Acute exposure of rabbit jejunum to ethanol

The effect of acute exposure of rabbit jejunum to ethanol on the uptake of three hexoses was examinedin vitro. With ethanol present in the preincubation medium for 30 min, or directly in the incubation medium for 6 min, glucose uptake was reduced. Kinetic analysis demonstrated that ethanol in the preincubation medium was associated with a rise in the value of the apparent Michaelis constant (K_m^*), whereas the inhibition of glucose uptake observed with ethanol present directly in the incubation medium was associated with a reduction in the apparent passive permeability coefficient (P_d^*), a reduction in the maximal transport rate (J_d^m), and an increase inK_m^*. When increasing concentrations of ethanol were added to the preincubation or to the incubation medium, there was a reduction in the uptake of both 1 mM and 40 mM glucose, galactose, and 3-O-methyl glucose. The addition of 40 mM galactose or 1 mM phloridzin to 40 mM glucose was associated with a 50% reduction in glucose uptake, but this uptake was not further inhibited by the addition of 6% ethanol (v/v). Similarly, the uptake of 3-O-methyl glucose was inhibited by the addition of 40 mM glucose or galactose but no further reduction in uptake was achieved by adding ethanol. Finally, galactose uptake was inhibited by adding 40 mM glucose or 40 mM 3-O-MG, but the addition of 6% ethanol was associated with no further decline in the uptake of galactose. Previous studies have shown that ethanol has no effect on the effective resistance of the intestinal unstirred water layer when the bulk phase is stirred; thus the ethanol-related changes inK_m^* andP_d^* are associated with qualitatively similar changes in the values of the true Michaelis constant,K_m, and the true permeability coefficient,P_d. In summary, ethanol has a complex effect on the intestinal uptake of hexoses, influencing theK_m,J_d^m andP_d, but the type and extent of inhibition depends upon whether the intestine has previously been exposed to ethanol, or whether the ethanol is presented to the intestine concurrently with the hexose.