680 MIXING CARBOHYDRATES(CHO) - ADDITIVE AND COMPETITIVE EFFECTS ON ABSORPTION

When intestinal absorptive function is limited, it may be possible to enhance CHO absorption by combining CHOs having different digestive-absorptive pathways. Employing single pass perfusion studies in partially atrophic amylase-free canine jejunal Thiry-Vella fistulae we found that absorption of glucose(G), sucrose(S), and long chain glucose polymers (LCGP) was saturable with infusion conc. of 882, 378, and 347 mg/dl respectively. Absorption of S and LCGP was additive even from solutions containing 900 mg/dl of each sugar (S=159±16, LCGP=70±6, mixture=235±22 μgms/cm/min.). Virtually no G was found in the fistula effluents (<0.1 mg/ml). Adding 900 mg S to 900 mg LCGO did not improve CHO absorption beyond values for 900 mg/dl of G infused alone (378±16 μgms/cm/min.). Addition of the V_max conc. (400 mg/dl) of LCGP to the V_max conc. of G (900 mg/dl) causes mutual inhibition of the absorption of both (G, 346±23 vs. 232±25; LCGP, 63±8 vs. 28; p<.001). Additive absorption occurs with addition of 400 mg/dl LCGP to 500 mg/dl of G (LCGP=56±8, G=152±8, mixture=208±10).

Conclusions: 1)For G polymers and S, hydrolysis, not absorption of the resultant monosaccharides, is rate limiting for jejunal assimilation. 2)G and LCGP either interact in the glycocalyx or compete for absorptive pathways. 3)S does not compete with LCGP for absorption.

Speculation: In formulating enteral feedings or rehydration solutions mixtures of S and LCGP may enhance absorption, but addition of LCGP to G may be deleterious.