Effect of prostaglandin I2 on cyclical reductions of coronary blood flow

The effects of prostaglandin (PG) I2 and the agents which affect PG and thromboxane (TX) generating systems on cyclical reductions of blood flow in the partially constricted coronary artery of anesthetized dogs were examined. Cyclical reductions were eliminated by PG I2, but not by PG D2, and were augmented by 15-hydroperoxy arachidonic acid and tranylcypromine that inhibited synthesis of PG I2. The cyclical reductions were also eliminated by Cu-chlorophylline that inhibited synthesis of PG E2 and accelerated synthesis of TX A2, but were not by imidazole and 1-methyl imidazole that inhibited synthesis of TX A2. The results in this and in the previous studies indicate that not TX A2 but PG E2 participates as an inducer while PG I2 participates as an inhibitor in cyclical reductions of coronary blood flow.