The catecholamines are a group of neurotransmitters composed of the endogenous substances dopamine, noradrenaline (norepinephrine), and adrenaline (epinephrine), as well as numerous artificially synthesized compounds such as isoprenaline - an anti-bradycardiac medication. Their investigation constitutes a major chapter in the history of physiology, biochemistry, and pharmacology. Adrenaline was the first hormone extracted from an endocrine gland and obtained in pure form, before the word hormone was coined. Adrenaline was also the first hormone whose structure and biosynthesis was discovered. Second to acetylcholine, adrenaline and noradrenaline were some of the first neurotransmitters discovered, and the first intercellular biochemical signals to be found in intracellular vesicles. The β-adrenoceptor gene was the first G protein-coupled receptor to be cloned.
Adrenaline in the adrenal medulla
Forerunners
British physician and physiologist Henry Hyde Salter (1823–1871) included a chapter on treatment "by stimulants" in a book on asthma which was first published in 1860. He noted the benefits of strong coffee, presumably because it dispelled sleep, which favored asthma. Even more impressive to him, however, was the response to "strong mental emotion": "The cure of asthma by violent emotion is more sudden and complete than by any other remedy whatever; indeed, I know few things more striking and curious in the whole history of therapeutics. The cure takes no time; it is instantaneous, the intersect paroxysm ceases on the instant." The retrospective interpretation is that the "cure″ was due to the release of adrenaline from the adrenal glands.
At the same time, the French physician Alfred Vulpian also made discoveries about the adrenal medulla. Material scraped from the adrenal medulla turned green when ferric chloride was added. This did not occur with the adrenal cortex nor with any other tissue. Vulpian even came to the insight that the substance entered "le torrent circulator" ("the circulatory torrent"), as blood from the adrenal veins did give the ferric chloride reaction.
In the early 1890s, in the laboratory of Oswald Schmiedeberg in Strasbourg, the German pharmacologist Carl Jacob (1857–1944) studied the relationship between the adrenal glands and the intestine. Electrical stimulation of the vagus nerve or injection of muscarine elicited peristalsis. This peristalsis was promptly abolished by electrical stimulation of the adrenal glands. The experiment has been called "the first indirect demonstration of the role of the adrenal medulla as an endocrine organ and actually a more sophisticated demonstration of the adrenal medullary function than the classic study of Oliver and Schafer". While this may be true, Jacob did not envisage a chemical signal secreted into the blood to influence distant organs, the actual function of a hormone, but nerves running from the adrenals to the gut, "Hemmungsbahnen für die Darmbewegung".
Oliver and Schäfer 1893–1894
George Oliver was a physician practicing in the spa town of Harrogate in North Yorkshire while Edward Albert Schäfer was Professor of Physiology at University College London. In 1918, he prefixed the surname of his physiology teacher, William Sharpey, to his own to become Edward Albert Sharpey Schafer. The canonical story, told by Henry Hallett Dale, who worked at University College London from 1902 to 1904, runs as follows: