Long-term beta-blocker treatment prevents chronic creatine kinase and lactate dehydrogenase system changes in rat hearts after myocardial infarction.

OBJECTIVES: We tested the hypothesis that long-term beta-blocker treatment with bisoprolol prevents creatine kinase (CK) and lactate dehydrogenase system changes that occur after chronic myocardial infarction.
BACKGROUND: The mechanism of the beneficial effect of beta-blocker therapy is still unclear.
METHODS: Six groups of rats were studied. Sham operated (sham) and hearts with ligated left anterior descending coronary artery (myocardial infarction) were untreated, treated early (beginning 30 min after infarction) or treated late (beginning 14 days after infarction). After 8 weeks, hearts were isolated and buffer perfused isovolumetrically. With a left ventricular balloon, mechanical function was recorded at an end-diastolic pressure of 10 mm Hg. Biopsy samples of noninfarcted left ventricular tissue were taken. Enzyme activities were measured spectrophotometrically; isoenzymes were separated by agar gel electrophoresis; and total creatine levels were measured with high performance liquid chromatography.
RESULTS: The decrease in left ventricular developed pressure in untreated hearts (120 +/- 9 vs. 104 +/- 5 mm Hg [mean +/- SE], p < 0.05, sham vs. myocardial infarction) after myocardial infarction was prevented by early treatment (118 +/- 9 vs. 113 +/- 4 mm Hg). Late treatment failed to improve mechanical function. Reduction of CK activity occurring in untreated infarcted hearts (6.4 +/- 0.3 vs. 5.1 +/- 0.3 IU/mg protein, p < 0.05, sham vs. myocardial infarction) was prevented by early beta-blocker therapy. The increase in CK isoenzyme BB and MB levels, decrease in mitochondrial CK isoenzyme levels and increase in anaerobic lactate dehydrogenase isoenzyme levels in untreated infarcted hearts did not occur during bisoprolol treatment. The decrease in total creatine levels after myocardial infarction (74.2 +/- 4.9 vs. 54.9 +/- 3.3 nmol/mg protein, p < 0.05, sham vs. myocardial infarction) was prevented by bisoprolol treatment. Early treatment was more effective than late therapy in preventing CK and lactate dehydrogenase system changes. In addition, in sham hearts, a 40% increase of creatine levels above normal levels was detected.
CONCLUSIONS: Bisoprolol prevented changes in CK and lactate dehydrogenase system that occur after myocardial infarction. These observations may be related to the beneficial effects of long-term beta-blocker treatment in patients with chronic myocardial infarction.