Circulating natriuretic and kaliuretic factors in acute uremia: The role of the kidney

Abstract

The role of the kidney as a source or as the excretory route for natriuretic and kaliuretic factors present in acute uremia was studied using the technique of isovolemic cross-circulation in 49 pairs (eight groups) of anaesthetized rats. Marked and similar natriuresis, kaliuresis, and diuresis occurred in recipients undergoing cross-circulation with donors subjected to either bilateral nephrectomy or total intravenous urine reinfusion for 18 h previously, and were not seen with sham-operated donors. Similar and significant, but less marked, changes occurred in two groups with bilateral nephrectomy or urine reinfusion of only 3 h duration. Urea-loaded normal donors caused a natriuresis and kaliuresis which was similar to the two 18-h uremic donor groups. When donor animals were sodium depleted prior to bilateral nephrectomy, the natriuretic response in the recipients was significantly reduced. The results indicate that the kidney is not necessary for the rapid appearance of natriuretic and kaliuretic activity in the blood of acutely uremic animals, and that such activity results from the retention of factors of extrarenal origin. Natriuresis and kaliuresis result from inhibition of tubular reabsorption and are not dependent on changes in glomerular filtration or renal hemodynamics, Pitressin or aldosterone levels. Urea appears to be a major component of the circulating natriuretic and kaliuretic activity in acute uremia but evidence of other factors was also obtained.