Shirley D G, Skinner J
Department of Physiology, Charing Cross and Westminster Medical School, London.
Exp Physiol. 1994 Mar;79(2):161-73. doi: 10.1113/expphysiol.1994.sp003749.
In order to investigate the effect of chronic sodium depletion on renal proximal tubular reabsorption, studies were performed in conscious, unrestrained Brattleboro rats. Since these animals lack circulating vasopressin, fractional water reabsorption in the distal nephron can be assumed to be constant and changes in urine flow rate should therefore reflect changes in end-proximal fluid delivery. Sodium depletion was induced by placing rats on a low-sodium diet (4 mmol Na (kg dry wt)-1) and administering frusemide (40 mg (kg body wt)-1) by gavage on the first 2 days. Extracellular volume, measured after 7-9 days, was reduced by 19% (P < 0.02) as compared with that of rats maintained on a control diet. Urine flow rate, measured during days 4-7 of the low-sodium diet, was significantly lower than that of control rats (142 +/- 8 vs. 168 +/- 5 ml day-1, P < 0.01). Since renal papillary interstitial fluid osmolality was found to be reduced in the sodium-depleted rats (693 +/- 38 vs. 812 +/- 36 mosmol (kg H2O)-1, P < 0.05), it is unlikely that water reabsorption from sites beyond the proximal tubule had increased. The observed reduction in urine flow rate therefore strongly suggests a reduction in end-proximal fluid delivery. In the second part of the study, a single group of Brattleboro rats was used, in which osmotic minipumps were implanted in the peritoneal cavity for continuous infusion of [14C]inulin. After recovery from the operation, the rats were maintained on a control diet for 6 days (pre-control period), then subjected to sodium depletion (low-sodium diet for 6 days, frusemide administration on the first 2 days), and finally returned to the control diet for 6 days, with access to 0.46 M NaCl solution on the first 2 days, in order to restore sodium balance (post-control period). On the final 2 days of each phase, urine flow rate and [14C]inulin clearance (= glomerular filtration rate, GFR) were measured. Urine flow rates during the pre-control, sodium depletion and post-control periods were 169 +/- 7, 132 +/- 8 (P < 0.001) and 176 +/- 8 microliters min-1, respectively; corresponding values for fractional water excretion were 7.0 +/- 0.3, 6.0 +/- 0.5 (P < 0.01) and 7.4 +/- 0.4%. Only a small reduction GFR, of borderline statistical significance, was observed during sodium depletion.(ABSTRACT TRUNCATED AT 250 WORDS)
为了研究慢性钠缺乏对肾近端小管重吸收的影响，我们对清醒、无束缚的布拉特洛维大鼠进行了研究。由于这些动物缺乏循环血管加压素，因此可以假定远端肾单位的水重吸收率恒定，尿流率的变化应反映近端小管末端液体输送的变化。通过给大鼠喂食低钠饮食（4 mmol Na/(kg干重)）并在头两天通过灌胃给予速尿（40 mg/(kg体重)）来诱导钠缺乏。与喂食对照饮食的大鼠相比，7 - 9天后测量的细胞外液体积减少了19%（P < 0.02）。在低钠饮食的第4 - 7天测量的尿流率显著低于对照大鼠（142 ± 8 vs. 168 ± 5 ml/天，P < 0.01）。由于发现钠缺乏大鼠的肾乳头间质液渗透压降低（693 ± 38 vs. 812 ± 36 mosmol/(kg H₂O)，P < 0.05），近端小管以外部位的水重吸收增加的可能性不大。因此，观察到的尿流率降低强烈提示近端小管末端液体输送减少。在研究的第二部分，使用了一组布拉特洛维大鼠，在其腹腔内植入渗透微型泵以持续输注[¹⁴C]菊粉。手术后恢复后，大鼠先喂食对照饮食6天（对照前期），然后进行钠缺乏处理（低钠饮食6天，头两天给予速尿），最后再回到对照饮食6天，头两天可饮用0.46 M NaCl溶液以恢复钠平衡（对照后期）。在每个阶段的最后两天，测量尿流率和[¹⁴C]菊粉清除率（=肾小球滤过率，GFR）。对照前期、钠缺乏期和对照后期的尿流率分别为169 ± 7、132 ± 8（P < 0.001）和176 ± 8 μl/min；水排泄分数的相应值分别为7.0 ± 0.3、6.0 ± 0.5（P < 0.
