Postnatal carbon monoxide exposure: immediate and lasting effects in the rat

Groups of newborn rats inhaled 500 ppm CO for 32 days, after which they continued development in ambient air. The ratio of heart weight to body weight increased sharply after birth, peaked at 14 days of age, and then fell progressively but remained above that of normal rats at 68 and 107 days of age. At 14 days of age, the weight of the left ventricle plus interventricular septum (LV + S) exceeded the controls by 80%, whereas the weight of the right ventricle (RV) was 100% greater. RV weight remained significantly greater than that of the controls at 68, 107, and 217 days of age. The ratio of RV weight to LV + S weight remained higher than that of the controls both during and after CO exposure. Myocardial deoxyribonucleic acid (DNA) concentration (microgram/mg dry wt) declined more rapidly in the CO-exposed groups during the first 2 wk. DNA content (microgram/LV + S + RV) was not significantly different. There were no differences in DNA concentration or content after CO exposure. Hydroxyproline, used as an index of collagen content, was unaffected by postnatal cardiomegaly. Hydroxyproline concentration was depressed only during the first 3 wk. Cardiac cytochrome c concentration was depressed and lactate dehydrogenase M subunit composition elevated only during CO exposure. Neither lactate dehydrogenase specific activity nor myoglobin concentration was altered during or after CO treatment. Neither the DNA nor hydroxyproline data provide an explanation for "persistent cardiomegaly."