Drinking and blood pressure responses to central injection of L-NAME in conscious rats

The drinking behavior and blood pressure responses to ICV administration of artificial cerebrospinal fluid (aCSF) or NG-nitro-L-arginine methyl ester (L-NAME, 10, 250, or 500 mu g), an inhibitor of nitric oxide synthase, were examined in conscious rats following either osmotic stimulation (1.0 M NaCl, 15 ml/kg, SC) or induction of hemorrhage (0.7 ml/min to a 20% blood volume loss). Water intake increased in all animals. L-NAME at doses of 250 and 500 mu g, but not 10 mu g, significantly attenuated water consumption induced by both stimuli. The mean arterial blood pressure (MABP), which increased after osmotic stimulation, was maintained at presser levels by 250 and 500 mu g of L-NAME, but decreased progressively and reached basal levels after treatment with aCSF and the lowest dose of L-NAME (i.e., 10 mu g). Hemorrhage significantly decreased MABP in all rats. The fall in blood pressure associated with hemorrhage returned to control levels in animals treated with 250 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 the regulation of drinking behavior and may play an important role in the central control of blood pressure during osmotic stimulation and hypotensive hemorrhage.