Factors Affecting Metabolism and Absorption of L(+)-Lactate-U-14C by Bovine Rumen Epithelium in vitro2

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Abstract
The metabolism and absorption of L(+)-lactate-U-14C by rumen epithelium from Holstein-Angus cattle was investigated using respiration and diffusion techniques. The effects of mucosal buffer pH and lactate concentrations were studied using factorial designs. In respiration trials, variation in oxygen uptake, lactate utilization and amount of label appearing in tissue protein was attributed to buffer pH. Oxygen uptake and CO2 production were affected by substrate concentration. Approximately 25% of the label from the lactate appeared in the incubation media as alanine at pH 7.5, but none was formed at the lower pH levels. Some B-hydroxybutyrate was detected at pH 6.8 and small amounts of glutamate at pH 5.8. Absorption of L(+)-lactate by rumen epithelium was dependent on both mucosal pH and lactate concentration, when absorption was expressed as µmoles per unit of dry tissue per unit time. When absorption was expressed as percentage transfer of the lactate, it appeared that the interaction between the effects of pH and lactate concentration was of most importance. L(+)-lactate was absorbed as the free acid, with little conversion to any other metabolite. Substitution of blood serum for phosphate buffer on the serosal side of the epithelial tissue appeared to stimulate lactate absorption. Copyright © 1969. American Society of Animal Science . Copyright 1969 by American Society of Animal Science

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