Neuropeptide Y affects secretion of luteinizing hormone and growth hormone in ovariectomized rats.

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Abstract
Neuropeptide Y (NPY) was localized in the rat hypothalamus. The effects of NPY on hypothalamic and pituitary function were evaluated by injecting NPY into the 3rd ventricle in vivo and by examining its action on perifused pituitary cells in vitro. Injection of NPY into the 3rd ventricle of conscious ovariectomized rats led to a dramatic and highly significant reduction in plasma luteinizing hormone (LH) relative to pretreatment levels in these animals or to those of controls injected with physiological saline. Significant inhibition was obtained with doses ranging from 0.02-5.0 .mu.g (4.7-1175 pmol) of NPY. These inhibitory effects on LH release were dose dependent and lasted for at least 120 min after injection of 5.0 .mu.g of NPY. Intraventricular injection of NPY also significantly decreased plasma growth hormone; however, the threshold dose was 2.0 .mu.g (470 pmol), a dose 100-fold greater than the lowest dose that inhibited LH release. Plasma FSH was unaffected by injection of NPY. NPY (10-6 and 10-7 M) stimulated secretion of LH, growth hormone and FSH from perifused anterior pituitary cells loaded in a Bio-Gel P-2 column. NPY acts on structures adjacent to the 3rd ventricle to inhibit the secretion of LH and growth hormone but not FSH, whereas it can directly stimulate the secretion of all 3 hormones from the cells of the anterior pituitary in vitro. Since NPY is found in the hypothalamus and median eminence, it may play a physiologically significant role at both hypothalamic and pituitary sites: influencing secretion of pituitary hormones.