Simultaneous excretion of thiamine and thiamine phosphates by the dog

¹ Department of Physiology, Faculty of Medicine, University of São Paulo, São Paulo, Brazil

The fate of intravenously infused thiamine phosphates was studied in the dog. The degree of dephosphorylation by blood, tissue perfusion, and by the kidney was measured. Clearance determinations showed smaller values for these substances than those for creatinine. Concentrated glucose infusions did not change these clearances significantly, but they were increased by inorganic phosphate infusion. Extraction-ratio determinations on unanesthetized dogs showed considerable dephosphorylation by the kidney itself and suggested the possibility of tubular reabsorption. The influence of phosphates was shown to be mainly a protection against dephosphorylation. Perfusion of isolated dog kidneys confirmed these observations and the absence of active tubular excretion of thiamine phosphates, in opposition to active tubular excretion of free thiamine.