Turnover of bone zinc during normal and accelerated bone loss in rats

The ability of the skeleton to serve as a reservoir of available zinc was investigated in weanling and 7-week-old rats. Bone turnover was measured by the loss of previously incorporated 3H-tetracycline (TC), in conditions of normal turnover accompanying growth or accelerated loss produced by calcium deficiency. The 4-week studies involved four experimental groups per age group (all combinations of high and low calcium, high and low zinc). By measuring loss of 3H-TC and whole bone (humerus) contents of Zn and Ca, it was possible to calculate the deposition and resorption of Zn and Ca during the experimental period. Several conclusions emerged from the study: 1) availability of Zn from the skeleton was dependent on the rate of bone resorption, but not on Zn status; 2) redeposition of Zn in the skeleton following resorption was extensive, and independent of the rate of bone mineral deposition; and 3) in Ca deficiency there was an increased deposition of Zn, suggesting a partial substitution of Zn for Ca in bone mineral. The results support the concept that the skeleton does not serve as a reservoir for Zn. Very little Zn is made available by bone resorption, and even then Zn is lost only in a passive manner that is dependent on, but does not influence, bone turnover. The availability of Zn from the skeleton is not mediated by Zn status.