Metabolism and transport of galactose by rat intestine

Intestinal uptake and metabolism of galactose were examined in everted jejunal rings from fasted adult rats using 0.2-28 mM sugar. After 60-min incubations, the total uptake (free tissue plus amount metabolized) of galactose ranged from 1.75 mumol/g at 0.2 mM to 21 mumol/g at 28 mM. Free tissue galactose was 17% of the former and 73% of the latter amount while that oxidized to 14CO2 represented only 6-16% of amount taken up. Compared to glucose, similar amounts of galactose are taken up at 0.2-2.0 mM, however, gllcose rtween 0.2 and 2 mM similar amounts of both sugars are metabolized, although a greater portion of the glucose is oxidized to 14CO2. Above 2.0 mM, 2-3 times more glucose is metabolized than galactose. Both uptake and metabolism showed saturability and kinetic analysis revealed two limbed Linweaver-Burk plots, suggesting operation of a high affinity low Km and a low affinity high Km system for sugar transport. In a series of in vivo studies, to assess the role of the intestine in the total body metabolism of galactose, 14C-labeled galactose injected intraperitoneally at a dose of either 50 or 300 mg into fasted normal, sham operated and enterectomized rats, no observable difference in 14CO2 production resulted in between the groups. It would thus appear that although extensive metabolism of galactose may take place in intestinal tissue in vitro, the intestine does not play a significant role in galactose disposition in vivo.