40 T. F. Gallagher 



Gallagher: The pregnanediol conversion comes out to be about 80 

 per cent of theory, based, of course, on the assumption that blood 

 cholesterol is the precursor. The conversion to cholic acid is higher, of 

 the order of 90 per cent. 



Bloch: This is assuming that progesterone is an intermediary stage? 



Gallagher: Yes. And it's also based on the assumption that you 

 do not lose any of the deuterium at C-6. I think the metabolic trans- 

 formation is accomplished before there is any opportunity for extensive 

 exchange with the medium. These calculations confirm the view that 

 deuterium is an excellent tracer element even if it is in a chemically 

 labile position; it is not necessarily labile in the animal body. 



