Abstract
Serotonin [5-hydroxytryptamine (5-HT)] is involved in the production of emesis associated with cisplatin treatment. Serotonin released from intestinal enterochromaffin cells may act either directly on vagal afferents and/or pass to the circulation and stimulate central emetic centers. However, the role for circulating 5-HT has not been determined. In this study, i.v. microdialysis probes were used to investigate 1) cisplatin-induced changes in 5-HT release and metabolism assessed through changes in blood dialysate levels of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA), 2) whether free 5-HT in blood increases after cisplatin, and 3) whether granisetron and ondansetron exert different effects on cisplatin-induced 5-HT release and metabolism. Control experiments conducted in 10 healthy volunteers revealed stable 5-HT and 5-HIAA dialysate levels for a period of 6 h. In patients with cancer (n = 16), baseline blood dialysate 5-HIAA concentrations averaged 2.98 ± 0.38 ng/ml, which were equivalent to a total of 94 ± 10 pg in the 30-min collection period at a flow rate of 1 μl/min. Cisplatin (89 ± 2.9 mg of cisplatin/m2) produced a gradual increase in blood dialysate 5-HIAA levels (104 ± 4% increase at 4 h). Increases in dialysate 5-HIAA were associated with increases in the urinary excretion of this metabolite. After cisplatin, dialysate 5-HIAA levels increased to 5.89 ± 0.5 ng/ml in granisetron and to 5.27 ± 0.9 ng/ml in ondansetron-treated patients (P > .1). Similar time courses and percentages of increase in blood dialysate and urinary 5-HIAA levels were observed in ondansetron- and granisetron-treated patients. Contrary to 5-HIAA, no significant increases in dialysate 5-HT were observed from 2 to 8 h after cisplatin either for the total group or for each of the groups separately. In conclusion, i.v. microdialysis probes coupled to HPLC-EC allowed the continuos monitoring of free-5-HT and 5-HIAA in blood. Cisplatin-induced increases in blood 5-HIAA were not associated with increases in 5-HT blood dialysates. These results argue against a possible action of free 5-HT in plasma on the chemoreceptor trigger zone (unprotected from the blood brain barrier) but support the view that 5-HT released within the intestinal wall triggers emesis after cisplatin. Our results argue against the view that at clinically effective doses, granisetron and ondansetron exert different actions on cisplatin-induced 5-HT release and metabolism.
Footnotes
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Send reprint requests to: Dr. Luigi X. Cubeddu, 3200 South University Dr., HPD, NOVA Southeastern University, Fort Lauderdale, FL 33328. E-mail: lcubeddu{at}hpd.nova.edu
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↵1 This work was supported by Grant CONICIT-S1-95001534 to X.P. and L.X.C.
- Abbreviations:
- 5-HT
- 5-hydroxytryptamine (serotonin)
- 5-HIAA
- 5-hydroxyindoleacetic acid
- Received May 7, 1999.
- Accepted July 21, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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