Nutrient reabsorption of intestine in vitro: Effects of ethanol and caffeine

We studied the effect of ethanol and caffeine on the intestinal reabsorption (jejunum from SD rats) of glucose (Glu) and amino acids. Since most of the studies on the effect of ethanol utilized high concentration, we first characterized the effect of 8% (~ 1.4 M) ethanol on the activity of Na⁺-coupled nutrient transport. Consistent with previous reports, ethanol (> 1M) was found to inhibit the uptake rates of glucose and its non-metabolizable analogue 3-O-methyl-glucose (3 - OMG) by 30%, while leucine (Leu) uptake was inhibited by 60%. Phloridzin, a specific inhibitor for Na⁺-coupled sugar transport, at 1mM concentration could inhibit Glu and 3-OMG uptake by more than 60% without affecting Leu uptake. We then compared the effects of various concentrations of ethanol on about 20 intestinal segments taken from the same animal. We consistently observed transport inhibition at high concentration of ethanol but at low concentrations (up to 200 mM), there was no consistent effect, while phloridzin or low-Na media (86% of Na replaced by choline) significantly reduced the rate of nutrient uptake in the same experiment. Thus, it appeared that low concentrations of ethanol had no significant effect on Na⁺-coupled nutrient uptake. We also determined the effect of caffeine on intestinal 3 - OMG uptake. At concentration of 0.05 mM, caffeine inhibited 3 - OMG uptake by about 15% (p < 0.05). The level of inhibition was not significantly different at 0.5 mM, but a slightly higher level of inhibition (20%) was reached at 5mM. The action of caffeine could be mimicked by dibutyryl cAMP (1mM).