Hypertension Alters Slope and Range but Not Sensitivity to Vasoconstrictor and Vasodilator Agents in the Rabbit Hindquarter

Abstract

The vascular reactivity (slope and range) and location parameter (ED50) of dose-response curves in the hindquarter vascular bed in conscious rabbits previously subjected to renal cellophane wrapping or sham operation were examined. The animals were instrumented with pulsed Doppler flow transducers and chronic indwelling aortic catheters for intra-arterial drug infusion. The rabbits were ganglion-blocked with mecamylamine before constructing full dose-response curves to intra-arterial infusions of methoxamine, noradrenaline, angiotensin II, acetylcholine, adenosine and serotonin. Curves relating dose to conductance were fitted to the experiments involving constrictors and curves relating dose to vascular resistance fitted to those involving dilator drugs. With both classes of drugs the reactivity was significantly higher in the hypertensive animals than in sham-operated rabbits. There was no difference in sensitivity (ED50 value) between the hypertensive and control animals for any agonist tested. The increased reactivity, but not sensitivity, could be entirely accounted for by the vascular amplifier action of medial hypertrophy in hypertension.