It has been known that arteries of hypertensive animals and patients are generally thicker and more rigid than those of normal subjects, resulting from the morphological changes induced by an increased stress on the vessel wall. Factors proposed to be responsible for these changes are smooth muscle hypertrophy, increased amount of collagen, hyperplasia of smooth muscle cell and changes in cross-linkages of the fibrous proteins. The present study was conducted to define whether enalapril, a converting enzyme inhibitor of angiotensin II generation from angiotensin I, can restore the structural alterations of aortic media in spontaneously hypertensive rat(SHR).

For this purpose, SHR were treated for 22 weeks with 2mg/kg/day enalapril and morphologic changes were compared between enalapril-treated SHR and normotensive Wistar-Kyoto rats.

The increased thickness of the aortic media in SHR was reduced and intervening elastic laminae were narrowed by enalapril treatment. Subcellular analysis of cytoplasmic composition and nucleus in the aorta of hypertensive rats revealed some modification with enalapril. Some irregularly arranged collagen fibrils in aortic media of SHR were regularly distributed and the periodic bands of the fibrils which were the fragmented were clearly apparent by enalapril treatmed SHR group.

From the above experimental results, it is concluded that subcellular changes of smooth muscle cells and collage fibrils of aortic media in SHR could be repaired by long-term treatment with enalapril.