Aminotriazole, thyroid function, and catecholamines in nephrogenic hypertension in rats

Abstract

Administration of graded doses of the antithyroid agent aminotriazole (ATZ) to male rats whose kidneys were bilaterally encapsulated with latex envelopes provided protection against the elevation of systolic blood pressure to the level of untreated, renal-encapsulated controls. The doses used were 5, 10, 50, and 250 p.p.m. mixed thoroughly into food. Blood pressures of the groups treated with either 50 or 250 p.p.m. ATZ were within the range of the non-encapsulated controls during the last 7 weeks of the 15-week experiment. Hypothyroidism accompanied administration of the highest dose of ATZ in that heart rate was reduced, and thyroid weight increased, beyond the levels observed for renal-encapsulated control rats. A sigmoid relationship was observed between heart to body weight ratio and systolic blood pressure for all rats. This relationship suggests that heart weight is unaffected by change in blood pressure until the threshold pressure of 150–159 mm Hg is reached. Beyond this threshold pressure, heart weight increased sharply to reach a level approximately 30% above that observed within the blood pressure range of 120–149 mm Hg. Treatment of hypertensive rats with ATZ failed to affect heart and adrenal norepinephrine and adrenal epinephrine concentrations, suggesting a lack of correlation between blood pressure and concentration of these catecholamines in the heart and adrenal glands.