Effects of administration of mannitol and furosemide in the renal hemodynamics of the dog.

The action site of mannitol and furosemide in the nephron level was studied in two groups of dogs which, alternatively, were given both diuretics. The furosemide preferential action site was confirmed in the ascending limb of Henle's loop. It is suggested that mannitol acts on the descending limb of this loop, and that the dilution effects of this diuretic on the ascending limb are due to contamination. Changes in urinary excretion of potassium were not observed during mannitol administration. This fact coincides with the action site suggested for this substance.