Bartoli E, Romano G, Favret G
Cattedra di Medicina Interna, Università di Udine, Italy.
Nephrol Dial Transplant. 1996 Oct;11(10):1996-2003. doi: 10.1093/oxfordjournals.ndt.a027087.
We wanted to validate by direct measurements in rat tubules a technique used to calculate segmental volume absorption by each segment of the human nephron.
Experiments were performed on 17 rats during hypertonic Na infusion prior to and after frusemide administration. Tubular samples were taken from early distal and last proximal sites. The rate of filtration of single nephrons (SNGFR) was calculated by the technique of total collection of tubular fluid using labelled inulin as a marker. Reabsorption was computed by the tubular fluid to plasma (TF/P) inulin concentration ratio.
SNGFR was 50 +/- 4 nl/min at the distal (n = 82), 51 +/- 3 nl/min at the proximal sampling site (n = 112, P > 0.65) during baseline conditions. Percent reabsorptions were 85 +/- 1 and 69 +/- 2% respectively (P < 0.0001). During frusemide these values were 52 +/- 6 nl/min and 76 +/- 2% at the distal, 49 +/- 5 nl/min and 66 +/- 2% at the proximal site. In 83 paired proximal collections, fractional (68 +/- 1 versus 67 +/- 1% P > 0.32), absolute reabsorption (34 +/- 2 versus 33 +/- 2, P > 0.50) and SNGFR (50 +/- 2 nl/min versus 50 +/- 3 nl/min, P > 0.99) were not different between baseline and frusemide. In 25 re-collections from the distal tubule these same values were 83 +/- 2% versus 76 +/- 2%, and 48 +/- 4 nl/min versus 55 +/- 6 nl/min respectively. Very similar results were obtained in 55 paired distal-proximal collections during baseline and 42 such pairs during frusemide. In the presence of the diuretic the fractional urine excretion was significantly correlated (R = 0.83, P < 0.0001) with fractional proximal delivery, Na+ resorption by Henle's loop was 22 +/- 2% calculated from clearance data and 23 +/- 1% of GFR from micropuncture data respectively. They were not significantly different (P > 0.70) and were significantly correlated (R = 0.57, P < 0.02).
These data demonstrate that frusemide does not act proximally and that delivery beyond the proximal tubule approximates urine flow rate during the action of the drug. The values of segmental reabsorption along the nephron computed on clearance measurements are superimposable upon those obtained directly by micropuncture.
我们希望通过在大鼠肾小管中的直接测量来验证一种用于计算人类肾单位各节段的节段性容积吸收的技术。
在17只大鼠身上进行实验，在给予速尿前后进行高渗钠输注。从早期远端和最后近端部位采集肾小管样本。使用标记的菊粉作为标志物，通过肾小管液总收集技术计算单个肾单位的滤过率（SNGFR）。通过肾小管液与血浆（TF/P）菊粉浓度比计算重吸收。
在基线条件下，远端的SNGFR为50±4 nl/min（n = 82），近端采样部位为51±3 nl/min（n = 112，P>0.65）。重吸收百分比分别为85±1%和69±2%（P<0.0001）。在速尿作用期间，远端这些值分别为52±6 nl/min和76±2%，近端部位为49±5 nl/min和66±2%。在83对近端收集样本中，基线和速尿期间的分数（68±1%对67±1%，P>0.32）、绝对重吸收（34±2对33±2，P>0.50）和SNGFR（50±2 nl/min对50±3 nl/min，P>0.99）无差异。在25次远端肾小管重新收集样本中，这些相同的值分别为83±2%对76±2%，以及48±4 nl/min对55±6 nl/min。在基线期间的55对远端-近端收集样本和速尿期间的42对样本中获得了非常相似的结果。在利尿剂存在的情况下，分数尿排泄与分数近端输送显著相关（R = 0.83，P<0.0001），根据清除率数据计算，亨氏袢的钠重吸收为22±2%，根据微穿刺数据计算为GFR的23±1%。它们无显著差异（P>0.70）且显著相关（R = 0.57，P<0.02）。
这些数据表明速尿不在近端起作用，并且在药物作用期间，近端小管以外的输送量接近尿流率。根据清除率测量计算的沿肾单位的节段性重吸收值与通过微穿刺直接获得的值是可叠加的。
