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Prostacyclin (PGI2) release from systemic bovine, sheep, canine, and fetal lamb arterial segments has been evaluated in a template device and in cultured cell monolayers employing a radioimmunoassay for 6-keto-PGF1α.  Canine segments released the greatest concentration of PGI2 and fetal sheep the lowest under unstimulated conditions. After exposure of the various vascular segments to the ionophore A23187, PGI2 release was increased 5-20 fold over baseline. Similar responses were observed following stimulation with arachidonic acid. Bradykinin induced a dose-dependent release of PGI2 from bovine vascular segments. Pulmonary arterial segments were more responsive than aortic. When exposed to thrombin, all tissues examined except canine did not demonstrate an increase in PGI2 release over baseline. After thrombin stimulation, canine segments slightly increased their PGI2 release from 91.4 ± 15.7 pmoles/ml/15 min to 152.7 ± 21.8 pmoles/ml/15 min. The other fetal and adult systemic vascular segments were unresponsive to thrombin as a releasing agent for PGI2 as were cultured monolayers of bovine and sheep systemic endothelium. This feature contrasted to prior studies with cultured human umbilical venous endothelial cell monolayers in which thrombin released PGI2. Cultured bovine endothelial cell monolayers were employed to examine thrombin-cell interactions more extensively. High affinity binding sites for thrombin were demonstrated on cultured bovine aortic and pulmonary endothelium. Examination of vascular tissue from diverse species has confirmed the presence of PGI2 in super- natents obtained from these vessel segments. Studies with the template model suggest that the vasodilator effects of bradykinin could be a consequence of the release of PGI2 from the endothelium. Our results also suggest that either thrombin binding is causally unrelated to PGI2 release from systemic animal endothelium or that this endothelium lacks a mediator required for thrombin to exert its effect.

Prostacyclin Release From Ex Vivo Vascular Endothelium: Comparative Studies With Ionophore A23187, Arachidonic Acid, Bradykinin, And Thrombin