biology zoology blog benno meyer rochow testosterone

What the cockerel needed to turn into a cock

The story of testosterone

Every day on my way to my office in the Electron Microscopy Unit of the University of the West Indies in Jamaica, I passed a small monument, dedicated to a famous British scientist. It was Ernest Henry Starling, who was buried in Jamaica in 1927 and commemorated with that monument. Starling was a physiologist who had made significant contributions to our understanding of the function of the heart, muscles, and kidneys, but who is perhaps remembered most for having coined the word “hormone” for the chemical messengers in human and animal bodies.

The hormones are chemicals can be classified as steroids, proteins, amino acids or fatty acid derivatives and are produced by endocrine glands that released them into the blood stream. Transported in the blood the hormones reach specific target organs to either decrease or increase their functions or to affect an organ’s role in growth and development. The specific role of one hormone later called “testosterone” was discovered by the 19th-century German physician Arnold Berthold, who in 1849 carried out a pioneering study.

Berthold was a chicken lover (but perhaps not exactly a chicken “lover” as we will see, but perhaps a chicken keeper). He noticed that when he castrated a cockerel (an immature male chicken) the bird failed to develop the typical characteristics of a cock, i.e., the castrated bird never crowed a cock-a-doodle-doo, never had a fight and never sported a comb and wattles. That gave Berthold to think that there was perhaps something in the testicles he had removed, which the immature male chicken needed to turn into a proper cock. He therefore surgically implanted testicles into the castrated cockerel and even placed testicles into its stomach. He then noticed that the bird, supplied with testicles not in any way connected to the nervous system, developed all the features of a cock. He discovered the hormone testosterone, without a name for it or aware that he had ushered in the field of experimental endocrinology.

The steroid testosterone is produced by the Leydig cells of the testicles and is responsible in males for increases in muscle mass, change in voice, growth of a beard and maturation of the sex organs. It has some other effects too and small amounts of it are also produced by females and the adrenal glands. Although extremely well studied, there are still open questions with regard to the function of testosterone in a human male’s life. For instance, loss of hair on the head is thought to be related to testosterone levels, but as a man ages, his virility decreases parallel to a decrease in testosterone. However, a man’s chest hair growth increases with age, while the hair on his head decreases. Men that are a bit chubby (I don’t want to say fat), which fits the idea of a lower testosterone level, also often don’t have much hair on their scalp, and that does not fit the idea of a low blood testosterone level. What goes on? Do we need another Arnold Berthold with some ingenious experiment to solve this contradictory outcome?

Perhaps, but there might be another ‘player’ involved. How about the thymus? A gland considered pivotal with regard to our immune responses, but a gland that is large only in childhood, shrinking as we get older. So why? Is there any interaction between an increase of testosterone during puberty and the decrease of the thymus at that time? During my high school days I experimented with axolotls that I fed only with cattle thymus and I wondered if I might observe some effect in the axolotl’s behaviour or reproductive success. Alas, I was not an Arnold Berthold and my experiments yielded no result (luckily not even a dead axolotl!).

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2019.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s