Inhibition by D 600 of norepinephrine- and clonidine-induced responses of the aortae from normotensive (WKY) and spontaneously hypertensive rats (SHR).

Comparison was made of the inhibition by D 600 of the norepinephrine (NE)- and clonidine-induced responses of aortic strips from normotensive (WKY) and spontaneously hypertensive rats (SHR). Clonidine-induced responses of aortae from both strains of rats were markedly more susceptible to inhibition by D 600 than those of NE. Omission of calcium from the physiological solution resulted in a greater reduction in response to clonidine. Aortae from SHR were less susceptible to inhibition by D 600 but showed no difference from WKY rats in their responses in nominally calcium-free physiological solutions. Our results clearly indicate a greater dependence on extracellular calcium by clonidine-induced responses of the aortae relative to those of NE.