PGA2 is a naturally occurring prostaglandin in gorgonian corals where it may function in self defense. It is generally not present in mammals. PGA2 has low biological potency in most bioassays, but it does show some antiviral/antitumor activity.[1] At a 25 uM concentration, PGA2 blocks the cell cycle progression of NIH 3T3 cells at the G1 and G2/M phase .[2] It has also been shown to act as a vasodilator with natriuretic properties.[3]

Reference:
[1]. Fukushima, M., Kato, T., Narumiya, S., et al. Prostaglandin A and J: Antitumor and antiviral prostaglandins. Adv. Prostaglandin Thromboxane Leukot. Res. 19, 415-418 (1989).
[2]. Hitomi, M., Shu, J., Strom, D., et al. Prostaglandin A2 blocks the activation of G1 phase cyclin-dependent kinase without altering mitogen-activated protein kinase stimulation. J. Biol. Chem. 271(16), 9376-9383 (1996).
[3]. Frolich, J.C., Sweetman, B.J., Carr, K., et al. Assessment of the levels of PGA2 in human plasma by gas chromatography-mass spectrometry. Prostaglandins 10(1), 185-195 (1975).