Fromm M, Hegel U
Pflugers Arch. 1978 Dec 15;378(1):71-83. doi: 10.1007/BF00581960.
Functionally isolated segments of rat colon and rectum were perfused in situ in a closed loop system. Rectum was defined as the lower 25--35% of the length of large intestine (cecum excluded). Perfusion conditions were optimized at 0.5 ml.min-1 and 3 cm H2O luminal pressure. Variation of perfusion rate between 0.2 and 2 ml.min-1 did not influence net volume transport (JNV). Luminal distension following elevation of hydrostatic pressure to 18 cm H2O reversibly increased Jnv. Under control conditions Jnv and Na+-transport rates (JnNa) of colon were 2--3 times higher than those of rectum. In colon transepithelial electrical potential difference (psims) was time independent --12 mV (lumen negative) whereas rectal psims increased with time from --6 mV, reaching a plateau of --67 mV within 6 h. Amiloride 10(-4) mol.l-1 had no effect on psims, Jnv, and JnNa in colon but did slightly depress K+-secretion in colon descendens. In contrast, psims in rectum was dose-dependently depressed, being reversed to +7 mV at 10(-4) mol.l-1. Jnv and JnNa were decreased by half. Acetazolamide in addition to amiloride lowered the positive post-amiloride rectal psims by half. Adrenalectomy had no effect on colonic psims, but abolished psims of the rectum. A single dose of 40 microgram.kg-1 b.w. aldosterone during the experiment restored the typical time course of rectal psims, but did not affect psims in colon. It is concluded that aldosterone induces an amiloride-sensitive Na+-pathway only in rectum, but not in colon, and that colon and rectum differ basically in their transport properties, quantitatively as well as qualitatively, as do the kidney distal convoluted tubule and the cortical collecting duct.
在闭环系统中对大鼠结肠和直肠的功能隔离段进行原位灌注。直肠定义为大肠长度的下25%-35%（不包括盲肠）。灌注条件在0.5 ml·min⁻¹和3 cm H₂O腔内压力下进行优化。灌注速率在0.2至2 ml·min⁻¹之间变化不影响净体积转运（JNV）。将静水压力升高至18 cm H₂O后引起的管腔扩张使Jnv可逆性增加。在对照条件下，结肠的Jnv和Na⁺转运速率（JnNa）比直肠高2-3倍。在结肠中，跨上皮电位差（psims）与时间无关，为-12 mV（管腔为负），而直肠psims随时间从-6 mV增加，在6小时内达到-67 mV的平台期。10⁻⁴ mol·L⁻¹的氨氯地平对结肠的psims、Jnv和JnNa无影响，但略微抑制降结肠中的K⁺分泌。相反，直肠中的psims呈剂量依赖性降低，在10⁻⁴ mol·L⁻¹时逆转至+7 mV。Jnv和JnNa降低一半。乙酰唑胺除了氨氯地平外，还使氨氯地平后直肠psims的正值降低一半。肾上腺切除术对结肠psims无影响，但消除了直肠的psims。实验期间单次给予40 μg·kg⁻¹体重的醛固酮可恢复直肠psims的典型时间进程，但不影响结肠中的psims。结论是醛固酮仅在直肠而非结肠中诱导氨氯地平敏感的Na⁺途径，并且结肠和直肠在转运特性上在数量和质量上基本不同，就像肾远曲小管和皮质集合管一样。
