DNA synthesis in atrial myocytes of rats with aortic stenosis.

Indices of labeled myonuclei have been determined in hypertrophying hearts of adult Wistar rats by autoradiography after single-pulse or repeated [3H]thymidine administration. After single [3H]thymidine injections, only 1.36 +/- 0.66 and 1.32 +/- 0.87% labeled myonuclei were observed in the left and right atria, respectively. In the experiments with multiple [3H]thymidine administration, the first injection of this precursor was given on the seventh day after aortic constriction; thereafter, 30 or 42 injections of [3H]thymidine were given at 12-hr intervals up to the fourth postoperation week. Following 30 repeated [3H]thymidine injections, 29.75 +/- 4.65 and 16.78 +/- 3.33% labeled myonuclei were visible in left and right atrial muscle cells, respectively. The cumulative labeling index for left atrium myocytes clearly correlates (r = 0.65-0.73) with an increase in the weight of the heart. Increase in heart weight to more than 160% of controls corresponds to [3H]thymidine labeling of 38.06 +/- +/- and 21.67 +/- 4.16% in left and right atrial myocytes, respectively, whereas in hearts weighing less than 140% of controls, [3H]thymidine labels only 8.20 +/- 1.93% in the left atrium and 3.94 +/- 1.57% in the right one. In the ventricles, cumulative indices of myonuclear labeling do not exceed 0.217 +/- 0.11% even in hearts weighing nearly 180% of controls. Cumulative frequencies of labeling for AV system myocytes are almost ten times higher (1.97 +/- 0.38). These results, together with our data concerning mycocardial infarction (27-29,31), make it necessary to reconsider the role of cardiomyocyte hyperplasia in different experimental and pathological conditions, paying special attention to the proliferative behavior of the atrial muscle cells. DNA synthesis in atrial myocytes seems to be stimulated by heart hyperfunction.