Application of prompt gamma ray analysis to biological samples

Prompt γ-ray activation analysis using the internal monostandard method was applied to organs taken from rats. After B, Cd, or Hg was injected into the rats, the content ratios of B/H, Cd/H, and Hg/H were determined in the brain, kidney, liver, bone, and muscle to study their distribution and metabolism. B was distributed in all organs but was metabolized rapidly. Cd slowly accumulated in the liver and kidney throughout the 65 hours study but no Cd was detected in the brain. Hg accumulated mainly in the kidney 3hrs after the injection. Currently, the concentrations of trace metals in animals and plants are determined by various methods for clarifying the roles played by trace metals in specific organs and their biodistributions. Generally, a living animal has to be killed to determine elemental concentrations in organs. Therefore, it is difficult to study the variation of elemental distributions with an elapse of time after the administration of elements within the same individual. If this elemental distribution study or a metabolism study can be carried out for living an- imals, unique information can be obtained which is free from inaccuracy due to fluctuation among individuals. PGAA is a promising method for carrying out such studies on living animals. Actually, the in-vivo PGAA has been de- veloped for analysis of nitrogen in a living body to estimate a protein mass. 1) As a practical application of the PGAA using the internal monostandard method for large samples with an irregular shape, 2) we propose to investigate the time variation of elemental concentrations in various organs after the administration of certain elements to a living animal. As a preliminary stage of such in vivo analysis of a living animal, PGAA analyses of B, Cd, and Hg, which are highly sensitive elements in PGAA, were carried out using the in- ternal monostandard method for the organ samples of rats dissected at various elapsed times after the injection of B, Cd, and Hg solutions. Experimental Rats used for the metabolism study by PGAA were of Wis- tar descent, male and 7 weeks old, and weighted about 155 g each. Four solutions, that is, containing 1.5 mg of B in the chemical form of H3BO3, containing 0.3 mg of Cd in CdCl2, containing 3 mg of Hg in HgCl2 and physiological saline, were each administered into the abdominal cavity of the rats. (In this paper, we refer to them as B-rat, Cd-rat, Hg-rat, and Normal-rat.) Three hrs, 22 hrs, and 65 hrs after the adminis- tration of the reagent, their brains, kidneys, livers, muscles, and bones were taken out. The blood in the liver was im- mediately substituted for the physiological saline. Then, the organs were kept frozen until irradiation. The typical sizes and weights of the brains, kidneys, and livers were: 15 mm × 20 mm, 1.6 g; 25 mm × 15 mm, 1.6 g; and 35 mm × 30 mm, 7.3 g, respectively. After thawing the sample organs without additional treatments, each organ was put in a 25-µm-thick fluorinated ethylene propylene resin film bag and irradiated with cold neutrons (1.1 × 10 8 n/cm 2 /s) or thermal neutrons (2.4×10 7 n/cm 2 /s) for 60-120 min using the prompt gamma-