OBJECTIVETo investigate the effect of apelin on vasodilatation of isolated pulmonary arterial rings in rats and its relationship to the nitric oxide (NO) pathway, and to observe the difference of vasodilatation between hypoxic rats and normoxic rats.

METHODSThirty-six male Sprague-Dawley (SD) rats were randomly divided into hypoxic group and normoxic group. The effects of accumulated apelin on pulmonary arterial rings preconstricted with norepinephrine (NE) were observed by using tissue organ bath system. After pulmonary arterial rings were pretreated with three methods: removing the endothelium, pretreating with nitric oxide synthase inhibitor L-NAME or soluble guanylatecyclase inhibitor ODQ, the different effect of apelin was observed. In addition, the difference of vasodilatation between hypoxic rats and normal rats were observed.

RESULTS(1) Exposure of intact endothelium pulmonary arterial rings preconstricted by NE to apelin at concentration (0.01 - 100 nmol/L) induced a significant concentration dependent relaxation. The maximal vasorelaxant effect of apelin was 10.62% +/- 2.60%, which was inhibited by removal of the endothelium (P < 0.01), pretreatment with L-NAME (P < 0.01) or ODQ (P < 0.01). (2) Response of pulmonary arterial rings from hypoxic pulmonary hypertension rats was decreased (P < 0.05). Compared to normal rats, at a concentration of 100 nmol/L, the response to apelin on arteries from hypoxic rats decreased 60.45% (P < 0.01). But the values of EC50 were not significantly different (P > 0.05).

CONCLUSIONThese results indicate that apelin relaxes the pulmonary arterial rings of rats in an endothelium dependent manner, which may have a relationship to NO signaling pathway. The response of vasodilatation is decreased in the pulmonary arterial rings from the hypoxic rats.