ET release by the renal epithelial Madin-Darby canine kidney (MDCK) cell line was investigated under isosmotic (300 mosmol/kg H2O; pH 7.4) and hyperosmotic (400, 500, or 600 mosmol/kg H2O) culture and assay conditions by the use of a specific and sensitive RIA. During isosmotic incubation, MDCK cells, which may be of collecting duct origin, secreted by far more ET into the cell culture supernatant (495.7 +/- 25.5 fmol.mg of protein-1.24 h-1) than did the proximal tubule-derived LLC-PK1 (2.42 +/- 0.20 fmol.mg of protein-1.24 h-1) and opossum kidney (3.12 +/- 0.47 fmol.mg of protein-1.24 h-1) cells. ET secretion by MDCK monolayers increased progressively within 24 h and then only slightly declined up to 48 h. Phosphoramidon (100 mumol/L) inhibited the constitutive ET synthesis in MDCK cells by 60%, indicating the participation of a phosphoramidon-sensitive ET-converting enzyme in the processing of bigET to ET in these cells. MDCK epithelia grown on filter inserts showed a clear polarity in their ET release. The baseline secretion of ET was 2.5 times higher to the basolateral than to the apical side, which might be in support of a predominantly basolateral action of the peptide. Short-term incubation of MDCK cells in hyperosmotic NaCl media for 24 h dose dependently decreased ET production. When urea was used as the solute to generate hyperosmolality, ET release by MDCK cells significantly increased. In contrast, when raffinose was added to increase osmolality to 500 mosmol/kg H2O, a decrease of ET production in a range similar to the effect of NaCl was seen.(ABSTRACT TRUNCATED AT 250 WORDS)