Levine D Z, Iacovitti M, Nash L, Vandorpe D
Department of Medicine, University of Ottawa, Canada.
J Clin Invest. 1988 Jun;81(6):1873-8. doi: 10.1172/JCI113533.
We have performed microperfusion studies on distal tubule bicarbonate reabsorption (JtCO2) of fed and fasted rats to extend our previous observations of in vivo bicarbonate secretion and to resolve certain discrepancies between free-flow and microperfusion data. When rats are fasted overnight, as in previous free-flow studies, distal tubule microperfusion with a 28-mM tCO2 solution results in significant JtCO2 (53 +/- 6 pmol.min-1.mm-1) at normal flow and increases briskly (91 +/- 16 pmol.min-1.mm-1) with bicarbonate load. This response is not influenced by the addition of other normal tubular fluid constituents. However, when normally fed rats are used, as in our previous microperfusion studies, distal tubule JtCO2 is not different from zero when a 28-mM tCO2 solution is perfused at normal flow rates but becomes negative (-54 +/- 13 pmol.min-1.mm-1) at high flow rates, which indicates the existence of bicarbonate secretion against a concentration gradient. Alkali loading of fasted rats also elicits bicarbonate secretion at high flow. These results demonstrate for the first time that normal feeding or alkali loading can induce bicarbonate secretion in a mammalian nephron segment in vivo, and resolves previous discrepancies between free-flow and microperfusion data.
我们对喂食和禁食大鼠的远端小管重吸收碳酸氢盐（JtCO2）进行了微灌注研究，以扩展我们之前对体内碳酸氢盐分泌的观察，并解决自由流和微灌注数据之间的某些差异。与之前的自由流研究一样，当大鼠禁食过夜时，用28 mM tCO2溶液进行远端小管微灌注，在正常流量下会导致显著的JtCO2（53±6 pmol·min-1·mm-1），并且随着碳酸氢盐负荷的增加而迅速增加（91±16 pmol·min-1·mm-1）。这种反应不受添加其他正常肾小管液成分的影响。然而，当使用正常喂食的大鼠时，如我们之前的微灌注研究，以正常流速灌注28 mM tCO2溶液时，远端小管JtCO2与零无差异，但在高流速时变为负值（-54±13 pmol·min-1·mm-1），这表明存在逆浓度梯度的碳酸氢盐分泌。禁食大鼠的碱负荷也会在高流量时引发碳酸氢盐分泌。这些结果首次证明，正常喂食或碱负荷可在体内诱导哺乳动物肾单位节段分泌碳酸氢盐，并解决了之前自由流和微灌注数据之间的差异。
