Endothelial dysfunction exacerbates the impairment of relaxation by lysophosphatidylcholine in porcine coronary artery

1. Current evidence suggests that lysophosphatidylcholine (LPC), a component found in oxidized low-density lipoprotein (Ox-LDL), inhibits endothelium-dependent relaxation (EDR) mediated by endothelium-derived relaxing factor (EDRF) and endothelium-derived hyperpolarizing factor (EDHF). An objective of the present study ws to characterize the roles of the different elements of EDR in LPC-induced impairment within the procine coronary artery. Concomitantly, we sought to determine whether impairment of one component of EDR would increase the sensitivity of the endothelium to LPC. 2. Bradykinin (0.1 mmol/L-0.3 mu mol/L) relaxed U46619 (30 nmol/L)-precontracted porcine coronary artery rings in a concentration-dependent manner. A reduction in the bradykinin-elicited response was observed in N-G-nitro-L-arginine methyl ester (L-NAME; 300 mu mol/L)- and ouabain (50 mu mol/L)-treated rings. Pretreatment with LPC (20 mu mol/L), which on its own had no effect on normal endothelial relaxation, resulted in further inhibition of EDRF- and EDHF-induced relaxations. 3. Our results demonstrate that EDRF and EDHF are the primary mediators of EDR in the procine coronary artery. Our data also show that while a low concentration of LPC (20 mu mol/L) does not impair EDR, it can evoke vascular dysfunction following blockade of either the effects of EDRF or EDHF. Therefore, these data suggest that the partially damaged vascular endothelium could be more sensitive to threshold levels of this atherogenic phospholipid.