Leukocyte transketolase activity as an indicator of thiamin nutriture in rats

The purpose of this study was to evaluate the possibility of using leukocyte transketolase activity (TKA) as an index of thiamin status. It was shown previously that hepatic TKA in rats is altered by changes in the type and amounts of carbohydrate, protein, and fat in the diet. It was, therefore, essential to determine whether leukocyte TKA in rats is affected by dietary factors other than thiamin intake. Hepatic TKA and leukocyte TKA both varied with dietary thiamin intake; maximum activity was attained when the diet contained 3 to 4 mg thiamin/kg diet. Administration of oxythiamin resulted in decreases in TKA in both liver and leukocytes. The changes in leukocyte and hepatic TKA induced by varying degrees of thiamin deficiency were closely correlated. The responses of thiamin content were also closely correlated in liver and leukocytes. However, only hepatic TKA was altered by increasing the fat or protein content of the diet or by substituting fructose for glucose. None of the dietary manipulations studied except the production of thiamin deficiency had any effect on leukocyte TKA. We conclude from our results that leukocyte TKA is a sensitive and specific indicator of thiamin nutriture in rats.