76 General Discussion 



REFERENCES 

 Hill, A. V. (1928-29). Proc. roy. Soc. Ser. B., 104, 39. 

 Kirk, J. E., and Johnsen, S. G. (1951). Circulation, 4, 478. 



DISCUSSION 



McCance: To what extent do you consider these tissues are ahve? I 

 could not see any part of that apparatus designed to keep those cells 

 aerated, and we all know now from the work which is going on at a 

 cellular level, that if you do not keep even a single cell oxygenated its 

 metabolism is completely disorganized; it swells up, changes its size, 

 changes its osmotic pressure, and it can scarcely be regarded as a cell at 

 all until you put it back into oxygen and allow it to recover. That seems 

 to me to be a major criticism of this work, if it is valid. 



Kirk: I did not go into all the details of the experiments because of the 

 limitation of time. In the diffusion studies which I reported at least 

 one of the two compartments of the apparatus contained oxygen. It has 

 been demonstrated in a previous study (J. Gerontol., 9, 10, 1954) that 

 human aortic tissue after removal from the body will continue to show 

 respiration for periods of up to several weeks when kept under sterile 

 conditions. The Q02 values of such tissue preparations can be measured 

 by means of a technique which we developed recently (J. hiol. Chem., 

 199, 675, 1952; 208, 17, 1954). This technique is considerably more 

 sensitive than the ordinary Warburg procedure, since it permits deter- 

 mination of Q02 values as low as 01. We have shown that under ordi- 

 nary circumstances the aorta can be supplied in a thickness of 1 • 2 mm. 

 with oxygen by diffusion, leaving a reserve margin of about 30 per cent. 



McCance: It's extremely interesting how little oxygen tension is needed 

 to provide, say, the cell of the intima with the amount of oxygen it 

 requires because, physiologically, it is bathed, as a rule, in a medium 

 containing so much. x\m I right in thinking that you separate the 

 muscular tissue from the intima before incubating the latter? 



Kirk: No. In the media we have some smooth muscle cells, but the 

 values I gave for the Qo^ refer to the aortic wall. And there is not much 

 difference in the Qo.^ of the human intima and media. The maximum 

 value is about 0-30. 



Franklin: Have you done any experiments on animals? Because I 

 think it might answer Dr. McCance's question if you took some of these 

 pieces and used them to repair blood vessels in other animals. 



Kirk: Well, I have carried out determinations of the rate of respiration 

 and glycolysis of the dog aorta (J. Gerontol., 9, 10, 1954). The studies 

 showed that the Qoo of the dog aorta is approximately twice that of the 

 hmuan aorta; about • 65-0 • 70 is the maximum Q02 found in dogs. Our 

 observations on the respiration of aortic tissue stored at refrigerator 

 temjicrature between tests are in essential agreement with the data by 

 Pierce and his associates {Ann. Surg., 129, 333, 1949), who showed that 



