Microvascular blood flow in the normotensive and spontaneously hypertensive rat.

Abstract

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 were determined in 7- to 8-wk-old animals. By direct micriscopic 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 5 arterial branching orders from the entering artery (1st order) to the terminal arteriole (5th order). Both these measurements and 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 per 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 5th 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 per 100 g vs. 45.5 .+-. 4.2). In spite of this, the control state flow differences beyond the 2nd order vessels were eradicated by the dilation as were the diameter differences except in the 1st 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. The higher vascular resistance and corresponding lower blood flow of the SHR can be attributed in part to : smaller arterial diameters, locally and/or neurally controlled in the 2nd through 5th order arteries and structurally determined in the 1st order artery and a smaller number of arterial branches.