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Protamine sulfate causes endothelium-indepen-dent vasorelaxation via inducible nitric oxide syn-thase pathway

Le sulfate de protamine cause un vasorelâchement indépendant de ľendothélium par la voie de ľoxyde nitrique synthase inductible



The precise mechanism of systemic hypotension frequently observed with the use of protamine is unclear. Although it has been reported that protamine stimulates the release of nitric oxide (NO) from endothelium NO synthase (eNOS), the association with inducible NOS (iNOS) remains unknown, despite the induction of iNOS by lipopolysaccharides (LPS) and/or inflammatory cytokines during cardiopulmonary bypass (CPB). The purpose of this study was to determine whether protamine stimulates the release of NO from iNOS induced by LPS.


We performed prospective and controlled functional examinations with isolated endothelium-denuded thoracic aortas from 21 male Wister rats. Aortic strips were mounted in Krebs solution and treated with LPS (1 µg·mL-1) for six hours to induce iNOS. Changes in tension caused by L-arginine (a substrate of NOS), protamine or a heparin-protamine complex (heparin: protamine = 1 unit: 10 µg) were measured in strips pre-contracted by phenylephrine.


No drug relaxed the strips before LPS-treatment, but each drug relaxed the strips in a dose-dependent manner after LPS-treatment (P < 0.05). Aminoguanidine (an iNOS inhibitor) and methylene blue (a guanylyl cyclase inhibitor) inhibited the relaxations.


These results indicate that protamine and the heparin-protamine complex stimulated the release of NO from iNOS. As iNOS is induced during CPB, protamine or a heparin-protamine complex might cause systemic hypotension, at least in part, by stimulating iNOS.



Le mécanisme précis de ľhypotension générale souvent observée avec ľusage de protamine n’est pas clair. Il a été démontré que la protamine stimule la libération ďoxyde nitrique (NO) à partir de la NO synthase (NOS) de ľendothélium, mais ľassociation avec la NOS inductible (NOSi) est inconnue malgré ľinduction de NOSi par les lipopolysaccharides (LPS) et/ou les cytokines inflammatoires lors de la circulation extracorporelle (CEC). Notre étude veut déterminer si la protamine stimule la libération de NO à partir de la NOSi induite par les LPS.


Nous avons réalisé des examens fonctionnels prospectifs et contrôlés ďaortes thoraciques sans endothélium prélevées chez 21 rats mâles Wister. Les bandes aortiques ont été montées dans des solutions de Krebs et traitées avec des LPS (1 µg·mL-1) pendant six heures pour induire la NOSi. Les modifications de la tension causées par la L-arginine (un substrat de la NOS), la protamine ou un complexe ďhéparine-protamine (héparine: protamine = 1 unité 10 µg) ont été mesurées dans les bandes précontractées par la phényléphrine.


Aucun médicament n’a détendu les bandes avant le traitement aux LPS, mais chaque médicament les a détendues en fonction de la dose après le traitement aux LPS (P < 0,05). Ľaminoguanidine (un inhibiteur de NOSi) et le bleu de méthylène (un inhibiteur de la guanylyl cyclase) ont inhibé les relâchements.


La protamine et le complexe ďhéparine-protamine ont stimulé la libération de NO à partir de NOSi. La NOSi étant induite pendant la CEC, la protamine ou un complexe ďhéparine-protamine peuvent, en partie, causer une hypotension générale en stimulant la NOSi.


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Correspondence to Ko Takakura or Maki Mizogami or Satoru Fukuda.

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Takakura, K., Mizogami, M. & Fukuda, S. Protamine sulfate causes endothelium-indepen-dent vasorelaxation via inducible nitric oxide syn-thase pathway. Can J Anesth 53, 162–167 (2006).

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