Effect of cisplatin on the disposition of endogenous serotonin and its main metabolite, 5-hydroxyindole-3-acetic acid, in rats and dogs

Differential involvement of neurotransmitters through the time course of cisplatin-induced emesis as revealed by therapy with specific receptor antagonists

Advances in antiemetic therapy for chemotherapy-induced emesis have resulted in improved protection against symptoms occurring within 24 h of chemotherapy. However, the vomiting which tends to occur beyond 24 h after chemotherapy (delayed-phase vomiting) is still relatively poorly controlled by the currently available drugs, suggesting that more than one mechanism may mediate these symptoms. The standard antiemetic regimen currently recommended for prevention of chemotherapy-induced emesis includes a serotonin (5-HT(3)) antagonist and a corticosteroid. The neurokinin-1 (NK(1)) antagonist aprepitant represents a new class of antiemetic currently in clinical development. Using data obtained in 2 Phase II clinical trials of aprepitant in patients receiving chemotherapy based on the highly emetogenic chemotherapeutic agent cisplatin, we compared the time course of antiemetic effect of aprepitant, a 5-HT(3) antagonist, or a combination of both. Over the entire observation period (up to 7 days post-cisplatin), patients who received the NK(1) antagonist had a superior prevention of emesis. However, in the first 24 h after cisplatin, emesis occurred in fewer patients who received the 5-HT(3) antagonist than in patients who did not receive this class of drug. Furthermore, the majority of treatment failures in patients who received the NK(1) antagonist occurred within the first 8-12 h of chemotherapy, whereas the treatment failures in patients who received a 5-HT(3) antagonist were more evenly distributed over time. Patients who received both drugs had superior control of symptoms compared with patients who received one or the other. The difference in the time course of emesis blockade observed with two different classes of receptor antagonists provides substantial evidence for involvement of separate pathophysiological mechanisms in chemotherapy-induced vomiting. Serotonin mediates the early vomiting process that occurs within 8-12 h following cisplatin-based chemotherapy, after which time substance P acting at NK(1) receptors becomes the dominant mediator of vomiting

Plasticity in the mesenteric afferent response to cisplatin following vagotomy in the rat

The aim of this study was to investigate the actions of the cytotoxic drug cisplatin on populations of mesenteric afferents supplying the rat jejunum. Extracellular whole mesenteric nerve discharge was monitored and the activity of individual single afferent units determined using waveform discriminator software. Baseline whole nerve discharge was 21.5 +/- 3.8 impulses s(-1). Nerve discharge began to increase approximately 10 min after cisplatin administration, reached a plateau around 30 min, and remained elevated at 60 min (35.3 +/- 5.7 impulses s(-1), p < 0.01). Granisetron reversed the increase in nerve activity indicating that the response to cisplatin was mediated by the release of endogenous 5-HT acting on 5-HT3 receptors. Single afferent units, selected by waveform analysis on the basis of their response to exogenous 5-HT, showed a similar time course of activation following cisplatin. In contrast, the discharge frequency of afferent units that were insensitive to 5-HT was unaffected by cisplatin or granisetron. The sensitivity of mesenteric afferent bundles to exogenous 5-HT was absent in chronically vagotomized animals. However, cisplatin elicited an increase in nerve discharge in vagotomized animals that was not different from control (34.6 +/- 8.9 impulses s(-1)) but this increase was unaffected by treatment with granisetron. Thus, after vagotomy there is a switch from 5-HT3 mediated activation of vagal afferents to a 5-HT3-independent activation of non-vagal (possibly splanchnic) afferents. Since this later mechanism of activation is absent in control animals, it appears that there is plasticity in the gastrointestinal afferent sensitivity to cisplatin.

Serotonin-independent model of cisplatin-induced emesis in the ferret

para-Chlorophenylalanine (PCPA, 100-200 mg/kg) was used as a pharmacological tool to characterize the 5-hydroxytryptamine (5-HT) involvement in the emesis occurring 24 hr after the administration of cisplatin (10 mg/kg) in the ferret. PCPA was effective to antagonize the initial 8 hr period of retching and vomiting, but potentiated the emesis that occurred during the remaining 8- to 24-hr observation period. Tissue samples removed from the brainstem at 24 hr post injection of cisplatin alone revealed an elevation of 5-HT, dopamine and homovanillic acid that was antagonized by the injection of PCPA. Cisplatin also induced increases in the urinary levels of 5-hydroxyindoleacetic acid that was similarly antagonized by PCPA. Results are discussed in terms of the relevance of 5-HT to the model of cisplatin (10 mg/kg)-induced emesis in the ferret compared to the problem of acute and delayed emesis in man. The residual or delayed phase of cisplatin-induced emesis may involve a 5-HT-independent mechanism.