Einfluß von alimentärem Zn-Mangel auf die Konzentration von Wachstumshormon (GH), insulinähnlichem Wachstumsfaktor-1 (IGF-1) und Insulin im Serum von Ratten in Abhängigkeit von der Futteraufnahme

Development of alimentary zinc deficiency in growing rats is retarded at low dietary protein levels

The aim of the present study was to determine whether the level of dietary protein would influence the onset of zinc deficiency in rats because zinc-deprived rats have problems metabolizing dietary protein. Young male Sprague-Dawley rats were fed isoenergetic Zn-deficient diets (0.8 mg Zn/kg diet) or control diets substituted with zinc sulfate (54 mg Zn/kg diet) and protein levels of 2, 5, 8, 10, 15, 20 or 25 g/100 g for 21 d to determine whether changing the protein level of Zn-deficient diets affects the Zn status of the rats. In rats fed low dietary protein levels of 2 and 5%, feed intake, growth and appearance did not differ between the Zn-deficient rats and the control rats because the low zinc requirement was met by mobilization of zinc from the skeleton. At higher dietary protein levels, the Zn-depleted rats developed marked signs of Zn deficiency and had reduced feed intake, growth, alkaline phosphatase activity in the serum and Zn concentrations in serum and femur compared with the control rats. The reduced feed intakes and decreased growth of Zn-depleted rats fed high dietary protein levels (20 and 25%) compared with control rats may be due to disturbed protein synthesis, as demonstrated by the increased activities of alanine aminotransferase, glutamate dehydrogenase and carbamoylphosphate synthetase in the liver. Zinc as an essential component of the diet is thus vital for the efficient utilization of dietary protein.

[Diagnosis of zinc deficiency]

Though far more common, particularly in elderly people, than was previously assumed, marginal zinc deficiency does not lead to the classical manifestations of zinc deficiency and is therefore difficult to diagnose. There is therefore a need for sensitive parameters that can reliably demonstrate even marginal zinc deficiency, as suboptimal zinc status can seriously impair human health, performance, reproductive functions, and mental and physical development. The most important criteria for the diagnosis of zinc deficiency are critically discussed. The laboratory parameters currently considered to be the most useful indicators of marginal zinc deficiency are zinc-binding capacity and serum/plasma alkaline phosphatase activity before and after zinc supplementation (zinc tolerance test!). In order to obtain a reliable assessment of a patients zinc status, a number of different diagnostic parameters should always be measured.