Actually, yes. Prostaglandins were named because they were first detected in human seminal fluid obtained from the prostate gland. They are important biologically active molecules that resemble hormones in their effects, but are chemically quite different. They were not detected for many years because they occur in such low concentrations and have such short half-lives. Prostaglandins are present in almost all cells and tissues, and they are one of the most potent of all biological agents. As little as a nanogram can be biologically active!