THROMBOXANE A(2) ANALOG CONTRACTS PREDOMINANTLY THE HEPATIC VEINS IN ISOLATED CANINE LIVER

Thromboxane A(2) (TxA(2)) is a potent vasoconstrictor and has been imp licated as a mediator of liver diseases such as ischemic-reperfusion i njury. We determined the effects of TxA(2) and the well-known hepatic venoconstrictor histamine, on the vascular resistance distribution and liver weight in isolated canine livers perfused with blood via the po rtal vein. The stable TxA(2) (STA(2); 20 mu g, n = 5) and histamine (5 mu g, n = 6) similarly increased the hepatic total vascular resistanc e, 2.5- and 2.4-fold, respectively. The increase in the hepatic venous resistance was significantly greater than that of the portal resistan ce (threefold vs. 1.9-fold for STA2; threefold vs. 1.8-fold for histam ine). Predominant hepatic venoconstriction induced by both agents was confirmed in Livers perfused in a reverse direction from the hepatic v ein to the portal vein, as shown by marked precapillary vasoconstricti on. STA(2) transiently increased liver weight loss (-3.6 g/100g liver weight), followed by a gradual weight gain (9.0 g/100 g). Histamine ca used a progressive weight gain (9.1 g/100 g). In conclusion, similar t o histamine TxA(2) constricts predominantly the hepatic vein in isolat ed canine livers.