科研之友
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摘要
We explored the possibility of using natural calcium (Ca) isotope variations in the urine (delta Ca-44/40(urine)) as a proxy for the Ca balance in the human body. We chose two test persons extremely different in their health status, gentler and age (4-year-old healthy boy and a 60-year-old woman known to suffer from osteoporosis). During a 5 day interval the Ca isotope composition of the individual diet (delta Ca-44/40(diet)) was monitored for both test persons to be in general agreement to the Ca isotope composition of the normal western European diet (similar to - 1.02 +/- 0.1 parts per thousand.). However, measurements showed that (1) delta Ca-44/40(urine) of both test persons are similar to 1.37 and similar to 2.49 parts per thousand, respectively, heavier than delta Ca-44/40(diet) and that (2) the delta Ca-44/40(urine-boy) is similar to 1.1 parts per thousand heavier when compared to the value of the woman. The individual offset between diet and test persons is interpreted to reflect individual Ca reabsorption rates in the kidneys being the result of Rayleigh type Ca isotope fractionation related to the partitioning of Ca between the glomerular filtrate and filtered residue. The relative difference between delta Ca-44/40(urine-boy) and delta Ca-44/40(urine-woman) of similar to 1.1 parts per thousand may reflect individual differences in the balance of bone mineralization and demineralization processes related to age, gender and health status. By arbitrarily defining an equilibrium value for Delta Ca-44/40(diet-urine) of -1.93 parts per thousand being the arithmetic mean of delta Ca-44/40(urine) for both test persons the measured delta Ca-44/40(urine) values may be applied to model the individual bone mineralization and demineralization processes in a qualitative way. Note, second order influences of intestinal Ca absorption during sequestration of Ca between intestine and blood have to be subject of further studies.
- 出版日期2010-4
