The Influence of Diuretics on the Fractional Fluid and Electrolyte-Excretion in Renal Insufficiency

Summary

In patients with renal insufficiency, ethacrynie acid and furosemide effect a more potent filtrate-dependent diuresis than in healthy renal subjects. This effect is demonstrable up to a reduction of filtrate to 10 ml/min. Under azetolamide, only in cases of moderate limitation of renal function (GFR 80–40 ml/min), a relative increase of effect could be shown.

Hydrochlorothiazide does not cause a definite change of effect in the individual filtrate-sectors.

Humoral factors, among others, might be discussed as the origin of the varying filtrate-dependent excretion. To explicate the foregoing : Increases by the 1.3 to 10.0 fold of the control value were seen in determinations of the pyrocatechin amines in the urine after application of 20 mg furosemide, whereby the rise was registered as directly proportional to the glomeru-lum filtration and to the absolute fluid excretion.

In addition, furosemide and ethacrynie acid caused direct activation of the renin/angiotensin-system which is at its maximum at the peak of diuresis.

It is assumed that the antidiuretic and sodium-retaining properties of pyrocatechin amines and angiotensin diminish the effect of the diuretic on the nephron. This effect ought to present itself more extensively in healthy renal subjects due to a higher total fluid excretion and stronger activation of humoral factors than in patients with renal insufficiency, who, in addition are “protected” by an osmotic diuresis.