Endothelial cells play an important role in the antiaggregatory effect of nitric oxide.
OBJECTIVE
To investigate the role of endothelial cyclooxygenase in the antiaggregatory effect of nitric oxide, and to investigate the significance of the time span between contact of nitric oxide and platelets and laboratory evaluation by platelet aggregation.


METHODS
Prospective, controlled, in vitro study.


METHODS
Research laboratory of a university hospital.


METHODS
Three healthy volunteers.


METHODS
Incubation of platelets with different concentrations (30 microM, 100 microM, 500 microM, 1000 microM) of the nitric oxide-donor S-nitroso-N-acetyl-d,l-penicillamine (SNAP) for varying incubation times (0 hrs, 1 hr, 2 hrs, 4 hrs) with and without endothelial cells. Induction of platelet aggregation with adenosine diphosphate. Inhibition of the effect of SNAP by 100 microM of the guanylate cyclase inhibitor 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ). Inhibition of prostacyclin production by endothelial cells with COX inhibitors acetyl salicylic acid (1 mM) and indomethacin (10 microM).


RESULTS
Incubation with endothelial cells (= controls) had no effect on platelet aggregation. Platelet aggregation was significantly inhibited by all concentrations of SNAP. Time course studies with 30 microM of SNAP showed an inhibitory effect only after 0, 1, and 2 hrs of incubation, whereas after 4 hrs of incubation the inhibition of platelet aggregation could not be detected any more. Endothelial cells significantly increased the inhibitory effect of SNAP after 1 and 2 hrs of incubation. Incubation with ODQ with and without endothelial cells reversed the SNAP-mediated inhibition of maximum platelet aggregation regardless of the incubation time. Pretreatment of the endothelial cells with the COX inhibitors acetyl salicylic acid and indomethacin blocked the increased inhibitory effect of the endothelial cells after 1 and 2 hrs of incubation.


CONCLUSIONS
The time span between nitric oxide contact with platelets and induction of platelet aggregation by adenosine 5'-diphosphate is important for correct estimation of the antiaggregatory effect of nitric oxide. Endothelial cyclooxygenase plays an important role in the nitric oxide-mediated inhibition of platelet aggregation.
Klinge
Jens M
JM
Klinik mit Poliklinik für Kinder und Jugendliche, University of Erlangen-Nuremberg, Germany.
Topf
Hans-Georg
HG
Trusen
Burkhardt
B
Rauh
Manfred
M
Rascher
Wolfgang
W
Dötsch
Jörg
J
D000255:Adenosine Triphosphate / Q000494:pharmacology; D001241:Aspirin / Q000494:pharmacology; D002478:Cells, Cultured; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D009569:Nitric Oxide / Q000502:physiology*; D010396:Penicillamine / Q000031:analogs & derivatives* / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology*; D011446:Prospective Studies; D013997:Time Factors
D016861:Cyclooxygenase Inhibitors; C110881:S-nitro-N-acetylpenicillamine; D009569:Nitric Oxide; D000255:Adenosine Triphosphate; D010396:Penicillamine; D001241:Aspirin; D007213:Indomethacin