Diabetes mellitus is one of the most dangerous diseases of our time, writes itoronto.info. Many people remain unaware they have this condition until symptoms become persistent, by which point the disease is often advanced. At this stage, patients are prescribed insulin therapy.
What many do not know is that the process of discovering this “miraculous substance,” capable of reducing blood sugar levels, was far from simple. Numerous individuals played pivotal roles in this achievement. But ultimately, success was achieved, and humanity gained a powerful tool to combat diabetes.
In this article, with references to utoronto.ca we tell the story of how insulin was discovered.
A Crucial Insight
In October 1920, Canadian surgeon Frederick Banting made a significant scientific observation. He realized that digestive secretions (previously studied by Minkowski) destroyed the secretion of the islets of Langerhans.
Banting also knew from his surgical experience that when the pancreatic duct was blocked, the pancreas atrophied while the islets of Langerhans remained intact. This led him to hypothesize that obtaining a pure extract from the islets—essentially untreated insulin—would be possible if the pancreatic ducts were tied off.
Skepticism and Initial Efforts
In the spring of 1921, Banting arrived in Toronto to share his hypothesis with Professor John Macleod, an expert in the field. Macleod was skeptical of Banting’s idea, primarily because it lacked prior experimental verification.
Nevertheless, Macleod provided Banting with a laboratory where he could test or refute his hypothesis.
The First Breakthrough
Banting decided to test his idea on a dog. On July 30, 1921, after tying off the pancreatic duct in a dog, he successfully extracted a substance from the islets. The extracted material was then injected into a diabetic dog, resulting in a 40% drop in blood sugar levels within one hour.
This marked the discovery of insulin.
The Second Attempt
Banting shared his findings with Macleod, who criticized the methodology and suggested repeating the experiment with more dogs and better equipment. Banting conducted the second experiment successfully, meeting Macleod’s expectations.
A New Approach
However, tying off the pancreatic ducts in dogs proved challenging. This prompted Banting to explore extracting insulin from calf embryos, which had not yet developed digestive glands.
Eventually, even the use of embryos became unnecessary as Banting found success in extracting insulin from the pancreases of adult cows.
Meanwhile, Macleod paused his work to assist Banting in purifying the insulin extract. For this, he enlisted biochemist James Collip.
Practical Application
On January 11, 1922, Leonard Thompson, a teenager with diabetes, received the first injection of insulin at Toronto General Hospital. Unfortunately, the extract was impure, leading to a severe allergic reaction.
Over the next 12 days, the scientists worked tirelessly to refine the extract and make it much purer.
Finally, on January 23, 1922, Leonard received a second dose of insulin. This time, there were no side effects, and his body successfully accepted the injection.
This monumental discovery transformed diabetes treatment and saved countless lives. From its early trials on dogs and calves to its successful application in humans, insulin became a cornerstone of modern medicine. It also solidified Toronto’s reputation as a global leader in medical innovation.Photo: novochag