Bastl C P
J Clin Invest. 1987 Aug;80(2):348-56. doi: 10.1172/JCI113079.
A dose response curve for glucocorticoid-induced proximal and distal colonic cation transport in vivo was established in adrenalectomized rats. All doses (0.5-50 nmol/100 g body wt) stimulated sodium absorption. Distal sodium absorption did not saturate at dexamethasone levels that saturate the glucocorticoid receptor but also bind to greater than 35% of aldosterone receptors. Saturation of the pure glucocorticoid response occurred in both segments with RU26988, a synthetic glucocorticoid that does not occupy aldosterone receptors. Maximum velocities for pure glucocorticoid-induced sodium absorption were 15 and 16 mu eq/min per g dry tissue, and Michaelis constants (Km) were 4.2 and 4.6 X 10(-9) mol/liter for proximal and distal colon. Kms are similar to the dissociation constant for the colonic glucocorticoid receptor and too low for significant aldosterone receptor occupancy. Dexamethasone increased sodium absorption significantly within 30 min of injection, suggesting the response is not dependent on new protein synthesis. Similar time and dose responses in proximal and distal colon suggest glucocorticoids stimulate the same pathway in both segments.
在肾上腺切除的大鼠体内建立了糖皮质激素诱导的近端和远端结肠阳离子转运的剂量反应曲线。所有剂量（0.5 - 50 nmol/100 g体重）均刺激钠吸收。在使糖皮质激素受体饱和但也与超过35%的醛固酮受体结合的地塞米松水平下，远端钠吸收并未饱和。使用RU26988（一种不占据醛固酮受体的合成糖皮质激素）时，在两个节段中均出现了纯糖皮质激素反应的饱和。纯糖皮质激素诱导的钠吸收的最大速度分别为每克干组织15和16 μeq/分钟，近端和远端结肠的米氏常数（Km）分别为4.2和4.6×10⁻⁹ mol/升。Km与结肠糖皮质激素受体的解离常数相似，对于显著占据醛固酮受体来说过低。地塞米松在注射后30分钟内显著增加钠吸收，表明该反应不依赖于新蛋白质合成。近端和远端结肠相似的时间和剂量反应表明糖皮质激素在两个节段中刺激相同的途径。
