Discussion 247 



conditions this function has an upper limit. If Vitamin A is fed this 

 action is elevated, and it is called trophic action. It would be interesting 

 to give old people Vitamin A and see if this normal Tmp^H for physio- 

 logical conditions could be elevated in this way. 



Shock : We infused lactate in some of these older people who had low 

 Tms and we found that this did raise the Tm by providing additional 

 substrate; you can almost double the Tm for PAH in both old and 

 middle-aged subjects (McDonald, R. K., Shock, N. W., and Yiengst, 

 M. J. (1951). Proc. Soc. exp. Biol., N.Y., 77, 686). In other words the 

 tubules that are still present in the old kidney, as far as we have been 

 able to determine, are just as good as in the young. This is all very dis- 

 tressing to me because I am convinced that there must be progressive 

 changes. The tubule just cannot be working beautifully today and gone 

 tomorrow, but unfortunately this is the way the data come out so far. 



Heller : We all know that there has been a lot of difficulty in the choice 

 of parameters when attempting to compare renal function in adults and 

 infants. I should therefore like to ask Dr. Shock whether he has tried to 

 express his data in terms of other parameters like, for example, total 

 body water. That would seem important because it might reveal cor- 

 relations which may have a functional significance. 



Shock: Yes, we have done that, and if you refer metabolism to total 

 body water you wipe out the age change. However, the age decrement 

 in renal function remains, even when calculated on the basis of body 

 water. 



Hingerty: When you selected your subjects, Dr. Shock, did you ex- 

 clude obese patients? 



Shock : We did not use any index of body weight to exclude patients, 

 but I would say immediately that in our population we do not see obese 

 people over the age of 65. These patients were all males so we do not 

 know anything about the weight of females. 



Hingerty : It seems to me that the decline in kidney function sets in at 

 about the 50-year mark, and that is about the age when you would expect 

 a higher incidence of obesity in the general population. 



Shock: Actually the body surface area decreases with increasing age 

 in all groups of subjects we have studied. The major factor that contri- 

 butes to this reduction in surface area is the body height, which goes 

 down more than body weight. There is a wide scatter in height in our 

 population, but there is a statistically significant linear decrement 

 between the ages of 30 and 90. There is no significant regression of 

 weight on age in the population of male^ that we have studied. 



Black: Is there any serial change in the blood urea with age? It seems 

 very odd that if you give some lactate these tubules can hypertrophy in 

 function to twice their previous extent, and yet when you study them 

 without any stimulus they are apparently in a fairly low state of func- 

 tion. If the blood urea does not go up then it looks as if the remaining 

 tubules are perfectly able to cope with the diminished urea formation 

 within the body. 



Shock : The subjects used in our renal function studies had no elevation 

 in blood urea because this was one of the selection criteria. Every 



