Amphetamine analogs increase plasma serotonin: Implications for cardiac and pulmonary disease

Clinical Psychopharmacology Section, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, 5500 Nathan Shock Drive, Baltimore, MD 21224, USA.
Journal of Pharmacology and Experimental Therapeutics (Impact Factor: 3.97). 09/2006; 318(2):604-10. DOI: 10.1124/jpet.106.101618
Source: PubMed


Elevations in plasma serotonin (5-HT) have been implicated in the pathogenesis of cardiac and pulmonary disease. Normally, plasma 5-HT concentrations are kept low by transporter-mediated uptake of 5-HT into platelets and by metabolism to 5-hydroxyindoleacetic acid (5-HIAA). Many abused drugs (e.g., substituted amphetamines) and prescribed medications (e.g., fluoxetine) target 5-HT transporters and could thereby influence circulating 5-HT. We evaluated the effects of amphetamines analogs [(+/-)-fenfluramine, (+/-)-3,4-methylenedioxymethamphetamine, (+)-methamphetamine, (+)-amphetamine, phentermine] on extracellular levels (i.e., plasma levels) of 5-HT and 5-HIAA in blood from catheterized rats. Effects of the 5-HT uptake blocker fluoxetine were examined for comparison. Drugs were tested in vivo and in vitro; plasma indoles were measured using a novel microdialysis method in whole blood. We found that baseline dialysate levels of 5-HT are approximately 0.22 nM, and amphetamine analogs evoke large dose-dependent increases in plasma 5-HT ranging from 4 to 20 nM. The ability of drugs to elevate plasma 5-HT is positively correlated with their potency as 5-HT transporter substrates. Fluoxetine produced small, but significant, increases in plasma 5-HT. Although the drug-evoked 5-HT concentrations are below the micromolar levels required for contraction of pulmonary arteries, they approach concentrations reported to stimulate mitogenesis in pulmonary artery smooth muscle cells. Additional studies are needed to determine the effects of chronic administration of amphetamines on circulating 5-HT.

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    • "Recent studies in rats show that METH also produces significant dose dependent increases in plasma serotonin (Zolkowska et al., 2006; Rothman et al., 2008; Yubera-Lahoz et al., 2012). Because platelets and neurons express the same serotonin transporter (SERT) protein (Lesch et al., 1993) and 99% of the circulating serotonin is stored in platelets (Zolkowska et al., 2006), the elevations in plasma serotonin may well be mediated, at least in part, via interactions of METH with these platelet SERT proteins (Zolkowska et al., 2006; Rothman et al., 2008; Yubera-Lahoz et al., 2012). The association between METH-induced plasma serotonin and body temperature changes was, however, not examined in these studies and remains to be investigated. "
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