The change of disposition kinetics for thiourea accompanied by growth in mice

The whole blood levels and whole-body autoradiography following intravenous administration of thiourea, which is considered to covalently bind to the macromolecules in the body, were investigated in 1-day-old, 1-week-old, 3-week-old and 8-week-old mice in order to clarify the change of disposition kinetics accompanied by growth. The total body clearance for thiourea was remarkably lower in 1-day-old and 1-week-old mice than in more aged mice. The lower metabolic clearance as well as renal clearance in 1-day-old and 1-week-old mice seemed to be responsible for this observation. The whole-body autoradiograms obtained at 60 min following intravenous administration of 14C-thiourea showed the homogeneous distribution of radioactivity throughout the body in 1-day-old and 1-week-old mice and the high radioactivity localized in the liver and lung in more aged mice. This remarkable difference was assumed to be brought about by the difference in quantity of the macromolecules in the liver and lung which can covalently bind with thiourea. This assumption was supported by the result of gel filtration on Sephadex G-10 of the liver and lung homogenates.