A prostaglandin is any member of a group of lipid compounds that are derived enzymatically from fatty acids and have important functions in the animal body. Every prostaglandin contains 20 carbon atoms, including a 5-carbon ring. Leukotrienes are fatty molecules of the immune system that contribute to inflammation in asthma and bronchitis. Leukotriene antagonists are used to treat asthma and bronchitis.