Moretó M, Amat C, Puchal A, Buddington R K, Planas J M
Departament de Ciències Fisiològiques Humanes, Facultat de Farmàcia, Universitat de Barcelona, Spain.
Am J Physiol. 1991 Mar;260(3 Pt 1):G457-63. doi: 10.1152/ajpgi.1991.260.3.G457.
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 (Vmax between 1.6 and 3.2 nmol.mg-1.min-1), and a lower capacity Na(+)-independent system (Vmax 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, Vmax was significantly higher in the 5-wk-old group than in the other groups. 3) MG transport is by a Na(+)-dependent system. Vmax values (nmol.mg-1.min-1) were 0.32 (2 days), less than 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.(ABSTRACT TRUNCATED AT 250 WORDS)
我们研究了雏鸡出壳后发育过程中近端盲肠（PC）对氨基酸和糖的吸收特性。采用体外外翻肠囊法，在出壳后2天、5周和13周测量L-脯氨酸（Pro）和α-甲基-D-葡萄糖苷（MG）的吸收速率。对于每个年龄段，将PC和空肠中段组织块置于含有0.1 - 50 mM Pro或MG的溶液中孵育，并测定Pro和MG吸收的主动和被动成分。可得出五个结论。1）PC中存在两种介导Pro转运的载体系统：一种是容量较高的Na⁺依赖性系统（Vmax在1.6至3.2 nmol·mg⁻¹·min⁻¹之间），另一种是容量较低的Na⁺非依赖性系统（Vmax为0.3 - 0.8 nmol·mg⁻¹·min⁻¹）。2）虽然在5周和13周时PC中两种Pro转运系统均存在，但在2天时仅发现Na⁺依赖性系统。尽管发育过程中Na⁺依赖性系统每毫克组织的转运速率下降，但以名义表面积进行标准化后，5周龄组的Vmax显著高于其他组。3）MG转运通过Na⁺依赖性系统进行。Vmax值（nmol·mg⁻¹·min⁻¹）分别为0.32（2天）、小于0.43（5周）和 = 0.55（13周）。这些差异不受表面积标准化的影响。4）由于在生理浓度下Pro和MG的被动内流可忽略不计，PC对氨基酸和糖的吸收将依赖于载体介导系统的存在。（摘要截断于250字）
