CHANGES IN EATING BEHAVIOR AND THERMOGENIC ACTIVITY FOLLOWING INHIBITION OF NITRIC-OXIDE FORMATION

The effects of the inhibition of nitric oxide (NO) production on eatin g behavior and thermogenesis were evaluated in the present experiments . N-G-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO produ ction, was injected intraperitoneally or intracerebroventricularly, an d food intake, oxygen consumption rate, and interscapular brown adipos e tissue (BAT) temperature were evaluated in conscious rats. The firin g rate of sympathetic nerves innervating interscapular BAT was recorde d in urethan-anesthetized animals. L-NAME, intraperitoneally injected, decreased food intake, oxygen consumption, temperature, and firing ra te of sympathetic nerves innervating interscapular BAT. Intracerebrove ntricular injection of L-NAME decreased food intake and enhanced oxyge n consumption, temperature, and firing rate of sympathetic nerves inne rvating BAT. The latter changes were similar to those found after late ral hypothalamic lesions. The opposite changes in oxygen consumption, temperature, and sympathetic activity of BAT that followed L-NAME inje ction through the two different routes were probably due to different effects of the molecule on sympathetic output. Impaired brain producti on of NO, which followed intracerebroventricular L-NAME, directly incr eased sympathetic activity, whereas the same activity that followed in traperitoneal L-NAME was depressed by increased blood pressure, which was elicited by the impaired peripheral production of NO.