Prostaglandin H2 (PGH2) was first isolated from incubations of arachidonic acid with ovine seminal vesicle microsomes, and was described as a potent vasoconstrictor.[1] PGH2 is the precursor for all 2-series PGs and thromboxanes (TXs), [2] and is a TP receptor agonist which irreversibly aggregates human platelets at 50-100 ng/ml.
Reference：
[1]. Hamberg, M., Svensson, J., Wakabayashi, T., et al. Isolation and structure of two prostaglandin endoperoxides that cause platelet aggregation. Proceedings of the National Academy of Sciences of the United States of America 71, 345-349 (1974).
[2]. Samuelsson, B., Goldyne, M., Granström, E., et al. Prostaglandins and thromboxanes. Annu. Rev. Biochem. 47, 997-1029 (1978).