Urinary Excretion of Thiamin and Thiochrome

Although there are a number of urinary metabolites of thieunin, a significant amount of the vitamin is excreted unchanged or as thiochrome, especially if intake is adequate, and therefore the urinary excretion cem provide useful information on nutritional status. Excretion decreases proportioneilly with intake in adequately nourished subjects but, at low intakes, there is a threshold below which further reduction in intake has little effect on excretion. 

The excretion of a test dose of thieimin has eilso been used eis em index of status after a parenteral dose of 5 mg (19 / rmol) of thiamin, adequately nourished subjects excrete more them 300 nmol of the vitamin over 4 hours, whereas deficient subjects excrete less than 75 nmol. 

---

To investigate thiamine metabolism in mammals, thiamine (R values 0.16, 0.04, and 0.03), urinary excretion of thiamine metabolites [thiochirome (Rf values 0.31, 0.28, and 0.33), thiazole (Rf values 0.85, 0.79, and 0.81), and 2-methyl-4-amino-pyrimidinecarboxylic acid (Rf values 0.42, 0.21, and 0.26)], and related compounds [pyrimidinesulfonic acid (Rf values 0.48, 0.39, and 0.46), a-hydroxyethylthiamine (Rf values 0.23, 0.09, and 0.06), 7/ -methylnicotinamide (Rf values 0.31, 0.06, and 0.05)] were analyzed and identified by TLC on silica gel with acetonitrile-water (40 10 vol/vol) adjusted to a pH of 2.54, 4.03, and 7.85 with formic acid as solvents, respectively. Although A -methylnicotinamide and thiochrome could not be separated in single-phase chromatography at pH 2.54, a second phase at right angle, with a pH 4.03 solvent, separated these quite clearly without affecting the resolution of the other compounds. ... 

Thiamine, or vitamin Bi, is a water-soluble compound which is rapidly broken down by moist heat in neutral or alkaline solutions into its constituent pyrimidine and thiazole rings. The ready destructability of thiamine is important in human nutrition, since much may be lost in the preparation of food. Some of the biochemical methods used in evaluating thiamine nutrition are based on reactions with the thiazole and pyrimidine portions of the thiamine molecule. The thiochrome method is widely used in assaying biological materials for thiamine, while determination of the urinary excretion of pyramine (a pyrimidine-like compound) has been used to assist in assessment of nutritional status. 

---