Biosynthesis and biological properties of prostaglandin endoperoxides and thromboxane A2

Two prostaglandin endoperoxides, i. e. PGG2 and PGH2 were detected and isolated. They were unstable in aqueous medium (t1/2 at 37 degrees C about 5 min) and were converted to PGF2alpha by mild reducing agents. Human platelets as well as guinea pig lung and spleen converted the endoperoxides into thromboxane A2, an unstable (t1/2 at 37 degrees C about 30 s) oxetane/oxane derivative. Thromboxane A2 was converted into a stable hemiacetal derivative, thromboxane B2, by addition of 1 H2O. The two prostaglandin endoperoxides as well as thromboxane A2 caused platelet aggregation and the platelet release reaction. In addition they were potent stimulators of vascular and airway smooth muscle in vitro and in vivo.