The postnatal development of intestine is associated with a decline in brush border lactase activity in rodents. This is similar to adulthood hypolactasia, a phenomenon prevalent in humans worldwide. In the present study, the effect of luminal proteases from adult rat intestine was studied in vitro on intestinal lactase activity in saline control, thyroxine, insulin and cortisone treated rat pups. Lactase levels were determined by enzyme analysis and Western blotting. mRNA levels encoding lactase were determined by Northern blotting. Administration of thyroxine for 4 days reduced (P<0.05) lactase activity, but insulin treatment had no effect in 8-day-old rat intestine. However, cortisone administration augmented (P<0.01) lactase activity, under these conditions. Western blot analysis showed decreased lactase signal corresponding to 220-kDa protein band in thyroxine treated animals. However, the intensity of lactase signal was high in cortisone treated animals compared to controls. mRNA levels encoding lactase showed a 6.8-kb mRNA transcript in saline and hormone treated rats. mRNA levels encoding lactase were increased in cortisone treated animals but were reduced in thyroxine injected pups compared to controls. Microvillus membranes from saline (P<0.01) and thyroxine (P<0.05) or insulin (P<0.01) treated rats upon incubation with luminal wash from adult rat intestine showed a significant decline in lactase activity. These findings suggest that thyroxine, insulin or cortisone induced changes in lactase expression in suckling rat intestine make it susceptible to luminal proteases, which may in part be responsible for observed maturational decline in lactase activity in adult rat intestine.

译文

出生后肠道发育与啮齿动物刷状缘乳糖酶活性下降有关。这类似于成年性低乳酸症,这是全世界人类普遍存在的现象。在本研究中,在体外研究了成年大鼠肠道的luminal蛋白酶对盐水对照,甲状腺素,胰岛素和可的松处理的大鼠幼崽的肠乳糖酶活性的影响。通过酶分析和蛋白质印迹法确定乳糖酶水平。编码乳糖酶的mRNA水平通过Northern印迹测定。给予甲状腺素4天降低 (P<0.05) 乳糖酶活性,但胰岛素治疗对8天大的大鼠肠道没有影响。然而,在这些条件下,给予可的松增加 (P<0.01) 乳糖酶活性。Western印迹分析显示甲状腺素处理的动物中对应于220-kDa蛋白带的乳糖酶信号减少。然而,与对照组相比,可的松治疗的动物的乳糖酶信号强度很高。编码乳糖酶的mRNA水平在盐水和激素处理的大鼠中显示6.8-kb mRNA转录本。与对照组相比,经可的松处理的动物中编码乳糖酶的mRNA水平升高,但经甲状腺素注射的幼崽中编码乳糖酶的mRNA水平降低。用来自成年大鼠肠的管腔洗涤液孵育后,来自盐水 (P<0.01) 和甲状腺素 (P<0.05) 或胰岛素 (P<0.01) 处理的大鼠的微绒毛膜显示乳糖酶活性显着下降。这些发现表明,甲状腺素,胰岛素或可的松诱导乳鼠肠道中乳糖酶表达的变化使其对腔蛋白酶敏感,这可能部分是成年大鼠肠道中乳糖酶活性成熟下降的原因。

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