Effect of diazoxide on aortic reactivity to calcium in spontaneously hypertensive rats

Diazoxide (10^-4 M) reduced the maximum response to noradrenaline of aortic strips from normotensive and spontaneously hypertensive rats (S.H.R.). The extent of this inhibition was the same for aortae from both types of rat and was greater than the depression of maximum response to KCl. The percent reduction of maximum response to noradrenaline after exposure of aortae to calcium free solution for various times was the same for tissues from normotensive and hypertensive rats. When calcium was added to calcium free solution containing either noradrenaline or KCl, a greater inhibition of contraction of aortae from S.H.R. than from normotensive rats was produced by diazoxide. Under the special conditions of the latter experiments, these results are consistent with the hypothesis that vascular smooth muscle of normotensive and S.H.R. differ in their reaction with diazoxide, and that this agent could exert its antihypertensive effect at a site that is not specifically related to adrenergic α receptors.