Influence of combined intravenous and oral glucose administration on splanchnic glucose uptake in man.

The influence of intravenous plus oral glucose administration on splanchnic glucose handling was examined in healthy young individuals by combining the hepatic vein catheterization technique with the double glucose tracer method. After 1 h of steady state hyperglycaemia (11.7 mM) induced by intravenous glucose alone (hyperglycaemic clamp technique), subjects ingested 89 +/- 1 g of glucose, and the hyperglycaemic plateau was maintained for the subsequent 4 h by adjusting the exogenous glucose infusion rate. Over the 4-h absorptive period, only 51 +/- 4 g of oral glucose (i.e. 58 +/- 4% of the ingested load) appeared in the systemic circulation, while 193 +/- 15 g (1.072 +/- 0.83 mol) of glucose had to be infused exogenously to sustain the hyperglycaemia. Endogenous glucose production was suppressed by over 60%. Net splanchnic glucose balance switched from a positive value (i.e. net uptake) of 5.06 +/- 2.56 mumol min-1 kg-1 with intravenous glucose alone (0-60 min) to a negative one (i.e. net output) of 12.50 +/- 2.44 mumol min-1 kg-1 during 4 h (60-300 min) of intravenous + oral glucose. The mean rate of splanchnic glucose uptake was estimated to be 6.39 +/- 4.67 mumol min-1 kg-1 with intravenous glucose alone, and 8.83 +/- 4.28 mumol min-1 kg-1 with intravenous + oral glucose. In either case, the large majority (80-90%) of the glucose appearing in the systemic circulation was disposed of by extrasplanchnic tissues. These results indicate that pre-existing hyperglycaemia and/or hyperinsulinaemia inhibit gastrointestinal glucose absorption, and that oral glucose administration does not result in a major redistribution of intravenous glucose between splanchnic and extrasplanchnic tissues.