Serotonin metabolism following platinum-based chemotherapy combined with the serotonin type-3 antagonist tropisetron

5-Hydroxyindoleacetic acid and substance P profiles in patients receiving emetogenic chemotherapy

Background. Even though direct cause and effect has not been proved, clinical evidence suggests serotonin and substance P (SP) are involved in the emetic response following chemotherapy. Because of several parallels, we hypothesized that SP release, like serotonin, may be propagated by chemotherapy and both substances can be measured in biological fluids, and correlated with a particular phase of emesis.

Methods. Urinary 5-hydroxyindoleacetic acid (5-HIAA) was assessed by HPLC; serum and urine SP were measured by immunoassay. In addition to construction of neurotransmitter profiles, all SP data were grouped according to cisplatin dosages, = or>75 mg/m 2 versus <75 mg/m2, and phase of emesis, acute versus delayed. Analyses of these data were performed by repeated measures analysis of variance.

Results. Samples were collected over a 72-hour period from 26 adult patients who received cisplatin-( n=13) or non-cisplatin-containing ( n=13) chemotherapy. Mean baseline 5-HIAA: creatinine ratios were 5.23 and 5.16 in females and males, respectively; mean baseline SP levels were 392 and 181 pg/mL in females and males, respectively. Comparisons between SP data stratified by cisplatin dosage and emetic phase were significantly different, P <0.0001.

Conclusions. Laboratory studies provide additional evidence that serotonin and SP are involved primarily, though not exclusively, in acute and delayed vomiting, respectively.

Irritability rather than depression during interferon treatment is linked to increased tryptophan catabolism

OBJECTIVE

Treatment with recombinant interferon is associated with high rates of psychiatric comorbidity. We investigated the relation between catabolism of the essential amino acid tryptophan, being rate-limiting of peripheral and cerebral serotonin formation, and psychiatric symptoms in patients undergoing combination treatment with interferon-alpha and ribavirin.

PATIENTS AND METHODS

Eighteen patients with viral hepatitis C who received interferon were included. A psychiatrist screened patients before and while on interferon-alpha treatment for 2 months, using a structured diagnostic interview. Fasting plasma tryptophan and platelet serotonin levels were measured at each visit.

RESULTS

At baseline no evident psychopathology was observed. After 2 months of interferon treatment, 10 patients experienced increased irritability. No other structural psychopathology was observed. Decreased plasma tryptophan level correlated with the presence of irritability (p = .047). Platelet serotonin levels were found to be decreased during treatment (p = .002).

CONCLUSIONS

Aggressive impulse dysregulation is highly prevalent in patients receiving interferon treatment. This is associated with decreased plasma tryptophan levels which may lead to attenuated peripheral and central serotonergic neurotransmission.

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.