Renal excretion of radiofluoride in the dog

¹ Departments of Physiological Chemistry and of Physiology, University of Minnesota Medical School, Minneapolis, Minnesota

Renal clearances of continuously infused radiofluoride were measured in 10 dogs in which a large part of the skeleton had been excluded from the system in order to produce a more constant plasma radiofluoride concentration. The results were evaluated to describe the factors of glomerular filtration and tubular reabsorption of fluoride under several conditions. The animals that received carrier-free radiofluoride infusions excreted urine with a mean radiofluoride concentration 3.4–14.5 times that of the plasma. The urine-to-plasma concentration ratios obtained with animals given a load of stable fluoride was 13.5–29.6. An increased urine volume resulted in a decreased tubular reabsorption of fluoride and the clearance was increased. Chlorothiazide increased radiofluoride excretion but decreased the urine concentration. The radiofluoride clearances were always less than the creatinine clearances but were 7.8–179 times the chloride clearances. The effect of chlorothiazide was to decrease the ratio of fluoride to chloride clearance by increasing chloride clearance more than fluoride clearance.