Prostaglandin

Prostaglandin, variety of naturally occuring aliphatic acids with various biological activities including increased vascular permeability, smooth muscle contraction, bronchial constriction, and alteration in the pain threshold. Seminal fluid contains lipid-soluble substances that stimulate smooth muscle, and it has been suggested that the active principle should be called prostaglandin. Although prostaglandins are present in highest concentration in seminal fluid, they have been found in numerous other tissues, such as the kidney, iris, pancreas, lung, and brain.