Effect of nitroglycerine on PGI2 generation in cultured human vascular endothelial cells

Vasodilating activity of nitroglycerine (NTG) has not been completely analyzed so far. Recently it is reported that its mode of action resembles Ca antagonists. We have reported that NTG enhances the PGI2 generation in cultured vascular endothelial cells. This paper reports the effects of NTG on the PGI2 generation with reference to cyclic nucleotide metabolism. Endothelial cells isolated from human umbilical veins were cultured by a modified method of Jaffe et al. The released 6-keto PGF1α, in the medium and intracellular cAMP level were assayed by RIA, and 6-keto PGF1α level was employed as a parameter of PGI2 generation. PGI2 generation induced by NTG in the presence of arachidonic acid was diminished when the endothlial cells were pretreated by phospholipase A2 inhibitor mepacrine. This results suggests that the stimulation of PGI2 generation by NTG was dependent on the activation of the phospholipase A2 level. The PGI2 generation induced by A-23187 or NTG was markedly reduced by preincubating the cells with TMB-8. Intracellular Ca++ was observed to affect mainly the early steps of arachidonic acid cascade in the generation of PGI2. The augmented PGI2 generation by A-23187 or NTG disappeared in the Ca++ free medium. In the presence of MIX, intracellular cAMP level was increased and PGI2 generation was decreased. NTG had no effect on the content of cAMP in this experimental system. These results indicate that the increase in PGI2 generation in the vascular endothelial cells by NTG may contribute to the vasodilating activity chiefly through the activation of phospholipase A2 in the arachidonic acid cascade, without influencing on the level of intracellurar cAMP.