Effects of phospholipases A2 from Vipera russelli snake venom on blood pressure, plasma prostacyclin level and renin activity in rats.

Vipera russelli venom contains several isoenzymes of phospholipase A2 (PLA2) which were isolated by column chromatography. The effects of PLA2 fractions on blood pressure, plasma prostacyclin level and renin activity were studied in normotensive and renal hypertensive rats. PLA2 fractions II-5, II-7, III-3 and III-6 (0.1 mg/kg) injected i.v. into rats decreased the arterial blood pressure. The hypotensive action of PLA2 fractions was not affected by heat treatment (70-80 degrees C, 30 min, pH 6.8). After indomethacin (30 mg/kg, i.v.), the hypotensive response to PLA2 was markedly reduced. Plasma prostacyclin (PGI2) and thromboxane A2 (TXA2) levels were measured by radioimmunoassays of their degradation products, 6-keto-PGF1 alpha and TXB2, respectively. PLA2 fractions (0.1 mg/kg) induced an increase in plasma PGI2 and TXA2 levels. There was a positive linear correlation between the PLA2-induced hypotensive effect and the ratio of increased 6-keto-PGF1 alpha to TXB2 (r = 0.83) in normotensive rats. In renal hypertensive rats, the increase in PGI2 level was larger than in normotensive rats. Plasma renin activity was also measured by the radioimmunoassay. Plasma renin activity was reduced by PLA2 fractions in renal hypertensive rats, but not in normotensive rats. These results suggest that the hypotensive effect of PLA2 fractions in normotensive rats may be partly due to the increase in plasma prostacyclin and thromboxane A2 levels. In addition to the larger increase in plasma PGI2 level, the reduction in plasma renin activity may also contribute to the greater hypotensive effect of PLA2 fractions in renal hypertensive rats.