Changes of vascular smooth muscle reactivity in hypertensive rats

Mechanical responses produced by high potassium solution (high-K), norepinephrine (noradrenaline; NA) and phenylephrine (Phe) were examined in the thoracic aorta isolated from control (WKY) and spontaneously hypertensive rats (SHR). In the SHRs the tissues showed increased sensitivity to high potassium compared with those from the control rats. Mechanical removal of endothelium in tissues from the controls did not change the response. The effects produced by NA and Phe were also increased in tissues from SHRs. The amplitudes of contractions were enhanced after removal of the endothelium in tissues from the controls. The relaxation in response to endothelium-dependent vasodilators (acetylcholine and histamine) was significantly depressed in aortic rings from SHRs. Experiments using modified sandwich preparations suggest that the defect in the relaxant ability of vascular smooth muscle is coupled to a reduced functionality of the endothelium.