prostaglandin

any of a group of compounds, derived from ESSENTIAL FATTY ACIDS , that act in a way that is similar to HORMONES . They are found in most body tissues (but especially SEMEN ), where they are released as local regulators (in the UTERUS , BRAIN , LUNGS , etc). A number have been identified, two of which act antagonistically on BLOOD VESSELS , pge causing dilation, pgf constriction. Certain prostaglandins cause contraction of the UTERUS in LABOUR , and others are involved in the body's defence mechanisms.