EFFECT OF PHYSIOLOGICAL CONCENTRATIONS OF ESTRADIOL ON PGI(2) AND NO IN ENDOTHELIAL-CELLS

Objectives: To elucidate the mechanisms by which estrogens protect aga inst occlusive vascular disorders, we studied the effect of 17 beta-es tradiol on the production of prostacyclin (PGI(2)) and nitric oxide (N O) in primary cultures of human umbilical vein endothelial cells (HUVE Cs). Methods: To study the effect of 17 beta-estradiol on PGI(2) produ ction, HUVECs were incubated in the absence and presence of 17 beta-es tradiol (0.01-10 nmol/l) encapsulated within beta-cyclodextrin for 12 h in serum-free medium. To study the effect of 17 beta-estradiol (100 nmol/l) on maximal calcium-dependent NO production: we used different approaches. First, HUVECs were incubated with 2 mu mol/l calcium ionop hore A23187 with or without 17 beta-estradiol (100 nmol/l) for 24 h in serum-free medium. Second, HUVECs were preincubated with or without 1 7 beta-estradiol (100 nmol/l) for 12 h in medium supplemented with 2% fetal calf serum, and thereafter incubated in serum-free medium with 2 mu mol/l of A23187 and with 100 nmol/l of 17 beta-estradiol (cells wh ich contained 17 beta-estradiol during the preincubation period as wel l as cells which did not) or without it (only cells which did not cont ain 17 beta-estradiol during the preincubation period) for 6 h or 24 h . Results: 17 beta-Estradiol (0.1 nmol/l) increased the concentration of 6-keto-prostaglandin F-1 alpha, a stable metabolite of PGI(2) in th e incubation medium, by 16%, and no further increase occurred with hig her 17 beta-estradiol concentrations. The stimulation was prevented by tamoxifen. 17 beta-Estradiol did not affect NO production in any of o ur experiments measured as accumulation of nitrate and nitrite in the experimental medium. Conclusions: The stimulatory effect on PGI(2) pro duction of physiological concentrations of 17 beta-estradiol, shown no w for the first time, may provide one explanation for the ability of 1 7 beta-estradiol to protect against occlusive vascular disorders.