Enhanced G-protein coupled receptors-mediated contraction and reduced endothelium-dependent relaxation in hypertension.

The present study was designed to demonstrate a hypothesis that some G-protein coupled receptors are up-regulated and a dysfunction of endothelium occurs in hypertension. The arteries from hypertensive patients and spontaneously hypertensive rats (SHR) were tested. An in vitro myograph system was used to obtain concentration-contraction curves mediated by endothelin ET(A), endothelin ET(B), 5-hydroxytryptamine 2A (5-HT2A)-receptors and alpha1-adrenoceptors in the arterial segments. In hypertensive patients, the maximum contractions (Emax) induced by endothelin ET(B), endothelin ET(A) and 5-HT receptors were significantly increased with elevated pEC50 values, while a significantly leftward shift of alpha1-adrenoceptor-mediated contraction was seen. Similar results were obtained in SHR. Specific antagonists for 5-HT2A receptors or alpha1-adrenoceptors rightward shifted the concentration-contractile curves induced by 5-HT or noradrenaline, while the Emax were not significantly altered, suggesting that the contractions were mediated by 5-HT2A receptors and alpha1-adrenoceptors, respectively. Endothelium-dependent maximum relaxation (Rmax) in the arterial segments induced by acetylcholine was significantly decreased in both hypertensive patients and SHR. In addition, nitric oxide- and endothelium-derived hyperpolarizing factor-mediated dilatations were decreased significantly and the arterial endothelial cells were in part lost in SHR. In conclusion, endothelin ET(B), endothelin ET(A), 5-HT2A receptor- and alpha-adrenoceptor-mediated contractions were increased in hypertension, while the endothelium and its functions were damaged.