Acute in vivo studies on glucose absorption from the small intestine of lambs, sheep and rats.

I . Rates of disappearance of glucose from ligated loops of small intestine in lambs, adult sheep and young rats were studied. The concentration of glucose in the lumen decreased exponentially with time, suggesting that within a range of concentrations of 166-277 m-moles/l glucose was absorbed mainly by passive diffusion. 2. The rate of absorption of glucose from a 166 mM-solution based on either zero or first order kinetics and expressed as m-moles/m small intestine per h decreased along the intestine from the duodenum to the ileum in lambs and rats. The decrease was slight in adult sheep. 3. The total absorptive capacity of the small intestine of adult grazing sheep for glucose from 166 mM-solutions ( 0 6 m-moles/kg body-weight per h) was approximately 25 % of that for lambs less than I week of age. 4. Young rats had a greater absorptive capacity of the small intestine (12.9 m-moles/kg body-weight per h) than adult sheep of about 40 kg body-weight (0.6 m-moles/kg body-weight per h) and this largely reflected a longer small intestine per unit body-weight. 5. The absorptive capacity of lambs for glucose was greater when the level of voluntary lactose intake was increased before an experiment. The absorptive capacity of the ileum of adult sheep given wheat was greater than that of grazing adult sheep. 6. Developmental changes in glucose absorption are discussed in relation to normal changes in diet and to changes in the morphology of the small intestine with age.