The turnover of 65Zn in rats fed a zinc-deficient diet

Renal metallothionein responds rapidly and site specifically to zinc repletion in growing rats

Metallothionein (MT) is important for heavy metals and free radical protection in the kidney. MT is responsive to zinc and primarily localized within the renal cortex. However, site-specific renal responses to dietary zinc repletion are understudied. The objective of this study was to examine the effects of dietary zinc deficiency and repletion on renal MT concentration and immunolocalization in rats. Weanling male Sprague Dawley rats were randomly assigned to either a zinc-deficient, zinc control, or pair-fed to zinc-deficient group. Half of the zinc-deficient and pair-fed rats were repleted with the control diet ad libitum for an additional 24h. Renal tissue samples were assessed for total zinc, MT concentrations and MT immunostaining. Dietary zinc deficiency reduced renal zinc and MT concentrations, and attenuated intensity and localization of MT. Dietary zinc repletion for 24h restored renal zinc and MT concentrations, the latter primarily in the proximal convoluted tubules of the cortex. Concentrations of renal MT, but not zinc, were elevated by diet restriction and MT (microg/mg protein) and partially normalized by 24h diet repletion. In conclusion, renal MT modification due to zinc deficiency or diet restriction can be rapidly normalized in a site-specific manner with normal dietary zinc intake. The results support a role for MT in kidney homeostasis, in particular at the level of the proximal tubules in the cortex. The speed of MT repletion may have clinical implications for dietary zinc in the treatment of acute and chronic renal pathology due to toxins and free radicals.

Effects of 1,25-dihydroxycholecalciferol on fracture healing. Calcium, phosphate, and zinc in callus and serum

The incorporation of calcium, phosphate, and zinc into the callus of closed tibial fractures was studied in adult rats fed a standard diet. Low doses (60 ng/kg per day) of 1,25(OH)2D3 5 days a week greatly increased early callus mineralization. This was not related to an increased serum calcium-phosphate molar product but rather to a decreased ratio. The incorporation of zinc into callus seemed to be correlated to the mineralization process but not to the 1,25(OH)2D3 administration as such. The question of a direct, indirect, or a complex role of 1,25(OH)2D3 in bone formation and mineralization is discussed.

Zinc deficiency-induced trace element concentration and localization changes in the central nervous system of albino rat during postnatal development. II. Atomic absorption spectrophotometric examinations

The changes in the zinc and copper concentrations in the central nervous system (spinal cord, cerebellum, cerebrum, hippocampus, corpus striatum) of albino rat were studied by atomic absorption spectrophotometry in a state of zinc deficiency induced experimentally during the first 30 days of postnatal ontogenesis. It was found that in these structures the zinc deficiency is able to influence the changes and tendencies in the trace element content essentially only in an area undergoing intensive development in the given period, or which is sensitive to unsatisfactory dietary influences. The results lead to the assumption that the state of zinc deficiency is accompanied by a change in the distribution of the trace element content within the cells.

Absorption, retention and excretion of 65Zn in rats with wounds treated with 65Zn-labelled zinc tape

Absorption, retention and excretion of 65Zn in rats from excisional wounds treated with 65Zn-labelled zinc tape were studied. The absorption of 65Zn was marked and indicates that the absorption of zinc from the tape is more than sufficient to account for the increases in zinc concentrations seen in several tissues. The distribution, retention and excretion of 65Zn from the zinc tape followed a pattern similar to that of 65Zn injected into non-operated and operated rats. This indicates that the zinc from the tape is present in the body not as zinc oxide, as it is in the adhesive substance of the tape, but as zinc in those forms which are originally found in the body and that zinc oxide is ionized before absorption. In tissues with a rapid uptake of zinc more than 50% of the total concentration of zinc derived from the zinc tape after eight days of treatment. In operated animals which were not treated with zinc tape a decline was seen in the serum zinc concentration and excretion of zinc with a concomitant increase in the liver concentration of zinc.

Bioavailability of zinc in milk and soy protein-based infant formulas

Total femur zinc of young rats was used to evaluate the biological availability of zinc in milk and soy protein-based infant formulas. A zinc deficient diet (0.8 mug Zn/g) containing egg white protein was supplemented with graded levels of zinc from zinc sulfate, milk and soy protein-based infant formulas. A plot of total femur zinc (log) after feeding the diet for 3 weeks versus the zinc added to the diet gave a linear relationship over the range of 0, 3, 6, 9 and 12 mug/g added zinc. By using a slope-ratio bioassay model, the relative biological availability of endogenous and added zinc in milk-based formula was estimated to be 0.86 and that of soy-based formula 0.67 (zinc sulphate = 1.00) with corresponding 95% fiducial limits being 0.82 to 0.91 and 0.62 to 0.71. Thus, to provide equivalent amounts of available zinc, the total zinc content of the soy protein-based formula would need to be at least 20% higher than that of the formula containing milk protein.

Binders of intravenously administered 65-zinc in rat liver cytoplasm

The fate of an i.v. injected trace dose of 65Zn2+ in the rat, was studied over a period of 10 days after injection. Tissue distributions were determined and a special study was made of 65Zn binders in liver cytoplasm. A total of 6 65Zn-binding fractions were observed in liver cytoplasm with apparent molecular weights of about 113,000, 66,400, 47,400, 29,000, 23,000 and 11,400. A time study showed that 4 hours after the injection the most prominent cytoplasmatic 65Zn binders are the 113,000, 66,400 and 23,000 molecular weight fractions. A tentative identification of the main Zn binders in the six 65Zn fractions is given, using the collected data regarding their apparent molecular weight, time dependent prominence and content of stable Zn.

Turnover of 65Zn and 82Sr in growing rats. A comparative investigation

Analysis of bone retention data using 2- or 3-compartment models gives nearly equal relative accretion rates for zinc and calcium (85Sr) in endochondral bone and calcifying cartilage. The rate for zinc in cortical bone is 70% of that for calcium. As the existence in cortical bone of large, slowly exchanging compartments limitating accretion is consistent with the data, the relative accretion rate for zinc may more closely reflect the relative accretion rate of cortical bone.