Lung growth in response to altered metabolic demand in hamsters: influence of thyroid function and cold exposure.

This study examines the relation between whole body O2 requirements and lung growth. 6-week-old hamsters were exposed to cold (5 degrees C) or injected with thyroid hormone. These treatments elevated O2 consumption by 26% over a 28-day period. Both alveolar surface area and total lung air volume were increased by approximately 25% in each group. Morphometric data suggest that lung enlargement was due to an increase in the number or complexity, rather than size of individual alveolar units. Further elevating O2 demand by increasing thyroid dosage did not enhance lung size beyond the level observed with the lowest dose used. Depressing metabolic rate with an antithyroid drug for four weeks had no effect on lung structure (in this animal model). Results indicate that in hamsters, increased physiologic O2 demand may be met to a certain extent by augmentation of the pulmonary diffusing surface.