• Hasan B Ulusoy, Husamettin Gul, Melik Seyrek, Oguzhan Yildiz, Cunay Ulku, Vedat Yildirim, Erkan Kuralay, Turgay Celik, and Omer Yanarates.
• Department of Pharmacology, Gulhane School of Medicine, Ankara, Turkey.
• J. Cardiothorac. Vasc. Anesth. 2008 Aug 1; 22 (4): 560-4.

ObjectiveTo quantitate the contractile effect of methylene blue on isolated human internal mammary artery (IMA) as used in the vasoplegic syndrome.DesignAn in vitro experimental study.SettingCardiovascular Pharmacology Laboratory, Department of Medical Pharmacology.ParticipantsIMA segments were used from 24 patients undergoing coronary artery bypass surgery.InterventionsThe responses to methylene blue, norepinephrine, and acetylcholine were recorded isometrically by a force-displacement transducer in an isolated organ bath.Measurement And Main ResultsMethylene blue (10 nmol/L-100 micromol/L) produced concentration-dependent contraction in the arteries. The maximal contraction to methylene blue was 44.2% +/- 3.8% of KCl (68 mmol/L) maximum contraction; the pEC(50) (-log(10) of 50% effective concentration) value was 5.5 +/- 0.1. Methylene blue caused an insignificant leftward shift of the concentration-response curve of norepinephrine. Acetylcholine-induced relaxation in submaximal contracted rings with phenylephrine recovered nearly 6 hours after the methylene blue challenge.ConclusionMethylene blue caused concentration-dependent contraction in human IMAs. Furthermore, the inhibition of ACh-induced relaxation for 6 hours after the methylene blue challenge points out an additional mechanism (ie, receptor occupation). The concentration-dependent contractile effect of methylene blue justifies its use in the vasoplegic syndrome. The findings also suggest that the time course of contraction is longer than the exposure to methylene blue.

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