Use of intravenous microdialysis to monitor changes in serotonin release and metabolism induced by cisplatin in cancer patients: Comparative effects of granisetron and ondansetron

Serotonin [5-hydroxytryptamine (5-HT)] is involved in the production of eme sis associated with cisplatin treatment. Serotonin released from intestinal enterochromaffin cells may act either directly on vagal afferents and/or p ass to the circulation and stimulate central emetic centers. However, the r ole for circulating 5-HT has not been determined. In this study, i.v. micro dialysis probes were used to investigate 1) cisplatin-induced changes in 5- HT release and metabolism assessed through changes in blood dialysate level s 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 c ollection period at a flow rate of 1 ml/min. Cisplatin (89 +/- 2.9 mg of ci splatin/m(2)) 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 cisplati n, dialysate 5-HIAA levels increased to 5.89 +/- 0.5 ng/ml in granisetron a nd 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 obser ved 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 incre ases in 5- HT blood dialysates. These results argue against a possible acti on of free 5-HT in plasma on the chemoreceptor trigger zone (unprotected fr om the blood brain barrier) but support the view that 5- HT released within the intestinal wall triggers emesis after cisplatin. Our results argue aga inst the view that at clinically effective doses, granisetron and ondansetr on exert different actions on cisplatin-induced 5-HT release and metabolism .