Concentration dependent contractile effect of methylene blue in human internal mammary artery.

Abstract

Objective: Methylene blue (MB), an inhibitor of soluble guanylate cyclase, may a lifesaving drug which improves hemodynamic parameters in vasoplegic syndrome. We investigated the relation between MB concentration and vascular responses to clarify the rationale of its use in vasoplegic syndrome.Methods. The study was performed in organ bath in human isolated internal mammary artery (IMA). The responses were recorded isometrically by a force‐displacement transducer.Results: MB (10 nM‐100 μM) produced concentration‐dependent contraction in the arteries. The maximal contraction to MB was 44.2% ± 3.8 of 45 mM KCl maximum contraction. pEC50 value was 5.5 ± 0.1. MB caused an insignificant leftward shift of the concentration‐response curve of norepinephrine. Acetylcholine‐induced relaxation in submaximal contracted rings with phenylephrine was recovered nearly six hours later than MB challenge.Conclusions: We showed that MB caused concentration‐dependent contraction in human IMA. MB inhibited ACh‐induced relaxation during six hours considering muscarinic receptor occupation. The contractile effect of MB is predominantly related to its own effect which proves a rationale for its use in cathecolamine refractory vasoplegic syndrome.