76 EUROPEAN JOURNAL <strong>OF</strong> MEDICAL RESEARCHFebruary 27, 2004because of secondary physiological changes. Thiswas the reason for the present in vitro experiments.On the other hand it is clear that the invitro findings cannot be directly translated intothe in vivo, let alone clinical situation. Vascularresponses may be different in vessels in situ andafter isolation in an organ bath (Gordon et al.2003). Therefore the in vitro cell culture approachcan be useful to generate hypotheses with theunderstanding that the results need to be verifiedin vivo.To our knowledge this is the first study on theinteraction between extracellular alkalosis/hyperosmolalityand endothelial vasoactive factors invitro. The results show an inverse correlationbetween hyperosmolality and endothelin secretedinto the incubation media. There was no differencebetween alkaline and neutral hyperosmolarity.Neither alkalosis nor hypertonicity induced asignificant change of the concentration of cGMPin the tissue culture supernatants after lysis of thecells. cGMP was used as a surrogate marker forNO (Mitchell et al. 1991). EA.hy 926 cells haveNO synthase (Li et al. 2002) and generate NO(Swiatkowska et al. 2000).In summary, despite the inherent limitations ofthe in vitro approach the results of the present experimentsprovide evidence for an inverse correlationbetween extracellular hypertonicity and endothelin,but not nitric oxide in EA.hy 926 cellsin vitro. They also suggest that under static invitro conditions hypertonicity is a more importantfactor in this interaction than alkalosis, sincealkalosis had no additional effects that could notbe ascribed to hyperosmolality alone. 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