Effects of long-term zinc-deficient feeding to the growth of rats

The experiment on Wister rats (about 90g of initial weight) given the zinc supplemented diets (21.1 ppm of zinc, DZ (+) group) or the zinc-deficient diets (1.1 ppm of zinc, DZ (-) group) for 3 and 8 weeks was performed in order to know the effect of the different feeding periods. There was no difference in body weight between the DZ (-) groups fed for 3 and 8 weeks. Compared with the control DZ (+) group, the body weight gain was approximately 1/10 and 1/16 in the DZ (-) group fed for 3 and 8 weeks, respectively. The DZ (-) group showed the decreased weight of every organ and the decreased ratios of the kidney and the adrenal gland to the body weight. Unlike the other organs, the thymus of the DZ (+) group fed for 8 weeks was smaller than that fed for 3 weeks, which is considered as a consequence of degeneration of the thymus concomitant with growth. There was no difference in the serum zinc content between the DZ (-) groups fed for 3 and 8 weeks, while it of the DZ (+) group fed for 8 weeks of feeding decreased 50% of that fed for 3 weeks. The alkaline phosphatase activity showed the same tendency as the serum zinc content. Total protein content was low in the DZ (-) group fed for 8 weeks, but no significant difference in albumin/globulin (A/G) ratio compared with that fed for 3 weeks. The A/G ratio of the DZ (-) group fed for 3 and 8 weeks was higher than that of the DZ (+) group. The DZ (+) group fed for 3 weeks showed the high creatin phosphokinase activity but no significant difference compared with the DZ (-) group. On histological examination, the thick sinusoids were observed in the liver of the DZ (-) group due to the lack of proper fat around the nucleus. The renal corpuscle of the DZ (-) group appeared to be small probably as a consequence that the DZ (-) kidney itself was smaller than that of the DZ (+) group. There were no differences in the liver and kidney between the DZ (-) groups fed for 3 and 8 weeks. These results suggest that the examination on the alimentary zinc-deficiency can be sufficiently performed for 3-week feeding.