NITRIC-OXIDE PRODUCED BY ENDOTHELIAL-CELLS INCREASES PRODUCTION OF EICOSANOIDS THROUGH ACTIVATION OF PROSTAGLANDIN H SYNTHASE

The endothelium serves many functional roles, including the modulation of vascular smooth muscle tone through the release of vasoactive agen ts such as nitric oxide (NO) and the eicosanoids. We proposed that NO produced by endothelial cells would increase the production of eicosan oids through enhanced expression and/or activation of prostaglandin H synthase. NO and eicosanoid synthesis were stimulated in a bovine coro nary microvessel endothelial cell line with the calcium ionophore A231 87 (1 mu mol/L). Our data demonstrated the following: (1) A23187 stimu lated NO synthesis along with prostacyclin and thromboxane production. (2) Inhibition of NO synthesis with N-G-nitro-L-arginine methyl ester (0.1 mmol/L) significantly diminished both prostacyclin and thromboxa ne production. (3) Cells incubated with hemoglobin (2 mu g/mL), which inactivates NO, decreased A23187-stimulated prostacyclin production, w hereas cells incubated with superoxide dismutase (20 U/mL), which prot ects NO from superoxide anions, enhanced prostacyclin production. (4) Exogenous NO stimulated prostacyclin production. (5) The interaction o f NO with prostacyclin persisted in the presence of excess exogenous a rachidonic acid (100 mu mol/L). (6) Cyclooxygenase activity in cell ly sates increased in the first hour of NO stimulation. (7) NO stimulatio n of prostacyclin occurred within 1 hour and continued for 8 hours. (8 ) Neither constitutive nor inducible prostaglandin H synthase enzyme e xpression was altered by NO. (9) Cycloheximide (10 mu mol/L) had no ef fect on A23187 stimulation of prostacyclin production. (10) Exogenous cGMP (10 mu mol/L) or a phosphodiesterase inhibitor (1 mmol/L) did not affect prostacyclin production. These data indicate that stimulating synthesis of endogenous NO in cultured endothelial cells increased eic osanoid production through activation of prostaglandin H synthase.