[Diuretic agents in urine extracts: clearance studies, tubular glucose absorption and blood pressure]

We previously described diuretic agents of human urine. The extracts cause a significant decrease in sodium and plasma albumin concentration in the medulla of the kidney. In the present study further investigations were performed to detect the site of action of these fractions. In the bio-assay of sodium depleted rats urine extracts of hydrated, healthy human volunteers cause a significant increase in water and sodium excretion. In a dose of 100 micrograms/kg b.w. the rise in water elimination exceeds that of sodium excretion. Compared with control the glomerular filtration rate (inulin clearance), the renal plasma flow (PAH-clearance), and the systemic blood pressure (Statham element) are not affected. There is no change in the tubular glucose absorption of glucose loaded rats. In contrast to the glucose induced increase of the renal water elimination the diuretic potency of the urine extracts is only modest. The data provide further evidence of the existence of a diuretic factor in human urine extracts. The results show that the diuretic activity is not caused by an enhanced glomerular filtration rate or by an augmented renal plasma flow. However, an effect on the renal medullary hemodynamics, that is not detected by the PAH-clearance, could play an important role.