Pituitary adenylate cyclase-activating peptide-38 (PACAP)-38 is released into hypophysial portal blood in the normal male and female rat.

Pituitary adenylate cyclase activating polypeptide (PACAP) was first isolated from ovine hypothalamus as two molecular forms, the basic 38 residue amidated peptide PACAP-38 and the N-terminal 27 amino acid sequence PACAP-27. A dense plexus of PACAP immunoreactive fibres is present in the internal and external layers of the median eminence and in other parts of the hypothalamus with PACAP cell bodies in the paraventricular and supraoptic nuclei. The present study shows, for the first time, that, as assessed by radioimmunoassay of extracted plasma, the amount of PACAP-38 in hypophysial portal is significantly greater than in peripheral blood, and that as assessed by reversed phase high performance liquid chromatography, PACAP 1-38 is the major form in portal blood. This evidence is crucial for the fact that PACAP-38 may be a hypothalamic-pituitary regulatory factor.