Microvascular blood flow in the normotensive and spontaneously hypertensive rat.

To help assess the microcirculatory component in the etiology of hypertension, blood flow, vessel diameter, and the distribution of blood flow in the spontaneously hypertensive (SHR) and normotensive (WKY) microvasculature of the rat cremaster muscle have been determined in 7- to 8-week-old animals. By direct microscopic observation of the cremaster muscle, blood velocity (dual-slit method), arterial diameters (eyepiece micrometer), and blood flow calculated from these measurements were determined in each of five arterial branching orders from the entering artery (first order) to the terminal arteriole (fifth order). These measurements as well as the determination of the lengths between consecutive branches were made under control conditions and following the application of 1 mM adenosine to produce a dilated vasculature. Under control conditions, total cremaster blood flow in the SHR (11.1 ± 1.0 ml/min/100 g) was less than in the WKY group (21.1 ± 2.3); the distribution of total blood flow to each branching order was less in the SHR; and the arterial vessel diameters in the SHR group were smaller than the WKY counterparts except in the fifth order arteries. After dilation, blood flow increased in both groups, but flow in the SHR remained significantly less than in the WKY (27.0 ± 1.9 ml/min/100 g vs 45.5 ± 4.2). In spite of this, the control state flow differences beyond the second order vessels were eradicated by the dilation as were the diameter differences except in the first order vessel. Finally, under both control and dilated conditions, the distances between consecutive vessel orders were consistently longer in the SHR group suggesting a smaller number of branches. These results indicate that the higher vascular resistance and corresponding lower blood flow of the SHR can be attributed in part to: 1) smaller arterial diameters, locally and/or neurally controlled in the second through fifth order arteries and structurally determined in the first order artery; and 2) a smaller number of arterial branches. (Hypertension 4: 264–271, 1982)