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INERT GASES IN THE KIDNEY: INFLUENCE OF THE COUNTERCURRENT MULTIPLICATION OF SODIUM
Author(s) -
Abernethy JD
Publication year - 1972
Publication title -
australian journal of experimental biology and medical science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.999
H-Index - 104
eISSN - 1440-1711
pISSN - 0004-945X
DOI - 10.1038/icb.1972.31
Subject(s) - chemistry , sodium , countercurrent exchange , chromatography , partial pressure , thermodynamics , oxygen , organic chemistry , physics
Summary Small, but significant, partial pressure differences between urine and blood can be detected, indicating that in passage through the kidney N 2 tension is reduced by 1·35% (7 mm Hg) whereas argon tension is increased by 0·77%. This differential behaviour is viewed as an inevitable side effect of the countercurrent multiplitation of sodium in the medulla given the known propensity of electrolytes for increasing the chemical potential of non‐polar solutes, i.e. the salting‐out effect. The primary event in sodium multiplication— removal of sodium from the ascending limb of Henle's loop—is then of necessity accompanied by a local reduction in partial pressure of dissolved gas. This initiates a chain of events culminating in active countercurrent attenuation of partial pressure, the effect being greater for the gas with the greater diffusivity (N 2 ). The multiplication of sodium which parallels this attenuation tends also to offset it: increased salt concentration of necessity potentiates partial pressure through a direct salting‐out effect. The net result is a dynamic balance determined for each gas by its diffusivity and salting‐out factor. Because there is an equilibrium between inner medulla and urine (verified for hydrogen gas) these changes in the inner medulla are also reflected in the urine, This analysis is supported by a single‐loop model which predicts a value for maximal sodium concentration in the inner medulla reasonably close to physiological values (particularly if the contribution of urea to salting‐out is included). Low values of helium in urine found during inhalation experiments were also consistent with the model, although there were indications that attenuation takes several hours longer than potentiation for completion. The implications for acute (non‐steady state) experiments are that urine concentrations of non‐ electrolytes will tend to be elevated with respect to blood, a probable example of this being the ethanol concentration of urine in forensic studies.