The absorption of [58Co]cyanocobalamin by unweaned rats

Abstract

1. ‘⁵⁸Co’cyanocobalamin was given by stomach tube to Wistar albino rats aged between 6 h and 24 days. The fraction of the dose absorbed was assessed by measuring the amount retained by the animals after 7 days, by total body counting.2. Rats up to 4 days old absorbed about 90% of the test dose, compared with a mean of 83% at the age of 8 days, 66% at 16 days and 47% at 24 days.3. The proportion of the test dose absorbed did not appear to be affected by starvation for up to 24 h, by increasing the dose from 0·05 ng to 0·25 ng/g body-weight, or by giving the ‘⁵⁸Co’cyanocobalamin mixed with rat's milk.4. The results support earlier suggestions that newborn rats absorb vitamin B₁₂ by a different mechanism from that in adults.