AJP - Heart and Circulatory Physiology, Vol 243, Issue 5 722-H728, Copyright © 1982 by American Physiological Society
Effect of thyroxine treatment on exogenous myocardial lactate oxidation
M. Fintel and A. H. Burns
The effect of thyroxine treatment on myocardial lactate oxidation was
examined by use of an isolated, working rat heart preparation. Thyroxine
treatment, both acute and chronic, was associated with a decrease in
lactate oxidation, when the heart was perfused with a physiological blend
of substrates (free fatty acids, lactate, and glucose). This decrease in
lactate oxidation was not caused by a generalized impairment in
mitochondrial oxidation of acetyl coenzyme A (CoA), as oxygen consumption
was normal and fatty acid oxidation was elevated in the treated animals.
The block in lactate oxidation was localized to the conversion of pyruvate
to acetyl CoA, as indicated by the depressed oxidation of pyruvate and
lactate. Thyroxine treatment was associated with a decrease in pyruvate
dehydrogenase activity. The decrease in pyruvate dehydrogenase activity was
reversible and was attributed to the enhanced myocardial oxidation of free
fatty acids.
