General Discussion 125 



old rats, but there is a tremendous differenee in the rate at whieh that 

 calcium mf)ves out of the blood, ft is out of the blood within twenty- 

 four hours in a youno- rat, but you can still measure it very easily at the 

 end of a week in an old rat or dog. So the absorption seems to lie be- 

 tween the blood vessel and the bone rather than between the intestinal 

 wall and the blood. 



NicoUujsen: Yes, absorption is different in young and old adults. The 

 removal from the blood is very complicated, as you know; it is worked 

 out in an equation with four exponential terms. The first two are 

 identical to those for the removal for sodium, then follows the slower 

 one, which is a summary of ionic exchanges and recrystallization, and 

 the last one represents the term excretion. 



McCay: There is a problem of adaptation in the rat: if one maintains 

 rats from early youth on a low calcium diet, one finds that they go into 

 negative calcium balance later in old age, and it is easier to maintain 

 their calcium in old age than if they are from early youth on high 

 calcium diets. And also, if rats are fed diets very rich in milk, one finds 

 that their bones are denser and have more calcium when they die in old 

 age and they excrete more calcium in their urine than if the diet had 

 some other source of calcium like bone meal. So there must be other 

 factors in milk that modify this utilization of calcium in old age, don't 

 you think? 



Nicolaysen: In three years of preliminar}^ experiments we studied the 

 adaptation of Ca absorption in adult rats. The absorption was tested 

 on a -25 per cent Ca diet following intervals of up to four months on a 

 • 04 per cent Ca diet, in the course of w hich the rats lost 2-4 per cent 

 body Ca. However, we could in no instance find an improved absorption. 

 Therefore, we introduced a more severe Ca deprivation, either by giving 

 a diet free of Ca or by giving the • 04 per cent Ca diet with added oxalate. 

 Now the losses increased above 5 per cent, and in the foUow^ing weeks 

 on the 0-25 per cent diet a greatly increased speed of absorption was 

 seen, falling off successively in a staircase-like way. Thus adaptation 

 had been clearly developed. Vitamin D was given to all these rats 

 throughout. 



Auh: If you are looking for osteoporosis, why do you use men instead 

 of women? Isn't it somewhat rarer in men? 



Nicolaysen: Well, an eminent clinician told me he had seen it in many 

 men, and again on the way over here I asked the Head of a hospital for 

 old people, and he said that it was very frequent in old men. 



Tunbridge: I think Prof. Nicolaysen htis fully demonstrated the need 

 for longitudinal studies as well as longevity studies. 



