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Studies on the effects of dietary zinc dose on 65Zn absorption in vivo and on the effects of Zn status on 65Zn absorption and body loss in young rats

Published online by Cambridge University Press:  09 March 2007

D. E. Coppen
Affiliation:
Rowett Research Institute, Bucksburn, Aberdeen AB2 9SB
N. T. Davies
Affiliation:
Rowett Research Institute, Bucksburn, Aberdeen AB2 9SB
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Abstract

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1. Weanling male rats were maintained on diets containing 5, 10, 20, 40, 80 or 160 mg zinc/kg for 14 d. On day 15 they received 65Zn either by intraperitoneal injection or in a test meal containing 20 mg Zn/kg. After dosing, the rats were again maintained on the diets they had received previously.

2. Whole-body 65Zn retention was measured immediately after dosing and daily for a further 9 d. From regression analysis of the semi-logarithmic plots of 65Zn retention from 0 to 192 h after 65Zn administration, the true extent of 65Zn absorption and the biological half-life (t1/2) of body 65Zn stores were calculated.

3. At the end of the experiment, the rats were killed and the entire small intestines of some rats from each group were rapidly flushed out to remove food and faecal residues, frozen in liquid nitrogen and stored under an atmosphere of N2 at –20° before separation of cytosolic Zn-binding fractions by gel filtration on Sephadex G–75.

4. The results suggest that rats which received diets that were either deficient(5 mg Zn/kg), marginal (10 mg Zn/kg) or adequate (20–80 mg Zn/kg) in Zn achieved homeostatic regulation of body Zn by changes in both the extent of Zn absorption and excretion. However, when Zn supply was excessive, increasing from 80 to 160 mg Zn/kg, no further changes were seen in Zn absorption, and homeostatic control appeared to be effected entirely by changes in rates of body Zn loss.

5. Gel chromatography of intestinal cytosol on Sephadex G-75 revealed that Zn was associated with two major fractions. The first (peak 1) had a molecular weight (MW) > 75 kdaltons and the second (peak 2), a MW of approximately 10 kdaltons and was assumed to be metallothionein.

6. There was no obvious relation between the amount of Zn bound to peak 1 and dietary Zn content. In contrast, the amount of Zn recovered in peak 2 increased linearly with increasing dietary Zn content.

7. Comparisons between the effect of dietary Zn content on Zn bound to peak 2 and 65Zn retention may, depending on the range of Zn intakes, indicate possible roles for intestinal metallothionein in the control of Zn absorption or excretion.

8. A study of the effects of dietary dose of 65Zn on the extent of 65Zn absorption in rats of normal Zn status indicated a possible biphasic relation. At low doses (5–40 mg Zn/kg) 65Zn absorption appeared to exhibit a curvilinear response to increasing 65Zn dose, indicating possibly a saturable process. At higher doses (40–160 mg Zn/kg) the capacity of this process appeared to be exceeded and 65Zn absorption increased in a linear fashion.

Type
Papers on General Nutrition
Copyright
Copyright © The Nutrition Society 1987

References

REFERENCES

Bremner, I. & Davies, N. T. (1975). Biochemical Journal 149, 733738.CrossRefGoogle Scholar
Cousins, R. J. (1979 a). American Journal of Clinical Nutrition 32, 337345.CrossRefGoogle Scholar
Cousins, R. J. (1979 b). Nutrition Reviews 37, 97103.Google Scholar
Davies, N. T. (1980). British Journal of Nutrition 43, 189203.Google Scholar
Evans, G. W., Johnson, E. C. & Johnson, P. E. (1979). Journal of Nutrition 109, 12581264.Google Scholar
Flanagan, P. R., Haist, J. & Valberg, L. S. (1983). Journal of Nutrition 113, 962972.CrossRefGoogle Scholar
Heth, D. A. & Hoekstra, W. G. (1965). Journal of Nutrition 85, 367374.Google Scholar
Methfessel, A. H. & Spencer, H. (1973). Journal of Applied Physiology 34, 5862.CrossRefGoogle Scholar
Olafson, R. W. (1983). Journal of Nutrition 113, 268275.CrossRefGoogle Scholar
Richards, M. P. & Cousins, R. J. (1976). Journal of Nutrition 106, 15911599.Google Scholar
Richards, M. P. & Cousins, R. J. (1977 a). Biochemical and Biophysical Research Communications 75, 286294.CrossRefGoogle Scholar
Richard, M. P. & Cousins, R. J. (1977 b). Proceedings of the Society of Experimental Biology and Medicine 156, 505508.CrossRefGoogle Scholar
Smith, K. T. & Cousins, R. J. (1980). Journal of Nutrition 110, 316323.Google Scholar
Smith, K. T., Cousins, R. J., Silbon, B. C. & Failla, M. L. (1978). Journal of Nutrition 108, 18491857.Google Scholar
Starcher, B. C., Glauber, S. G. & Madaras, J. G. (1980). Journal of Nutrition 110, 13911397.Google Scholar
Van Campen, D. R. & Mitchell, E. A. (1965). Journal of Nutrition 86, 120124.Google Scholar
Weigand, E. & Kirchgessner, M. (1980). Journal of Nutrition 110, 469480.Google Scholar
Williams, R. B. & Mills, C. F. (1970). British Journal of Nutrition 24, 9891003.Google Scholar