Peroxide mediated effects of homocysteine on arterial prostacyclin synthesis

The effects of homocysteine on the synthesis of arterial prostacyclin (PGI2) were investigated. Homocysteine at 10 mM and 1 mM concentration inhibited PGI2 synthesis from both exogenous and endogenous arachidonic acid. While concentrations of 100 microM and 1 microM stimulated PGI2 synthesis. Similar inhibitory effects of H2O2 on PGI2 synthesis were observed. High concentrations (100 microM and 500 microM) of H2O2 inhibited PGI2 production while low concentrations (1 microM) of H2O2 stimulated it. Catalase overcame the inhibitory effect of H2O2 (100 microM). Homocysteine induced O2 uptake and catalase inhibited the O2 uptake by homocysteine. Thus the inhibitory and stimulatory effect of homocysteine may be dependent on the oxidation of homocysteine and subsequent H2O2 generation.