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 number of bioactive peptides other than inherent pituitary hormones. One of these peptides is vasoactive intestinal peptide (VIP). The localization of VIP has not known and so the present study was undertaken to determine 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 cells. Both the double immunostaining technique and the flip-flop section method revealed VIP-like immunoreactivity, mainly in gonadotropes. This immunostaining was lost when the anti-VIP was preabsorbed with synthetic 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 gonadotropes in the anterior pituitary. The physiological significance of such localization of VIP is discussed in relation to the regulation of PRL secretion.