ENDOGENOUS NEUROPEPTIDE-Y REGULATES THYROID BLOOD-FLOW

Neuropeptide Y (NPY) is present in thyroid sympathetic nerve fibers. T o assess the involvement of endogenous NPY in the regulation of thyroi d function, a NPY antiserum was produced in a rabbit, characterized, a nd used for immunization of normal and hyperthyroid rats. Plasma thyro xine, thyroid-stimulating hormone (TSH), thyroidal, and other organ bl ood flows (BF) were measured in anesthetized (ketamine and pentobarbit al sodium) male Sprague-Dawley rats at 1 h after intravenous administr ation of 1 ml of the antiserum, normal rabbit serum, or saline. Immuni zation against NPY had no effect on the plasma levels of thyroxine, TS H, or arterial blood pressure, but it significantly increased thyroida l BF in normal rats. In the hyperthyroid rats (treated with 5 mug.100 g body wt-1.day-1 thyroxine for 6 days), the NPY antiserum reversed th e hyperthyroidism-induced decrease in thyroid BF and significantly inc reased duodenal and testicular BF values, but it did not alter BF valu es in four other organs. These results indicate that endogenous NPY re gulates thyroid BF in normal rats. They also provide an example of NPY involvement in the pathophysiological adjustment of some organs to hy perthyroidism.