Aprotinin impairs endothelium-dependent relaxation in rat aorta and inhibits nitric oxide release from rat coronary endothelial cells.
OBJECTIVE
Aprotinin, a non-specific serine protease inhibitor, reduces postoperative bleeding after coronary artery surgery. The mechanism of action for this 'blood-sparing' effect of aprotinin is only partially clarified. We therefore aimed to investigate the effect of aprotinin on the release of nitric oxide (NO), a vasodilator and antiaggregant factor, from rat coronary microvascular endothelial cells and on the NO-mediated endothelium-dependent relaxation of rat thoracic aorta.


METHODS
Endothelium-intact and endothelium-denuded thoracic aortic rings from Wistar rats (250-300 g) were suspended in organ chambers. Contractile and relaxant responses in the absence and presence of aprotinin (125, 250 and 500 KIU/ml) were recorded via a mechanotransducer. Coronary microvascular endothelial cells (CMEC) were isolated on a Langendorff system by collagenase perfusion of the hearts from the same rats. Calcium ionophore- (1 microM) induced release of NO from confluent cells was determined spectrophotometrically by measuring its stable metabolites, nitrite and nitrate, via Griess reaction.


RESULTS
Aprotinin selectively enhanced phenylephrine-induced contractions in endothelium-intact rat thoracic aortic rings, but not in the endothelium-denuded rings. The use of a nitric oxide synthesis inhibitor Nomega-nitro-L-arginine methyl ester (100 microM) on endothelium-intact rings produced a similar increase in phenylephrine-induced contractions. KCl-induced contractions remained unaltered. Aprotinin inhibited acetylcholine-, calcium ionophore- and L-arginine-induced endothelium-dependent relaxations, but not sodium nitroprusside-induced endothelium-independent relaxation. Aprotinin had no significant effect on basal nitrite-nitrate release from CMEC, while it inhibited calcium ionophore-induced total nitrite accumulation in the supernatants.


CONCLUSIONS
Aprotinin selectively impairs endothelium-dependent relaxation as well as basal NO availability in rat thoracic aortic rings and inhibits NO release from rat CMEC. This effect of the drug may contribute to its 'blood-sparing' action and may also account for the increase in perioperative restenosis risk observed in clinical practice during aprotinin therapy.
Ulker
S
S
Department of Pharmacology, School of Medicine, Ege University, 35100 Bornova, Izmir, Turkey. sgoskel@alpha.med.ege.edu.tr
Cinar
M G
MG
Bayraktutan
U
U
Evinç
A
A
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000502:physiology; D007611:Aprotinin / Q000494:pharmacology*; D018929:Cell Culture Techniques; D046508:Culture Techniques; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D006490:Hemostatics / Q000494:pharmacology*; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology*; D014661:Vasoconstriction / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects*
D006490:Hemostatics; D009573:Nitrites; D015842:Serine Proteinase Inhibitors; D010656:Phenylephrine; D009569:Nitric Oxide; D007611:Aprotinin