Effect of injection of L-NAME on drinking response

The drinking behavior responses to centrally administered N-G-nitro-L-argin ine methyl ester(L-NAME; 10, 20 or 40 mu g/mu l), an inhibitor of nitric ox ide synthase, were studied in satiated rats, with cannulae stereotaxically implanted into the lateral ventricle (LV) and subfornical organ (SFO). Wate r intake increased in all animals after angiotensin II (ANG II) injection i nto the LV, with values of 14.2 +/- 1.4 ml/h, After injection of L-NAME at doses of 10, 20 or 40 mu g/mu l into the SFO before injection of ANG II (12 ng/mu l) into the LV, water intake decreased progressively and reached bas al levels after treatment with 0.15 M NaCl and with the highest dose of L-N AME (i,e., 40 mu g). The water intake obtained after 40 mu g/mu l L-NAME wa s 0.8 +/- 0.01 ml/h. Also, the injection of L-NAME, 10, 20 or 40 mu g/mu l, into the LV progressively reduced the water intake induced by hypertonic s aline, with values of 5.3 +/- 0.8, 3.2 +/- 0.8 and 0.7 +/- 0.01 ml/h, respe ctively. These results indicate that nitric oxide is involved in the regula tion of drinking behavior induced by centrally administered ANG II and cell ular dehydration and that the nitric oxide of the SFO plays an important ro le in this regulation.