Experimentelle Untersuchungen zur Diagnose von marginalem Zinkmangel

Animal Physiology Nutrition

Wher

Rambeck

et al. 2002

The objective of the present study was to investigate the effect of changing skeletal Zn load (mobilization/restoring) on bone mineral composition and bone tissue metabolism. For this purpose, 36 65Zn-labelled, young-adult female rats were fed with either a purified diet with sufficient Zn (21 microg/g, control) for 26 days, or deficient Zn (1.4 microg/g) for 12 days followed by 14 days repletion with the control diet. The animals were killed at the onset of the study (reference: n=4), at the end of the Zn deficiency episode (control: n=4; Zn deficiency: n=4), subgroups (n=4) of Zn repleted animals at repletion days 2, 4, 7, 10 and 14, and at day 14 the remaining controls also (n=4). Zn deficiency reduced skeletal Zn concentration from 198 to 155 microg/g of bone dry matter. About half of mobilized skeletal Zn was refilled within 2 days of repletion and was completely restored until the end of the study. Concentrations of bone ash, Ca, P and Mg remained constant (means in bone dry matter: 51% bone ash, 191 mg Ca/g, 95 mg P/g, 4.4 mg Mg/g). Blood plasma concentrations of osteocalcin and daily urinary excretions of pyridinoline PYD and dexoxypyridinoline DPD were unaffected by treatment (mean: 57 ng/ml, 222 nmol/day, 137 nmol/day). Also daily urinary excretions of Ca, P and Mg remained fairly constant (means: 0.26 mg/day, 16 mg/day, 1.5 mg/day). 65Zn autoradiography of femur sections revealed a pronounced Zn exchange in the area of the metaphysis and epiphysis. We conclude that transient mobilization and restoration of skeletal Zn occurs mainly in trabecular bone, and does not involve major changes in bone mass, macro mineral content, or bone tissue turnover in young-adult rats.

Section: Discussionmentioning

confidence: 75%

Effect of Zn deficiency and subsequent Zn repletion on bone mineral composition and markers of bone tissue metabolism in ⁶⁵Zn‐labelled, young‐adult rats

Animal Physiology Nutrition

Wher

Rambeck

et al. 2002

“…An important precondition for this purpose is a distinct change in reaction pattern of the status parameter as mineral intake passes from deficient to sufficient supply. An example for such reaction dynamics is the alkaline phosphatase which exhibits a sharp break from a dose‐dependent increase in activity to a plateau at the borderline between deficient and sufficient zinc intake (R oth and K irchgessner 1979). However, in the present experiment neither GSH‐Px activity nor Se concentration in blood plasma met the precondition of a distinct break in reaction pattern between deficient and sufficient Se supply.…”

Section: Discussionmentioning

confidence: 99%

Homeostatic adjustments of selenium metabolism and tissue selenium to widely varying selenium supply in ⁷⁵Se labeled rats

Kirchgeßner

Gabler

Animal Physiology Nutrition

1997

Summary Thirty‐two growing rats were fed restrictively 10 semisynthetic diets which were adjusted to Se contents of 40, 70, 100, 150, 200, 300, 450, 600, 1000 and 3000 ng/g by adding Na selenite. After 3 weeks of collecting the faecal and renal excretions the animals were killed. True absorption and endogenous faecal excretions were determined by the isotope‐dilution technique after an injection of 75Se at day 7 of the experiment. True absorption and endogenous faecal excretion of Se averaged 96% and 7% of intake irrespective of the Se supply. Renal excretions accounted for 12% of intake between dietary Se levels of 40 and 100 ng/g, increased abruptly to 32% at 150 ng/g, rose degressively to a maximum of 68% at 1000 ng/g and fell to 63% at highest Se intake. The Se retention was proportional to Se intake up to dietary Se levels of 100 ng/g, remained constant up to 200 ng/g and then increased at rising extent as dietary Se rose. The tissue Se concentrations increased with rising dietary Se contents, especially between 40 and 150 ng/g and between 1000 and 3000 ng/g. The most pronounced changes were observed in the liver which acted as Se storage. In brain, testes and hair the Se concentrations remained constant except at highest Se supply. Rising Se intake intensified the elimination of injected 75Se mainly via urine and reduced the final whole body 75Se activity from 88% of injected dose at 40 ng/g to 7% at 3000 ng/g. Below 150 ng/g the contribution of liver 75Se to whole body 75Se was reduced in favour of testes and other tissues. At high Se supply, the 75Se contribution of skeletal muscles increased. This may indicate the existence of a slow exchanging or immobile Se compartment within this tissue. The recovery of injected 75Se was complete irrespective of the level of Se supply. Se exhalations were therefore not of quantitative importance. The GSH‐Px activity in blood plasma increased degressively with rising Se supply. Due to its continuous change the GSH‐Px activity could not be used to identify the transition from a deficient to a sufficient dietary Se supply. In conclusion, the homeostatic control of Se metabolism is based on the urinary Se excretion. The onset of this regulation at dietary Se levels between 100 and 150 ng/g indicates the transition of a deficient to a sufficient dietary Se supply. The compensatory capacity of Se homeostasis seems to be overloaded at dietary Se contents above 600 ng/g. Zusammenfassung Homöostatische Anpassung des Se‐Stoffwechsels sowie des Gewebeselens an eine über einen weiten Bereich hinweg variierende Se‐ Versorgung 75Se‐markierter Ratten 32 wachsende Ratten erhielten restriktiv 10 semisynthetische Diäten, deren Se‐Gehalte mit NaSelenit auf 40, 70, 100, 150, 200, 300, 450, 600, 1000 bzw. 3000 ng/g eingestellt waren. Die Kot‐ und Harnausscheidungen wurden quantitativ gesammelt und die Tiere nach 3 Wochen getötet. Die wahre Absorption und endogene fäkale Exkretion wurde über die Isotopen‐Verdünnungsmethode nach Injektion von 75Se am 7. Versuchstag ermittelt. Die wahre Abso...

“…oxalic acid, fiber constituents, polyphenolic compounds) has a substantial effect on the status of supply to the organism. For example, the Zn requirement of rats fed purified diets without any complexing agents is substantially less than for diets containing phytates [6,7,8,9,10]. The difference might be regarded as a non-metabolic "requirement" to compensate for the capability of strong chelators, e.g.…”

Section: Interactions During Digestion and Absorptionmentioning

confidence: 98%

Interaction of chemical species with biological regulation of the metabolism of essential trace elements

2001

Anal Bioanal Chem

Variations in the chemical speciation of dietary trace elements can result in the provision of different amounts of these micronutrients to the organism and might thus induce interactions with trace-element metabolism. The chemical species of Zn, Fe, Cu, and Mn can interact with other components of the diet even before reaching the site of absorption, e.g. by formation of poorly soluble complexes with phytic acid. This might considerably modify the amount of metabolically available trace elements; differences between absorptive capacity per se toward dietary species seems to be less important. Homeostasis usually limits the quantities of Zn, Fe, Cu, and Mn transported from the gut into the organism, and differences between dietary species are largely eliminated at this step. There is no homeostatic control of absorption of Se and I, and organisms seem to be passively exposed to influx of these micronutrients irrespective of dietary speciation. Inside the organism the trace elements are usually converted into a metabolically recognizable form, channeled into their biological functions, or submitted to homeostatically controlled excretion. Some dietary species can, however, be absorbed as intact compounds. As long as the respective quantities of trace elements are not released from their carriers, they are not recognized properly by trace element metabolism and might induce tissue accumulation, irrespective of homeostatic control.