Effect of increased carbohydrate utilization potential on cardiac isomyosin in thyroidectomized rats

Previous studies have shown that dietary carbohydrate (CHO) can impact on cardiac isomyosin expression in hormonally deficient animals. The primary objective of this study was to determine whether a high-CHO diet alters cardiac isomyosin expression in severe thyroid-deficient rats. Also the effects of targeting the heart with episodes of biasing cardiac metabolism toward CHO were studied. Female Sprague-Dawley rats were assigned to one of two major groups: 1) normal control and 2) thyroidectomized (TX) propylthiouracil treated. The TX rats were allocated into four experimental subgroups as follows: 1) mixed diet; 2) high-CHO diet; 3) high-CHO diet and treated with oxfenicine, a fatty acid oxidation inhibitor; and 4) high-CHO diet, treated with oxfenicine, and trained. Results show that, at the end of 12 wk of thyroidectomy, there was a marked shift in cardiac isomyosin distribution to predominance of the V3 isoform. However, 6 wk of experimental manipulation failed to redirect cardiac isomyosin expression in TX rats. It is concluded that increased CHO utilization does not influence cardiac isoenzyme expression in markedly hypothyroid female rats. Dietary effects of CHO on cardiac isomyosin require some critical level of thyroid hormone for mediating the response.