A Review of Effects of Hypothyroidism on Vascular Transport in Skeletal Muscle During Exercise

Abstract

Hypothyroidism is a common thyroid disease characterized by exercise intolerance. Both exercise capacity and endurance are compromised in the hypothyroid state. Studies involving rats performing treadmill running have shown that blood flows during exercise to high oxidative, extensor-type muscles are lower in hypothyroid rats compared with those in euthyroid rats. Abnormal cardiac and vascular function appear to contribute to this hxpoperfusion. Experiments involving isolated arterial vessel segments have demonstrated that potential for constriction is normal in vessels from hypothyroid animals; however, reduced vasodilator potential is associated with hypothyroidism. Dysfunction of both endothelium and vascular smooth muscle appear to contribute to blunted potential for vasodilation. Altered ability to generate vasodilatory substances and/or changes in responses to these vasodilators may account for vascular dysfunction. It appears that impaired vascular function interacts with other factors such as poor myocardial function and changes in energy metabolism to compromise exercise tolerance. Key words: blood flow, vasodilation, endothelium, smooth muscle, cGMP