Age dependence of cardiac growth in the normal and carbon monoxide-exposed rat

Abstract

“Young” rats, 5 days of age, and “old” rats, 25 days of age, inhaled 500 ppm carbon monoxide in air until 50 days of age. Heart weight (HW) relative to same-age controls was maximal at 25 days of age in the young rats, a time at which hemoglobin and hematocrit reached minimal values. Weight of the right ventricle (RV), left ventricle (LV), and combined atria showed a similar pattern. HW and weights of LV and RV of the old rats were intermediate to those of the young rats and controls at 40, 45, and 50 days of age. DNA content of the LV and RV increased sharply in the young rats after initial CO exposure, departing significantly from equal-age controls. DNA content in both ventricles in both young and control rats reached plateaus after 20–25 days of exposure, with the former more than 50% above the latter. DNA content of both ventricles of the old rats was similar to the controls at 50 days of age. In addition, both DNA concentration and protein to DNA ratios were examined in the three groups. The study supports the notion that the potential for cardiac DNA synthesis and probably muscle cell hyperplasia in the rat comes to an end during the 5th through 25th days of postnatal life.