Microvascular responses to norepinephrine in renovascular and spontaneously hypertensive rats

Closed-circuit television microscopy was used to quantitate the responses of in vivo small arteries (50-140 micrometer diam) and veins (95-265 micrometer) to topically applied norepinephrine in the cremaster muscle of four groups of urethan-chloralose anesthetized rats. The rat groups were: Sprague-Dawley control (SDC), Sprague-Dawley renovascular hypertensive (RVH), Wistar-Kyoto control (WKY), and spontaneous hypertensive (SHR). The cremaster muscle with intact circulation and innervation was suspended by sutures in a 60-ml bath of bicarbonate-buffered Krebs solution. The vascular responses to the addition of progressively higher concentrations of norepinephrine to the bath were quantitated to obtain concentration-response curves. We found that the RVH (vs. SDC) had a decreased small-artery control diameter and decreased sensitivity to norepinephrine, whereas the SHR (vs. WKY) had tachycardia and decreased small-vein control diameter. Thus, the microvascular characteristics of these two types of hypertension appear to be quite different.