Possible Interaction: Morphine and Tryptophan

“When plasma tryptophan falls below normal levels, brain 5-HT falls and morphine requirements are reduced.”

“Chronic administration of morphine , nicotine or phenobarbitone has previously been shown to inhibit rat liver tryptophan pyrrolase activity by increasing hepatic [NADPH], whereas subsequent withdrawal enhances pyrrolase activity by a hormonal-type mechanism.”

“Serotonin precursors, 5-HTP and TP evidently potentiated the morphine induced catalepsy.”

“ Morphine and β‐endorphine increased the concentrations of tyrosine and tryptophan , and naloxone decreased the cerebral tryptophan concentration.”

“ Daily tryptophan administration to rats and mice during a 3-day morphine pellet implantation period increased the rates of both morphine tolerance development and development of physical dependence.”

“Both morphine and methadone increased the cerebral concentrations of tryptophan and tyrosine and naloxone antagonized these effects.”

“The possible involvement of hepatic tryptophan metabolism in morphine dependence is briefly discussed.”

“A large dose of tryptophan antagonised the antinociceptive action of morphine in the rat.”

“An acute dose of morphine increased brain tryptophan in mice.”

“ Morphine increased brain tryptophan in rats.”

“Abstract Morphine increased brain concentrations of tryptophan and tyrosine 1–2 hr after administration in a dose-dependent manner in male rats.”

“ Morphine induces naloxone-reversible increases of tryptophan and 5-hydroxyindoles in rat cerebral hemispheres, thalamus and cerebellum, but does not do so in striatum, hypothalamus, hippocampus and brain stem.”