The effect of chronic hypoxia on pulmonary arteries in young rats.

The effect of hypoxia on the postnatal development of rat lung from 8 days of life and continuing for 3, 7, 14, 21 and 28 days is described, with particular emphasis on the pulmonary arterial circulation. In hypoxic rats, absolute lung volume and body weight increases more slowly than in age-matched controls but lung volume relative to body weight is greater. After three days hypoxia intra-acinar arterial concentration is reduced and medial thickness of small arteries increased but by Day 7, both features return to "normal" values. By Day 14, right ventricular hypertrophy is apparent as is reduction in lumen diameter of preacinar arteries. From Day 21, muscle is seen in smaller and more peripheral arteries than normal: By Day 28 arteries of all sizes show increased medial thickness, and arterial and alveolar concentration is reduced. Compared with adult rats the growing lung seems to be somewhat "protected" in that the hypoxia-induced changes occur slowly although ultimately their severity is similar. At the end of the exposure period, however, the young lung is small for age suggesting that the changes are more severe than in the adult.