Differences in inhibition of PGI2 production by aspirin in rabbit artery and vein segments

We have studied the prostaglandin I₂ production by endothelial and subendothelial cells of rabbit aortae and vena cavae. Rabbits were injected intravenously with 0, 10 or 100 mg/kg aspirin. One, 3, 6 or 30 hours later, segments of thoracic aorta or inferior vena cava were removed and their capacity to produce prostaglandin I₂ was measured, using a bioassay system. Both endothelial and subendothelial cells of the arteries and veins produced prostaglandin I₂ which was inhibited by aspirin in doses of 10 and 100 mg/kg. The inhibitory effect of aspirin on venous prostaglandin I₂ production was relatively short-lived and returned to baseline levels within 3 to 6 hours. In contrast, the inhibitory effect of aspirin on prostaglandin I₂ production by arteries lasted for at least 6 hours and by 20 hours had only returned to 50–70% of baseline. When experiments were performed in vitro, a similar difference in the duration of aspirin effect on venous and arterial prostaglandin I₂ production was also observed. These data are consistent with the hypothesis that the turnover of cyclo-oxygenase is more rapid in venous than in arterial cells.