Abstract: In order to examine the effects of protein kinase C activation on the impaired endothelium-dependent relaxation induced by hypercholesterolemia, New Zealand white rabbits fed with cholesterol chow were used and the effects of PMA(protein kinase C activator)and H-7(protein kinase C antagonist)on the endothelium-dependent relaxation and the vasoactive prostanoids production of thoracic aorta were evaluated in vitro. The results demonstrated that H-7 restored the impaired endothelium-dependent relaxation of aortic rings from the cholesterol group, and suppressed the abnormal release of Thromboxane B 2 from aorta with endothelium of the cholesterol group significantly. Rings from the control group treated with PMA showed decreased relaxation, and PMA significantly increased the release of Thromboxane B 2 from aortic segments with endothelium from the control group. PMA and H-7 did not cause any significant change in the production of 6-keto-Prostaglandin F 1a in either the control or cholesterol group. In conclusion, hypercholesterolemia impairs the endothelium-dependent relaxation by increasing the endothelial Thromboxane A 2 production, which is induced by the activation of protein kinase C.

Key words: hypercholesterolemia, endothelium, prostanoids, protein kinase C