Reactivity to norepinephrine and nature of the alpha adrenergic receptor in vascular smooth muscle of a genetically hypertensive rat

Abstract

Aortic smooth muscle from the so-called spontaneously hypertensive rat (SHR) did not exhibit supersensitivity or hyperreactivity to norepinephrine compared with two strains of normotensive Wistar rats. The dissociation constant K B of phentolamine reacting with alpha-adrenergic receptors in the aorta of the SHR was very similar to values reported for other alpha receptors. Thus, the adrenergic receptors mediating vascular contraction appear to be nearly identical in both SHRs and normotensive animals. Aortic strips from one strain of normotensive Wistar rat developed about as twice as much tension as either the other normotensive strain or the SHR. If two strains of normotensive rat had not been used as controls, an attempt to relate the degree of tension developed to hypertension in the SHR might have been made. It is clear that studies ulilizing the SHR to analyze mechanisms involved in hypertension must use multiple strains of normotensive rats in order to insure adequate controls.