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A B S T R A C T The renal conversion of glutamine to glucose and its oxidation to COs were compared in dogs in chronic metabolic acidosis and alkalosis. These studies were performed at normal endogenous levels of glutamine utilizing glutamine-14C (uniformly labeled) as a tracer. It was observed in five experiments in acidosis that mean renal extraction of glutamine by one kidney amounted to 27.7 /Amoles/min. Of this quantity, 5.34 umoles/min was converted to glucose, and 17.5 umoles/min was oxidized to C02. Acidotic animals excreted an average of 41 omoles/min of ammonia in the urine formed by one kidney. In contrast, in five experiments in alkalosis, mean renal extraction of glutamine amounted to 8.04 umoles/min. Of this quantity, 0.92 umole/min was converted to glucose, and 4.99 ,tmoles/min was oxidized to C02. Alkalotic animals excreted an average of 3.23 ,.moles/min of ammonia in the urine. We conclude that renal gluconeogenesis is not rate limiting for the production and excretion of ammonia in either acidosis or alkalosis. Since 40% of total C02 production is derived from oxidation of glutamine by the acidotic kidney and 14% by the alkalotic kidney, it is apparent that renal energy sources change with acid-base state and that glutamine constitutes a major metabolic fuel in acidosis.

Radioiodide and creatinine clearances were measured simultaneously in dogs. Osmotic diuresis was induced by loading with mannitol, sodium salts of various anions such as chloride, bromide, iodide, nitrate and ferrocyanide, and by the administration of mercurial diuretics. Results of these experiments are compared with those obtained during water diuresis. No evidence for active tubular reabsorption of radioiodide could be observed. Renal tubular reabsorption of I131 was found to be chiefly determined by the degree of tubular water reabsorption and hence the transtubular diffusion gradient of radioiodide. Nonspecific effects of other anions in the tubular urine may modify passive tubular reabsorption: anions less readily reabsorbed displace I131 from the urine and depress its renal clearance. Indirect evidence suggests that about 95% of filtered radioiodide is reabsorbed at a tubular site proximal to that of final water reabsorption.

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