Evaluation of radioiodinated histamine as isotope carrier in vivo

The iodo derivative of histamine labelled with I-125 has been used for many years to prepare tracers used in RIA systems. The aim of this study was to evaluate radioiodinated histamine as a potential isotope carrier for in vi vo applications. The biological behaviour of radioiodinated histamine has b een investigated in rodents. The observed absence of any specific iodohista mine uptake by a critical organ or tissue promises a very quick distributio n of the iodohistamine in soft tissues, and a rapid rate of whole-body clea rance via the urinary tract (e.g. over 50% of the injected dose (ID) during the first hour after administration). In spite of moderately low in vitro stability of iodohistamine in serum, biodistribution studies in rodents hav e not shown any significant release of iodine from the parent molecule in t he whole animal. Low uptake was observed in the thyroid (e.g. 0.22 and 0.11 % ID at 1 and 2 h after administration to rats), and not more than 3% of in jected activity was detected in the stomach in all of the biodistribution e xperiments. Moreover, our results refute any possibility of competition bet ween histamine and iodohistamine for receptor binding sites, and suggest th at radioactive mono-iodohistamine may be used successfully to develop some new radiolabelled bioactive molecules with potential application in vivo. ( (C) 2000 Lippincott Williams & Wilkins).