Thiamine whole blood pharmackinetics in rats using both a specific S-thiamine liquid scintillation assay and the thiochrome fluorescence assay

The study of factors altering the CNS and GI absorption of thiamine in rats required the development of a specific assay for thiamine from 100-microliter samples of blood and plasma and small quantities of tissue. The specific thiochrome fluorescence assay for thiamine was modified to handle microsamples and to use S-thiamine. This sensitive and specific radioassay using S-thiamine gave pharmacokinetic parameters for 4-mg/kg iv doses of thiamine in rats equivalent to those using the less sensitive thiochrome fluorescence assay. The new assay, because of its lower limit of detection, allowed the study of the time profile of thiamine after a 1-mg/kg iv dose in rats. Such a time profile could not have been followed using the standard thiochrome fluorescence assay.