Inhibition of EDRF release by native low-density lipoprotein from cultured porcine endothelial cells through intracellular mechanisms.

Cyclic GMP accumulation in endothelial cells-smooth muscle cells (EC-SMC) coculture induced by both receptor-dependent (thrombin, bradykinin, BK) and receptor-independent (Ca(2+)-ionophore A23187) stimulation, was inhibited by preincubation with low-density lipoprotein (LDL) in time- and concentration-dependent manner. At least 5 min was necessary for the complete blockade with LDL (protein 1 mg/ml). LDL did not affect cyclic GMP-increase by sodium nitroprusside (SNP), a direct stimulator of SMC, but oxidized (ox)LDL (50-250 micrograms/ml) markedly reduced it. An increase of cyclic GMP accumulation in SMC by eluate from stimulated EC columns was completely blocked by 10-min pre-incubation of the column with LDL with or without superoxide dismutase (SOD). In contrast, preincubation of the SMC dish with LDL did not affect cyclic GMP accumulation by the eluate from the stimulated EC column, but preincubation with oxLDL (protein 50-100 micrograms/ml) greatly reduced it. Exposure time of released EDRF to LDL in both coculture and column experiments was < 40-45 s. These results suggest that a brief exposure of EC to pathophysiologic concentration of LDL exclusively affects EC functions, attenuating endothelium-derived relaxing factor (EDRF) release through intracellular mechanisms, and consumption of released EDRF by LDL does not appear to be involved in this LDL inhibitory effect. Possible inhibitory mechanisms of LDL are discussed.