The relationship between fibrosis and lactate dehydrogenase isoenzymes in the experimental hypertrophic heart of rabbits.

Cardiac hypertrophy was induced in rabbits by injecting either thyroxine or isoprenaline or by surgically constricting the abdominal aorta. An increase in heart weight was associated with a change in the lactate dehydrogenase isoenzyme pattern and an increase in fibrosis (as measured by hydroxyproline concentrations). Isoprenaline treatment led to a moderate increase in heart weight, a marked decrease in the heart/skeletal muscle subunit ratio of lactate dehydrogenase, and a marked increase in hydroxyproline. Thyroxine treatment led to a small increase in both heart weight and hydroxyproline and a small decrease in the heart/skeletal muscle subunit ration. Coarctation of the aorta, in contrast, caused a marked increase in heart weight, a moderate decrease in heart/skeletal muscle subunit ratio, and a moderate increase in hydroxyproline. These results suggest that the decrease in the heart/skeletal muscle subunit ratio of lactate dehydrogenase in the experimental hypertrophic heart reflects the extent of myocardial fibrosis, rather than changes within the hypertrophied myocardial cells.