Thyroid Hormone Analog 3,5-diiodothyropropionic Acid Promotes Healthy Vasculature in the Adult Myocardium Independent of Thyroid Effects on Cardiac Function

Patients with hypothyroidism are at a higher risk for coronary vascular disease. Patients with diabetes and related vascular complications also have an increased incidence of low thyroid function. While thyroid hormones (THs) may be key regulators of a healthy vasculature, potential undesirable side effects hinder their use in the treatment of vascular disorders. TH analogs such as 3,5-diiodothyropropionic acid (DITPA) may provide a safer treatment option. However, the relative potency of DITPA on vascular growth, cardiac function, and metabolism is poorly understood. We hypothesized that the vascular growth-promoting effects of DITPA can be obtained with a minimum effect on cardiac function. Thyroidectomized Sprague-Dawley rats were given slow-release pellets with either thyroxine (T4, 2.7 or 5.2 mg) or DITPA (80 mg) for 6 wk and were compared with placebo. Heart mass, body mass, body temperature, serum THs, cardiac function (echocardiograms and hemodynamics), and myocardial arteriolar density were determined. Hypothyroidism led to reductions in cardiac function, heart mass, body temperature, and myocardial arterioles. High-dose T4 prevented arteriolar loss and the development of hypothyroidism. Low-dose T4 partially prevented the reduction in cardiac function but had minimal effects on arteriolar loss. In contrast, DITPA treatment prevented myocardial arteriolar loss but not the progression of hypothyroid-induced changes in cardiac function. The results suggested that DITPA can promote a healthy vasculature independently from its thyroid-related metabolic effects. Drugs in this class may provide new therapeutic options for patients with vascular disease.