Effects of intracerebral administration of neuropeptide-Y on secretion of luteinizing hormone in ovariectomized sheep.

Ovariectomized ewes received unilateral infusions of 20 micrograms neuropeptide-Y (NPY) at a total of 13 intracerebral sites. Episodic secretion of luteinizing hormone (LH) was transiently suppressed on more than one occasion by daily infusions at a total of five intracerebral sites. Four of the effective sites were located within the third ventricle (two sites) and the rostral and ventral part of a lateral ventricle (two sites). The precise neural site of action of exogenous NPY cannot be determined from intraventricular administration, but it indicates a neural rather than pituitary site of NPY action to inhibit LH-releasing hormone (LHRH) in sheep. The only tissue infusion site (ventromedial nucleus) at which NPY also suppressed LH/LHRH also supports a neural action on LHRH, but this single result is insufficient to establish the neural area at which NPY acted. It is known from other work that the production of endogenous NPY in neural tissue of underfed animals is increased, and if endogenous NPY exerts effects on LH/LHRH similar to the suppression presently observed following exogenous NPY this neuropeptide might serve as one neuroendocrine factor that suppresses reproduction in underfed animals.