Fetal lung growth: influence of maternal exposure to cold and exercise in rats.

The consequences of maternal exposure to low ambient temperature and exercise on maternal and fetal lung growth and in particular on the relationship between the three gas exchange organs (lungs and placenta) were studied in albino rats. Pregnant rats were subjected to 10 degrees C ambient temperature or to daily 10 min swimming exercise beginning at day 3 or day 11 of pregnancy till day 21 when they were sacrificed. Maternal lung growth was assessed by measuring the lung weight, lung air volume and lung DNA content, and the fetal lung growth by lung DNA content. Comparisons were made in rats with litter sizes of 9-14. The major findings were as follows. Cold increased: (1) the maternal lung, liver, kidney and heart size, and fetal body weight, in both groups, but to a greater degree in rats exposed to cold at day 3; and (2) fetal lung DNA content in rats subjected to cold at late gestation. It abolished the relationship between maternal and fetal lung DNA content which exists in large litter size pregnancies. Exercise did not enlarge the maternal lungs; it decreased the placental weight and fetal lung DNA content and abolished the relationship between maternal and fetal lung DNA content in rats subjected to exercise at early gestation. Neither cold nor exercise had an effect on fetal lung maturation. It is postulated that reduction in fetal lung DNA content with maternal exercise may result from the effects of hypoxemia which may be the consequence of reduced uterine blood flow; and that abolition of normally existing direct relationship between maternal and fetal lung DNA content may be the outcome of the effects of alterations in metabolic and endocrine functions, in both the mother and the fetus, in response to cold temperature and exercise, offsetting the influence the growing maternal lung may have on fetal lung growth.