Endothelial-dependent dynamic and antithrombotic properties of porcine aortic and pulmonary valves

Background. In the present study, the endothelium-dependent antithrombotic and dynamic properties of porcine aortic (AoV) and pulmonary valves (PuV) were investigated. Methods. Fifteen fresh AoV and 15 PuV were obtained from 25 9-month-old swines. The valves were examined for endothelial function by pharmacologic evaluation (with and without endothelium) of both the endothelial-releasing capacity of prostacyclin and the endothelial- dependent dynamic response to relaxing (acetylcholine from 10^-10 mol/L in AoV and PuV segments precontracted with norepinephrine [3 x 10^-6 mol/L]) and contracting (endothelial-1, from 10^-11 mol/L to 10^-5 mol/L; and N(G)-monomethyl-L-arginine, 10^-4 mol/L) drugs. The ultrastructural integrity of the endothelial valve layer was also examined with transmission electron microscopy. Results. Acetylcholine caused potent relaxation in both AoV and PuV specimens with, but not in those without, endothelium. Endothelium-1 produced a concentration-dependent tension increase in AoV and PuV with and without endothelium. However, the intrinsic activity of the peptide significantly increased in tissues without endothelium. N(G)- monomethyl-L-arginine evoked a progressive increase in resting tension of the preparations, but the AoV and PuV without endothelium were less sensitive to the inhibition of the nitric oxide generation. Aortic and pulmonary valves with an intact endothelium showed a spontaneous ability to release prostacyclin. The basal release of this lipidic autacoid significantly decreased in cardiac valves without endothelium, this phenomenon was observed in both basal conditions, and under stimulation with the aforementioned drugs. Transmission electron microscopy showed the perfect preservation of endothelial cells in all the preparations examined. Conclusions. Valvular endothelium of AoV and PuV seems to have similar antithrombotic and dynamic functions of vascular endothelium, actively participating in valvular homeostasis.