EFFECT OF ANGIOTENSIN-INDUCED HYPERTENSION ON RAT CORONARY-ARTERIES AND MYOCARDIUM

Abstract

Acute hypertension was produced in rats by the i.v. infusion of angiotensin amide for 4 h. Both control and hypertensive animals were injected i.v. prior to sacrifice with either horseradish peroxidase (HRP) or colloidal carbon. Epicardial arteries and blocks of ventricular myocardium containing intramyocardial arteries and arterioles were processed for EM. HRP appears to penetrate the endothelium of epicardial arteries from control animals within vesciles that bypass endothelial junctions and empty into interendothelial clefts. Peroxidase does not traverse the endothelium of intramural arteries and arterioles of controls over the 10-min period of observation. There is acceleration of lateral vesicular transport in the endothelium of epicardial arteries after angiotensin infusion and direct permeation of interendothelial clefts of intramural arterial vessels. Medial fragmentation and more extensive necrosis were observed in intramyocardial but not in epicardial arterial vessels. Foci of myocardial damage resembling irreversible ischemic or anoxic injury followed by reflow are described. The increased permeability of epicardial arteries may be due to elevated pressure, while the altered permeability and vascular lesions of intramural arteries and arterioles are more readily attributable to the vasoconstriction produced by angiotensin. The vascular and myocardial lesions are also discussed in relation to the regional actions of angiotensin on the coronary circulation and known effects of this vasoactive peptide on myocardium.