Relationship between maternal and fetal lung growth

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.

Fetal lung growth: influence of maternal hypoxia and hyperoxia in rats

The consequences of maternal hypoxia and hyperoxia 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 exposed to one of the following: (1) 10% O2 in N2 or 100% O2 for 2 days beginning at day 7, 11, 14, or 18 of pregnancy; (2) 10% O2 in N2 or 100% O2 for 10 h/day beginning at day 7; or (3) 14-11% O2 in N2 continuously beginning at day 14 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. Hypoxia and hyperoxia of short duration (2 days) had no significant effect on maternal and fetal lungs and placenta. The major findings with intermittent hypoxia and hyperoxia, and with 1 week continuous hypoxia were as follows: (1) hypoxia initiated enlargement in maternal lung, liver, kidney and heart, and growth retardation in the fetus; (2) the direct relationships which exist in normal pregnancy between placental weight or DNA content and fetal body weight were abolished by maternal hypoxia, and that which exists between maternal and fetal lung DNA content, by hypoxia and hyperoxia; (3) both hypoxia and hyperoxia, applied at early pregnancy, caused small for body weight placenta and lung; and (4) neither maternal hypoxia nor hyperoxia influenced fetal lung maturation. It is speculated that reduction in fetal lung DNA content with maternal hypoxia may result from the direct and indirect effects of hypoxia on fetal lung, namely inhibition of cell multiplication and reduced pulmonary blood flow; and that a small fetal lung with maternal exposure to 100% O2, may result from redistribution of blood flow and nutrient supplies to fetal organs with lungs receiving a smaller proportion of it.

Influence of maternal pneumonectomy on fetal lung growth

This study was conducted to test the hypothesis that the compensatory growth of the maternal lung during pregnancy influences fetal lung growth, specifically the fetal lung DNA content. A left pneumonectomy (PN) was performed in pregnant albino rats at different gestation days (GD 3, 7, 9, 10, 12, 14, 16 and 18) and the rats sacrificed at GD 21. Only mothers with litter size of 9-14 fetuses were used for this study. Maternal lung growth was assessed by measuring lung weight, lung air volume and lung DNA content, and the fetal lung growth by lung DNA content. The findings were: (1) pregnancy did not influence the rate of compensatory growth of the remaining lung following PN; (2) neither thoracotomy nor PN had any effect on placental weight or DNA content; (3) lung DNA content for body weight was larger in fetuses of PN rats when PN was performed in the first half of gestation; (4) there was a direct relationship between DNA content of the fetal lung and maternal lung in PN rats; and (5) neither thoracotomy nor PN in pregnant rats influenced the maturation of the fetal lung. The results suggest that a growth factor(s), specific for lungs, is released into maternal circulation following PN, crosses the placenta and enhances the fetal lung growth without affecting its maturation.

Maternal lung growth in surgically reduced litter size pregnancy

In our previous study (Faridy et al., this issue) we observed that pregnant rats with large litter size have larger lungs than rats with small litter size. The present study was conducted to test the hypothesis that in large litter size pregnancy, the maternal lung may not enlarge if, during pregnancy, the large litter size of 11-18 is surgically reduced to a small litter size of 3. A laparotomy was performed in pregnant albino rats at gestation day 7 (R7) or 14 (R14), all fetuses except 3 were removed and the rats were sacrificed at gestation day 21 (term 22 days). Maternal lung growth was assessed by measuring lung weight, lung DNA content and lung air volume, and the fetal lung growth by lung DNA content. The results were then compared with control pregnant rats of large (11-18) and small (1-3) litter size. The findings were: (1) reduction of litter size hindered maternal lung enlargement; (2) the earlier in pregnancy the surgical reduction was performed the smaller was the maternal lung, such that control (11-18) greater than R14 greater than R7 = control (1-3); (3) fetuses of R14 rats had larger lungs per body weight than R7 rats; (4) oxygen consumption of sham-operated rats with large litter size was higher (by 8-12%) than R7 rats. The results suggest that enlargement of maternal lung during pregnancy is related to litter size and perhaps to VO2. The fact that R14 fetal lung is larger than that of R7, supports our previous notion (Faridy et al., this tissue) that factors regulating the maternal lung growth similarly influence the fetal lung.