Effects of phospholipases A 2 from Vipera russelli snake venom on blood pressure, plasma prostacyclin level and renin activity in rats

Abstract

Vipera russelli venom contains several isoenzymes of phospholipase A 2 (PLA 2) which were isolated by column chromatography. The effects of PLA 2 fractions on blood pressure, plasma prostacyclin level and renin activity were studied in normotensive and renal hypertensive rats. PLA 2 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 PLA 2 fractions was not affected by heat treatment (70–80°C, 30 min, pH 6.8). After indomethacin (30 mg/kg, i.v.), the hypotensive response to PLA 2 was markedly reduced. Plasma prostacyclin (PGI 2) and thromboxane A 2 (TXA 2) levels were measured by radioimmunoassays of their degradation products, 6-keto-PGF 1α and TXB 2, respectively. PLA 2 fractions (0.1 mg/kg) induced an increase in plasma PGI 2 and TXA 2 levels. There was a positive linear correlation between the PLA 2-induced hypotensive effect and the ratio of increased 6-keto-PGF 1α to TXB 2 (r=0.83) in normotensive rats. In renal hypertensive rats, the increase in PGI 2 level was larger than in normotensive rats. Plasma renin activity was also measured by the radioimmunoassay. Plasma renin activity was reduced by PLA 2 fractions in renal hypertensive rats, but not in normotensive rats. These results suggest that the hypotensive effect of PLA 2 fractions in normotensive rats may be partly due to the increase in plasma prostacyclin and thromboxane A 2 levels. In addition to the larger increase in plasma PGI 2 level, the reduction in plasma renin activity may also contribute to the greater hypotensive effect of PLA 2 fractions in renal hypertensive rats.