EFFECTS OF METHIMAZOLE IN THE EARLY AND ESTABLISHED PHASES OF N-G-NITRO-L-ARGININE METHYL-ESTER HYPERTENSION

In the present study we evaluated the effects of methimazole. an antit hyroid drug, on blood pressure and other variables in the early and es tablished phases of hypertension induced by the inhibition of nitric o xide synthesis with the oral administration of N-G-nitro-L-arginine me thyl ester (L-NAME), 75 mg/100 mi in the drinking water. Moreover, we also evaluated the acute presser effect of L-NAME on systemic blood pr essure in control and rats treated chronically with methimazole, admin istered via drinking water (30 mg/100 mi). Oral administration of meth imazole maintained the blood pressure of L-NAME-treated rats at normal levels 25 days after induction of hypertension. However, after 25 day s of methimazole treatment in rats made hypertensive with L-NAME (for 25 days), high blood pressure was similar in methimazole-treated and n on-treated L-NAME rats, despite the fact that a hypothyroid state had been achieved in the methimazole-treated rats. Acute intravenous injec tion of L-NAME caused a similar increase in mean arterial pressure in control and methimazole-treated rats at the lowest dose; however, smal ler presser responses were observed with increasing doses in hypothyro id rats. These results clearly demonstrate that hypothyroidism induced by methimazole prevents, but does not reverse, L-NAME hypertension an d reduces the acute presser responsiveness to L-NAME administration.