Comparative responses of rats to different copper intakes and modes of supplementation

Purified diets deficient in copper and based on either sucrose, egg white, and corn oil or sucrose, casein, corn starch, and safflower oil were fed to young rats. Graded amounts of copper were supplied in drinking solutions with the former diet and by addition to the latter diet; anatomical, chemical, and physiologic responses were compared. Three micrograms Cu/ml and 5 micrograms Cu/g were sufficient to maximize the direct assessments of copper nutriture (copper in blood plasma, heart, and liver). Nutritional adequacy by indirect criteria (heart iron, plasma ceruloplasmin, heart weight divided by body weight, plasma cholesterol, and body weight) generally was found with 3 micrograms/ml and 4 micrograms/g. Anemia was an insensitive characteristic of deficiency. Liver iron was minimized by 4 micrograms Cu/ml and 5 micrograms Cu/g. Most of the differences in response to copper added to water in comparison to copper added to diet probably were explained by the lower amount of copper in the casein diet. Responses to the two dietary regimens were similar when variables were plotted against liver copper. Correlation coefficients with liver copper ranged from 0.52 for liver zinc to 0.96 for heart iron. Liver copper probably is the best index of copper nutriture.