Cross-circulation study of natriuretic factors in rats with reduced nephron mass.

The importance of humoral factors, including urea, in the adaptations in electrolyte excretion which occur with acute or chronic reduction in nephron mass was studied using isovolemic cross-circulation in 38 pairs of anesthetized rats. After initial clearance studies, donor rats with acute (48 h) three-quarter nephrectomy or sham operation, acute urea loading, or chronic (2-3 wk) three-quarter nephrectomy or sham operation, underwent cross-circulation with normal recipient animals. Donor rats with acute three-quarter nephrectomy caused a marked natriuresis-kaliuresis in normal recipients. Natriuresis resulted from inhibition of tubular reabsorption independent of changes in GFR or renal plasma flow. Urea was a major but not the only factor involved in the cross-circulation natriuresis-kaliuresis. The severity of reduction in nephron mass, as indicated by the GFR of the donor rat, correlated with the increase in electrolyte excretion in the recipient. Donor rats with chronic three-quarter nephrectomy produced a slight but significant natriuresis in recipients which was much less than that seen with acute three-quarter nephrectomy. Since the GFR and blood urea nitrogen level of donors with acute and chronic renal insufficiency were similar, it was evident that the chronicity of reduced nephron mass, through mechanisms that are not clear, had a significant effect on the level of circulating natriuretic and kaliuretic factors in renal insufficiency.