Aldosterone metabolism in isolated perfused rat kidney.

The renal metabolism and handling of [1,2-3H]aldosterone ([3H]A) was studied using isolated perfused rat kidney under different perfusion conditions. The metabolite production rate (MPR) and the urinary excretion of [3H]A together with its radiometabolites (UV/P3H) were studied. Among the formed metabolites, no acid-labile conjugate of aldosterone (ALC) was detected. The MPR was not altered in studies using nonfiltering kidney, a result that suggests that the majority of metabolites were formed without requirement of the process of glomerular filtration and tubular uptake of the hormone. High perfusion pressure (high PP) resulted in a striking increase in whole metabolic clearance rate of aldosterone (MCR[3H]A) due mostly to an enhanced urinary excretion of intact aldosterone and, to a lesser degree, to a significant increase in MPR. Factors determining the excretion rate of [3H]A and its metabolites were than investigated under administration of diuretics. Mannitol (44 mM) induced a marked increase in urine volume (UV) accompanied by a significant UV/P3H increase. Meanwhile, 0.1 mM furosemide resulted in an increase only in UV, but not in UV/P3H. These results revealed the UV dependence of aldosterone excretion in certain diuretic conditions.