Protective role of folic acid in thyroxine-induced cardiac hypertrophy in hyperthyroid rat

Hyperthyroidism is a common metabolic disorder with prominent cardiovascular manifestation. It causes a hyperdynamic circulatory state because of a marked reduction in peripheral vascular resistance and an increased total blood volume and heart rate. We studied the changes in the heart structure of hyperthyroid rat at the post-pubertal stage, in addition to the role of folic acid in treatment. Thirty male Wistar rats were equally divided into six groups; the first and second groups were the control and folic acid groups respectively while the third group was the hyperthyroid rat group; the fourth and fifth groups were co- and post-treated hyperthyroid rat with folic acid respectively and the sixth group was self-treated hyperthyroid rat group. Serum T₃ andT₄ levels were significantly increased while TSH levels were significantly depressed in rats receiving thyroxine indicating the induction of hyperthyroid state. Left ventricle section in the heart of hyperthyroid rats showed many abnormalities such as myocardial hyperatrophy, hydrophobic changes of myofibrillar structure with striations, and focal haemorrhage when compared with that in control. The PCNA label index in cardiac tissues was significantly increased in hyperthyroid rat (grade 4) and their levels were significantly decreased in co- and post-treated hyperthyroid rats with folic acid (grades 3 and 2 respectively) when compared with control (grade 0). Treatment of hyperthyroid rats with folic acid improves the histopathological alternation and the intensity of PCNA immunoreactive cells demonstrating the recovery of some injury. In conclusion, our results indicated that folic acid had ameliorative effect against cardiac hypertrophy induced by thyroxine and the best results were found in case of using the folic acid as an adjuvant therapy after returning to the euthyroid state.