ROLE OF THE RENIN-ANGIOTENSIN SYSTEM IN THE DEVELOPMENT THYROXINE-INDUCED HYPERTENSION

Objective: We evaluated the influence of chronic blockade of the renin -angiotensin system on hypertension induced by long-term thyroxine (T- 4) administration. To this end, we determined the effects of chronic t reatment with captopril on blood pressure, cardiac hypertrophy and oth er renal and metabolic variables of hypertensive hyperthyroid rats. Me thods: T-4 was administered s.c. at 0.38 mu mol/kg per day and captopr il was given in the drinking water (1.38 mmol/l). Both treatments were maintained for 6 weeks. Control rats received tap water, After the tr eatment period, the rats were placed in metabolic cages. Later, blood pressure was measured in conscious rats by intra-arterial determinatio n. Results: T-4-treated rats showed an increased mean arterial pressur e (MAP) whereas, in rats treated with T-4 plus captopril, MAP was simi lar to that of the control group, Captopril did not affect the increas ed heart rate or ventricular weight/body weight ratio of hyperthyroid rats, but it improved the reduced creatinine clearance of these animal s. Conclusions: The elevation in blood pressure produced by long-term T-4 administration was prevented by chronic blockade of the renin-angi otensin system, Captopril improved the renal function of hyperthyroid rats, but did not affect the relative cardiac hypertrophy of these ani mals.