Impact of enteral and parenteral nutrition on hepatic and muscle glucose metabolism

Liver and muscle metabolism were assessed in dogs adapted to long-term tota l parenteral (TPN) and enteral (TEN) nutrition. Studies were done in 13 con scious long-term catheterized dogs in which sampling (artery, portal and he patic vein, and iliac vein), infusion catheters (inferior vena cava, duoden um), and transonic flow probes (hepatic artery, portal vein, and iliac arte ry) were implanted. Fourteen days after surgery dogs were grouped to receiv e TPN or TEN. After 5 days of TPN/TEN, substrate balances across the liver and limb were assessed. The liver was a marked net consumer of glucose in b oth groups (23.6 +/- 3.3 vs 22.6 +/- 2.8 mu mol . kg(-1) . min(-1), TPN vs TEN) despite near normoglycemia (6.5 +/- 0.3 vs 6.7 +/- 0.2 mmol/l). Arteri al insulin levels were higher during TEN (96 +/- 6 vs 144 +/- 30 pmol/L; p < .05). The majority (79 +/- 13 vs 76% +/- 7%) of the glucose taken up by t he liver was released as lactate. Despite higher insulin levels during TEN the nonsplanchnic tissues consumed a lessor quantity of glucose (25.9 +/- 3 .3 vs 16.1 +/- 3.9 mu mol . kg(-1) . min(-1)). In summary, the liver underg oes a profound adaptation to TPN and TEN making it a major site of glucose uptake and conversion to lactate irrespective of the route of nutrient deli very. However, the insulin requirements are higher with TEN possibly second ary to impaired peripheral glucose removal.