Michael U F, Kelley J, Alpert H, Vaamonde C A
Am J Physiol. 1976 Mar;230(3):699-705. doi: 10.1152/ajplegacy.1976.230.3.699.
Free water clearance (CH2O) was measured during hypotonic saline infusion in Sprague-Dawley and in Brattleboro (DI) rats with 131I-induced hypothyroidism and their age-matched controls. At peak urine flow, which was similar in hypothyroid DI (HDI) and control DI (CDI) rats, inulin clearance (CIn/kg) and CH2O/kg were 23 and 20% (P less than 0.02) lower in HDI. Fractional urine flow and fractional sodium excretion were 30 and 40% (P less than 0.001) higher in HDI. Utilization of distal delivery of filtrate for CH2O, formation was 16% less in HDI (P less than 0.01). Papillary osmolality was not higher in HDI rats. Data in Sprague-Dawley rats were similar to those of the DI rats, indicating that endogenous ADH was effectively suppressed. It is concluded: 1) delivery of filtrate out of the proximal tubule was not diminished in hypothyroid rats in spite of a decrease in CIn; 2) despite a similar delivery of filtrate to the distal diluting site, CH2O formation was less in hypothyroid rats than in controls; 3) these data suggest that a defect in the diluting segment could be unmasked at high rates of filtrate delivered to the distal nephron; 4) this defect could be either due to impaired sodium chloride reabsorption or due to increased backdiffusion of water in the distal nephron.
在给患有131I诱导的甲状腺功能减退的斯普拉格-道利大鼠和布拉德福德大鼠（尿崩症大鼠）及其年龄匹配的对照大鼠输注低渗盐水期间，测量了自由水清除率（CH2O）。在甲状腺功能减退的尿崩症（HDI）大鼠和对照尿崩症（CDI）大鼠中，尿流峰值相似，此时，HDI大鼠的菊粉清除率（CIn/kg）和CH2O/kg分别低23%和20%（P<0.02）。HDI大鼠的尿流分数和钠排泄分数分别高30%和40%（P<0.001）。HDI大鼠对远端滤液输送用于CH2O形成的利用率低16%（P<0.01）。HDI大鼠的乳头渗透压并不更高。斯普拉格-道利大鼠的数据与尿崩症大鼠相似，表明内源性抗利尿激素被有效抑制。结论如下：1）尽管CIn降低，但甲状腺功能减退大鼠近端小管滤液的输送并未减少；2）尽管向远端稀释部位输送的滤液相似，但甲状腺功能减退大鼠的CH2O形成比对照组少；3）这些数据表明，在高滤液输送速率下，远端稀释段的缺陷可能会暴露出来；4）这种缺陷可能是由于氯化钠重吸收受损或远端肾单位水的反向扩散增加所致。
