BOTH POSITIVE AND NEGATIVE PORTAL VENOUS AND HEPATIC ARTERIAL GLUCOSEGRADIENTS STIMULATE HEPATIC GLUCOSE-UPTAKE AFTER THE SAME AMOUNT OF GLUCOSE IS INFUSED INTO THE SPLANCHNIC BED IN CONSCIOUS DOGS

We studied the effects of both positive and negative portal venous and hepatic arterial glucose gradients on hepatic glucose uptake after th e same amount of glucose was administered into the portal vein and/or hepatic artery. Studies were performed on eight unrestrained conscious dogs with catheters in the portal vein, hepatic vein, gastroduodenal artery, superior mesenteric vein, and femoral artery and Doppler flow probes on the portal vein and hepatic artery. Glucose was infused as f ollows: protocol 1, 55.6 mu mol/kg/min into the portal vein for the fi rst 90 minutes; protocol 2, 27.8 mu mol/kg/min into both the portal ve in and hepatic artery for the next 90 minutes; and protocol 3, 55.6 mu mol/kg/min into the hepatic artery for the last 90 minutes. The porta l venous and hepatic arterial plasma glucose gradient was 2.1 +/- 0.3, -3.0 +/- 0.5, and -7.1 +/- 0.6 mmol/L, the rate of hepatic glucose up take divided by the administered glucose load was 46% +/- 11%, 42% +/- 10%, and 57% +/- 8%, net hepatic glucose uptake was 25.4 +/- 5.9, 23. 5 +/- 5.6, and 31.6 +/- 4.6 mu mol/kg/min; and the fractional hepatic extraction of glucose was 10.7% +/- 2.2%, 11.6% +/- 2.5%, and 15.0% +/ - 2.1%, respectively (mean +/- SEM of three points at 60, 75, and 90 m inutes in each protocol). The rate of hepatic glucose uptake divided b y the administered glucose load, net hepatic glucose uptake, and fract ional hepatic extraction of glucose did not change significantly despi te the various portal venous and hepatic arterial glucose gradients. W e also studied the effect of the same amount of intraportal glucose in fusion for 240 minutes on net hepatic glucose uptake. From 60 to 240 m inutes, net hepatic glucose uptake did not change significantly. In co nclusion, the liver took up a large amount of glucose administered int o the portal vein and/or hepatic artery, regardless of positive or neg ative portal venous and hepatic arterial glucose gradients. Augmentati on of hepatic glucose uptake is not dependent on the signal of the pos itive or negative portal venous and hepatic arterial glucose gradient. Copyright (C) 1998 by W.B. Saunders Company.