The distribution of radioactive cobalt in pigs.

The discovery (Smith, 1948; Rickes, Brink, Koniuszy, Wood & Folkers, 1948) that vitamin B,, contains cobalt immediately suggested that it might be possible to label the molecule with radioactive cobalt. A radioactive form of the vitamin would be invaluable for many biochemical investigations. However, as was rather to be anticipated from earlier experiments (Flagg, 1941; McCallum & Hoshowsky, 1948), all our attempts (Fantes, Page, Parker & Smith, 1949) to label vitamin B, by direct exchange with either radiocobalt chloride or hexammino radiocobaltic chloride were unsuccessful. We, therefore, attempted the biosynthesis of radioactive vitamin h2 by feeding physiological doses of radiocobalt chloride to two piglets over a 6-week period. Probably because the experiment was undertaken during the months of December and January, no significant amounts of the anti-pernicious-anaemia factor could be detected in the liver (cf. Dedichen, 1949). The distribution of radioactive cobalt in the pig carcasses was studied at the same time, and our results are described in this communication. The earlier work on the metabolism of radioactive cobalt has been reviewed by Comar (1948). Copp & Greenberg (1941) administered radioactive cobalt to rats, and Greenberg, Copp & Cuthbertson (1943) extended the work to show the appearance of labelled cobalt in the bile, urine, faeces and liver of bile-fistula rats. Sheline, Chaikoff & Montgomery (1946) followed intravenously injected radioactive cobalt in the plasma, bile and pancreatic juice of dogs provided with bile and pancreatic fistulas. More recently, a group of workers at the Florida Agricultural Experiment Station (Comar, Davis & Taylor, 1946; Comar, Davis, Taylor, Huffman & Ely, 1946; Comar & Davis, 1947a, b) carried out experiments with physiological doses of cobalt on thirtytwo cows, two pigs, twenty rabbits and IOO rats. All the earlier work was performed with a mixture of W O , 57C0 and 5 8 C ~ obtained by the deuteron bombardment of iron in the cyclotron. Recently, B°Co, which is prepared by the neutron bombardment of ordinary cobalt in a nuclear pile, has become available for tracer work. A preliminary report by Lawrence (1947) on the metabolism of 6oCo, injected intravenously into mice, lists data for excretion rates and accumulation in various tissues; the data are in accord with the findings of the earlier workers, who used mixtures of WO, 57C0 and 68Co. The American workers gave one dose of radioactive cobalt to each of their animals and then measured the rate of excretion and distribution in the body. In our experi-