Cardiac cellular responses to altered nutrition in the neonatal rat.

Rats reared in litters of 18, 12, and 6 to determine whether preweanling nutritional state would alter rates of cardiac cell division, weighed 31.7, 39.1, 48.2 g, respectively, at 21 days of age. Weights of left ventricles also increased (93.2, 123.5, and 167.2 mg) as did those of right ventricles (29.9, 43.2, and 54.3 mg). Total DNA content rose in both ventricles in the pups reared 6 per litter vs. those reared 18 per litter (6/litter vs. 18/litter), but more so in the left ventricle (79%) than in the right (24%). Autoradiography confirmed that this increase in ventricular DNA resulted from increased proliferation of cardiac muscle cells, fibroblasts, and vascular endothelial cells. When 3H-labeled thymidine was injected on day 1, autoradiographs prepared on day 21 reflected an increased dilution of label in the 6/litter rats, consistent with enhanced proliferation. The labeling index and grains per nucleus of left ventricular muscle cells of the 6/litter rats were 29% (P less than 0.005) and 20% (P less than 0.001) less than those of the 18/litter rats. Less vigorous but definite hyperplasia occurred in the right ventricle, which appeared to respond with an increase more in cell size than in cell number.