Effect of prednisone on growth and zinc metabolism in rats

Growth failure and increased susceptibility to infection are common complications of prednisone administration, which may be associated with reduced zinc nutriture. To test the hypothesis that prednisone administration interferes with zinc metabolism and impairs growth, 41 male, weanling Charles River rats weighing 43–60 g were randomly assigned to four groups. Three groups of 12 rats received prednisone daily for five weeks at dosages of 0.5, 2.0 and 8.0 mg/kg body weight per day, respectively. A fourth group receiving the maximum dose of prednisone. In the fifth week, all the animals received 65Zn at 0.5 uCi/100 g body weight by stomach tube. The retention of radioactivity was measured in a small animal whole body gamma counter. The results show that the rate of weight gain decreased in the prednisone-treated animals. In addition, while there were no significant differences in food intake between the three groups of prednisone-treated rats, the food efficiency ratio of 0.10±0.03 of the maximally-treated group was significantly lower (P<.001) than that of the pair-fed controls at 0.36±0.03 as well as those at the lower levels of prednisone treatment (with values between 0.25 to 0.29). The whole body 65Zn retention in the pair-fed control animals at 24 and 216 hours was greater than 90% and 60%, respectively, as compared with the retention of 60% and 10% at 24 and 216 hours in the rats administered the highest dose (8 mg/kg/day). Prednisone treatment depressed the capacity of the liver, kidney, muscle, bone and testes to accumulate 65Zn. Urinary excretion of zinc and nitrogen increased in proportion to the doses of prednisone used. We conclude that using growing rats, prednisone treatment impaired body weight gain and reduced food efficiency. At a high dosage the steroid decreased whole body 65Zn retention and increased the relative dry liver weight.