Prolactin-releasing activity of porcine intestinal peptide (PHI-27).

Porcine intestinal peptide (PHI), a twenty-seven amino acid peptide isolated from porcine gut extracts, is a close structural homolog of the secretin family hormones. The structural and biological similarities of PHI to vasoactive intestinal peptide (VIP) together with its presence in the rat hypothalamus suggested a possible role for the peptide in the control of prolactin (PRL) secretion. PHI induced significant, dose-related stimulations of PRL release from cultured, dispersed rat pituitary cells in vitro. The minimum effective dose is 10(-7) molar, compared to 10(-9) molar for VIP. No interactive effect with thyrotropin-releasing hormone was observed; however, PHI partially overcame the dopamine inhibition of PRL release.