EFFECTS OF N-W-NITRO L-ARGININE METHYL-ESTER ON THE RESPONSE TO NACL LOAD IN HYPERTHYROID AND HYPOTHYROID RATS

We assessed the effects of the inhibition of endogenous nitric oxide ( NO) synthesis with N-W-nitro-L-arginine methyl ester (L-NAME) on water and sodium handling after NaCl load containing the inhibitor at 0, 0. 5, 5 and 50 mg/kg in conscious control, hyper- and hypothyroid rats. L -NAME at 0.5 mg/kg caused a similar decrease in diuresis and natriures is in control and hypothyroid rats, whereas no changes were seen in th e hyperthyroid group. The saline load with 5 mg/kg of L-NAME produced no significant changes with respect to the 0 dose in any variable in c ontrol and hypothyroid rats, but increased natriuresis in the hyperthy roid group. The highest dose of L-NAME (50 mg/kg) increased the diuret ic and natriuretic response in control and hyperthyroid groups, wherea s in the hypothyroid group no urinary variable was significantly modif ied with respect to the 0 dose. These results indicate that the antidi uretic and antinatriuretic effects of L-NAME at low doses are suppress ed in hyperthyroid rats, whereas the diuretic and natriuretic effects at high doses are absent in hypothyroid rats. Our findings suggest tha t the modulatory role of NO on sodium and water excretion is affected in both thyroid disorders. In addition, the highest dose of L-NAME kil led hyperthyroid rats, indicating that NO plays an essential role for life in hyperthyroidism.