11/24/17: THE DISCOVERY OF TRYPTOPHAN INTOXICATION: The First Demonstration of Serotonin’s Effect on Mood






Before I tell you about tryptophan intoxication, one of the wonderful discovery stories from my father’s high-flying days at the National Heart Institute in the 1950s and ‘60s, I must tell you a little about serotonin.

Most laypeople believe that serotonin is only in the brain, but the majority of this organic compound is in the gastrointestinal tract and blood platelets, not the central nervous system. In fact, more than 90 percent of the body’s serotonin, which people know primarily as a mood elevator, is in the gut, where it does not elevate mood. 🙂

The first physiological evidence of serotonin, which is a type of organic compound called an amine, occurred around the turn of the 20th century, when researchers perceived a vasoconstrictor activity in blood serum. This is how my father explained it in an interview that I did with him for my biography, “Starting With Serotonin: How a High-Rolling Father of Drug Discovery Repeatedly Beat the Odds”:

When you get a cut, the blood vessels constrict to try to stop the bleeding, and serotonin is involved in that. It’s released from the blood platelets. It was called the vasoconstrictor factor of shed blood. For a long time, it wasn’t known what it was. When blood clotted, there was something released in the serum that constricted the blood vessels. 

All amines, of which there are various types, have an ammonia group (NH2) in their chemical structure, which makes them pharmacologically active.

A Cleveland Clinic Foundation team of researchers, led by director and cardiovascular physician Irvine H. Page, who had studied this unknown vasoconstrictor substance for years, “discovered” serotonin. In 1948, organic chemist Maurice M. Rapport (1919-2011), just out of graduate school and working alone, isolated the serum constrictor from tons of slaughterhouse beef blood that he processed in a small lab in Page’s operation. Contrary to Rapport’s lifelong claim of credit, however, it was Page’s research partner, Canadian cardiovascular physiologist Arthur Curtis (A.C.) Corcoran, who gave the amine its name. Corcoran combined serum with tonin, his word for blood vessel-constricting substances, to create serum-tonin, serotonin.

Rapport deduced serotonin’s chemical structure to be 5-hydroxyl-indole-ethyl-amine. Indole-ethyl-amine is tryptamine, an amine first identified by German scientists in 1937 in guinea-pig assays, so serotonin is often referred to as 5-hydroxytryptamine.

I break down the serotonin formula in full in my book (p. 57), but I will not do so here. Instead, I’ll just mention that Rapport proposed the amine’s structure in an October 1949 article of The Journal of Biological Chemistry—and he was correct—but he couldn’t confirm it in the lab. When chemists from the Upjohn drug company approached him in May 1950 for permission to make serotonin, Rapport readily consented. Eventually, Upjohn and Abbott Laboratories vied to be the first to publish the chemical synthesis. If you’d like to know the rest of that story, you’ll have to read my book. 🙂 (There was no Big Pharma then. The pharmaceutical industry cooperated with researchers, both basic chemists, like Rapport, and clinicians, like my father, and vice versa.)


Serotonin is synthesized in the human body in what is called a “pathway” that starts with tryptophan, which is its dietary precursor (you get tryptophan from certain foods, notably meats), and ends with a metabolite, known as 5-HIAA (5-hydroxyindole acetic), which is released in urine. (This was the state of knowledge when my father started his studies in the 1950s. Melatonin and serotonin’s role in its production were not on the radar screen.)

The pathway from tryptophan to the metabolite 5-HIAA involves three different steps at which different enzymes alter the molecule’s chemical composition. There are two enzymatic conversions between tryptophan and serotonin. At the third step, the enzyme monoamine oxidase (MAO) breaks serotonin down into its metabolite, HIAA. When a chemical is metabolized, it is broken down, degraded, inactivated.

You may have heard of monoamine oxidase inhibitors, or MAO inhibitors, which were the first-ever antidepressants. Chemists at the Swiss drug company, Hoffman-LaRoche, made the first MAO inhibitors to treat tuberculosis—or at least they hoped their new compounds would treat TB. The discovery of their MAO-inhibiting compounds’ antidepressant effect was serendipitous and is another great story in my book. 🙂

My father, a cardiologist and pharmacologist, arrived at the National Heart Institute in 1952, and began brainstorming ideas about designing drugs for hypertension (high blood pressure), which was then an uncontrolled killer. Although a medical doctor, he was keenly interested in biochemistry. As he recalled:

I wanted to see what would happen if we blocked enzymes involved with substances that affect blood pressure. . . . I somehow got the idea, hey, if you pick the right enzyme, and you know something about it, and you block it, you’re going to get something interesting.

Dad remembered reading a 1952 article in the Journal of the American Medical Assn. “by a guy named Tom Spies, showing the effects of giving 2 milligrams of serotonin intravenously in a human subject.”

The blood pressure went up like that. It skyrocketed. This just nailed me. I saw that damn thing, and I said, “Wow!”

Sjoerdsma obtained some serotonin from Upjohn and started doing studies in animals of serotonin’s cardiovascular effects. Around the same time, he was referred to an already-celebrated biochemist/methodologist at the NIH named Sidney Udenfriend, who, with the very capable assistance of his first Master’s-Ph.D. student, Herbert Weissbach, had developed a colorimetric method to test for 5-HIAA in human urine. Weissbach would take a human urine sample, add two reagents to it, and then measure its 5-HIAA content according to the color produced on a paper chromatogram. Violet or blue signaled the presence of the metabolite.

My father and Sid Udenfriend quickly became associates and partners, and the rest truly is history. “Bench-to-bed” clinical research history. Dad developed drugs through rational design—by targeting enzymes—not through wing-and-a-prayer blind screening. Udenfriend and Sjoerdsma complemented each other and had a lot of fun. Sid, whom I remember, was severe and exacting, a taskmaster; Dad was affable and much looser, a mentor. Both were intense and loved to knock ideas around.

Among their many breakthrough clinical endeavors, Sjoerdsma and his “Experimental Therapeutics” unit tested all of the MAO inhibitors synthesized by drug companies to see if they did, in fact, inhibit monoamine oxidase. By 1961, they had studied eight MAO inhibitors that also lowered blood pressure in their hypertensive patients.

During their wide-ranging research, one of Dad’s exceptionally bright clinical associates, Dr. John A. Oates III, developed a urinary assay for tryptamine, another amine that derives from tryptophan and is metabolized by monoamine oxidase.

Oates gave “loading” doses of tryptophan to patients to raise the level of tryptamine in their blood and then applied his test to their urine. Patients who were taking an MAO inhibitor urinated copious amounts of tryptamine, because it wasn’t broken down. He followed up this test by developing a method for measuring the urinary content of tyramine, an amine that comes from the precursor, tyrosine.

For the tyramine test, he improvised, he said, explaining, “In Al’s lab, you started in a project, and people helped you . . . and then you ran with the ball, so to speak.”

Tyramine, too, made a dead-bang indicator of MAO inhibition. As Dad explained:

Gradually, we worked out methods to measure other amines in the urine. It became a matter of giving different MAO inhibitors to patients and seeing what happened in their urine. The most important of these were tryptamine and tyramine, which depend solely on MAO for inactivation. [Serotonin, it turned out, does not.]

And now, after much ado, you have the setup for the tryptophan intoxication story.


Sjoerdsma was intrigued by some psychic changes that he had observed in patients whom John Oates loaded with tryptophan. Remember, these were the early years of serotonin research, when the amine’s role in the brain wasn’t well-understood.

Dad wondered:  What kind of central-nervous-system (CNS) response could he induce by giving large doses of tryptophan and tyrosine to MAO-inhibited patients?

Surely, the patients’ production of serotonin and tryptamine would increase, but, how would the increased amounts affect their brains, their consciousness? Sjoerdsma decided to push the pharmacological envelope.

We were interested in doing this because trytophan is converted directly to tryptamine, but has two steps to serotonin. Both tryptamine and serotonin are metabolized by monoamine oxidase. So we wanted to see what would happen if we gave tryptophan after we blocked monoamine oxidase. Same with feeding tyrosine to produce tyramine.  . . . If you feed an amino acid, it’s very hard to know what the hell happens to it. . . . It’s broken down, it’s incorporated into proteins, and all these kinds of things. . . . We didn’t get any CNS effects with any amino acids except tryptophan.

And, in the process, they made serotonin history.

Sjoerdsma and Oates fed seven hospitalized hypertensive patients 20 mg. to 50 mg. of tryptophan (which has a bitter taste) per kilogram of body weight in 200 gm. of apple sauce before breakfast. In studies with control subjects, such doses produced no detectable CNS effects. Unlike controls, however, the experimental subjects also received 25 mg. of the MAO-inhibiting drug, Catron®, daily for at least four days. Depending on the tryptophan dosage and the time of its administration, each patient exhibited drowsiness, staggering and trembling (leg and foot hyperreflexia), and/or clonus (jerking) of the jaw.

They appeared drunk and happy.

This was the first demonstration of a pharmacologic effect of tryptophan. We called it tryptophan intoxication. . . . I’ll never forget this one patient, whom we had on an MAO inhibitor and had been feeding tryptophan. He felt great. He says, “Doc, that tryptophan is great stuff.”

About two hours after his tryptophan dose, the 52-year-old man said he felt “as if he had had a drink of whisky,” and described his mood as “wildish,” according to Sjoerdsma and Oates’s report. Appearing to be inebriated, the researchers said, he “walked about the unit in a somewhat inappropriate expansive mood, slapping people on their backs and talking loudly. He suspected that this tryptophan was not the same as [the tryptophan] he received before beginning the inhibitor and was quite happy about it all.”

But, we wondered, what happens if he eats a steak? Steaks and other meats—most famously, turkey—are loaded with tryptophan. [See my Thanksgiving Eve blog for the answer to that question, 11/22/17.]

A younger male patient compared his altered state of mind to being “on a cheap drunk,” which he considered “just rosy.” He became “intoxicated” just 90 minutes after his tryptophan boost, slurring his words, staggering, and acting silly. At times, his jaw jerked spontaneously, and his teeth clattered as if he were chilled. After eight hours, the patient could speak clearly again and walk without difficulty, but his jaw clonus and lower-extremity hyperreflexia continued. Within 24 hours, all of the man’s neurologic changes had disappeared.

While tryptophan caused a range of disorienting effects in the patients, it did not endanger them. At no time did the four women and three men who participated in the study (and gave their informed consent) experience worrisome changes in their blood pressure or heart rate.

According to Oates, “The tryptophan opened up everybody’s personality. There were elements of mood change apparent.”

Sjoerdsma and Oates published these results in 1960, but few professionals in the business of altering mood seemed to notice. We published in “Neurology” of all the god-awful places and got overlooked. Nobody ever saw it.

The two researchers reasoned that it had to be the MAOI-induced accumulation of serotonin and tryptamine, not the tryptophan, that caused the patients’ “intoxication.” To test this theory, they designed another study, in which they evaluated the effects of a decarboxylase inhibitor (Hoffman-LaRoche’s Ro 4-4602) on the manifestations of tryptophan loading in both hypertensive patients and animals.

(Ro 4-4602 was later marketed as Madopar®, to inhibit the decarboxylation of L-DOPA, which is the amino-acid precursor to dopamine. As I mentioned in my 11/22/17 blog, L-DOPA crosses the blood-brain barrier. When an enzyme decarboxylates a molecule, it removes a carbon-dioxide atom from it, and, thus, changes its structure. Therefore, if you inhibit the decarboxylation of L-DOPA, you preserve—and, thus, boost—the amount of DOPA in the body.)

If Ro 4-4602, which was known to penetrate readily into the brain, reduced or abolished the tryptophan effects, then it was the amines—serotonin and/or tryptamine—not the amino acid, that were responsible for the CNS stimulation.

It did.

Ro 4-4602’s inhibition of tryptophan decarboxylation markedly reduced or altogether blocked the CNS effects in MAOI-treated humans and guinea pigs.     

While Sjoerdsma and Oates thought that serotonin exerted more influence in producing central excitation than tryptamine did, they hedged their bets in a follow-up article, concluding: “It remains uncertain which of the two amines, serotonin or tryptamine, is primarily responsible for the central nervous stimulation seen following tryptophan administration.”

Later, John Oates readily inferred that these early tryptophan studies exposed serotonin’s effect on mood for the first time.

“These experiments didn’t prove the difference between serotonin and tryptamine,” he acknowledged, “but I think from what we know now, it would have to be serotonin.”

Sjoerdsma and Oates enthusiastically passed their research on to Seymour S. Kety, chief of the National Institute of Mental Health’s Laboratory of Clinical Science, expecting him to pursue it and to give them credit for the discovery. He did neither.

A University of Pennsylvania-trained physiologist, “Kety was known for being the first person to measure cerebral blood flow in the intact human,” said Sjoerdsma, a major achievement, but not one that qualified him to be the NIMH’s inaugural scientific director, which he had been. In 1956, Kety stepped down from the top NIMH job and established a research program on the biology of schizophrenia—despite lacking any training in clinical psychiatry.

“We told Kety [tryptophan intoxication] was very important,” Oates said, “and we thought it deserved evaluation by people who are behavioral scientists, but he did not pursue it. He dropped the ball. . . . [We thought then] that he was going to incorporate it into a study he was doing, and he didn’t. He went off in a different direction. . . . Later on, he exploited the idea.”

 As I recall, NIMH gave large doses of several amino acids, including tryptophan, to people and proclaimed their findings as original observations.

Sjoerdsma received more acclaim for another MAOI spinoff, when he and his team determined why people who were taking the antidepressant-MAO inhibitor, Parnate®, suddenly developed throbbing occipital headaches—like a sledge hammer pounding on the back of their heads—profuse sweating, nausea and vomiting, heart palpitations, tachycardia, arrhythmia, and other life-threatening symptoms, after eating cheese. (Yet another wonderful story of discovery in my book. 🙂 )

Some years later, Dad conducted an extended REM-sleep trial with tryptophan, whose soporific potency had been evaluated outside of the NIH with mixed results. It was not long after this research that tryptophan began appearing in tablet, capsule, and powder form in health-food stores, marketed as a remedy for insomnia, premenstrual syndrome, depression, obesity, anxiety, and other ills. It is readily available today for purchase in stores and on the Internet.

Ann, 11/24/17


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