Reduction of prostacyclin synthesis as a possible cause of transient flow reduction in a partially constricted canine coronary artery.
Coronary blood flow decreases cyclically in a partially occluded coronary artery of anesthetized dogs. Spontaneous aggregation and deaggregation of platelet plugs in the constricted artery have been indicated to be responsible for this phenomenon. A current hypothesis is that platelet aggregation may be determined by a balance between proaggregatory platelet product, thromboxane A2 (TXA2), and antiaggregatory substance, prostacyclin (PGI2). To elucidate the relationship between the cyclical reduction of coronary flow (CRCF) and metabolic alterations of TXA2 and PGI2, we attempted to determine the plasma levels of their stable catabolites, thromboxane B2 (TXB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), in the coronary circulation of 69 dogs. Of 40 cases, 20 cases exhibited CRCF accompanying a significant increase in TXB2 in the coronary sinus (CS) (P less than 0.05) and constant levels of 6-keto-PGF1 alpha in the CS and aorta (Ao). Another 20 cases did not exhibit CRCF that accompanied a marked increase in 6-keto-PGF1 alpha (P less than 0.05) with virtually no change in TXB2 in the CS and Ao. A higher dose of indomethacin (10 mg/kg, i.v.) was capable of evoking CRCF in cases not exhibiting CRCF spontaneously. Under these conditions, a significant decrease in 6-keto-PGF1 alpha was seen both in the CS and Ao compared with lower doses of indomethacin (1 to 3 mg/kg, P less than 0.01), that produced less pronounced reduction of 6-keto-PGF1 alpha without CRCF. Intravenous infusion of PGI2 (0.1 microgram/kg/min.) completely abolished spontaneously and indomethacin-induced CRCF with a marked elevation of 6-keto-PGF1 alpha in the CS and Ao. Although OKY-1580, a TXA2 synthetase inhibitor, relieved spontaneously-evoked CRCF with a marked increase in 6-keto-PGF1 alpha and a slight reduction of TXB2, indomethacin-induced CRCF was not abolished by this agent. These results are consistent with the hypothesis that the reduction of endogenous PGI2 synthesis in the vascular wall is related to the occurrence of CRCF after partial constriction of coronary artery and indomethacin.
D015121:6-Ketoprostaglandin F1 alpha / Q000378:metabolism; D000818:Animals; D003326:Coronary Circulation / Q000187:drug effects; D003327:Coronary Disease / Q000378:metabolism*; D003331:Coronary Vessels / Q000378:metabolism; D004285:Dogs; D011464:Epoprostenol / Q000096:biosynthesis* / Q000494:pharmacology; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D009206:Myocardium / Q000378:metabolism; D011863:Radioimmunoassay; D013928:Thromboxane A2 / Q000378:metabolism; D013929:Thromboxane B2 / Q000378:metabolism
D013929:Thromboxane B2; D013928:Thromboxane A2; D015121:6-Ketoprostaglandin F1 alpha; D011464:Epoprostenol; D007213:Indomethacin