TRANSPORT OF L-PROLINE AND ALPHA-METHYL-D-GLUCOSIDE BY CHICKEN PROXIMAL CECUM DURING DEVELOPMENT

We examined the characteristics of amino acid and sugar absorption by the proximal cecum (PC) of chickens during posthatch development. Rates of absorption of L-proline (Pro) and alpha-methyl-D-glucoside (MG) were measured at 2 days, 5 wk, and 13 wk after hatch with an in vitro everted-sleeve method. For each age, pieces of PC and midjejunum were incubated in solutions containing 0.1-50 mM Pro or MG, and the active and passive components of Pro and MG absorption were determined. Five conclusions may be stated. 1) There are two carrier-mediated transport systems for Pro in the PC: a higher capacity Na+-dependent system (V(max) between 1.6 and 3.2 nmol.mg-1.min-1), and a lower capacity Na+-independent system (V(max) 0.3-0.8 nmol.mg-1.min-1). 2) Whereas both Pro transport systems are present in the PC at 5 and 13 wk, only the Na+-dependent system was found at 2 days. Although rates of transport per milligram tissue by the Na+-dependent system fell during development, when rates were normalized to nominal surface area, V(max) was significantly higher in the 5-wk-old group than in the other groups. 3) MG transport is by a Na+-dependent system. V(max) values (nmol.mg-1.min-1) were 0.32 (2 days), < 0.43 (5 wk), and = 0.55 (13 wk). These differences were not affected by normalization to surface area. 4) Because at physiological concentrations passive influx of Pro and MG would be negligible, absorption of amino acids and sugars by the PC would be dependent on the presence of carrier-mediated systems. 5) The higher affinity of the MG transport system of the PC is compatible with anticipated extremely low concentrations of sugars. The higher ratios for the absorption of Pro relative to MG suggests the PC is better adapted for the uptake of amino acids than sugars. The transport processes of the PC provide a mechanism whereby chickens are able to obtain nutrients supplied by the microflora.