Abstract
Summary
Mice were injected with a 19 to 1 mixture of unlabeled and I125 labeled beef insulins and sacrificed 2, 5, 10 or 25 minutes later. Insulin in especially prepared tissue extracts and fractions was estimated by: (a) immunoassay, and (b) I125 count. Using either assay procedure, insulin (1) reached its highest concentration in liver sooner than it did in kidney, (2) was far more highly concentrated by kidney than by liver, (3) showed decrease in tissue concentration in the order plasma>liver>kidney, and (4) was rapidly and highly concentrated in liver particles brought down between 700 g and 105,000 g. Insulin added to liver ho-mogenate was not concentrated by these particles. These findings are in accord with the hypotheses that radioiodinated and unlabeled forms of insulin are metabolized in similar manner, and that both forms of insulin are capable of penetrating into liver and kidney cells.
We are indebted to Drs. James Ashmore and Peter Wright of our Department for guinea pig anti-insulin serum, to Dr. Mary Root of Eli Lilly Co. for beef insulin of low glucagon content, and to Dr. Howard Rickenberg, Microbiology Department, Indiana University, for use of a tissue ultrasonicator.
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