The Effect of a Tryptophan-Free Diet on Prolactin and Corticosterone Release by Serotonergic Stimuli

Summary

Dietary alterations in amino acid precursors to brain neurotransmitters are known to alter the concentration of the neurotransmitter in brain. For example, tryptophan availability influences brain serotonin concentration. The purpose of the present study was to determine if a dietary-induced tryptophan deficiency would cause changes in the physiological regulatory processes that control prolactin and corticosterone secretion. Male rats fed a tryptophan-free diet or a normal diet were given serotonergic stimuli (5-hydroxytryptophan either alone or in combination with fluoxetine) 45 min before collection of blood for prolactin and corticosterone assay. The elevation of serum prolactin and corticosterone by serotonergic stimuli was greater in rats fed a tryptophan-free diet than in controls. Elevation of serum prolactin by haloperidol a dopamine receptor antagonist, was not different in rats fed the tryptophan-free diet compared to controls. The tryptophan-free diet lowered brain serotonin concentration to about half of normal.

The results indicate that rats fed a tryptophan-free diet develop a serotonin supersensitivity similar to that found after administration of serotonin neurotoxins. Rats on a tryptophan-free diet did not differ from control rats in their response to blockade of dopamine receptors by haloperidol. Thus, dietary manipulation of tryptophan can result in changes in physiological control mechanisms in brain serotonergic systems.

Key-Words

Tryptophan - Prolactin - Serotonin - Diet - Neurotransmitter - CNS - Supersensitivity - Corticosterone