Effects of the Interrelationship between Dietary Protein and Minerals on Tissue Content of Trace Metals in Streptozotocin-Diabetic Rats

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Abstract
Zinc, iron and copper concentrations were measured in several organs from streptozotocin-diabetic and normal male, Long-Evans rats that were maintained for 21 days on a dietary regimen designed to study the combined or singular effects of insulin-dependent diabetes, dietary protein and dietary minerals on the tissue content of trace metals. The diets contained either 20 ppm zinc and iron, 5 ppm copper and 20% protein (HMHP); 8 ppm zinc and iron, 2 ppm copper and 8.3% protein (LMLP); 20 ppm zinc and iron, 5 ppm copper and 8.3% protein (HMLP) or 8 ppm zinc and iron, 2 ppm copper and 20% protein (LMHP). The concentrations of zinc, iron and copper in liver, zinc and iron in kidney and iron in femur were elevated in the diabetic rats and were not influenced by dietary protein and mineral interaction. However, dietary protein, mineral or protein × mineral interaction significantly affected trace metal concentrations of several organs in diabetic rats but had no significant effect in normal rats. Specifically, copper concentration in kidney and duodenum of diabetic rats were influenced by protein × mineral interaction, duodenal zinc concentrations were higher in diabetic rats fed high mineral diets (HMPH and HMLP) compared to diabetic rats fed low mineral diets (LMPH and LMLP) and femur zinc concentration was higher in diabetic rats fed high protein diets (HMHP and LMLP) compared to diabetic rats fed low protein diets (HMLP and LMLP). While hepatic picolinic carboxylase was elevated severalfold in diabetic rats, it was highest in the diabetic rats fed high protein diets (HPHM and HPLM) suggesting that picolinic acid may, at least in part, mediate the effects of dietary protein and minerals on tissue trace metal concentrations in diabetic rats.