Maintenance of hepatic arterial blood flow during hemorrhage is mediated by adenosine

The effect of hemorrhage (1.91 mL/min, 10 mL/kg) on splanchnic blood flow was determined in cats anesthetized with pentobarbital. The hepatic artery (HA) is relatively protected during hemorrhage and does not constrict, whereas the superior mesenteric artery (SMA) undergoes significant vasoconstriction. Adenosine receptor antagonism with 8-phenyltheophylline blocks the dilator response to infused adenosine selectively (does not block responses to isoproterenol). The dilator response to reduced portal blood flow (the HA buffer response) is also antagonized and adenosine receptor blockade converts the HA response to hemorrhage to one similar to that of the SMA. Thus, the protective dilation of the HA during hemorrhage is mediated by adenosine. In contrast, the vasodilation of the HA seen with reinfusion of the shed blood is not altered by adenosine receptor antagonism.