The influence of diuretics on the osmotic work done and on the efficiency of the isolated kidney of the dog

Abstract

THE external work performed by the kidney is almost entirely represented by the osmotic work done in the formation of urine from plasma.The osmotic work which can be calculated is the theoretical minimum work and is independent of the mechanism of formation of urine. It is perhaps the most significant way of summarizing the functions of the kidney as an excretory organ. The osmotic work plays much the same part in renal physiology as does the mechanical work in muscle physiology; asynchronous contraction of muscle fibres and deviation from a longitudinal direction of pull makes it likely that the mechanical work done by individual muscle fibres would add up to something considerably greater than the observed external work done by the muscle; similarly, if we could measure the osmotic work done in different segments of the renal tubule, and suppose that positive work done by the kidney in one segment could not be neutralized by negative work in another segment, we should obtain a value for osmotic work done by the kidney which is greater than the theoretical minimum external work in which such neutralization is presupposed.The relation between the external work done and the chemical energy degraded in the organ, as indicated by the oxygen consumption, is of interest in two connexions. First, the efficiency so calculated has been found [Borsook & Winegarden, 1931] to be only of the order of 1%-much lower than the maximum efficiency of muscle. This comparison is, 1 Assisted by a grant from the Medical Research Council.

The Oxygen Consumption of the Human Kidney During Heavy Tubular Excretory Work

“…In experiments on dogs it was shown by Van Slyke, Rhoads, Miller and Alving (1934) that an increase of the urea output did not increase the oxygen consumption of the kidneys. This was confirmed by Eggleton, Pappenheimer and Winton (1940) who found that even a very considerable augnientation of diuresis, osmotic work, urea excretion and tubular resorbtion of urea were of very little influence on renal blood flow and renal oxygen consumption in dogs. According to these authors the kidney answers the demand for increased work not by increased metabolism but by increased working efficiency.…”

The mechanisms of dilution diuresis in the isolated kidney and the anaesthetized dog

“…This value of 21 mm. may be a few per cent too high for reasons given elsewhere [Eggleton et al 1940b], and our fairest estimate of the change in hydrostatic pressure head across the glomerular membrane equivalent to a change by 1% in serum protein would be 20 mm. Hg in the isolated kidney.…”

“…The urine flow may be kept constant by variations in ureter pressure (Fig. 6) [Eggleton, Pappenheimer & Winton, 1940b] and this complicates the interpretation of the changes in composition of the urine.…”

The Metabolism, Excretion, and Human Requirements of Calcium

“…Thus Borsook and Winegarden (1931), who set out to calculate in great detail the osmotic work performed by the kidney in producing one litre of urine, came to the conclusion that the total work amounted to 704 gramme calories and that the quota of this due to the calcium ion was only 1 gramme calorie-i.e., about 0.14%. Previous estimates of the total work of the kidney in producing a litre of urine had been of the same order (Cushny, 1926), and the principles and methods of all these authors were accepted as being substantially correct by Eggleton, Pappenheimer, and Winton (1940)..…”