Endothelium-dependent vascular relaxing effects of different citrus and olive extracts in aorta rings from spontaneously hypertensive rats

Three citrus fruit extracts (orange, grapefruit and lemon), an olive leaf extract and a citrus–olive mixed extract (Citrolive), which was obtained from olive leaf and bitter orange fruits, were characterized by HPLC and investigated for their endothelium-dependent vascular relaxing ability. Subsequently, aorta rings from SHR were mounted in tissue baths. They were pre-contracted with methoxamine and exposed to the extracts. Intact, endothelium-denuded, L-NAME-, indomethacin- and sirtinol-treated preparations were used. All extracts exhibited endothelium-dependent relaxations that were totally reversed by L-NAME and partly blocked by sirtinol. Indomethacin also decreased the relaxing effect of high doses of lemon and olive extracts, but the arterial relaxations caused by low doses of the different extracts and those caused by high doses of Citrolive extract (a mixed extract) were potentiated by indomethacin. This study confirms Mediterranean plants as an excellent source of functional compounds, showing the relaxing effect of the assayed plant extracts in aorta rings from SHR. Moreover, the results obtained demonstrate the endothelium-dependent vascular relaxing effect of the studied extracts. Endothelial NO release seems implicated in the effect of all extracts and prostacyclin probably participates in the effect of lemon and olive extracts. Nevertheless, enhanced vasoconstrictor endoperoxides seem to be of special importance in the endothelial tissue of SHR, and the release of these products may impair, at least in part, the endothelium-dependent vascular relaxation caused in these animals by orange, grapefruit, lemon, olive, and in particular, Citrolive extracts.