The effects of desiccated thyroid on the rat lung.

Pressure-volume characteristics of whole lungs were measured in euthyroid rats and in rats fed 0.4% desiccated thyroid for eight weeks. The lungs were degassed by incising the diaphragm after the animals had breathed 100% oxygen for ten minutes. The pressure-volume characteristics were measured by inflating and deflating the lungs at a rate of 3.5 cc/min. Total lung capacity (TLC) was considered to be that volume of air required to produce a transpulmonary pressure of 30 cm H2O. At TLC there was 35% greater lung volume in the thyroid-treated animals than in their littermate controls. Similar results were observed in saline-filled lungs. Alveolar surface are (Sa) increased from 0.28m2 in the lungs of control animals to 0.75m2 in lungs of thyroid-treated animals. There was an 85% increase in the alveolar surface density (SVa) in the thyroid-treated animals. These results, obtained by morphometric analysis, suggest that greater lung volume in the thyroid-treated animals resulted from alveolar hyperplasia or "partitioning."