Age Changes in Renal Function 245 



ammonium chloride produces displacements of the acid-base 

 equilibrium in both old and young subjects. However, young 

 individuals are able to readjust equilibrium within a period of 

 eight hours, following a single dose of 10 g. of ammonium 

 chloride, whereas the older subjects require as much as 24-36 

 hours for the process (Shock and Yiengst, 1948). When 

 repeated daily doses of 1 • 5 m-equiv. ammonium chloride/kg. 

 body weight /day were administered to normal subjects for 

 4-14 days, readjustment of the acid-base equilibrium occurred 

 within 5-7 days in the young subjects, but the aged subjects 

 (65-73 years) were unable to attain equilibrium under this 

 load of ammonium chloride (Hilton, Goodbody and Kruesi, 

 1955). It was also found that the degree of metabolic acidosis 

 induced by a standard dose of ammonium chloride showed a 

 greater severity in the older subjects than in the young. We 

 have now initiated a study of age differences in the ability of 

 the individual to regulate plasma and extracellular fluid 

 volume following the imposition of an oncotic load. 



Thus, the evidence now available indicates that in spite of 

 the reduction in discrete renal functions with age, the kidney 

 retains sufficient capacity to regulate both concentrations and 

 volumes fairly closely under conditions of rest. However, 

 when experimental displacements are produced, age differ- 

 ences in the speed of readjustment appear. 



There are obviously many other questions, such as age dif- 

 ferences in glomerular permeability and the activity of specific 

 cellular enzymes in the kidney, which remain unanswered. 

 Studies on cellular enzymes are now in progress in our labora- 

 tory, using the rat as an experimental animal. Although we 

 have found a reduction in the total oxygen uptake for kidney 

 tissue between the ages of 12 and 24 months in the rat, these 

 differences disappear when an appropriate correction for cell 

 number is introduced. There are, however, some specific 

 enzymes, such as succinoxidase, which show an age reduction 

 which is apparently not dependent on the number of func- 

 tioning cells in the kidney preparation (Barrows et al., 1957). 

 It is our aim to extend these observations to include the 



