Biochemical and morphological study of cardiac hypertrophy. Effects of thyroxine on enzyme activities in the rat myocardium

Abstract

Experimental hyperthyroidism induced in rats by daily injections of 3,3',5,5'-tetraiode-L-thyroxine (0.5 mg/kg i.p.) for 14 days resulted in a significant increase in heart weight and heart weight/body weight ratio. Hemodynamic and morphological studies were performed in one group. Thyroxine-treated rats showed a characteristic cardiovascular hyperdynamic state, such as tachycardia and augmented rate of contraction, but no evidence of heart failure such as elevated end-diastolic pressures. The cardiac cells in hyperthyroid rats had a significantly larger diameter and more mitochondria than did those of the control rats. In another group the activities of cardiac enzymes involved in energy utilization and liberation were measured biochemically and compared with those of normal controls. Hyperthyroidism resulted in increased specific activity of cytochrome C oxidase and actomyosin ATPase in the myocardium. The specific activity of long-chain acyl-CoA synthetase, carnitine palmityl-transferase, carnitine acetyltransferase, malate dehydrogenase and citrate synthase showed a moderate to marked increment, whereas the specific activity of lactate dehydrogenase and pyruvate kinase remained at the control values. These results suggest that in hyperthyroid rat hearts the functions of both energy liberation and utilization systems are enhanced to meet the added workload. Moreover, the increased activity of the enzymes participating in fatty acid metabolism suggest that in thyroxine-induced hypertrophic and hyperdynamic rat hearts, fatty acids contribute more to the energy supply than do carbohydrates.

Insulin, thyroid hormone, and heart function of diabetic spontaneously hypertensive rat.

“…36 Thyroid hormone may relieve some of these stresses in diabetic SHR, perhaps by increasing the use of fatty acid by the myocardium, 37 by stimulating glucose uptake and use, 38 or by augmenting glucoseinduced insulin secretion, 39 although our data (Table 1) did not support the latter possibility. Thyroid hormone may also enhance the responsiveness of the myocardium to sympathoadrenal influences (see below).…”

Thyroid hormone controls carnitine status through modifications of γ-butyrobetaine hydroxylase activity and gene expression

“…In rats, induced hyperthyroidism was previously reported to result in a cardiovascular hyperdynamic state with tachycardia [25]. The cardiac cells in hyperthyroid rats had a significantly larger diameter and more mitochondria than those of control rats.…”

Mitochondrial pathology in cardiac failure

“…Findings from in vitro systems and animal models Thyroxin can also modulate increases in mitochondrial enzyme activities [73]. It has been proposed that regulation 4.4.…”