Differential role of endothelium in hawthorn fruit extract-induced relaxation of rat cerebral, coronary, carotid, and aorta

Abstract

The present study was aimed to examine the role of endothelium in the relaxant effect of hawthorn fruit extract of Crataegus pinnatifida in four different types of rat arteries, posterior cerebral communicating artery, right descending coronary artery, common carotid artery, and aorta. In <TEX>$9,11-dideoxy-11{\alpha}$</TEX>, <TEX>$9{\alpha}-epoxy-methanoprostaglandin$</TEX> <TEX>$F_{2{\alpha}}$</TEX> (U46619)-preconstricted arterial rings except for aorta, the extract produced endothelium-independent relaxations with similar potency. This relaxation was unaffected by pretreatment with <TEX>$100\;{\mu}M\;N^G-nitro-L-arginine$</TEX> methylester (L-NAME, the nitric oxide synthase inhibitor), <TEX>$3\;{\mu}M$</TEX> 1H-[l,2,4]oxadiazolo<TEX>$[4,2-{\alpha}]$</TEX>quinoxalin-1-one (ODQ, the guanylate cyclase inhibitor), or <TEX>$10\;{\mu}M$</TEX> indomethacin (the cyclooxygenase inhibitor). Putative <TEX>$K^+$</TEX> channel blockers (charybdotoxin plus apamin or glibenclamide) did not affect the extract-induced relaxation in cerebral or coronary artery rings. In contrast, in rat aortic rings the extract produced significantly smaller relaxant response in endothelium-denuded rings than that in endothelium-intact rings. Pretreatment with L-NAME or ODQ abolished the extractinduced endothelium-dependent aortic relaxation, whilst indomethacin <TEX>$(3\;{\mu}M)$</TEX> had no effect. The present results indicate that hawthorn fruit extract possesses a vasorelaxing effect in cerebral, coronary and carotid arteries and this effect is independent of the presence of a functional endothelium. However, the extract-induced endothelium-dependent relaxation in rat aorta was mediated through endothelial nitric oxide and cyclic GMP-dependent mechanisms, suggesting that active components in the extract may act on endothelium to stimulate release of nitric oxide in large conduit arteries of the rats.