The Excretion of Sulfates by the Dog

Among the first studies inspired by Cushny’s theory of renal function was the one undertaken by Mayrs, who investigated the excretion of sulfates as compared with the elimination of a number of other substances. He injected sodium sulfate intravenously into rabbits in order to raise the concentration of sulfate in the plasma to allow its determination with a sufficient degree of accuracy and found that sulfates were concentrated approximately twice as much as urea (maximum: 2.75, minimum: 1.50). In a subsequent series of experiments the degree of concentration of sulfates (“concentration ratios”) was compared with that of phosphates and of creatinine and all these values were found to be approximately the same. White could not find as satisfactory agreement between ratios of concentration of different substances as compared with the concentration ratio of sulfates and concluded that “no fixed rule such as Cushny sought to apply in his ‘modern theory’ can be assigned to the process of sulphate elimination.” The same investigator, in collaboration with Monaghan, in a subsequent study of phlorhixinized dogs was led to recognize the important fact that “the sulphate clearances are always greater with high plasma sulphate levels than with normal, with rough proportionality.” In man the endogenous sulfate clearances were studied by Macy, who reported that they were 10 to 50 per cent less than those of urea. Cope found essentially analogous clearance ratios. He could not discover any influence of moderately increased sulfate levels as obtainable by the oral administration of sodium sulfate on sulfate clearance. Hayman, on the other hand, recognized a very definite tendency of the concentration ratio of sulfates to approach that of creatinine after the intravenous administration of the former. In the last few years, thanks to the work of Richards, Smith and Shannon, and Van Slyke and co-workers along the lines of Cushny’s theory, the equality of the clearances of creatinine, inulin and ferrocyanide in dogs has been firmly established. Apparently the magnitude of these clearances at the same time indicates the extent of glomerular filtration. Generalizing, it can be said that in the dog a rate of excretion in excess of simul-