Santella R N, Maddox D A, Gennari F J
University of Vermont, College of Medicine, Burlington 05405.
J Clin Invest. 1991 Feb;87(2):631-8. doi: 10.1172/JCI115040.
In the intact rat kidney, bicarbonate reabsorption in the early proximal tubule (EP) is strongly dependent on delivery. Independent of delivery, metabolic acidosis stimulates EP bicarbonate reabsorption. In this study, we investigated whether systemic pH changes induced by acute or chronic respiratory acid-base disorders also affect EP HCO3- reabsorption, independent of delivery (FLHCO3, filtered load of bicarbonate). Hypercapnia was induced in rats acutely (1-3 h) and chronically (4-5 d) by increasing inspired PCO2. Hypocapnia was induced acutely (1-3 h) by mechanical hyperventilation, and chronically (4-5 d) using hypoxemia to stimulate ventilation. When compared with normocapneic rats with similar FLHCO3, no stimulation of EP or overall proximal HCO3 reabsorption was found with either acute hypercapnia (PaCO2 = 74 mmHg, pH = 7.23) or chronic hypercapnia (PaCO2 = 84 mmHg, pH = 7.31). Acute hypocapnia (PaCO2 = 29 mmHg, pH = 7.56) did not suppress EP or overall HCO3 reabsorption. Chronic hypocapnia (PaCO2 = 26 mmHg, pH = 7.54) reduced proximal HCO3 reabsorption, but this effect was reversed when FLHCO3 was increased to levels comparable to euvolemic normocapneic rats. Thus, when delivery is accounted for, we could find no additional stimulation of proximal bicarbonate reabsorption in respiratory acidosis and, except at low delivery rates, no reduction in bicarbonate reabsorption in respiratory alkalosis.
在完整的大鼠肾脏中，近端小管起始段（EP）的碳酸氢盐重吸收强烈依赖于滤过负荷。与滤过负荷无关的是，代谢性酸中毒会刺激EP的碳酸氢盐重吸收。在本研究中，我们调查了急性或慢性呼吸性酸碱紊乱引起的全身pH变化是否也会影响EP的HCO₃⁻重吸收，且与滤过负荷（FLHCO₃，碳酸氢盐的滤过负荷）无关。通过增加吸入的PCO₂，在大鼠中急性（1 - 3小时）和慢性（4 - 5天）诱导高碳酸血症。通过机械过度通气急性（1 - 3小时）诱导低碳酸血症，并使用低氧血症刺激通气慢性（4 - 5天）诱导低碳酸血症。与具有相似FLHCO₃的正常碳酸血症大鼠相比，急性高碳酸血症（PaCO₂ = 74 mmHg，pH = 7.23）或慢性高碳酸血症（PaCO₂ = 84 mmHg，pH = 7.31）均未刺激EP或近端总体HCO₃重吸收。急性低碳酸血症（PaCO₂ = 29 mmHg，pH = 7.56）并未抑制EP或总体HCO₃重吸收。慢性低碳酸血症（PaCO₂ = 26 mmHg，pH = 7.54）降低了近端HCO₃重吸收，但当FLHCO₃增加到与血容量正常的正常碳酸血症大鼠相当的水平时，这种作用被逆转。因此，当考虑滤过负荷时，我们发现在呼吸性酸中毒中近端碳酸氢盐重吸收没有额外的刺激，并且除了在低滤过负荷率时，在呼吸性碱中毒中碳酸氢盐重吸收没有减少。
