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Abstract

On rats anesthetized by Inactin i.p. a crossincision was made at the upper pole of the ureter so that a small area of the kidney medulla was accessible to micropuncture studies. Samples taken from vasa recta, collecting duct and from arteria renalis were sucked in a microglasselectrode for measuring the actual pH. The construction of this pH-electrode (suction type) is described in details, pH values after equilibration of each sample with three known CO₂-pressures yielded a calibrating line for calculating the P_CO2 from the measured actual pH value. The bicarbonate concentration of the samples was calculated by using the Henderson-Hasselbalch equation. Experiments were done on infusion to the animal with following various solutions: 1. containing isotonic bicarbonate only; 2. bicarbonate and Diamox; 3. bicarbonate and carbonic anhydrase (CA); 4. isotonic NaC1 solution used as control. In the control animals there was no difference of blcarbonate-concentratiou in vasa recta and arteria renalis samples. It suggests, that bicarbonate is not involved in the concentrating process of the medulla. The bicarbonate concentration in vasa recta did not arise before the bicarbonate concentration in collecting ducts reached high values. During bicarbonate infusion the CO₂-pressure in vasa recta blood was the same as in control but about 10 mm Hg above that of arteria renalis samples. Inhibition of carbonic anhydrase with Diamox enlarged the CO₂-pressure difference between arteria renalis and vas rectum up to 40 mm ttg. So it is concluded that the increase of P₂ in the kidney medulla is mainly due to delayed dehydration of carbonic acid. However, the CO₂-pressure in collecting duct samples in both conditions was significantly higher than that in vasa recta. The CO₂-pressure difference indicated delayed dehydration, since the samples from collecting duct contained no CA and the carbonic acid came to equilibrium with CO₂-pressure after the collection. When in contrast to these experiments the animal was infused with carbonic anhydrase, there was no delayed dehydration in all nephron sections. Therefore the P_CO2, in collecting duct and vasa recta samples became equal.