Aortic Reactivity of Rats with Genetic and Experimental Renal Hypertension

The isometric tensions produced by low concentrations of norepinephrine (1 × 10−10 and 3 × 10−10M) or potassium (10 mM) were greater in aortic rings from mature rats with hypertension produced by bilateral renal encapsulation and from rats with genetic hypertension than from Car-worth normotensive Wistar rats. This hyper-reactivity was not associated with a hypersensitivity to low calcium concentrations in the presence of 80 mM KCl. Similarly the loss of maximum response to KCl with time in calcium-free solution was the same for aortic smooth muscle from normotensive and hypertensive rats. However, the rate of relaxation after 80 mM KCl was washed from the bath with normal Krebs solution was much faster for aortic smooth muscle from normotensive than from hypertensive animals. Spontaneous contractions were observed in aortic rings obtained from eight of 12 renal hypertensive rats but were not observed in rings from either spontaneously hypertensive or normotensive rats. An elevated thyroid activity was not associated with the increase in systolic blood pressure to 185 mm Hg in the renal encapsulated rats. The results suggest that the hypersensitivity to norepinephrine of the aortic smooth muscle is due to an altered cell membrane rather than a specific alteration of the adrenergic α-receptors.