Effects of methimazole on low-renal-mass hypertension: changes in blood pressure and pressor responsiveness to vasoconstrictors.

The administration of the antithyroid drug methimazole to rats via drinking water prevented the development of hypertension that usually accompanies subtotal nephrectomy and saline drinking (1% NaCl). In methimazole-treated rats, elevated blood pressure induced 5 weeks previously returned to normotensive levels. Pressor responsiveness to angiotensin, vasopressin and norepinephrine in unanesthetized rats was studied after prevention of hypertension in control, low-renal-mass hypertensive (LRM) and low-renal-mass methimazole-treated (LRM-M) rats, and in the reversion study in LRM and LRM-M rats. In LRM rats, responsiveness to vasoconstrictors was increased, whereas responsiveness to vasoconstriction was clearly reduced in LRM-M rats after prevention and reversion studies. These results suggest that (a) thyroid hormones are required in the early and established phases of LRM hypertension, and (b) the decreased pressor responsiveness to vasoconstrictors may play a role in the prevention and reversion of this type of hypertension following methimazole administration. However, the changes in pressor responsiveness may also be secondary to the reduction in blood pressure.