Vitamin B 12 nutrition and metabolism in the baboon (Papio cynocephalus)

Abstract

1. Measurement of the vitamin B 12 content of baboon tissues showed that the liver contained the highest concentration, followed by the pituitary, kidney, heart, spleen and pancreas. 2. The dietary vitamin B 12 requirement of the baboon for the maintenance of satisfactory body stores was between 1 and 2 μg/d. 3. Satisfactory liver vitamin B 12 stores were invariably associated with serum levels above 125 pg/ml, whereas liver levels were usually low when the serum level was below 50 pg/ml. 4. Increased methylmalonic acid (MMA) excretion after a valine load occurred when the liver vitamin B 12 level was less than 0·40 μg/g. L- and DL-valine were approximately equally effective as precursors of MMA, whereas sodium propionate, whether given orally or intra-peritoneally, was less effective. 5. The distribution of radioactivity along the wall of the intestinal tract after an oral dose of [ 57 Co]cyanocobalamin suggested that the distal half of the small intestine was the main site of vitamin B 12 absorption. However, the utilization of vitamin B 12 put direct into the middle part of the small intestine was much lower than that of an oral dose. 6. The unsaturated vitamin B 12 -binding capacity of baboon serum was not related to the serum vitamin B 12 level. There was a significant difference between the unsaturated vitamin B 12 -binding capacities of the two subspecies of baboon ( Papio cynocephalus cynocephalus and P. cynocephalus anubis ) studied.