Growth rate, tissue zinc levels and activities of selected enzymes in rats fed a zinc-deficient diet by gastric tube.

Male Sprague-Dawley rats (125 g) were fed by gastric tube either a zinc-deficient or a zinc-adequate diet for 32 days. In an additional study, rats were administered similar diets per os. Growth rate, zinc levels in plasma and tissues, and selected enzyme activities were measured. In tube fed rats receiving 13.5 g/day of a zinc-deficient diet, growth rates were similar to controls for 25 days but were somewhat lower by 32 days. The mean food intake of the rats fed the zinc-deficient diet per os was 7.6 +/- 2.1 g/day, and on day 25 growth rate was significantly lower than pair-fed and ad libitum-fed controls. Zinc levels of plasma and tissues and delta-aminolaevulinic acid dehydratase (ALAD) activity in erythrocytes and liver were reduced in rats fed the zinc-deficient diet in both studies. Alkaline ribonuclease activity remained unchanged. The larger nutrient intake provided by gastric tube feeding appears to delay the growth-retarding effect of zinc-deficient diets, but changes in zinc tissue levels and ALAD activity are similar in tube fed and per os fed rats.