John James Rickard Macleod

John James Rickard Macleod (1876-1935), Scottish physiologist and co-winner of the 1923 Nobel Prize in physiology or medicine for his contribution to the discovery of insulin, a hormone used in the treatment of diabetes. The 1923 prize was shared by Macleod and Canadian surgeon Frederick G. Banting.

Born in Cluny, Scotland, Macleod studied medicine at Marischal College at the University of Aberdeen, Scotland, graduating in 1898 with a degree in surgery. After further study at the University of Leipzig, Germany, he was a lecturer in biochemistry at the London Hospital Medical School for two years. Macleod moved to the United States in 1903 to become a professor at Western Reserve University (now Case Western Reserve University) in Cleveland, Ohio. In 1918 he was appointed professor of physiology at the University of Toronto, Canada, where most of his work on insulin took place. Macleod returned to Scotland in 1928 and finished his career at the University of Aberdeen.

Macleod was particularly interested in how the body metabolizes, or breaks down, carbohydrates such as glucose, a form of sugar in starchy foods. In 1913 he published a textbook on diabetes mellitus, the most common form of diabetes in which the body fails to process glucose. When glucose cannot be properly stored and used as an energy source by the body’s cells, levels of glucose in the bloodstream rise, resulting in a variety of dangerous complications. At that time, diabetes mellitus was usually a fatal disease.

Macleod and other researchers in the field found that the pancreas, a small organ located near the stomach, secretes insulin, a substance that regulates the transfer of glucose into the body’s cells. Later research revealed that diabetes mellitus involves a failure of the pancreas to produce insulin.

In 1921 Banting approached Macleod to ask for his help in isolating insulin. Macleod provided Banting with laboratory facilities, dogs for use as experimental subjects, and the assistance of Charles Best, a medical student. Banting and Best began a series of experiments in which they surgically altered the pancreas in dogs by separating the specialized cells that secrete insulin. They then extracted the insulin from the separated cells and injected it into the dogs that had been rendered artificially diabetic. Banting and Best found that the insulin injections controlled the dogs’ glucose levels.

Macleod and Canadian biochemist James Bertram Collip then worked with Banting and Best to refine methods for extracting and purifying insulin from pancreatic tissue taken from livestock. In 1922 Banting and Best injected insulin into a 14-year-old diabetic boy, effectively treating his condition and inaugurating the use of insulin therapy in the control of diabetes in humans. After receiving the Nobel Prize, Macleod and Banting shared their prize money with Best and Collip.