Protamine sulfate causes endothelium-independent vasorelaxation via inducible nitric oxide synthase pathway.
OBJECTIVE
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.


METHODS
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 microg x 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 microg) were measured in strips pre-contracted by phenylephrine.


RESULTS
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.


CONCLUSIONS
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.
Takakura
Ko
K
Department of Anesthesiology, Asahi University, 1851-1 Hozumi, Mizuho, Gifu 501-0296, Japan. takakura@dent.asahi-u.ac.jp
Mizogami
Maki
M
Fukuda
Satoru
S
D000818:Animals; D001013:Aorta, Thoracic; D001120:Arginine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000378:metabolism / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006146:Guanidines / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D006494:Heparin Antagonists / Q000494:pharmacology*; D066298:In Vitro Techniques; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D008751:Methylene Blue / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011479:Protamines / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D014664:Vasodilation / Q000187:drug effects*
D004791:Enzyme Inhibitors; D006146:Guanidines; D006494:Heparin Antagonists; D008070:Lipopolysaccharides; D011479:Protamines; C030101:protamine heparin aggregate; D009569:Nitric Oxide; D006493:Heparin; D001120:Arginine; D052247:Nitric Oxide Synthase Type II; C004479:pimagedine; D008751:Methylene Blue