Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0085383 (hypocapnia)
 1,697 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
 ...
PMID:Delivery dependence of early proximal bicarbonate reabsorption in the rat in respiratory acidosis and alkalosis. 199 47

Renal acidification in renal proximal tubule is thought to be mediated by luminal Na-H antiporter and the HCO3- generated by this antiporter is removed from the cell by a basolateral Na-HCO3 cotransporter. To study the effect of respiratory acid-base disorders on these transport systems, we have measured the Na-HCO3 cotransport in basolateral membranes and Na-H antiporter in luminal membranes in control rabbits, rabbits exposed to 10% CO2 (chronic hypercapnia), and rabbits exposed to 10% O2-90% N2 (chronic hypocapnia). The Vmax of HCO3(-)-dependent 22Na uptake was significantly higher in chronic hypercapnia than controls (2.54 +/- 0.03 vs. 1.18 +/- 0.21 nmol.mg protein-1.3 s-1, P less than 0.001). Likewise, the Vmax of the Na-H antiporter was also increased compared with controls (924.9 +/- 42.1 vs. 549.1 +/- 62.8 fluorescence units (FU).300 micrograms protein-1.min-1). In chronic hypocapnia, the Vmax of Na-HCO3 cotransport was lower than controls (0.72 +/- 0.11 vs. 1.18 +/- 0.21 nmol.mg protein-1.3 s-1, P less than 0.05). There was no difference, however, in the Vmax of the Na-H antiporter between hypocapnia and control (524.2 +/- 24.3 vs. 549.1 +/- 62.8, FU.300 micrograms protein-1.min-1). The Vmaxs of the Na-HCO3 cotransport and of the Na-H antiporter in hypocapnic, control, and hypercapnic rabbits were linearly related (r = 0.81), suggesting a simultaneous adaptation of the two systems in respiratory acid-base disorders.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Na-HCO3 cotransport and Na-H antiporter in chronic respiratory acidosis and alkalosis. 256 56

The early proximal tubule is the major site for renal bicarbonate reabsorption but little is known about the influence of acidosis on transport in this segment. This study examined early proximal bicarbonate reabsorption in rats with chronic metabolic acidosis (MA) (induced by NH4Cl administration). Rats were studied by free-flow micropuncture techniques, after varying degrees of plasma volume expansion to vary the filtered load of bicarbonate (FLHCO3). At FLHCO3 less than 700 pmol/min, both control and acidotic animals reabsorbed greater than 80% of the filtered load by 2 mm from Bowman's space. At higher FLHCO3 (700-1,100 pmol/min), reabsorption in the early proximal tubule was significantly greater in MA rats vs. control (633 +/- 26 vs. 449 +/- 24 pmol/min, between 1 and 2 mm from Bowman's space, P less than 0.001). This MA-induced stimulation of early proximal bicarbonate reabsorption was completely reversed by restoring systemic pH to normal either by acute hypocapnia or alkali infusion. Thus bicarbonate reabsorption in the early proximal tubule correlated closely with changes in systemic pH in rats with MA when bicarbonate delivery was increased by plasma expansion. The mechanism of this effect remains to be determined.
 ...
PMID:Metabolic acidosis stimulates bicarbonate reabsorption in the early proximal tubule. 275 Sep 23