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.