628 p. GOLDHABER 



fetal mouse bones grown in tissue culture. Both the cartilage matrix 

 and the bone were destroyed, the effect being more pronounced the 

 younger the limb-bone rudiments and the higher the concentration 

 of vitamin A. Biochemical evidence was obtained in support of the 

 hypothesis that vitamin A acts on cartilage matrix by enhancing the 

 enzymic activity of chondrocytes and by increasing proteolytic ac- 

 tivity through alteration of lysosome permeability (Dingle et ah, 

 1961; Lucy et ah, 1961; Dingle, 1961). Of interest was the finding 

 that vitamin A in low concentrations released a protease from iso- 

 lated lysosomes of rat liver cells (Fell et ah, 1961). This in vitro 

 effect of vitamin A upon lysosomes has been demonstrated recently 

 in an in vivo system by Janoff and McCluskey (1962). These in- 

 vestigators have reported that peritoneal macrophages and poly- 

 morphonuclear leucocytes of vitamin A-treated guinea pigs showed 

 a marked loss of acid phosphatase, presumabh' due to disruption of 

 the intracellular lysosomes which contain the enzvme. 



Although Fell and Mellanby ( 1952 ) reported the presence of only 

 a few osteoclasts in most of their vitamin A experiments, it would 

 be of interest to learn whether the acid phosphatase content of these 

 cells is depleted. 



Attempts to demonstrate a direct effect of vitamin A on mouse 

 calvaria in our own tissue culture system have been successful. In 

 cultures gassed with 50 per cent 0-, the addition of 30 units of 

 crystalline vitamin A alcohol per ml of medium produced bone re- 

 sorption. The addition of 3 units of vitamin A per ml of medium had 

 less effect, whereas 300 units of vitamin A per ml had the least effect 

 (Fig. 29). It should be noted that our effective dose of approxi- 

 mately 30 units of vitamin A per ml was similar to that found by 

 Fell and Mellanby ( 1952 ) . 



Of further interest was the finding that there was an interdepend- 

 ence between vitamin A and oxygen tension similar to that found 

 for parathyroid extract. From Figs. 30 and 31 it may be seen that 

 vitamin A-treated cultures (24 units per ml) showed no gross ef- 

 fect as compared with untreated controls when both groups were 

 gassed with 10 per cent O2. Definite enhancement of resorption was 

 obtained with 20 per cent O2 and vitamin A. The most intensive 

 resorption, comparable to the effect observed with 0.5 unit of para- 



