Tpiorium Distribution and Excretion Studies I. Patterns Following Parenteral Administration

Abstract

The distribution and excretion patterns of thorium administered in the citrated form to the rat have been determined after four routes of injection. These routes are intravenous (IV), intramuscular (IM), intraperitoneal (IP), and intratracheal (IT). Two levels of thorium (thorium-234 and thorium-232) were used in the injections, one at a dose of 5.5 × 10−6 g thorium per kg body weight and the other at 6.4 × 10−3. Thorium at the higher level appeared to be more insoluble and of a particulate nature, either concentrating in tissues of the reticuloendothelial system or depositing in the tissue into which it was introduced (i.e. lung (IT), muscle (IM)). At the lower (“tracer”) level, deposition was greater in bone (per g) than in other tissues, with the lung after IT injection being very nearly equal to it. The choice of a “critical” organ is clearly a function of the route of entrance to the body and of the concentrations of thorium involved. The pattern of deposition in the skeleton as a function of the level of thorium administered is discussed using data of several investigators from IV administration to rats.