In the nicotinic acid supplemented rats, the uptake of
14C-tyrosine into brain was lower than that of the nicotinic acid deficient rats at 2 hours after the administration of
14C-tyrosine. The causes of decrease in the uptake of
14C-tyrosine into the brain by the administration of nicotinic acid to the nicotinic acid deficient rats was described in this paper.
(1) The nicotinic acid deficient rats converted
14C-tyrosine more slowly to
14CO
2 than the nicotinic acid supplemented rats. And the disappearance of
14C-tyrosine from serum was rapid by the administration of nicotinic acid to the nicotinic acid deficient rats.
(2) Nicotinic acid caused no change in tyrosine concentrations in the liver. Therefore, increased production of labeled CO
2 by the administration of nicotinic acid did not affect the dilution of the labeled tyrosine by cold tyrosine.
(3) Tyrosine transaminase activity observed in the nicotinic acid deficient rats was lower than that of the nicotinic acid supplemented rats.
Therefore, the increased activity of tyrosine transaminase in liver and the increased turnover of
14C-tyrosine in the body after the administration of nicotinic acid to the nicotinic acid deficient rats decreased the uptake of
14C-tyrosine into the brain.
View full abstract