Question

Endocrinology is a relatively young field. It essentially described a “novel” mechanism for tissues to exert effects on each other from a distance. What was the original presumed mechanism. Describe the key classical experiment (in dogs) that led to the identification of the first endocrine hormone.

Answer 1

Before the discovery of hormones, the nervous system was believed to control the activity of tissues.

The experiments carried out by Ernest Starling led to the discovery of the first hormone: secretin. They severed the nerve supply to the pancreas of the animal by cutting all the nerves to the pancreas. They then placed dilute hydrochloric acid in the bowel of this dog and collected the extract from this bowel and injected it into another dog. This extract induced the secretion of pancreatic juice in the recipient dog. This led to the conclusion that a substance released by the intestinal lining stimulates the secretion of pancreatic juice and named it as secretin (this process is not governed by the nervous system).