Prostaglandin Synthesis and Regulation (Homo sapiens)
They are mediators and have a variety of strong physiological effects, such as regulating the contraction and relaxation of smooth muscle tissue. Prostaglandins are not hormones, but autocrine or paracrine, which are locally acting messenger molecules. They differ from hormones in that they are not produced at a discrete site but in many places throughout the human body. Also, their target cells are present in the immediate vicinity of the site of their secretion (of which there are many).
The prostaglandins, together with the thromboxanes and prostacyclins, form the prostanoid class of fatty acid derivatives, a subclass of eicosanoids.Source: Wikipedia (wikipedia:Prostaglandin)