BONE RESORPTION IN TISSUE CULTURE 



629 



Fig. 29. Gross appearance of 2-week roller-tube cultures exposed to 50 per 

 cent Oo and various concentrations of crystalline vitamin A alcohol. Although 

 bone resorption was obtained with 3 or 300 units of vitamin A per ml, the 

 gi'eatest effect \\'as found with 30 units per ml. 



thyroid extract per ml of medium and 50 per cent O2, was obtained 

 in those tubes containing vitamin A and 30 per cent Oi-. Surprisingly, 

 the response to vitamin A and 50 per cent O2 was not so marked, 

 suggesting that the optimal oxygen tension for bone resorption with 

 vitamin A-containing cultures is at a lower level than that for para- 

 thyroid extract-containing cultures. 



Attempts to demonstrate enhancement of bone resorption in our 

 tissue culture system with /3-carotene were unsuccessful, confirming 

 Barnicot's negative results with the vitamin A precursor (Barnicot, 

 1948). 



Effect of Vitamin D 



Although one of the major functions of vitamin D is control of 

 calcium absorption from the gut, it is believed that the vitamin can 

 also influence bone resorption (McLean and Urist, 1961). Not only 



