THE LOCALIZATION OF VASOACTIVE-INTESTINAL-PEPTIDE (VIP)-LIKE IMMUNOREACTIVITY IN GONADOTROPES OF THE RAT ANTERIOR-PITUITARY

The anterior pituitary gland has recently been shown to contain a numb er of bioactive peptides other than inherent pituitary hormones. One o f these peptides is vasoactive intestinal peptide (VIP). The localizat ion of VIP has not known and so the present study was undertaken to de termine which type of pituitary cell contains this peptide. The adult rat anterior pituitary was immunohistochemically examined with two VIP antisera. One of these antisera successfully stained some pituitary c ells. Both the double immunostaining technique and the flip-flop secti on method revealed VIP-like immunoreactivity, mainly in gonadotropes. This immunostaining was lost when the anti-VIP was preabsorbed with sy nthetic VIP or with pituitary adenyl cyclase activating peptide (PACAP ), 68% of the 1-28 portion of which is homologous to VIP. When tested with anti-PACAP, however, no immunoreactivity was observed in anterior pituitary tissue. These results indicate that VIP is localized in gon adotropes in the anterior pituitary. The physiological significance of such localization of VIP is discussed in relation to the regulation o f PRL secretion.