Morphometry of canine coronary arteries, arterioles, and capillaries during hypertension and left ventricular hypertrophy.

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Abstract
The mechanisms responsible for the increase in minimal coronary vascular resistance per unit mass of myocardium in animals with chronic hypertension and left ventricular hypertrophy remain unidentified. Because increases in wall thickness of resistance vessels in some vascular beds in response to hypertension may decrease luminal diameter, we hypothesized that similar changes may occur in the coronary vasculature. To test this hypothesis, we performed hemodynamic and morphometric studies on eight dogs with renovascular hypertension (one kidney, one clip) of 6 weeks' duration, and in six normotensive dogs. Hypertension evoked a 27% increase in left ventricular mass and was associated with a 67% increase in left ventricular minimal coronary vascular resistance per 100 g calculated from coronary perfusion measured with microspheres during adenosine infusion. The vasculature was fixed via perfusion of glutaraldehyde and tissue samples from the left ventricle were embedded in Epon. Wall:lumen ratios, determined by light microscopy, of coronary arteries and arterioles were similar in hypertensive and normotensive dogs. Lumen diameters of large epicardial arteries (greater than 640 microns) of hypertensive dogs increased significantly so that wall:lumen ratios were normal despite an increased medial thickness. Ultrastructural analysis, however, showed an enhancement of the relative extracellular compartment of the tunica media of large coronary arteries of hypertensive dogs: 36.4 +/- 3.4% vs. 26.5 +/- 1.6% (mean +/- SEM). Capillary numerical density and surface area (surface area:tissue volume) were significantly lower in the endomyocardium, while capillary volume density (volume:tissue volume) was lower in the midmyocardium and endomyocardium of hypertensive dogs compared to normotensives.(ABSTRACT TRUNCATED AT 250 WORDS)