A Scanning Electron Microscopic Study on Microvascular Changes in the Monocrotaline-induced Rat Lung by Corrosion Casting Method

ABSTRACT

To investigate the microvascular changes in primary pulmonary hypertension, the lungs of 24 Sprague-Dawley rats were treated by an intraperitoneal injection of 2% monocrotaline(MCT) solution and then examined with scanning electron microscopy(SEM) after microvascular corrosion casting. Histologic examination revealed significant medial thickening in the small to medium-sized pulmonary arteries. Scanning electron microscopic findings of the normal lungs showed two kinds of microvascular structures. One showed a well-fortned three-dimensional basket structure of uniform flat-tubular alveolar capillaries, which were connected to each other in a T or Y shape or at right angles. The other revealed a two-dimensional reticular sheet of round tubular branches mainly in the bronchial artery-supplying regions. The MCT-treated groups(remodelling) showed apparent changes in both kinds of microvasculatures in comparison to the normal group but the more prominent change was found in Lbe bronchial artery microvasculature showing the dense thick encasement around large pulmonary arteries. Alveolar microvasculature of the pulmonary artery revealed individually enlarged angular appearance, with generally deformed alveolar architecture. Quantitatively, the significant enlargement of diameter and intercapillary distance appeared in both microvasculatures of MCT-induced rat lungs, but the density was increased only in the bronchial artery microvasculature. In conclusion, our three-dimensional microvascular study of the MCT-treated rat lungs demonstrates a new morphologic finding of vascular remodeling in primary puhnonary hypertension, which is thought to play an important vascular role in the pathogenesis in addition to interstitial fibrosis.