INTERACTIONS OF ENDOTHELINS AND EDRF IN BOVINE NATIVE ENDOTHELIAL-CELLS - SELECTIVE EFFECTS OF ENDOTHELIN-3

The tone of vascular smooth muscle is influenced by factors released from the endothelium, including endothelin (ET)-1 and endothelium-derived relaxing factor (EDRF). To better understand the interactions between these two mediators, we examined the release of both immunoreactive ET-1 (ir-ET-1) and EDRF from bovine aortic intact endothelium. Bovine aortas were opened longitudinally, washed, and clamped with the endothelium uppermost between two plates. The upper plate contained six openings forming identical and independent wells of endothelial cell monolayer. In experiments examining the release of EDRF, measured as accumulated NO2- and NO3- (NOx-), we found that ET-3, calcium ionophore A23187 (A23187), acetylcholine (ACh), or ADP caused significant increase in NOx- release, whereas ET-1 did not. These were significantly reduced in the presence of the EDRF/NO synthase inhibitor, N(G)-methyl-L-arginine (L-NMA). In a parallel series of experiments measuring EDRF release by stimulation of guanosine 3',5'-cyclic monophosphate (cGMP) accumulation in rat fetal lung (RFL)-6 cells, ET-3 but not ET-1 was also found to be active as a releaser of EDRF. A23187 caused an increase of ir-ET-1 release, whereas ACh, ADP, or the NO-containing compound sodium nitroprusside decreased the release of ir-ET-1. The depression in ir-ET-1 release in the presence of ACh or ADP was not seen when the endothelium was treated with L-NMA. When the cells were pretreated with 8-bromoguanosine 3',5'-cyclic monophosphate (8-bromo-cGMP), the release of ir-ET-1 in response to A23187 was significantly depressed. These results suggest that bovine aortic endothelial cells express ET-3-selective receptors, activation of which leads to the release of EDRF/NO, which in turn depresses the release of ir-ET-1, possibly via a cGMP-mediated mechanism.