Central 5-hydroxytryptaminergic function in irritable bowel syndrome

BACKGROUND

Psychological factors may contribute to the aetiology and exacerbation of symptoms in irritable bowel syndrome (IBS), suggesting that the central nervous system may be an important site of dysfunction in IBS. Hormonal responses after a serotonergic challenge assess the functional integrity of central 5-hydroxytryptaminergic pathways and are diminished in depression. The aim of this study was to determine whether hormonal responses in IBS after a serotonergic challenge would be decreased, as in depression, or exaggerated, as have been reported in another functional gastrointestinal disorder, nonulcer dyspepsia.

METHODS

Fourteen IBS patients, 16 healthy volunteers, and 9 patients with inflammatory bowel disease were given 30 mg d-fenfluramine, a selective stimulus to central 5-hydroxytryptaminergic pathways.

RESULTS

Plasma prolactin and cortisol concentrations during the following 5 h increased to a similar extent in all three subject groups, despite increased levels of anxiety and depression (as scored on the Hospital Anxiety and Depression Scale and Beck Depression Inventory) in the IBS and inflammatory bowel disease patients compared with the healthy controls. Base-line cortisol concentration correlated with the magnitude of affective disorder.

CONCLUSION

In contrast to the alterations of central 5-hydroxytryptamine receptor sensitivity seen in depression and non-ulcer dyspepsia, central 5-hydroxytryptaminergic pathways function normally in IBS.

[The serotonin syndrome: review of the literature and description of an original study]

In animals the occurrence of a behavioural syndrome consisting of hyperactivity, stereotyped movements and increase of temperature has been induced by MAOIs, 5-HT precursors (L-tryptophan) and 5-HT reuptake inhibitors. Most of these manifestations were specifically blocked by a pretreatment with an inhibitor of serotonin synthesis. In humans, the association of myoclonus, diarrhea, confusion, hypomania, agitation, hyperreflexia, shivering, incoordination, fever and diaphoresis, when patients are treated with serotoninergic agents, could constitute a "serotonin syndrome". Such cases of serotonin syndrome were reported after treatments with L-tryptophan, MAOIs, serotonin reuptake inhibitors and tricyclics alone or in association. The authors prospectively evaluated all the "serotonin-related" symptoms in 38 depressed inpatients fulfilling DSM III-R criteria of major depression. 16 (42%) out of 38 patients presented at least one symptom of serotonin syndrome. In 14 cases tremor and myoclonus occurred simultaneously and 10 patients presented at the same time tremor, myoclonus, diaphoresis and shivering. Except for two patients, symptoms were transient, lasted less than one week and disappeared with the pursuit of the treatment. Most often, serotonin syndrome thus corresponds to a reaction induced by a combination of serotoninergic agents at high dosages. In very rare cases, a toxic and potentially fatal interaction can occur between MAOIs, tricyclics and selective serotonin reuptake inhibitors at therapeutic dosages. Serotonin syndrome also provides an heuristic model of the putative mode of action of antidepressants. Serotonin-related symptoms are the physical and objective expression of the antidepressant-induced increase in serotonin. The specificity of serotonin-related syndrome also needs to be discussed since most of the symptoms, such as tremor and diaphoresis, are not in all cases related to an increase in serotonin.

The serotonin syndrome. Implicated drugs, pathophysiology and management

The serotonin syndrome has increasingly been recognised in patients who have received combined serotonergic drugs. This syndrome is characterised by a constellation of symptoms (confusion, fever, shivering, diaphoresis, ataxia, hyperelflexia, myoclonus or diarrhoea) in the setting of the recent addition of a serotonergic agent. The most common drug combinations causing the serotonin syndrome are monoamine oxidase inhibitors (MAOIs) and serotonin selective reuptake inhibitors (SSRIs), MAOIs and tricyclic antidepressants, MAOIs and tryptophan, and MAOIs and pethidine (meperidine). This syndrome is caused by excess serotonin (5-hydroxytryptamine; 5-HT) availability in the CNS at the 5-HT1A-receptor. There may also be some interaction with dopamine and 5-HT2-receptors. This syndrome probably has a low incidence, even among patients taking these drug combinations, and there is likely to be some other as yet unidentified inciting factor causing some patients to develop a full serotonin syndrome. Because fatalities and severe complications have accompanied the serotonin syndrome, the previously described drug combinations should be used cautiously or not at all. The serotonin syndrome is usually mild and, if managed with drug withdrawal and supportive therapy, generally improves within hours. Patients who develop hyperthermia should be treated aggressively with external cooling and paralysis. Methysergide and cyproheptadine appear to be useful adjuncts in treating the serotonin syndrome.

Bilateral acute angle-closure glaucoma after dexfenfluramine treatment

We report the case of a patient with narrow angles who had an attack of bilateral acute angle-closure glaucoma precipitated by dexfenfluramine, a serotoninergic drug developed for appetite suppression. Although the exact mechanism remains uncertain, the pupillary block observed in our case may be the result of the serotoninergic or indirect parasympatholytic properties of the drug on the iris sphincter muscle. Serotonergic psychoactive drugs should be prescribed cautiously in patients with known narrow angles and should be monitored by an ophthalmologist.