The Emergence of Endocrinology as a Medical Science

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The Emergence of Endocrinology as a Medical Science

Overview

As scientific knowledge increased, our concepts of the human body have gone through a transformation. The nineteenth-century "Concept of Internal Secretions" gave way to a more thorough understanding of bodily secretions. When this information was combined with seemingly unrelated ideas and discoveries it evolved into the branch of medical science called endocrinology. Although there was significant work done in this area prior to the twentieth century, and some of this information dates to antiquity, endocrinology really did not blossom as a science until the turn of the century.

Background

Endocrinology is a branch of medicine that studies the role of hormones and other biochemical mediators in regulating bodily functions. It further provides treatment methods when hormone levels become unbalanced. The properly functioning endocrine system includes tissues and glands that secrete chemical mediators directly into the bloodstream, which then produce effects at distant target cells that have the proper receptors to bind the chemical mediator. Thus, imbalances in the system can result from too much or too little hormone secretion or from the inability of the body to utilize the hormone effectively.

The study of the endocrine system and its functions owes some degree of its development to the gifted French physiologist Claude Bernard (1813-1878). He reported that organisms go to great lengths to maintain the consistency of what he called the "milieu interieur" or internal environment. Walter Cannon (1871-1945) later coined the term homeostasis to describe this phenomenon. The endocrine system in conjunction with the nervous system helps to preserve homeostasis. While certain aspects of endocrinology such as the endocrine disorder diabetes mellitus have been known since antiquity, the emergence of it as an independent science is a fairly recent occurrence.

For thousands of years Chinese medicine has been effectively treating certain disorders that were endocrine in nature. While they did not understand the mechanism of action, they realized the effectiveness of the treatment. As an example, seaweed, a compound that is high in iodine, was prescribed for an enlarged thyroid gland (goiter). There is evidence from early Egyptian writings that they recognized that some people could have sugar in the urine. It is now thought that they were describing symptoms of the endocrine disorder diabetes mellitus. Castration of men was another example of practice that had a direct endocrine effect. It was used to safeguard the chastity of women living in harems and to preserve singing voices in young males. The obvious conclusion was that something released from the testicle was important for male characteristics.

The first recorded recognition of the endocrine system came from Friedrich Henle (1809-1885) in 1841. Henle reported that unlike glands that released their products into a duct, he had found a class of glands that released its product directly into the bloodstream. The famous physiologist Claude Bernard was able to differentiate the products released from ductless glands from other chemicals and termed these "internal secretions." This idea was the forerunner to our modern concept of a hormone. Charles Brown-Seguard used extracts from animal testes in an attempt to treat male aging. After injecting extracts from animal testes into his own body, Brown-Segued concluded that they contained some sort of vital substance. This first effort of endocrine therapy in 1889 was ineffective, but it provided the impetus for further research that was essential to the discovery of cortisone and thyroid hormone.

Impact

The first hormone to be purified was secretin in 1902. This event marked the birth of the science of endocrinology. The English physiologists William Bayliss (1860-1924) and Ernest Starling (1866-1927) discovered secretin. They injected dilute acid into the denervated intestine of a dog. The inner lining of the bowel was scraped, boiled, and filtered. The resulting compound was then injected into the blood of the dog. After the injection, there was a large increase in the release of pancreatic juice. There was something in the material that they injected that had caused this increase in pancreatic secretions. They gave this unidentified substance the name "secretin" after its mechanism of action. This experiment is significant in that it gave concrete evidence that chemicals can act at distant sites to regulate bodily functions. In 1905 Walter Cannon coined the term hormone (Greek for "to set in motion") to describe specific chemicals, such as secretin, that travel through the blood to stimulate a distant target cell.

Diabetes mellitus is an endocrine disorder caused by either the inability to release the hormone insulin or the inability of cell to properly respond to the presence of insulin. Diabetes mellitus is the most common endocrine disorder and causes deleterious effects on millions of people throughout the world. It took over 30 years of intensive effort to find the cause of this disease. In 1889 the German physicians Joseph von Mering and Oskar Minkowski removed the pancreas in dogs, which resulted in the disease. American pathologist Eugene L. Opie described degenerative changes within clumps of cells in the pancreas in 1901. Later Edward Sharpey-Schafer concluded that these cells in the pancreas secrete a substance that controls the metabolism of carbohydrate. The discovery of insulin in 1921 by Canadian surgeon Frederick Banting (1891-1941), with the assistance of Charles Best (1899-1978) and J.J.R. Macleod (1876-1935), was one of the most dramatic events in modern medicine. First, it provided needed therapy for those afflicted with diabetes mellitus. Patients now had the prospect of leading a long and healthy life, instead of the early demise that resulted from untreated diabetes. In addition, it helped to provide important clues regarding the endocrine function of the pancreas.

Another important discovery was that of cortisone and its use as an anti-inflammatory agent. Cortisone was isolated and purified by Edwin Kendall (1886-1972) in 1935. Philip Hench (1896-1965) and colleagues determined its therapeutic properties in 1949 at the Mayo Clinic. They discovered that a substance isolated from the adrenal gland had alleviated many of the symptoms associated with rheumatoid arthritis. Cortisone is a steroid hormone that has potent anti-inflammatory properties. It is useful in controlling many acute diseases and is a valuable compound in research.

An important realization regarding hormone action was purposed by Fuller Albright and colleagues in 1942. They reasoned that ineffective hormonal action on the target cell could produce symptoms similar to hormone deficiency. They made this assertion after studying a patient who exhibited all of the characteristics of a hormone deficiency, yet did not respond to treatment. This led Albright to conclude that the disturbance was actually the inability to respond to the hormone, not the lack of it. This idea paved the way for later important work.

The endocrine system has been shown to determine emotions. The James-Lange theory was an accepted, early influential hypothesis regarding the link between emotions and the body. This theory held that an emotion is the perception of phenomena from within the body. As an example, people are happy because they smile. Walter Cannon saw flaws with this approach and proposed an alternative theory with his colleague, Philip Bard, known as Cannon-Bard theory. According to this approach, the experience of an event leads to the simultaneous determination of emotion and changes in the body. The brain, upon receiving information from the senses, interprets an event as emotional while at the same time preparing the body to deal with the new situation by stimulating the nerves and releasing hormones. Thus, emotional responses and changes in the body are preparations for dealing with a potentially dangerous situation. Cannon demonstrated this was true through a series of experiments where he showed that emotions cause the excitation of nerves, which, in turn, lead to specific, but widespread, changes such as increases in heart rate and blood pressure. Many of these changes are mediated through the release of hormones.

Substantial progress was made in the first half of the twentieth century with all of the major classes of hormones. Many of these, like the discovery of insulin, led to treatment therapies for the afflicted and substantially increased our fundamental knowledge of physiology.

JAMES J. HOFFMANN