Hans Walter Kosterlitz FRS was a German-born British biologist, who graduated Doctor of Medicine in Berlin. He emigrated to Scotland in 1934, after the takeover of the Nazi Party in Germany. He joined the staff of Aberdeen University in the same year where he later served as professor of pharmacology and chemistry from 1968 until 1973 when he became director of the university's drug addiction research unit.
Kosterlitz is best known for his work on endorphins. He performed a famous experiment that he envisioned in a dream while sleeping. He stimulated a strip of guinea pig intestine electrically and was able to record the contractions with a polygraph. He then found that if you added opiates to the solution, the intestine would not contract. Opiates inhibit intestinal contraction. Those contractions were later found to resume in the presence of both opiates and an antagonist such as naloxone. Later, endogenous endorphins were discovered by applying tissue to the apparatus. This caused the contractions to cease. The degree to which an opiate agonist inhibits contractions in the guinea pig ileum is highly correlated to its potency.