Effect of verapamil on monocrotaline-induced pulmonary artery hypertension and endothelial cell dysfunction in rats

Verapamil, a calcium channel blocker has been used with partial success in cases of primary pulmonary hypertension, as well as to reduce hypoxia-induced pulmonary hypertension (PH) in rats. However, its effect on monocrotaline (MCT)-induced PH in rats is not known. We studied the effect of verapamil on MCT-induced PH. Three weeks after a single injection of MCT, significant PH was noted in the MCT-injected rats compared with control (44.35 +/- 3.5 vs. 22 +/- 2.5 mmHg). MCT-injected rats on daily verapamil showed significant reduction in PH (31.5 +/- 3.4 mmHg). The main pulmonary artery of MCT-injected rats revealed subendothelial thickening, thinning and fragmentation of elastic laminae, smooth muscle cell hypertrophy and necrosis or loss of smooth muscle cells, and increased amounts of collagen in media and adventitia. In contrast, the main pulmonary artery of MCT + VP-treated rats showed less intimal thickening, some smooth muscle cell hypertrophy, but little necrosis or loss of cells in addition to disappearance of outer elastic laminae. Smaller pulmonary arteries (less than 150 microns in diameter) in MCT + VP-treated rats showed less medial thickening than MCT groups. However, diminished lung angiotensin-converting enzyme activity suggestive of endothelial cell dysfunction was noted in both MCT and MCT + VP-treated rats. This study indicates that verapamil attenuates MCT-induced PH, but has no effect on pulmonary endothelial cell dysfunction.