Active and Passive Arteriolar Regulation in Spontaneously Hypertensive Rats

Abstract This study determined to what extent active and passive wall tensions increase in in vivo intestinal arterioles of 13- to 15-week-old and 25- to 27-week-old spontaneously hypertensive rats (SHR) to maintain normal or smaller arte-riolar diameters during microvascular hypertension. Acetyl-choline and nitroprusside were used to determine whether vascular muscle relaxation to endothelium-derived relaxing factor or cyclic GMP is impaired. Large arterioles of hyper-tensive rats have passive tension-circumference relations that are steeper and shifted to the left compared with those of age-matched controls; passive resistance to distension limits vasodilation in hypertensive rats except at their naturally elevated arteriolar pressure. Passive tension contributes ap-proximately 30 % of the total resting tension in arterioles of hypertensive and normotensive rats because a greater passiv