Site of Action of Furosemide

¹ Isotopic Department and Metabolic Unit and Department of Medicine, János Hospital, Budapest, Hungary.
² Isotopic Department and Metabolic Unit and Department of Medicine, Jnos Hospital, Budapest, Hungary.

In a patient suffering from psychogenic polydipsia, authors have studied during maximal sustained diuresis the effects of furosemide, chlosudimeprimyl, hydrochlorothiazide, chlorthalidone, as well as their combinations. It has been confirmed that (1) furosemide has an acute effect surpassing that of the other diuretics tested; (2) furosemide increases glomerular filtration rate; and (3) it acts on the proximal and distal nephron. Every compound tested diminished the free water excretion more markedly than furosemide. This indicates that the distal nephron action of furosemide is relatively weak; the drug acts mainly on the proximal tubules. In response to furosemide administered after pretreatment with chlosudimeprimyl, the free water clearance decreased more markedly than it did in response to the diuretics used alone. It has been suggested that the compounds in question block two separate sodium reabsorptive mechanisms in the distal nephron.

Note:

Furosemide (Lasix) has been obtained from the firm Hoechst (Frankfurt am Main), chlosudimeprimyl (Brinaldix) from Sandoz (Basle), hydrochlorothiazide (Esidrex) from Ciba (Basle), chlorthalidone (Hygroton) from Geigy (Basle) and spironolacton (Aldactone-A) from Searle (Chicago). Authors express their gratitude for the generosity of these firms.