Effect of low thyroid function on cardiac structure and function in spontaneously hypertensive heart failure rats.

BACKGROUND: Although low thyroid function is known to have detrimental effects on the cardiovascular system, including microvascular impairment, little is known about the pathophysiologic consequences of hypothyroidism in the background of hypertension. METHODS AND RESULTS: Hypothyroidism was induced in female spontaneously hypertensive heart failure (SHHF) rats by treatment with propylthiouracil (PTU) for 6 months. Untreated SHHF and normotensive Wistar Furth (WF) rats served as controls. In terminal experiments, heart weight, echocardiographic measurements, hemodynamics, and arteriolar morphometry were performed. Left ventricular internal diameter in systole and diastole were increased and wall thickness, ejection fraction, heart rate, systolic blood pressure, and +/-dP/dt were significantly decreased in the treatment group. Surprisingly, there were no observed differences in arteriolar density among the 3 groups. CONCLUSIONS: As expected, PTU treatment of SHHF rats led to systolic dysfunction and chamber dilation. However, PTU treatment did not lead to arteriolar loss as previously observed in normotensive rats treated with PTU. These finding suggest that induced hypothyroidism leads to detrimental changes in SHHF rats, but the overall effects were no worse than those previously observed in normotensive rats treated with PTU.