The fibrogenic response of adult rat lung to continuous propranolol treatment

Fibrogenesis is a common pulmonary response to injury, which is usually preceded by other severe reactions, including inflammation, fluid exudation, and alveolar epithelial damage and proliferation. The purpose of this study was to examine the morphologic effects on the distal lung of a continuous propranolol treatment. Adult male rats were treated, via a subcutaneous osmotic pump, with a continuous (approximately 0.5 mg/hour) dose of propranolol HCl, a potent wide range beta-adrenergic blocking agent, in saline, or saline alone. The animals were killed after one week or three weeks. Electron microscopy of the lungs of the propranolol-treated animals revealed a dramatic increase in the prominence of interstitial cells and fibers of the alveolar septa, along with focal thickening of endothelial cells and some morphologic changes in type II alveolar epithelial cells. In some animals an analysis of total protein content, as well as 3H-proline incorporation into total protein and collagen was undertaken. The results of this study indicated a significant increase in total protein content and proline incorporation into collagen in the lungs of animals treated for seven days with continuous propranolol. There was no evidence of stimulated blood cells, macrophages, edema or severe epithelial damage. This study provides morphologic evidence that continuous treatment with moderate levels of propranolol results in a fibrogenic response in the peripheral lung, in the absence of typical hallmarks of severe pulmonary damage.