Tissue chromium exchange in the rat.

This study of chromium (Cr) exchange in the rat combined measurements of 51Cr distribution and tissue Cr content to permit an assessment of tissue Cr exchange under control conditions and during varied Cr intakes. Liver Cr was found to be 50 to 100% exchangeable whereas pancreas Cr was only 34% exchangeable. In kidney, the specific activity of 51Cr exceeded that of serum by more than 100%, indicating a complex type of exchange involving both a rapidly exchanging Cr pool and an "inner" Cr pool with "sink-like" characteristics. Chromium deprivation of moderate degree reduced serum Cr and tissue exchangeable Cr pools but did not change total tissue Cr, 51Cr distribution, or glucose tolerance. Chromium supplementation and Cr overload increased serum Cr and total, exchangeable, and nonexchangeable tissue Cr pools but did not alter 51Cr distribution. These results indicate that the merging of tracer techniques with tissue Cr analyses yields a more complete view of Cr exchange than 51Cr distribution alone. The data support the hypothesis that specific transport characteristics exist in tissues that may regulate the biological role of Cr.