Tissue zinc distribution and exchange in adult rats at zinc deficiency induced by dietary phytate additions: II. Quantitative zinc metabolism of Zn-65-labelled adult rats at zinc deficiency

A total of 37 adult female Sprague-Dawley rats (207 g body weight) were div ided into a reference group (n = 6), a control group (n = 4) and nine treat ment groups (n = 3). The reference group was killed at the start of the exp eriment. The control group was a semisynthetic diet of sufficient zinc cont ent (21 mu g/g). The treatment groups received Zn-deficient diets (1.5 mu g Zn/g) supplemented with increasing amounts of sodium phytate (0, 1.2, 1.8, 2.6, 4.0, 5.9, 8.9, 13.3 and 20 mg/g). The diets were fed restrictively (8 g/day) for 28 days. Subsequently, the animals were killed and dissected qu antitatively into tissue fractions. The increase in dietary phytate additio n induced rising mobilizations of Zn (from 3 to 18 mu g/day). Concomitantly , the whole-body mass fell from 226 g (no dietary phytate) to about 200 g a t the highest phytate levels. The loss in body weight resulted mainly from a reduced soft tissue mass (especially in muscle and fat tissue and in skin ) whereas the tissue mass of the skeleton and most of the organs remained c onstant. The Zn concentration of total soft tissue averaged 20 mu g per g o f wet weight irrespective of treatment. The latter was also observed in mos t of the soft tissue subfractions. Zinc deficiency reduced the Zn concentra tion of the skeleton by 20% compared to the control level (128 mu g/g of we t weight) irrespective of the severity of Zn deficiency. Animals fed the ph ytate-free Zn-deficient diet contained less whole-body Zn than controls (63 45 vs 6859 mu g). The difference originated mainly from a lower Zn content of the skeleton (2453 vs 2894 mu g). Phytate additions reduced the whole-bo dy Zn in a dose-dependent manner to 5676 mu g at the highest phytate level. This was caused mainly by the loss in soft tissue mass. The amounts and co ncentrations of ash, Ca, P and Mg in the skeleton remained unchanged among all animal groups (in bone dry matter: 51% ash, 192 mg Ca/g, 78 mg P/g, 3.5 mg Mg/g). The results indicate that the skeleton is the primary Zn storage tissue in adult rats. Its capacity to mobilize Zn accounts for 20% of bone Zn which is equivalent to about 8% of whole-body Zn. At exhausted bone Zn storage, the mobilization of Zn seems to originate mainly from degradations of soft tissue mass.