Partial characterization of an ANF/urodilatin-like substance released from perfused rabbit kidney under hypoxia

An ANF-like material was detected by radioimmunoassay in the isolated perfused rabbit kidney. The production of ANF-like material after 90 min of perfusion under hypoxia was 3000 pg/ml vs 500 pg/ml under normoxia or control conditions. This material is partially inactivated by heat treatment at 100 degrees C for 5 min and is absorbed on a SEP-PAK column (C18, Waters) but, unlike ANF, cannot be recovered from the column. On Sephadex G25 chromatography, elution in water yielded two active fractions, one corresponding to the solvent front and the second obtained after one column volume. Four fractions with biological activity were eluted with water from Sephacryl 200. Several fractions were tested on rabbit aorta preconstricted with 1 microM phenylephrine, without removal of endothelial cells. Treatment of T84 cells in culture by the crude material promoted a dose-related increase (1:2, 1:5, 1:10) of the generation of cyclic GMP. In contrast to our material, ANF (atriopeptin III, 1 microM-10 fM) failed to activate guanylate cyclase in T84 cells, while the heat-stable E. coli enterotoxin (STa) significantly increased cyclic GMP levels at the dose of 5 microM. We propose that a new ANF/urodilatin/ST-like material was generated by the hypoxic kidney under perfusion, which we name FNS (Factor Natriureticus Similis).