The role of neuropeptide Y (NPY) in control of gonadotropin and prolactin release in the rat.

Neuropeptide Y is a peptide found in a variety of hypothalamic loci which is frequently colocalized with catecholamines. It is also secreted into hypophyseal portal vessels. We have previously evaluated the effects of this peptide on FSH, LH and prolactin release. In ovariectomized females neuropeptide Y inhibits LH release. It has similarly been reported to inhibit LH release in intact males; however, estrogen priming of ovariectomized animals converts this inhibitory action into a stimulatory effect. In ovariectomized animals the peptide has a direct stimulatory effect on perifused pituitary cells, enhancing the release of both FSH and LH, an effect which is contrary to that obtained with LH release after intraventricular injection of the peptide. In the present experiments the physiological significance of these effects has been evaluated by the intraventricular injection (3V) of highly specific antiserum directed against the peptide. In ovariectomized and in ovariectomized, estrogen-primed rats, the third ventricular injection of antiserum had no effect on gonadotropin release. In male rats intraventricular injection of the antiserum elevated LH, which indicates that the inhibitory action of the peptide seen in intact males is of physiological significance. However, it has been reported by others that the proestrous type discharge of LH-RH is blocked by intraventricular injection of neuropeptide Y antiserum. Neuropeptide Y might therefore play an essential role in the preovulatory release of LH. On the other hand, others have shown that intraventricular injection of neuropeptide Y in male rats can either stimulate, at low doses, or inhibit, at high doses, the release of prolactin. We have confirmed the inhibitory action, which appears to be of physiological significance since antisera directed against the peptide injected intraventricularly resulted in an elevation of prolactin release. The results of these studies indicate that neuropeptide Y plays a very important and often physiologically significant role in the control of LH and prolactin release by hypothalamic action.