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Summary1) The radioactivity of I131 labeled insulin injected by tail vein into mice was rapidly concentrated by liver and kidney, and converted by these organs from TCA insoluble into TCA soluble form. 2) Overnight fasting plus bromobenzene administration resulted in significant decreases in: (a) liver and kidney non-protein sulfhydryl (reduced glutathione) concentrations, and (b) abilities of these organs to convert radioactivity of administered labeled insulin from TCA insoluble into TCA soluble form. 3) Rapid repletion of liver and kidney GSH, previously depleted by use of bromobenzene, was obtained by use of L-cysteine. The accompanying bromobenzene induced impairment of mouse tissue abilities to solubilize radioactivity of labeled insulin was not restored by L-cysteine administration. 4) Benzyl chloride administration to overnight fasted mice resulted within 2 hours in marked decrease in liver GSH concentration, not accompanied by measurable change in insulin degradation. 5) It therefore appears unli...

Estimations have been made on abilities of certain tissues of mice injected intravenously with insulin I-131 to concentrate and degrade this compound; change of I-131 from TCA insoluble to TCA soluble form has been used as measure of degradation. Insulin I-131, estimated as TCA insoluble I-131, was concentrated by liver and especially by kidney; formation of TCA soluble I-131 occurred most rapidly in liver. With insulin I-131 held constant but total insulin progressively increased, concentration ratios for TCA insoluble I-131 progressively increased in kidney, and decreased in other tissues. In all tissues, conversion of I-131 from TCA insoluble to TCA soluble form decreased progressively with increase in total insulin. Prior mixing of insulin I-131 with excess guinea pig anti-insulin serum (AIS) resulted in loss of tissue abilities to convert the I-131 into TCA soluble form, and in loss of abilities of all tissues other than liver to concentrate this TCA insoluble I-131.

SummaryMice 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, t...

Guinea pig anti-insulin serum (AIS) opposes insulinase action in making 131 I of labeled insulin soluble in dilute trichloracetic acid (TCA). Partial reversal of this AIS effect may be obtained by use of unlabeled insulin. Hence estimations of unlabeled (endogenous) insulin may be made by conjoint use with the unlabeled insulin of labeled insulin, AIS, insulinase and TCA.