Further Observations on Distribution of Radioactivity Following Parenteral Administration of Co60 Vitamin B12.

Meyer, Leo M.; Arkun, S. N.; Jiminez-Casado, M.

doi:10.3181/00379727-92-22529

Cited by 7 publications

(2 citation statements)

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“…Several studies Willigan etal., 1958;Hall, 1964) have shown that the excretion of labelled vitamin B12 into bile, and the loss from the body in both faeces and urine, is relatively high during the first few days after administration. Radioactivity in the liver, in contrast to that in many other tissues, increases during this period to reach a maximum after several days to more than a week in different species (Glass et al, 1954(Glass et al, , 1955Booth & Mollin, 1956;Meyer et al, 1956;Grasbeck et al, 1961). The liver, and to a lesser degree the heart, were the only organs whose radioactive content was higher in the late period after isotope administration.…”

Section: Discussionmentioning

confidence: 92%

“…Despite the rapid decrease of total body radioactivity observed in the early period, the liver continues to take up radioactive vitamin B12, and a period of several days to more than a week elapses before maximum values of hepatic radioactivity are obtained (Glass, Boyd, Gellin & Stephanson, 1954;Glass, Boyd & Gellin, 1955;Booth & Mollin, 1956;Meyer, Arkun & Jiminez-Casado, 1956). The dynamic characteristics of hepatic vitamin B, release are relevant to studies of vitamin B I Z metabolism which depend upon measurement of radioactivity in liver, blood and urine over short intervals of time after the administration of radioactive cyanocobalamin.…”

Section: Introductionmentioning

confidence: 97%

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Heterogeneity of Hepatic Vitamin B12 in the Rat after Parenteral Cyanocobalamin

Cooksley

1975

Clinical Science

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1. The rate of radioactive vitamin B12 excretion into plasma and bile from the isolated perfused rat liver and into bile in vivo has been measured after the intramuscular injection of radioactive cyanocobalamin at various time-intervals before study. 2. With an interval of labelling of 10 or more days, the release of radioactive vitamin B12 over 4 h by the isolated perfused liver was linear and constituted approximately 3-5% and 1% of the hepatic radioactivity into plasma and bile respectively. 3. In contrast, after a shorter period of prelabelling (less than 7 days), there was a biphasic release of radioactive vitamin B12: an initial rapid rate followed by a slower rate after about 1 h of perfusion. The total radioactive vitamin B12 was considerably increased (e.g. 25% and 5% of hepatic radioactivity into plasma and bile respectively during a 4 h perfusion of a liver labelled 18 h previously). Confirmation of coexisting stable and labile pools of intrahepatic vitamin B12 was provided by: (a) the patterns of hepatic release after double labelling with 57Co-labelled and 58Co-labelled cyanocobalamin at different times before liver perfusion; (b) the rates of biliary excretion of 57Co-labelled and 58Co-labelled vitamin B12 in vivo after different periods of prelabelling. 5. The rate and pattern of release were not altered by changes in the quantity of precursor cyanocobalamin, by phenobarbitone treatment or by the addition of cycloheximide to the perfusion. 6. The injection into rats of subcellular preparations of rat liver labelled in vivo with radioactive vitamin B12 demonstrated that hepatic heterogeneity did not depend on physical compartmentation. 7. Despite the rapid release rate from the liver of recently administered radioactive cyanocobalamin, the hepatic radioactivity increased progressively with time after labelling in vivo, in contrast to the other tissues, where it decreased. In the presence of rapid bidirectional fluxes the ability of the liver to store vitamin B12 can be largely explained by the reduction in the rate of hepatic release that continues for about 10 days after parenteral administration of cyanocobalamin.

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