytes, but only when the hormone was added to a noradrenaline-free medium. Moreover, in both species antagonistic effects of noradrenaline and prolactin on the number of GV are observed. In cultured rat pinealocytes prolactin, in the presence of noradrenaline, strongly stimulates the ependymal-like protein/peptide secretory process. Contrary to what was observed in the process characterized by the formation of GV, synergic effects of noradrenaline and prolactin are found. The results obtained demonstrate that prolactin is involved in the regulation of pineal protein/peptide secretion, and point to the importance of pineal proteic/peptidic "hormones" in pineal endocrinology.