Effects of neuropeptide Y on gonadotropin and prolactin release in normal, castrated or flutamide-treated male rats.

This study was carried out to clarify the central effects of neuropeptide Y (NPY) on gonadotropin and prolactin (PRL) release in the male rat and to evaluate the hypothesis that it may play a role in negative feedback regulation of gonadotropin secretion in the male. NPY (4 micrograms in 2 microliters 0.9% NaCl) or an equal volume of saline was microinjected into the third cerebral ventricle of conscious, unrestrained rats and its effects on plasma luteinizing hormone (LH), follicle-stimulating hormone (FSH) and PRL concentrations, and the gonadotropin response to LH-releasing hormone (LHRH) were measured by radioimmunoassay in noncastrated, castrated (3 days before the experiment) rats or animals treated with flutamide, an androgen receptor blocker (10 mg/kg b.w. per day subcutaneously for 3 days). Blood samples were drawn periodically from a Silastic catheter in the external jugular vein just before and for 120 min after intraventricular injections. At 90 min after injection 25 ng of LHRH were infused intravenously and 3 additional blood samples were withdrawn at 10-min intervals after the injection. Normal male rats responded to NPY with a decrease in plasma LH concentrations at 60 min. Plasma LH was significantly lower at 120 min than values in the saline-injected controls. At that time there was a significant 2-fold augmentation of their response to LHRH. In contrast, NPY elevated plasma FSH significantly versus values in controls at 15 and 30 min after injection, but the FSH release in response to LHRH was not altered.(ABSTRACT TRUNCATED AT 250 WORDS)