CALCIUM AND ZINC BALANCE OF ZN-65-LABELED RATS AT DEFICIENT AND MODERATELY HIGH-CALCIUM SUPPLY .1. EFFECT OF A VARYING CALCIUM SUPPLY ON THE QUANTITATIVE CALCIUM AND ZINC EXCHANGE IN THE METABOLISM OF ADULT-RATS

A total of 32 female Sprague Dawley rats were reared for 28 days with a semisynthetic diet from 75 g up to 156 g body weight. The diet conta ined 0.41 % Ca, 17.5 ppm Zn and was labelled with 16 Bq Zn-65/mu g Zn. Subsequently, five of the almost adult animals were killed for refere nce. The remaining 3 x 9 animals were fed a Zn-65-free diet that unifo rmly contained 17.5 ppm Zn but different Ca concentrations (Ca deficie ncy: 0.01%; control: 0.41%; high Ca supply: 0.91%). Fecal and renal ex cretions were quantitatively collected and analysed for Ca, Zn and Zn- 65. At day 16, 23, and 30 after the introduction of differing Ca suppl ies three animals from each treatment group were killed. The different Ca supply did not affect body weight. The activity of alkaline phosph atase averaged 94 U/l and decreased non-significantly by 15 % at high Ca supply. The changed Ca intake was completely compensated for by a r espective adaptation of fecal Ca excretions. Renal Ca excretions decre ased at Ca deficiency and increased at high Ca supply however, the cha nges mere of minor quantitative relevance. Ca retention was 0 mg/day i n Ca deficiency and 16 mg/day in animals with normal and high Ca suppl y. Ca deficiency increased fecal and renal Zn excretions by 16 % and 1 3 %, respectively. High Ca intake increased fecal Zn excretions by 16 % and reduced renal Zn excretions by 40 %. The changes in fecal Zn exc retions were caused by increased endogenous losses in Ca-deficient ani mals and by a reduced true absorption of dietary Zn at high Ca intake. Daily Zn retention averaged - 2 mu g (Ca deficiency), 17 mu g (contro l) and 9 mu g (high Ca intake). The pool size of mobile Zn was not aff ected by the level of Ca supply (40 % of total body Zn). At normal and high Ca supply, the half-life lime of Zn exchange within the mobile Z n pool was 26 days and decreased to 20 days at deficient Ca supply.