Vascular amplifier properties in renovascular hypertension in conscious rabbits. Hindquarter responses to constrictor and dilator stimuli.

The local responses of the resistance vessels of the hindquarters of conscious, renal hypertensive (cellophane wrap) and sham-operated normotensive rabbits were studied during infusions of constrictor (norepinephrine, methoxamine, angiotensin II) and dilator (acetylcholine, adenosine, serotonin) drugs. The rabbits had implanted Doppler ultrasonic flow probes on the lower aorta and an indwelling catheter for intra-arterial infusion of drugs. Autonomic blockade with mecamylamine and propranolol was used to determine local vascular effects of each drug uncomplicated by reflex changes. Logistic dose-vascular response curves were characterized by their range from resting to maximum response, their 50% effective dose (i.e., sensitivity or dose at middle of the response range), and the average slope about the 50% effective dose. At maximum dilatation the vascular resistance was about 70% greater in hypertensive rabbits than in normotensive rabbits. There were no significant differences in 50% effective dose values between curves for hypertensive and normotensive rabbits for constrictor or dilator drugs. However, with all drugs the hypertensive rabbits showed about twice the change in vascular resistance per unit dose compared with the normotensive rabbits. These results suggest that hypertrophy of the muscles of the precapillary vessels makes them a nonspecific amplifier of vascular resistance changes evoked by constrictor and dilator stimuli. They do not support previous claims of specific changes in "sensitivity" or claims that local amplifier action is unimportant in hypertension.