1. The effects of ZK 36374, a prostacyclin analogue, were studied on adhesion of rabbit platelets to damaged rabbit aorta and on activation of platelets (judged by release of serotonin and formation of thromboxane-B2) in response to the processes of adhesion to the vessel surface and aggregation in response to microfibrillar collagen in suspension.

2. In the presence of ZK 36374 (10–100 nmol/l), platelet adhesion and fhromboxane-B2 formation were progressively reduced. The extent of serotonin release from adherent platelets was similar to that found for platelets aggregated with collagen. However, higher concentrations of ZK 36374 were required to inhibit serotonin release from adherent platelets than from aggregated platelets.

3. The results indicate that ZK 36374 acts similarly to native prostacyclin on adhesion and collagen-induced aggregation and unlike previously described analogues is equipotent.

4. The mechanism of release of serotonin induced by adhesion of platelets is less sensitive to the action of ZK 36374 than that of release induced by aggregation in response to microfibrillar collagen in suspension.

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