Comparative study of zinc, copper, manganese, and iron concentrations in organs of zinc-deficient rats and rats treated neonatally with l-monosodium glutamate.

Abstract

The effects of a zinc-deficient (ZD) diet on the growth and trace element concentrations of various organs (body hair, liver, kidney, gastrocnemius muscle, and femur) of male rats were studied. Furthermore, these trace element concentrations of the above-mentioned organs in male rats neonatally treated with l-monosodium glutamate (MSG) are compared with those of the ZD rats. The ZD rats showed growth retardation compared to rats fed a zinc- adequate diet (controls). The feed efficiency of the ZD rats was only one-fifth of the controls. This is one reason why the ZD rats showed retarded growth. Body hair concentration of zinc (Zn) in the ZD rats was significantly lower than in the controls. On the other hand, copper (Cu), manganese (Mn), and iron (Fe) concentrations in the body hair were significantly higher in the ZD rats than in the controls. Moreover, the apparent absorption rate of these trace elements was significantly higher in the ZD rats than in the controls. The reason for the decrease in Zn contents of the body hair in the ZD rats is probably the reduced dietary Zn intake. Liver and kidney concentrations of Zn in the ZD rats were significantly lower than in the controls. Femur Zn concentrations in the control rats showed higher values than in the ZD rats. Cu and Mn concentrations in the femur in the ZD rats showed higher values than in the controls. Ninh et al. suggested that growth retardation in ZD rats is the result of a decrease in protein biosynthesis. The results of this study support their theory. The reasons for the use of MSG-treated rats in this study are as follows. (1) We reported on the head hair concentration of the above-mentioned elements from pituitary dwarfism (human growth hormone deficient) patients. In that study, the sample was restricted to head hair from pituitary dwarfism patients. More detailed physiological data may be obtained by the used of MSG-treated rats. (2) We took notice of many resemblances between the pituitary dwarfism patients and the MSG-treated rats in morbidity. The MSG-treated rats showed a severe growth retardation compared to NaCl-treated controls. Zn concentration in the body hair was significantly higher in the MSG-treated rats that in the NaCl-treated controls. For other trace element concentrations, there were no significant differences between the MSG-treated rats and the NaCl-treated controls. The concentrations of these trace elements in the liver of the MSG-treated rats were lower than in the NaCl-treated controls. In the MSG-treated rats, the concentrations of Zn and Cu in the femur were higher than in the NaCl-treated controls. However, the Fe concentration in the femur of teh MSG-treated rats showed lower values compared with NaCl-treated controls. The results of this study suggest that the reduction of rat growth hormone (rGH) secretion and/or its synthesis are a consequence of the impairment of rGH anabolic effects. Furthermore it indicates that MSG-treated rats are useful as an in vivo model for the study of the effects of GH.