[Renal sites of action of diuretic agents in urine extracts]

In sodium depleted rats, urine extracts of hydrated healthy human volunteers cause a significant increase in water and sodium excretion. Single injection of 100 micrograms/kg bw. of the urine extracts as well as infusion of approximately 100 micrograms/h over several hours induce diuresis and to a lesser degree natriuresis. The sodium and plasma albumin concentrations show similar changes in kidney tissue: in the exterior medulla, the concentrations of sodium and albumin decrease by only 10 and 9%, respectively, whereas in the interior medulla they are decreased by 22 and 23%, respectively. The values obtained for the interior medullary zones are statistically significant. The data show that there is an inhibitory effect of the urine extracts on sodium absorption in the renal medulla. It is assumed that the modulation of sodium excretion occurs in the inner medullary areas.