Pancreatic polypeptide in the control of beta-endorphin and prolactin release from rat anterior pituitary in vivo and in vitro

This study was designed to examine the possible effects of pancreatic polypeptide (PP) on beta-endorphin (beta-EP) and prolactin (PRL) release from rat anterior pituitary in vivo and in vitro. Injection of 0.5 microgram or 2.0 micrograms PP into the third ventricle of the brain (3rd v.i.) produced a significant decrease of the beta-EP and PRL resting secretion. 0.5 microgram PP (3rd v.i.) did not affect restraint stress-induced release of beta-EP, but partially lowered stress induced release of PRL. 2.0 micrograms PP (3rd v.i.) partially reduced restraint stress-induced release of beta-EP and completely suppressed stress-induced release of PRL. In order to investigate a possible direct action of PP on beta-EP and PRL secretion from the anterior pituitary gland, we incubated dispersed anterior pituitary cells with synthetic PP (0.05, 0.625 and 1.00 micrograms) for 1 n, the secretion of beta-EP was not affected at any dosage tested, but 0.625 and 1.00 micrograms PP significantly decreased the PRL secretion. These data indicate that PP may have an inhibitory role in the control of beta-EP secretion at the level of the hypothalamus, and an inhibitory role in the control of PRL secretion at the level of either hypothalamus or anterior pituitary.