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 pos toperative bleeding after coronary artery surgery. The mechanism of action for this 'blood-sparing' effect of aprotinin is only partially clarified. W e therefore aimed to investigate the effect of aprotinin on the release of nitric oxide (NO), a vasodilator and antiaggregant factor, from rat coronar y microvascular endothelial cells and on the NO-mediated endothelium-depend ent relaxation of rat thoracic aorta. Methods: Endothelium-intact and endot helium-denuded thoracic aortic rings from Wistar rats (250-300 g) were susp ended in organ chambers. Contractile and relaxant responses in the absence and presence of aprotinin (125, 250 and 500 KIU/ml) were recorded via a mec hanotransducer. Coronary microvascular endothelial cells (CMEC) were isolat ed on a Langendorff system by collagenase perfusion of the hearts from the same rats. Calcium ionophore- (1 muM) induced release of NO from confluent cells was determined spectrophotometrically by measuring its stable metabol ites, nitrite and nitrate, via Griess reaction. Results: Aprotinin selectiv ely enhanced phenylephrine-induced contractions in endothelium-intact rat t horacic aortic rings, but not in the endothelium-denuded rings. The use of a nitric oxide synthesis inhibitor N omega -nitro-L-arginine methyl ester ( 100 muM) on endothelium-intact rings produced a similar increase in phenyle phrine-induced contractions. KCl-induced contractions remained unaltered. A protinin inhibited acetylcholine-, calcium ionophore- and L-arginine-induce d endothelium-dependent relaxations, but not sodium nitroprusside-induced e ndothelium-independent relaxation. Aprotinin had no significant effect on b asal nitrite-nitrate release from CMEC, while it inhibited calcium ionophor e-induced total nitrite accumulation in the supernatants. Conclusion: Aprot inin selectively impairs endothelium-dependent relaxation as well as basal NO availability in rat thoracic aortic rings and inhibits NO release from r at CMEC. This effect of the drug may contribute to its 'blood-sparing' acti on and may also account for the increase in perioperative restenosis risk o bserved in clinical practice during aprotinin therapy. (C) 2001 Elsevier Sc ience B.V. All rights reserved.