Age Changes in Renal Function 



233 



The maximum capacity of the renal tubule to excrete 

 diodrast also diminishes with age. Fig. 4 illustrates the 

 results of this test in the subjects studied. The average 

 diodrast Tm fell from 54-6 to 30-8 mg. iodine/1-73 m.^/min. 

 between the ages of 20 and 90 years. This represents a reduc- 

 tion of 43 • 5 per cent. The regression equation relating diodrast 



400 



u" 300- 



tn 



O 

 O ro 



2 



200 



100 — 



20-29 30-39 40-49 50-59 60-69 70-79 80-89 



AGE IN YEARS 



Fig. 5. Decrease in maximal tubular reabsorptive capacity with 

 age. The slope is drawn to connect the mean values for each 

 decade. The vertical lines represent ± one standard error of the 

 mean, while the open circles define the limits of ± one standard 

 deviation of the distribution. 



(From: Miller, McDonald and Shock, 1952). 



Tm to age is: Tm^ = 66-7 — 0-40 x age (in years).* The 

 reabsorptive capacity of the renal tubular epithelium for 

 glucose also shows a comparable diminution with age, as 

 shown in Fig. 5. The average glucose Tm fell from 328 to 

 223 mg. glucose/1- 73m. 7min. between the ages of 30 and 



* The maximum excretory capacity for PAH shows the following regression 

 on age: Tuipah = 120-6 - 0-865 X age (Watkin and Shock, 1955). 



