Thiamin deficiency effects on rat leukocyte pyruvate decarboxylation rates

Thiamin status usually is assessed by urinary excretion of thiamin or by exogenous thiamin pyrophosphate (TPP) stimulation of erythrocyte transketolase activity. Because of the possible great utility of a biologically and chemically sensitive alternative method for thiamin status assessment, studies were made of rat leukocyte pyruvate decarboxylation activity in thiamin deficiency. Pyruvate decarboxylation rates were determined by assaying 14CO2 produced by leukocytes from 1-14C-pyruvic acid in vitro. Reaction conditions were 5 mumoles pyruvic acid, 2.2 X 10(4) DPM 1-14C-pyruvic acid, leukocytes from 5 ml whole blood, 50 mumoles NaH2PO4, 5 mumoles MgSO4, and 1 mumole MnSO4 at pH 7.4 in 1 ml reaction volume at 25 C. Four weeks of thiamin deficiency decreased leukocyte pyruvate decarboxylation rates and markedly increased the TPP effect on this reaction. Dual weekly assays in the same rats showed that 21 days of thiamin deficiency significantly increased the TPP effect on leukocyte pyruvate decarboxylation rates. In contrast, the TPP effect on erythrocyte transketolase activity was significantly increased after only 7 days of thiamin deficiency. Erythrocyte transketolase is more sensitive than leukocyte pyruvate decarboxylation rate to early thiamin deficiency in rats.