The intestinal peptide PHI-27 potentiates the action of corticotropin-releasing factor on ACTH release from rat pituitary fragments in vitro.

Effects of rat corticotropin releasing factor (r-CRF) and of natural and synthetic porcine PHI-27 on ACTH release were studied by using freshly prepared anterior pituitary fragments of rats that were superfused with Krebs Ringer bicarbonate buffer (KRB). ACTH was measured in effluent medium samples by RIA. Superfusion with r-CRF-containing KRB caused a concentration-dependent (range 0.2-10 mM) increase of ACTH release. PHI alone did not alter the spontaneous release of ACTH at concentrations of up to 700 nM, but 2000 nM of natural or synthetic porcine PHI-27 enhanced the release rate of ACTH to 180 and 150% of basal ACTH release respectively. Addition of a subeffective concentration of PHI (300nM) to r-CRF containing KRB strongly potentiated its ACTH-releasing effect. Since PHI immunoreactive material is present in nerve fibres located in the external zone of the median eminence, we suggest that PHI or related products may play a physiological role in the control of ACTH secretion.