DISCUSSION 



DISCUSSION 



Professor Titterton : I wonder if you could tell us something of the distribution 

 of strontium in bone, whether it is uniform throughout the bone or if not, how it 

 varies. 



Dr. Loutit: We do not know anything at all of the distribution of ^Sr throughout 

 the bone, but, since by and large, the human subject is in equilibrium with his intake 

 and environment, we would imagine that the gSr and calcium are uniformly distri- 

 buted if the person is in a constant environment, but nowadays, with air travel and 

 so forth, so few of us are in a constant environment. But if you take radio-active 

 strontium and give a single dose, then this is distributed in bone inhomogenously, and 

 this merely represents the calcification and bone growth during any particular short 

 period of time. Thus, if one received in an accident, shall we say strontium by 

 inhalation, by mouth, and so on, the deposition of this strontium would be focal, 

 depending on which areas of bone were actually active at the time. But as far as, 

 shall we say, world-wide fall-out is concerned, provided the ^''Sr in the diet 

 is reasonably uniform over periods of time, then one would expect that these inhomo- 

 geneities would even out; the ''"Sr would become like ^Sr, the strontium would be 

 deposited with calcium and one would grow up with pretty well uniform deposition 

 of strontium. This postulates of course, that the skeleton is being uniformly turned 

 over. Now this is not necessarily true. Some parts of the skeleton may be laid down 

 at birth and be almost fixed for the rest of life. Other parts of the skeleton may well 

 be completely absorbed, remodelled, and reformed. So that the whole problem does 

 become rather complex, and as a first approximation for constant intake, you can 

 say that the distribution vis-d-vis calcium is constant, but this may be in error by a 

 factor of two or three or so. 



Professor Titterton: May I ask a supplementary question? These last remarks 

 you have made would lead one to believe that there would be differences between 

 bones, and I should therefore like to ask what ratios you would expect in, for example, 

 »oSr take-up between ribs, vertebrae, femur and so on ? 



Dr. Loutit: Measurements are being made of these bones at the moment, and 

 certainly our experience is that with yearling sheep, which have been on constant 

 diets over the last year, the activity is uniform in bones, ribs, vertebrae and femurs, 

 but there are data from the U.S.A. of human subjects given ""Sr where the variation 

 between bones is a factor of two or so. These are subjects with malignant disease and 

 I do not feel that they represent a fair comparison. They are not in normal calcium 

 metabolism and I think that this may just be an expression of their abnormal state 

 as of calcium-strontium metabolism. 



Dr. Poynton: I should like to ask Dr. Loutit whether any work has been done using 

 subjects with disorders of calcium metabolism, such as calcium losing nephritis or 

 parathyroid tumours or work using parathormone. It seems to me that possibly one 

 could compare the uptakes of strontium and calcium, using such subjects; one can 

 more or less clear a subject of calcium and then replace it with strontium, I suppose. 

 I am out of touch with central physiology but I am surprised that the placenta can 

 distinguish between strontium and calcium when it lets through enormous molecules 

 and antibodies and so forth. 



Dr. Loutit: If we can take the second question first — I do not have to tell you of 

 course that placentation varies enormously between species, and I do not think there 

 are any direct experiments on the human transmission, this was only an inference. 

 However, there are data on the rat mother and foetus and their calcium-strontium 

 relationships, and in this case the placental discrimination certainly does seem to 

 obtain, as far as the experimental results can be considered reliable. Of course, if 



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