Age Changes in Renal Function 



241 



of the falling cardiac output. This vasoconstriction is func- 

 tional in character and can be removed by an appropriate 

 physiological stimulus. Although the tubular epithelium 

 responds to the stimulus of the antidiuretic hormone as 

 quickly in the old as in the young, the functional capacity of 

 the tubular epithelium to perform osmotic work shows a 

 gradual reduction with age. 



opr 



201 

 180 — 

 I 60 — 

 140 

 120 

 100 



80 



60 



40 — 



20 — 



> 



25 



35 



45 



55 



65 



75 



65 



AGE IN YEARS 

 Fig. 11. Relationship between maximum U/P inulin following pitressin, 

 and age. The ordinate is the mean U/P ratio for periods 5 and 6. 

 (From: Miller and Shock, 1953). 



Although these experiments serve to define certain limita- 

 tions in renal function with increasing age, we must turn to 

 other observations to tell us how effective the aged kidney 

 is in maintaining volume and concentration characteristics of 

 the extracellular fluid. With regard to electrolyte concen- 

 tration of the plasma, there is no evidence of any system- 

 atic changes with age. Although Videbaek and Ackermann 

 (1953) reported a slight rise in plasma potassium concentra- 

 tions, 4 -0-4 -5 m-equiv./l., between the ages of 25 and 90, the 



