動脈壁のリン脂質代謝の研究 (3)

Abstract

The properties of phospholipase A2 (Plase A2) in rat arterial wall were studied using 1-palmitoyl-2-[1-14C] oleoyl-phosphatidylcholine (POPC) as a substrate. The Plase A2 activity increased linearilywith the protein concentration upto 250mg/tube. It was also proportionate to the incubation time upto 120min. Km for POPC in the arterial wall was 0.067mM, that was almost equal to that in rat liver. The aorta had two pH optima at 4.0 and 6.2. With cell fractionation, the highest activity was located in the cytosol fraction, although among the particulate fractions the lysosomal and microsomal fractions showed the highest activity at pH 4.0 and pH 6.2, respectively. The measurement of Plase A2 in various blood vessels, such as the thoracic aorta, the abdominal aorta, the brain microvessels and the mesenteric arteries, the aortas showed higher activities than the other vessels at pH 6.2. In the aorta, the abdominal aorta had five times higher activity than the thoracic aorta. In pathological conditions, Hypertensive rats (SHR) showed lower activity at both pH's than the controls. Cholesterolfed (for 20 weeks) rats had significantly higher activity at pH 6.2 than the controls. These results suggest that Plase A2 activity is closely related to a condition where lipid accumulation may occur in the arterial wall. The mechanism of action of and the significance of Plase A2 in the arterial wall remain to be further studied.