A negative arterial-portal venous glucose gradient increases net hepatic glucose uptake in euglycemic dogs

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Abstract
We investigated whether a negative arterial-portal venous (a-pv) glucose gradient, or “portal signal,” can increase net hepatic glucose uptake (NHGU) and decrease muscle glucose uptake at euglycemia as it does at hyperglycemia. Twenty 42-h fasted dogs were studied during a basal and two 120-min euglycemic periods ( period I and period II). Glucagon was maintained at basal levels, and insulin was raised 3-fold (3×Ins, n = 10) or 15-fold (15×Ins, n = 10). During period I, dogs received glucose only peripherally. During period II, one-half of the dogs continued the peripheral infusion; the other one-half received glucose intraportally (4 mg ⋅ kg−1⋅ min−1and reduced peripheral glucose infusion). A negative a-pv glucose gradient was present during intraportal glucose infusion. All 3×Ins and 15×Ins dogs had similar NHGU in period I. In period II, it was 2.1 ± 0.3 (3×Ins) and 2.5 (15×Ins) mg ⋅ kg−1⋅ min−1greater in the presence than in the absence of the portal signal ( P < 0.001). The net glucose fractional extraction data paralleled NHGU. In 3×Ins, but not in 15×Ins, whole body nonhepatic glucose uptake was lower in the presence of the portal signal than in its absence. In conclusion, in hyperinsulinemic, but not hyperglycemic conditions, the portal signal is effective in activating NHGU. The inhibition of nonhepatic glucose uptake, on the other hand, is minimal under euglycemic as opposed to hyperglycemic conditions.