Alterations in the microvasculature of one-kidney, one-clip hypertensive rats

The microcirculation was studied in the cremaster muscle of one-kidney, one-clip (1K-1C) hypertensive rats and uninephrectomized controls under chloralose-urethan anesthesia 1-2, 4-5, or 8-9 wk following renal artery stenosis. With the use of television microscopy, inside and outside diameters of first (1A) through fourth-order (4A) arterioles were measured before and after vasodilation with 10(-4) M adenosine. Mean arterial blood pressure was significantly elevated in the 1K-1C rats, rising to 170 +/- 6 mmHg by 8-9 wks vs. 93 +/- 2 mmHg in controls. Enhanced vasoconstriction, resulting in closure of arterioles, appeared only in the smaller arterioles of 1K-1C and diminished throughout the development of hypertension. Structural rarefaction appeared later and increased with the development of hypertension. Vasodilated inside diameters of control, but not 1K-1C, 1A, 2A, and 3As, increased with increasing age, leaving the hypertensive arterioles with structurally reduced lumens and increased wall-to-lumen ratios, but without increases in wall cross-sectional areas. Structural lumen reduction appeared first in the 1A and advanced downstream as hypertension developed. Thus vasoconstriction of the smallest arterioles is important initially in renal hypertension, but structural alterations become more important later.