Role of VIP in the regulation of LH secretion in the female rat.

Vasoactive intestinal peptide (VIP) is found within neurons throughout the body. It influences the secretion of several hormones of the anterior pituitary by neural and pituitary actions. We review work from our laboratory that indicates that VIP inhibits the secretion of luteinizing hormone (LH) by a hypothalamic action. Experiments involving neural lesions indicate that VIP acts on the receptor field in the paraventricular nuclei of neurons whose cell bodies are located in the suprachiasmatic nuclei. The effect on LH secretion is subsequently mediated by a nonVIPergic pathway, which does not appear to involve either dopamine or endogenous opioids. Experiments with the specific VIP antagonist, [4Cl-D-Phe6,Leu17]VIP, indicate that the actions on LH secretion of VIP and of the related peptides, growth hormone-releasing hormone and secretin, are mediated by VIP-preferring receptors. VIP also blocks the steroid-induced LH surge in the ovariectomized rat. The VIP antagonist induces a significant, but small increase in LH secretion in the intact rat, indicating that VIP has a modulatory, rather than deterministic, role in the regulation of LH secretion.