A novel action of the newly described prolactin-releasing peptides: cardiovascular regulation

The physiological relevance of the recently described prolactin-releasing p eptides (PrRPs) has yet to be established. Hen, we demonstrate the low pote ncy of the PrRPs (minimum effective dose: 100 nM), compared to that observe d for thyrotropin-releasing hormone (TRH, minimum effective dose: 1.0 nM), to stimulate prolactin (PRL) release from cultured pituitary cells harveste d from lactating female rats. Anatomic studies question the role of these p eptides in neuroendocrine control of lactotroph function. Instead, peptide and peptide receptor mapping studies suggest potential actions in hypothala mus and brainstem unrelated to the control of anterior pituitary hormone se cretion. Intracerebroventricular (i.c.v.) administration of both PrRP-20 an d PrRP-31 (0.4 and 4.0 nmol) resulted in significantly increased mean arter ial blood pressure in conscious, unrestrained rats [peak elevations vs, bas eline: PrRP-20, 10% and 16%, low and high dose peptide; PrRP-31, 7% and 10% ; compared to the response to 0.1 nmol angiotensin II (A II), 15-17%]. Simi lar doses of peptide did not significantly alter water drinking in response to overnight fluid deprivation, or thirst or salt appetite in response to an isotonic hypovolemic challenge. Thus, the effect on blood pressure appea red relatively specific. We suggest that these peptides, identified origina lly as ligands for a receptor found in abundance in pituitary gland, play a broader role in brain function and that the ability of them to stimulate P RL release may not represent their primary biologic function. (C) 2000 Else vier Science B.V. All rights reserved.