Cardiovascular response to triiodothyronine in Sprague-Dawley and spontaneously hypertensive rats

In this study we have compared the influence of triiodothyronine (T3) on cardiovascular function and heart weight in Sprague-Dawley and spontaneously hypertensive rats. We also investigated whether the effects induced by T3 are reversible. T3 was administered daily (0.2 mg/kg subcutaneously) for 14 days in female Sprague-Dawley and spontaneously hypertensive rats. Treatment was then stopped for 14 days. At the end of the treatment and of the period without T3, hemodynamic measurements were made in the intact, anesthetized animals by catheterization of the left ventricle with a Millar ultraminiature catheter pressure transducer. Cardiac output was measured by thermodilution. The development and regression of myocardial hypertrophy was measured by the ratio of heart to body weight. The systolic pressure in the left ventricle was higher in spontaneously hypertensive rats than in Sprague-Dawley rats matched for body weight. At the end of treatment with T3, the heart rate was increased to exactly the same extent in both groups. Left ventricular systolic pressure was increased by 15% in Sprague-Dawley rats, but was not altered significantly in spontaneously hypertensive rats. T3 induced an increase in left ventricular dp/dtmax by 106% in Sprague-Dawley rats, but by only 32% in spontaneously hypertensive rats. Cardiac output increased by 63% in Sprague-Dawley rats, but by only 31% in spontaneously hypertensive rats (statistically not significant). When T3 treatment was stopped for 14 days, all the functional changes returned to control values.(ABSTRACT TRUNCATED AT 250 WORDS)