THE EXCRETION OF PHENOL RED BY THE DOG

Abstract

Excretion of phenol red was examined with special reference to the effect of plasma level. In comparison with simultaneously detd. inulin clearances it was found that at plasma phenol red levels below 1.5 mgm.% the phenol red clearance has a maximum value averaging 1.7 times that of the inulin clearance. As the plasma level is raised the phenol red clearance falls, both absolutely and relative to the inulin clearance, until at plasma levels above 25 mgm.% the PR/I clearance ratio is less than 0.7. The depression of the phenol red clearance effected by raising the plasma level of the dye is perfectly reversible. The curvilinear relation described is analysed in terms of the relative fraction of dye that is excreted by filtration and by secretion. At plasma concn. of 0.5-1.5 mgm.% the relative fraction excreted by secretion approximates 83%, at plasma concn. of 40 mgm.% only 35% is excreted by secretion. The secretion of phenol red is not specifically influenced by phlorizin, nor is it quantitatively effected by wide changes in urine flow.