EFFECT OF l‐TRYPTOPHAN ON DIURESIS AND 5‐HYDROXYINDOLEACETIC ACID EXCRETION IN THE RAT

Abstract

Oral administration of L-tryptophan to rats produced two main biochemical and pharmacological effects: a marked increase in urinary 5-hydroxyindoleacetic acid excretion, and a significant reduction in the urine flow after a water load. Urinary 5-hydroxyindoleacetic acid excretion reached its maximum 2 to 6 hr after the administration of tryptophan, and it increased with the dose of the amino acid. Antidiuresis was seen after the administration of L-tryptophan, 200 mg/kg, or more. The effect appeared promptly and it was roughly proportional to the dose of the amino acid administered. Both antidiuretic effect and increase in urinary 5-hydroxyindoleacetic acid excretion were more intense after oral than after parenteral administration of L-tryptophan. D-Tryptophan, in oral doses up to 1,000 mg/kg, produced neither an increase in urinary 5-hydroxyindoleacetic acid nor a reduction of diuresis. Available evidence suggests that reduction of urine flow is a consequence of biosynthesis and release of 5-hydroxytryptamine by the gastrointestinal mucosa. Tryptamine produced by direct decarboxylation of L-tryptophan does not seem to play any important role.In the course of experiments on precursors of 5-hydroxytryptamine, it was observed that oral administration of L-tryptophan, the initial precursor of the amine, produced two main effects: a conspicuous increase in the urinary excretion of 5-hydroxyindoleacetic acid, and a significant reduction in the urine flow following a water load. The last effect seemed particularly worth studying, as it was caused in the normal animal by a common dietary amino acid.The present experiments were undertaken to investigate which compound was responsible for the observed antidiuresis, in order to provide additional information on the physiological role of 5-hydroxytryptamine in the control of diuresis, as well as on the biosynthesis and turnover rate of the amine in the enterochromaffin cell system, which is generally considered the main site of production of 5-hydroxytryptamine. METHODSExperimental animals. Adult albino rats of both sexes weighing 170 to 230 g, all of the same breed, were used. They were kept on a standard laboratory diet. During the afternoon preceding each experiment they -received a diet rich in water (soaked bread and vegetables); in the night the animals were deprived of food but allowed free access to water. On the next morning the animals were given tryptophan either orally (amino acid dissolved in 5 ml. tepid tap water/100 g of rat) or parenterally (amino acid dissolved in 3 ml. 0.9% sodium chloride solution/100 g of rat). Doses of the administered L-tryptophan varied from 50 to 1,000 mg/kg; those of D-tryptophan from 200 to 1,000 mg/kg. In some experiments the S

Formation of Serotonin by Rat Kidneys in Vivo

“…Similarly, carbidopa with or without L-tryptophan had little effect on renal function in our studies. Although L-tryptophan has been reported to decrease water and electrolyte excretion when administered in doses >200 mg/kg, this may relate to its conversion to serotonin in the gastrointestinal tract since oral administration is more effective than parenteral administration in accomplishing this effect (19). An additional result of our studies was the demonstration that the combination of L-5-HTP and carbidopa diminished blood pressure of our rats.…”

Biological Effects of Indole-3-Propionic Acid, a Gut Microbiota-Derived Metabolite, and Its Precursor Tryptophan in Mammals’ Health and Disease

“…Parenteral tryptophan infusion increases blood pressure in normotensive rats [112]. Additionally, tryptophan given orally and parenterally reduces sodium excretion in the kidneys revealing an antidiuretic effect [113,114]. On the other hand, parenteral infusion of tryptophan decreases blood pressure in spontaneously hypertensive rats [112].…”