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 antithyroid drug, on blood pressure and other variables in the early and established phases of hypertension induced by the inhibition of nitric oxide synthesis with the oral administration of N-G-nitro-L-arginine methyl 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 pressure in control and rats treated chronically with methimazole, administered via drinking water (30 mg/100 mi). Oral administration of methimazole maintained the blood pressure of L-NAME-treated rats at normal levels 25 days after induction of hypertension. However, after 25 days of methimazole treatment in rats made hypertensive with L-NAME (for 25 days), high blood pressure was similar in methimazole-treated and non-treated L-NAME rats, despite the fact that a hypothyroid state had been achieved in the methimazole-treated rats. Acute intravenous injection of L-NAME caused a similar increase in mean arterial pressure in control and methimazole-treated rats at the lowest dose; however, smaller presser responses were observed with increasing doses in hypothyroid rats. These results clearly demonstrate that hypothyroidism induced by methimazole prevents, but does not reverse, L-NAME hypertension and reduces the acute presser responsiveness to L-NAME administration.