Schlatter E, Greger R, Weidtke C
Pflugers Arch. 1983 Mar 1;396(3):210-7. doi: 10.1007/BF00587857.
The group of "high ceiling" diuretics consists of a variety of chemically different potent diuretic and saluretic substances. Appart from a few exemptions direct evidence for an action of these substances in the thick ascending limb of the loop of Henle (TAL) is still lacking. For furosemide, we have reported recently that it inhibits most likely the Na+-2 Cl--K+ cotransport system present in the lumen membrane of the TAL. The present study tests: 1. whether other "high ceiling" diuretics have a similar site and mode of action, and 2. how modifications of the furosemide molecule alter the inhibitory potency. Isolated cortical TAL (cTAL) segments (n = 185) of rabbit kidneys were perfused in vitro. The equivalent short circuit current (Isc = transepithelial PD/transepithelial resistance), as a measure of active salt transport was correlated to the dose of 64 substances. Several diuretics, such as 2-aminomethyl-4-(1,1-dimethyl-ethyl)-6-iodophenol hydrochloride (MK 447), hydrochlorothiazide, muzolimine, etozoline, tizolimide, amiloride, and triamterene were ineffective both from the lumen and basolateral side at concentrations as high as 10(-4) - 10(-3) mol X 1(-1). The phenoxyacetic acids ethacrynic acid, indacrinone (MK 196), and to less an extend tienilic acid were inhibitory active. They differed from furosemide in one or more of the following criteria: delayed onset, incomplete reversibility, stronger action from the bath, different slope of the dose response curve. Similarly, 1-ozolinone acted stronger from the bath. In contrast, the diuretics of the furosemide type and related compounds (bumetanide and piretanide) showed rapid onset and complete reversibility of inhibition. These substances acted stronger from the lumen. The individual positions in the benzyl ring of the diuretics were differently affected by substitutions, leading to parallel shifts in the dose response curves with halfmaximal inhibition at concentrations ranging between 8 X 10(-8) to greater than 10(-4) mol X 1(-1). For these substances the calculated Hill coefficients were close to unity: 0.96 +/- 0.05. We conclude that the so called "high ceiling" or "loop" diuretics consist of at least 3 groups: 1. drugs that do not interfere with the active salt transport in the cTAL segment, 2. drugs that interfere by so far not characterised mechanisms, and 3. drugs of the furosemide type which inhibit the Na+-2 Cl--K+ cotransport system in the lumen membrane of the cTAL segment.
“高效能”利尿剂组由多种化学结构不同的强效利尿和促尿钠排泄物质组成。除了少数例外情况，目前仍缺乏这些物质在髓袢升支粗段（TAL）发挥作用的直接证据。对于呋塞米，我们最近报道它很可能抑制TAL管腔膜中存在的Na⁺ - 2Cl⁻ - K⁺共转运系统。本研究旨在测试：1. 其他“高效能”利尿剂是否具有类似的作用位点和作用方式；2. 呋塞米分子的修饰如何改变其抑制效力。对兔肾分离的皮质TAL（cTAL）节段（n = 185）进行体外灌注。作为主动盐转运指标的等效短路电流（Isc = 跨上皮电位差/跨上皮电阻）与64种物质的剂量相关。几种利尿剂，如盐酸2 - 氨基甲基 - 4 -（1,1 - 二甲基乙基）- 6 - 碘苯酚（MK 447）、氢氯噻嗪、莫唑胺、依托唑啉、替唑胺、阿米洛利和氨苯蝶啶，在高达10⁻⁴ - 10⁻³ mol·L⁻¹的浓度下，从管腔侧和基底外侧给药均无效。苯氧乙酸类药物依他尼酸、茚达立酮（MK 196）以及程度稍轻的替尼酸具有抑制活性。它们在以下一个或多个标准上与呋塞米不同：起效延迟、不完全可逆、从浴液给药时作用更强、剂量反应曲线斜率不同。同样，1 - 氧唑啉酮从浴液给药时作用更强。相比之下，呋塞米类利尿剂及相关化合物（布美他尼和吡咯他尼）起效迅速且抑制作用完全可逆。这些物质从管腔侧给药时作用更强。利尿剂苄基环上的各个位置受取代基的影响不同，导致剂量反应曲线平行移动，半数最大抑制浓度范围在8×10⁻⁸至大于10⁻⁴ mol·L⁻¹之间。对于这些物质，计算得到的希尔系数接近1：0.96±0.05。我们得出结论，所谓的“高效能”或“袢”利尿剂至少由3组组成：1. 不干扰cTAL节段主动盐转运的药物；2. 通过迄今尚未明确的机制发挥干扰作用的药物；3. 抑制cTAL节段管腔膜中Na⁺ - 2Cl⁻ - K⁺共转运系统的呋塞米类药物。
