Effect of urea osmotic diuresis on potassium excretion

¹ Departments of Medicine, Veterans Administration Center, Mount Sinai Hospital, and University of California Center for the Health Sciences, Los Angeles, California

An increased solute load per remaining functioning nephron may enhance K excretion and aid in maintaining K balance in chronic renal failure. An analogous model was sought by inducing progressive osmotic diuresis with urea in a) water-loaded dogs with minimal K excretion, b) dogs receiving K infusions at intermediate rates of 207–280 µEq/min, and c) dogs receiving K infusions at maximal tolerated rates of 400–600 µEq/min. Urea diuresis significantly augmented K excretion in experiments in which basal K excreted-to-K filtered ratios (K_E:K_F) were minimal (.02–.03) or intermediate (.20–.73), but when control ratios approached 1.0, urea loading became progressively less effective. The slight increment in K excretion with low basal K_E:K_F ratios (19 µEq/min) suggested partial inhibition of proximal reabsorption; the more marked increment in K excretion at intermediate K_E:K_F levels (130 µEq/min) is consistent with enhancement of K secretion following increased delivery of Na to the distal exchange sites. Once distal K secretion was maximally stimulated by K loading, however, it was not further affected by solute diuresis or augmented Na excretion.

Key Words: nephron solute load • urea loading • Na excretion

Submitted on August 5, 1963