Role of hyperventilation in hypoxia on lung growth in rats

This study was conducted in an attempt to differentiate the contribution of hyperventilation, if any, from that of low PO2 on adaptive lung growth in response to hypoxia. Male albino rats were exposed to one of the following: (1) Room air for 7 days, as control; (2) 10% O2 in N2 for 7 days; (3) 10% O2 for 6 h, 1 day or 2 days and air for the remaining of 7 days; (4) 10% O2 for 2 days and 7% CO2 in air for 5 days; (5) air for 2 days and 7% CO2 for 5 days; or (6) 7% CO2 in air for 7 days. Lung growth was assessed by measuring the lung weight, lung air volume, lung DNA content and rate of DNA synthesis in lung explants. Hypoxia stimulated lung DNA synthesis even when administered for only 6 h, and the effects persisted for a few days after discontinuation of hypoxia. Hypercapnia did not stimulate DNA synthesis in lung. In 2 day hypoxic 5 day air rats the lung weight and lung DNA content increased, in 2 day air 5 day hypercapnic rats only the lung volume increased, and in 2 day hypoxic 5 day hypercapnic rats all parameters of lung growth, i.e., lung weight, DNA content and air volume increased as in 7 day hypoxic rats. The results suggest that adaptive or compensatory lung growth in hypoxia is brought about on one hand by the direct effect of low PO2 on lung cells, resulting in lung hyperplasia, and on the other hand by the mechanical stimulation of lung tissue by hyperventilation, causing lung distension.