title: Role of distal delivery of filtrate in impaired renal dilution of the hypothyroid rat.
abstract: 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.
mesh_terms: D000818:Animals; D003919:Diabetes Insipidus / Q000503:physiopathology*; D005260:Female; D005919:Glomerular Filtration Rate; D007037:Hypothyroidism / Q000503:physiopathology*; D007444:Inulin; D007668:Kidney / Q000032:analysis / Q000503:physiopathology*; D007671:Kidney Concentrating Ability; D007684:Kidney Tubules / Q000503:physiopathology*; D007686:Kidney Tubules, Distal / Q000503:physiopathology*; D008297:Male; D009929:Organ Size; D051381:Rats; D013974:Thyroxine / Q000097:blood; D014667:Vasopressins
chemical_list: D014667:Vasopressins; D007444:Inulin; D013974:Thyroxine