Endogenous natriuretic factors. 2: Characterization of natriuretic and vasopressive substances from human uremic urine.

It is our intention to isolate, purify, and characterize the putative low-molecular-weight "natriuretic hormone" responsible for extracellular fluid (ECF) homeostasis. Toward this end, we are purifying from human uremic urine, and identifying endogenous vasopressor and natriuretic compounds. Bioactive components from large volumes of pooled urine were purified by ultrafiltration (< or = 3 kDa), gel filtration chromatography, and sequential reverse-phase and normal-phase high-performance liquid chromatography (HPLC). After each HPLC step, the fractions were evaluated in vivo, were assayed for inhibition of Na+/K(+)-ATPase-mediated 86Rb+ uptake, and were checked for cross-reactivity with an anti-ouabain antibody. Fractions assayed in vivo were identified that induced natriuresis, altered mean arterial pressure, or increased plasma cyclic-GMP. Also, many fractions inhibited Na+/K(+)-ATPase and/or cross-reacted with anti-ouabain antibody. None of the in vitro assays correlates with natriuretic or pressor effects. This plethora of bioactivities, revealed only with increased sample purity, may account for much of the confusion and multiplicity of crude isolates claimed to be the putative hormone. Presently we are attempting to purify and identify these natriuretic materials. One of these, a 3-substituted indole, has been partially characterized.