BONE RESORPTION IN TISSUE CULTURE 621 



different from one another and from the control tubes without hor- 

 mone. In view of its sensitivity to small quantities of parathyroid 

 hormone, the present tissue culture system may provide a simple 

 assay method for the hormone, based upon scoring severity of re- 

 sorption microscopically. This approach has been of practical value 

 already in studies concerning the extraction of parath\'roid hormone 

 from rat and human parathyroids." 



Citrate and Lactate Production in Resorhing 

 and Nonresorbing Bone Cultures 



In a previous study (Kenny et al., 1959) it was shown that the 

 media from our resorbing bone cultures showed consistent increases 

 in citric acid, calcium, and phosphorus, which paralleled the bone 

 resorption seen morphologically. Lactic acid, on the other hand, 

 accumulated in the nonresorbing, control cultures. Whether the 

 accumulation of citric acid in the media of the resorbing cultures 

 and lactic acid in the media of the nonresorbing cultures was sig- 

 nificant with respect to the mechanism of bone resorption was not 

 known. This pattern of acid accumulation might have been coinci- 

 dental, for in those studies bone resorption was initiated by gassing 

 the experimental stationary cultures with 95 per cent O2 and 5 per 

 cent CO2, whereas the nonresorbing stationary cultures were main- 

 tained by gassing with 95 per cent air and 5 per cent CO2. It was to 

 be expected, therefore, that the experimental cultures would favor 

 aerobic metabolism and citrate production, whereas the control cul- 

 tures would favor anaerobic metabolism and lactic acid formation. 



The striking ability of parathyroid extract to stimulate bone re- 

 sorption in our tissue culture system ( both control and experimental 



* Studies in progress in collaboration with Drs. Paul L. Munson, Philip F. Hirsch, 

 and Amien J. Tashjian. 



Fig. 24. Gross appearance of control roller tubes ( 12 days in culture) gassed 

 with 10, 20, 30, or 50 per cent oxygen. It should be noted that some resorption 

 was evident microscopicalhj in tlie tubes gassed with the higher concentrations 

 of oxygen. 



Fig. 25. Gross appearance of experimental roller tubes (12 days in culture) 

 containing 0.5 unit of parathyroid extract per ml of medium. Note the increasing 

 effectiveness of the hormone on resorption as the oxygen tension is increased. 



