Stimulatory effect of peptide histidine isoleucine amide 1-27 on prolactin release in the rat.

Intravenous injection of pure peptide histidine isoleucine amide 1-27 (PHI) resulted in a prompt and significant increase of plasma prolactin (PRL) in conscious freely-moving male rats. Using a perifusion system of rat anterior pituitary tissues in vitro, effluent PRL levels were also increased by 10(-8)-10(-7) M PHI. A PRL releasing potency of PHI was almost similar with that of vasoactive intestinal polypeptide (VIP) or TRH both in vivo and in vitro. Coupled with the recent immunocytochemical studies showing the dense network of PHI immunoreactive fibers around the hypophysial portal vessels, PHI might be another candidate for PRL releasing factor.