| Abstract: | Material causing contraction of the isolated rabbit aorta (rabbit aorta contracting substance, RCS) was released from guinea pig lung following perfusion with arachidonic acid and from human blood platelets after addition of thrombin to induce aggregation. Prostaglandin endoperoxides (prostaglandins G2 and/or H2) were found both in the perfusate of guinea pig lung (1-3 ng/ml) and in the medium collected after platelet aggregation (13-37 ng/ml). The contractile response of the isolated rabbit aorta to the pure prostaglandins G2 and H2 was also determined. These data combined with the quantitative analyses of the endoperoxides released from the lungs and platelets showed that only a minor part of the rabbit aorta contracting activity was due to the prostaglandin endoperoxides. The major part of the activity consisted of very unstable material. The half life of this material was about 30 s at 37 degrees whereas at this temperature the prostaglandin endoperoxides had a half life of about 5 min. |
