CALCIUM, STRONTIUM, AND OSTEOGENESIS
Accumulated information on Sr/sup 90/ levels in the diet and in human bone, particularly in the British Isles, is considered, and its significance in Ca and Sr metabolism discussed. Full-term infants in the United Kingdom are born with approximately 28 g Ca and approximately 5.6 mg Sr in the skeleton. The Sr/ sup 90/: Ca ratio varies according to the recent maternal diet, the contamination of which varies from year to year; its value is about 1/10 of that of the maternal diet owing to discrimination between Sr and Ca by the mother in absorption, excretion, and transplacental passage. Maximal postnatal growth of the skeleton occurs in the first year of life and the discriminatory powers of such infants are less than those of adults. In the subsequent few years of life the observed values for Sr, Sr/sup 90/, and Ca suggest a very high rate of turnover of bone with a diminishing rate of accretion of new bone. In adolescence similar data suggest that accumulation of Sr/sup 90/ is mainly due to accretion of new bone with diminishing turnover. Evidence of discrimination in transplacental passage was obtained from assays of bones of the newborn for natural Sr. The mean value for newborn infants was 207 mu g/g Ca. For adult bone the value was 319 mu g Sr/g Ca, which corresponds closely to the value obtained for human plasma 30 to 40 mu g/l. The observed ratio, (OR) (Sr/Ca fetal bone: Sr/Ca maternal plasma), of Sr/sup 90/ but with less certainty. Thus the bones of newborn in 1959 had average values in pC Sr/sup 90//g Ca of 1.13. Maternal plasma values are too low for measurement, but if a representative OR human plasma + human diet of 0.25 be taken, and diet in 1959 averaged 9 pC/g Ca, the OR = 0.5. For the newborn, the Sr/sup 90/ content varies with the year of birth (average 0.44, 0.61, 0.62, 1.13, 0.88, and 0.72 pC/g Ca in the 6 years 1956 to 1961). Stable Sr alters little in the first 6 months but rises significantly to about 245 mu g/g Ca at 1 yr of age. The corresponding Sr/sup 90/ figure again varies according to the year, the maximum value for the annual mean being in 1959 at 4.3 pC/g Ca. Specific activity and total Sr/sup 90/ in the skeleton rose in the first year, when the proportionate accretion of new bone is maximal. The British diet and milk over this period contained 5 to 6 pC/g Ca, and, if 0.5 mg Sr/g Ca be assumed, this gives a specific activity of diet of approximately 11 pC/mg Sr, which is higher than the value deduced for bone (8.6). In the second year, when diet was more contaminated (national diet, 9.0 pC/g Ca) and diet of 1- and 2-yr olds was 14 pC/mg Sr, and accretion of new bone reduced to 50% of the pre-existing skeleton, the specific activity of bone rose with diet to 12.6 pC/mg Sr. For the third year (diet reduced as 9 pC/mg Sr) the specific acitivity of bone was 10.5 pC/mg Sr. For the fourth year with diet containing 8 pC/mg Sr, the value for bone was 6.8 pC/mg Sr. Thus, in these years the specific activity of bone followed that of the contemporary diet very closely. By contrast, the data similarly obtained for a representative adolescent in 1954, at the age of 7 would have had a skeleton of 264 g Ca virtually free of Sr/sup 90/. He would then enter the second burst of growth around the years of puberty, and show a progressive rise in specific and total activity of the skeleton from 1956 to 1961. The data are largely accounted for by accretion of new bone with specific activity corresponding to the national diet in these years (estimated as about 4 pC/mg Sr in 1956 and 1957, and as 4.5, 6.9, 4.9, and 4.8 in the subsequent years). During this 5-yr period the skeletal Ca was doubled, but the specific activity (Sr/sup 90//mg Sr) at the end of the period was still well below that of the diet. (BBB)
- Research Organization:
- Medical Research Council Radiobiological Research Unit., Harwell, Berks, Eng.
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-18-011609
- OSTI ID:
- 4095422
- Journal Information:
- Proc. Nutr. Soc. (Engl. Scot.), Journal Name: Proc. Nutr. Soc. (Engl. Scot.) Vol. Vol: 22
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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