Increased expression of the lactate dehydrogenase M subunit in myocardial regions with decreased thallium uptake

In ischaemic heart disease, the heart muscle is subjected to repeated episodes of regional ischaemia or to a constant underperfusion. The purpose of the present investigation was to study the myocardial metabolic adaptation to this stress.

Eighteen male patients with ischaemic heart disease were studied by biopsies taken from the left ventricular septum during bypass surgery. Citrate synthase, total lactate dehydrogenase and its H and M subunits, coenzyme Q10, and myoglobin were determined in all biopsies. Concentrations of ATP, ADP, and AMP were determined and energy charge calculated in the biopsies from the patients with ischaemic heart disease. Biopsies from the septal region of hearts obtained from brain dead kidney and liver donors were used as reference and preoperative myocardial thallium scintigraphy was performed in the patients with ischaemic heart disease to relate the myocardial biochemical markers to thallium uptake at the biopsy site.

Myocardial activities of citrate synthase as well as contents of coenzyme Q10 and myoglobin in patients with ischaemic heart disease were not different from those of the reference group, and no linear relation was found between these three markers on the one hand and thallium uptake on the other. The energy charge was directly related and the M subunit of lactate dehydrogenase inversely related to the thallium uptake.

The results suggest an absence of adaptation to ischaemia in terms of increased myocardial oxidative capacity and O2 transport and storage capacity. Furthermore, it is indicated that a stressed energy metabolism with increasing severity of ischaemic heart disease enhances anaerobic metabolism and induces a shift in myocardial lactate dehydrogenase subunit fractions.