SUMMARY: Residential heating with wood is an important source of ambient air pollution. Evidence links air pollution to serious health effects such as respiratory and cardiovascular mortality and morbidity. We hypothesized that prenatal exposure to wood smoke pollution causes morphological changes in the development of the rat lung, leading to altered lung structure and function during later life. We presumed that analysis of the fetal lung stereology provides novel insights into the underlying processes mediating particulate matter associated developmental changes and damage. The objective of the study was to investigate the effects of exposure during gestational period to wood smoke pollution on lung fetal morphology. To test this, pregnant rats were exposed during pregestational and gestational periods to wood smoke pollution. Complete lungs samples were obtained from 24 fetus from healthy female G3 rats subjected to cesarean at 19 days post-fecundation. The lungs were prepared for histological and stereological analysis. The volume fraction of terminal bronchioles VV [tb, lung] and volume fraction of parenchyma VV [par, lung], surface density of terminal bronchioles SV [tb, lung] as well as numerical density of bronchiolar exocrinocytes NA [ec,lung] were calculated by light microscopy. Statistical analysis detected significant differences between groups in volume density VV [tb, lung; %] (p=0.0012) and surface density SV[tb, lung; mm²/mm³] (p<0.0001) of the terminal bronchioles. However, it did not show differences between groups in the stereological parameter volume density VV [par, lung; %] (p=0.0838) and numerical density of bronchiolar exocrinocytes N [ec,lung; nº/mm²] (p=0.0705). The analysis of the evidence obtained indicates that exposure to environmental pollution was affects lung maturation, and particularly the proportion and area of terminal bronchioles in the fetal lung. In conclusion, maternal exposure to wood smoke pollution during pregnancy was associated with a decrease in the lower conducting airways of lungs, which, according to urban pollution studies, could be related to early childhood lower respiratory illness. The public health implications of this study are that reducing or avoiding exposure to wood smoke is important before and during pregnancy.

 KEY WORDS. Pollution; Smoke; Wood Smoke Pollution; Lung; Stereology; Rat; Temuco