Figure 1: Synthesis and signaling of PGs in the vascular system. Upon stimulation, AA is released from the endothelial cell membrane to the cytosol where it is enzymatically converted to PGH2 by COX1 and COX2. Subsequently, PGH2 is transformed to PGI2, PGE2, PGD2, PGF2α, and TxA2. These substances, as well as untransformed PGH2, are released out of endothelial cells and into the circulation, where they interact with their receptors localized on the smooth muscle cell surface and trigger vasoactive signals.