Impact of Hyperthyroidism and Its correlation on regional blood flow in rats

Abstract

Thyroid hormones (TH) exert multiple effects on the heart and vascular system. In the hyperthyroidism, besides the direct effects of TH on cardiac tissue inducing hypertrophy in rats, TH also lead to an important increase in heat rate and reduction in systemic vascular resistance. In the present study we evaluated the effect of hyperthyroidism (T3, 7ug/100g body wt/2 wk) on regional blood flow (coronary, lung and kidney) and blood pressure parameters in Wistar rats. Hyperthyroidism promoted significant left ventricular (+27.56%) and right ventricular (+33.56%) hypertrophy. Although T3 has promoted a marked increase on blood flow in the myocardium (+98,7%), an important decrease on lung blood flow (−35 %) was observed, which was followed by discrete but significant decrease on cardiac output (−14%). Regard to hemodynamic variables, the hyperthyroidism promoted a significant increase in mean, systolic and diastolic arterial pressure as well as HR compared to control group. These findings show that hyperthyroidism is accompanied by intense changes on the blood flow to lung and myocardium and hypertension. Considering that the reduction in cardiac output and pulmonary blood flow are associated with right ventricular hypertrophy, these findings may have clinical implications by serving as an explanation for the development of pulmonary hypertension and heart failure observed in hyperthyroid patients and point out the importance of adequate control of TH levels.