Aldosterone and plasma renin activity in hyperthyroid rats: effects of propranolol and propylthiouracil

Variations in renin- angiotensin-aldosterone system (RAAS) in experimentally induced hyperthyroidism were studied. The changes observed in the RAAS in these conditions, evaluated through the plasma renin activity (PRA), are parallel to serum aldosterone concentration (AC). An increase in PRA and AC is produced following the administration of triiodothyronine, possibly through elevated adrenergic activity: beta-blocker, propranolol, returned the PRA and AC to normal. The active hormone is seen to be triiodothyronine, confirmed by using the antithyroid preparation, propylthiouracil, to inhibit the conversion of thyroxine. Propylthiouracil administration to hyperthyroid animals lowers the PRA and AC.