The influence of aging and growth on the postnatal development of cardiac muscle in rats.

Abstract

SUMMARY We studied the effects of different rates of postnatal body growth on the growth of rat myocytes. Growth rates were altered by adjusting the number of newborn animals per litter to 4 (fast-growing), 8 (normal), or 16 (slow-growing). On the 21st postnatal day, average left ventricular weights (mg ± SEM) were 80 ± 5 in slowgrowing 131 ± 8 in normal, and 183 ± 5 in fast-growing rats. Average myocyte diameters, obtained from direct microscopic measurements in longitudinal sections prepared from eight animals in each group, were 8.6 ± 0.3, 9.8 ± 0.2, and 10.2 ± 0.3 fim, respectively. The total number and total length of myocytes constituting the left ventricle were estimated, assuming a constant length-to-width ratio and cyclindrical model of myocytes. The estimated total number of myocytes constituting the respective left ventricles were 23.6 ± 2.0, 24.5 ± 2.2, and 31.1 ± 2.1 millions. All differences between experimental groups were significant by analysis of variance. When the estimated total numbers of myocytes and their estimated total lengths were related to the left ventricular weights, a significant linear correlation was obtained, which indicated their dependence on the organ growth and their relative independence of age. These indications were strengthened further by analysis of covariance, which showed that the differences in all morphometric data among the three groups of hearts may be explained entirely by different growth rates of the left ventricle. These results also suggest that the accelerated growth of the heart during the early postnatal period is associated with increased proliferation of myocytes.PROLIFERATION of rat cardiac muscle cells declines rapidly during late embryonic and early postnatal development. Three to four weeks after birth, the total number of cardiac muscle cells is believed to be close to adult values, and further growth of the heart may be accounted for by the growth of the existing cardiac cells.1-1 However, one important question remains to be answered: are the individual cardiac cells "programmed" for a finite number of nuclear and cellular divisions for a given age or can the rate of proliferation previously observed during the early postnatal period be altered by other factors such as organ growth itself? Temporarily dissociating the growth-to-age relationship during the early postnatal period should provide an answer to the above question.The growth rate of the mammalian body is both agedependent and nutrition-dependent. In suckling rats, the number of young animals per litter is a decisive factor, because the source of food is limited to the mother. Thus, by varying the number of young rats per litter, the growth rate can be altered so that the body weight and heart weight may vary 2-4 times between the animals from the small litters (4 rats) and from the large litters (16 rats) when they are weaned at 21 days of age. This approach was used in our present experiments in order to study the effects of slow, normal, and accelerated body and heart growth rate on th...

MR study of postnatal development of myocardial structure and left ventricular function

“…First, the rate of heart growth could be affected by litter size due to different preweanling nutritional state. Smaller litter size has been previously reported to cause accelerated heart growth associated with increased proliferation of cardiac muscle cells during postnatal heart development (42,43). In the current study, similar litter size was maintained (ϳ8 rats /litter) before the rats were weaned at 21 days of age to minimize the influence.…”

Myocyte Morphological Characteristics Differ Between the Phases of Pulmonary Hypertension-Induced Ventricular Hypertrophy and Failure

“…The atrium and aorta were removed from the heart and Each sample provided at least 10,000 measurements, from which an average cell volume was calculated. Cell length, defined as the longest length parallel to the longitudinal axis of the myocyte, was measured in at least 40 cells in order to reduce the sampling error to less than 3%, 11) using a phase microscope (Nikon Corp., Tokyo), from which the average length was calculated. The cellular CSA was calculated by dividing the cell volume by the cell length.…”

Postnatal development of the M-band in rat cardiac myofibrils.

“…During this time, cardiac muscle of rodents also undergoes marked augmentation of the major systems involved in ATP synthesis and degradation (Baldwin et al, 1977;Nayler and Fassold, 1977). In addition, total cardiac mass is increasing rapidly by hyperplasia and hypertrophy of the myocytes (Katzberg et al, 1977;Rakusan et al, 1978;Anversa et al, 1980). Rapid myocardial growth also includes proliferative changes in the capillary vasculature of the tissue and its relationship to the population of contractile cells .…”