Glomerular and Tubular Influences on Sodium and Water Excretion

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Abstract
Earlier observations indicating that slight bilateral falls in GFR produce large acute falls in salt and water output are discussed. The PAH and inulin clearances and Na and water outputs of the 2 kidneys of trained, unanesthetized, trigone-explanted dogs were found to agree closely. Following light constriction of one renal artery, the Na and water outputs of the ligated side are permanently 20-50% those of the unligated, even without certainly detectable falls in PAH and inulin clearances; slight falls in GFR are assumed to have occurred. With greater constriction, where PAH and inulin clearances fall by 20-30%, the Na and water outputs fall permanently to only a few per cent of those of the unligated kidney. When the unligated kidney is removed, the outputs of the ligated kidney rise to the preoper-ative outputs of the 2 normal kidneys, although GFR remains well below that of the 2 normal kidneys. Two kidneys chronically subjected to the same humoral and nervous influences are thus observed. The only significant difference seems to be reduction of GFR on the ligated side. Since the companion kidney prevents the development of salt and water surpluses which would produce the usually observed alteration in tubular absorptive behavior, a slight fall in GFR produces great falls in salt and water output, just as is seen on slight bilateral falls in GFR in acute expts., before surpluses have had time to develop. The only difference is that in these unilateral ligation expts. the falls are permanent. When a surplus is permitted to develop after removal of the unligated kidney, the ligated kidney increases its output to achieve balance, just as occurs on chronic bilateral reduction of GFR.