DRINKING AND BLOOD-PRESSURE RESPONSES TO CENTRAL INJECTION OF L-NAME IN CONSCIOUS RATS

The drinking behavior and blood pressure responses to ICV administrati on of artificial cerebrospinal fluid (aCSF) or NG-nitro-L-arginine met hyl ester (L-NAME, 10, 250, or 500 mu g), an inhibitor of nitric oxide synthase, were examined in conscious rats following either osmotic st imulation (1.0 M NaCl, 15 ml/kg, SC) or induction of hemorrhage (0.7 m l/min to a 20% blood volume loss). Water intake increased in all anima ls. L-NAME at doses of 250 and 500 mu g, but not 10 mu g, significantl y attenuated water consumption induced by both stimuli. The mean arter ial blood pressure (MABP), which increased after osmotic stimulation, was maintained at presser levels by 250 and 500 mu g of L-NAME, but de creased progressively and reached basal levels after treatment with aC SF and the lowest dose of L-NAME (i.e., 10 mu g). Hemorrhage significa ntly decreased MABP in all rats. The fall in blood pressure associated with hemorrhage returned to control levels in animals treated with 25 0 and 500 mu g of L-NAME but not in those treated with aCSF or 10 mu g of L-NAME. These results indicate that nitric oxide is involved in th e regulation of drinking behavior and may play an important role in th e central control of blood pressure during osmotic stimulation and hyp otensive hemorrhage.