Abstract
Methamphetamine (METH), administered in large, repeated doses, compromises the dopaminergic and serotonergic systems as indicated by prolonged suppression of tyrosine hydroxylase and tryptophan hydroxylase activity and concurrent decreases in the content of dopamine and 5-hydroxytryptamine. Because dopamine is necessary for these dopaminergic and serotonergic deficits we postulated that dopamine and/or its reactive metabolites are responsible for these degenerative alterations. Because we previously demonstrated thatin vitro reducing conditions reverse the decrease in tryptophan hydroxylase activity, we reasoned that melatonin, a purported endogenous antioxidant, may alter this response. Rats were treated with METH and/or melatonin and trytophan hydroxylase activity and 5-hydroxytryptamine content were assessed; tyrosine hydroxylase activity and dopamine content were also measured. Not only did melatonin not prevent METH-induced deficits in serotonergic and dopaminergic parameters, but coadministration of melatonin with METH actually enhanced most of the monoaminergic effects of METH. This enhancing effect could not be attributed to alteration of body temperature. Because METH abuse causes insomnia and melatonin is promoted in some countries for insomnia, the implications of the interaction between these two drugs could be clinically important.
Footnotes
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Send reprint requests to: Dr. James W. Gibb, Department of Pharmacology and Toxicology, 112 Skaggs Hall, University of Utah, Salt Lake City, UT 84112.
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↵1 This work was supported by National Institute on Drug Abuse Grants DA 00869 and DA 04222.
- Abbreviations:
- DA
- dopamine
- 5HT
- 5-hydroxytryptamine
- 5-HTP
- 5-hydroxytryptophan
- 5-HIAA
- 5-hydroxyindoleacetic acid
- METH
- methamphetamine
- TPH
- tryptophan hydroxylase
- TH
- tyrosine hydroxylase
- Received March 26, 1997.
- Accepted July 14, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
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