Metabolism of selenocyanate in the rat

Rats injected subcutaneously with 2 mg Se/kg body weight of 75Se]selenocyanate or 14C, 75Se]selenocyanate excreted dimethylselenide (DMSe) in the breath and trimethyl-selenonium ion (TMSe) in the urine. The 24-h respiratory DMSe and urinary TMSe excretions were 26.8 +/- 8.1 and 14.5 +/- 5.1% of the dose, respectively. Tissue concentrations of 75Se were highest in the kidneys (1.89 +/- 0.2% dose/g), liver (1.46 +/- 0.2% dose/g), and blood (0.50 +/- 0.05% dose/ml), and lower (greater than 0.3% dose/g) in the other tissues. Trimethyl-selenonium was the major form (61%) of selenium in urine. Approximately 2% of the dose of doubly labeled SeCN- was excreted unchanged in urine (about 12% of urinary Se). 14C from doubly labeled SeCN- was not present in the methylated selenium metabolites, but a major 14C urinary metabolite was identified as thiocyanate. These results indicate that a substantial part of selenocyanate in the body undergoes metabolism and Se is excreted in methylated forms following scission of the C-Se bond.