124 General Discussion 



Tlie amount of phosphates in urine is above that in the faices when the 

 intake of vitamin D is sufficient, and the faeces content goes above that 

 of the urine when the intake of vitamin D is below normal requirements. 

 As soon as you give the necessary amount of vitamin D (about 4 ;ug./day), 

 then the proportion of phosphates in the urine is above the phosphate in 

 the faeces. That is a very sensitive method in man. In vitamin D 

 deficiency, when practically no phosphates are absorbed, vitamin D can 

 produce a tremendous increase in phosphate absorption with no effect on 

 calcium. 



Nicolaysen: I am a little sceptical of that method. I have done a 

 great many studies on the ratio of calcium to phosphate in the faeces, 

 and it only tells me that if there is no phytic acid in the faeces, the 

 phosphate varies with the calcium. 



Auh: In the faeces, yes, but not in the urine. Phosphate in the urine is 

 a very complicated problem — ^calcium excretion appears simpler, or at 

 least is better understood. There may be a very low phosphate in the 

 blood stream but a very large excretion in the urine, and the reverse 

 situation may also occur. The differences appear to be dependent 

 largely on the amount of reabsorption in the renal tubules. 



Brull: May I remind you that I demonstrated a threshold for phos- 

 phate about twenty-five years ago, and the influence of hormones and 

 other factors upon it? 



Nicolaysen: If you were to accumulate the phosphates in the faeces in 

 a soluble form you would soon get diarrhoea. 



Auh: I agree that phosphate excretion appears to depend on the 

 amount of calcium in the faeces. It appears in the faeces largely as 

 dibasic calcium phosphate, but it doesn't always appear in the urine in 

 that way, the excretion there appears more complicated. 



McCay: It is interesting that you have found vitamin D of importance. 

 We have tried for many years, off and on, and we have never been able 

 to show a vitamin D requirement in old rats. You have different diets 

 and conditions, and it shows that results vary enormously under different 

 experimental conditions. 



Nicolaysen: We have conducted a life-time study in rats which is 

 instructive on this point. The diet was free of vitamin D but when 

 vitamin D was added optimal growth was seen (in the D-free rats the 

 final body weight was 10 per cent lower). The calcium balance was 

 studied continuously over eighteen months. The difference in the 

 absorption of calcium between the +D group and the D-free group 

 disappeared after twelve weeks of experiment. The total calcium 

 retention per 100 g. body weight was about 10 per cent lower in the 

 D-free rats. Vitamin D given to such D-free rats resulted in a con- 

 siderably increased absorption. This was true for rats at the age of 

 thirty-five weeks as well as at seventy-five weeks. The amount of Ca 

 absorbed was many times higher than that seen in rats of the same age 

 which had been given vitamin D throughout. 



McCay: Absorption from the intestine is confirmed very well by radio- 

 active calcium work. There seems to be no difference in absorption of 

 radioactive calcium from the tracts of young and old dogs or young and 



