Lung growth in newborn guinea pigs: effects of endurance exercise

Newborn Hartley albino guinea pigs were exercised daily on a rodent treadmill at 25 m/min, 0 degree grade for a maximum of 1 1/2 h. Groups were exercised for 1, 2 and 3 weeks. Controls were age-matched sedentary animals. A separate group of animals was sacrificed after 12 h of life to establish baseline lung growth data. A morphological and biochemical comparison was made between the lungs of exercised and sedentary animals. No effect of exercise on lung growth was observed. After 2 weeks of exercise animals had diminished somatic growth compared to the controls. The data was pooled from exercised and control guinea pigs at 1 and 3 weeks, at which time there were no differences, in order to obtain normal growth data. The only change between 0 week and 1 week was a slight increase in femur length. Between 1 week (and also 0 week) and 3 weeks there were significant increases in lung volume, lung weight, protein content, inter-alveolar wall distance, mean chord length of alveoli and ducts, and gas exchanging surface area. The guinea pig lung is well alveolated at birth and there was no evidence of subsequent alveolar multiplication. Enlargement of airspaces suggested that lung growth was primarily brought about by dilation. The lack of alveolar multiplication following exercise may be due to the fact the alveoli are fully developed at birth.