METABOLISM OF LABELED PARATHYROID HORMONE II. BLOOD DISAPPEARANCE AND TISSUE DISTRIBUTION

摘要

The availability of a highly radioactive iodinated parathyroid hormone (*PTH) with full and unaltered biological activity prompted a study of the metabolism of the hormone in normal and thyroparathyroidectomized rats. Intravenously administered *PTH was rapidly cleared from the circulating blood giving a 3 exponential decay curve with half-times of 1.7, 9.9, and 81 minutes. Somewhat surprising was the rapid appearance in the circulation of a metabolite which, since it contains the iodine label and biological activity, is considered to be the hormone molecule intact to at least amino acid 43. This metabolite was less rapidly cleared from the blood with a half-life of about 90 minutes. Target organs, kidney cortex and bone showed high tissue fixation of the hormone (and/or metabolite), thirty times that found in soft tissue in general (muscle). Spleen, lung and liver showed some fixation, 3 times that in muscle. Liver deposition is deemed to be quantitatively quite significant.