The neuroendocrinological profile of roxindole, a dopamine autoreceptor agonist, in schizophrenic patients

Cortisol as an indicator of dopaminergic effects on nicotine craving

There is evidence that glucocorticoids mediate the activity of mesencephalic dopaminergic neurons which play an important role in drug-seeking behaviour and that the absence or presence of glucocorticoids determines the intensity of drug self-administration. Moreover, some experiments indicate that corticoids are increased after substance induced dopaminergic stimulation. These findings could imply (a) that differences in basal glucocorticoid levels are associated with differences in craving or (b) that dopamine (DA) induced corticoid release is an indicator of the sensitivity of the dopaminergic system. Therefore, in a sample of 36 male smokers whose DA system was challenged by a DA agonist (lisuride=LIS) and a DA antagonist (fluphenazine=FLU) in a balanced placebo controlled double-blind crossover design, it was investigated if (a) basal cortisol differences and (b) drug induced cortisol responses are related to the amount of nicotine craving after 3.5 h of deprivation from smoking. There were no differences in craving between subjects with high and low basal cortisol levels irrespective of the pharmacological treatment. However, the size of the cortisol change after the DA challenge and deprivation emerged as a good predictor for the amount of craving in that drug condition in which the cortisol response was most pronounced. Findings were interpreted as evidence for the role of cortisol as an indicator of DA sensitivity.

Neuroendocrine response to antipsychotics: effects of drug type and gender

BACKGROUND

To study the influences of drug type and gender on the neuroendocrine response to neuroleptic treatment, we compared the endocrine actions of two neuroleptics with different receptor affinity profiles--a substituted benzamide, amisulpride, a selective D2-like dopamine antagonist; and a thioxanthene, flupenthixol, a mixed D1/D2-like antagonist also blocking serotonin, H1, and D1 receptors--on anterior pituitary hormone secretion in schizophrenic patients (DSM-III-R).

METHODS

Blood was withdrawn at 15-min intervals to assess basal secretion of prolactin, growth hormone (GH), and thyroid-stimulating hormone (TSH). Four hundred micrograms of thyrotropin-releasing hormone (TRH) was injected i.v. to investigate drug effects on TRH-stimulated secretion of prolactin, TSH, and GH.

RESULTS

Prolactin plasma levels were markedly elevated in both treatment groups. In female, but not in male patients, this elevation was significantly more pronounced under amisulpride than under flupenthixol. The prolactin response to TRH was significantly blunted by amisulpride only in male subjects. While basal TSH secretion was significantly increased by both compounds, TRH-stimulated TSH secretion was elevated only in patients treated with amisulpride. Low basal prolactin levels predicted improvement of negative symptoms in patients treated with amisulpride.

CONCLUSIONS

Amisulpride's more pronounced endocrine effects may be a reflection of its distinguished pharmacology and pharmacokinetics.

Dopamine agonists in schizophrenia: a review

Although it is unlikely that the different types of course and severity of schizophrenia are caused by one neurochemical abnormality alone, indirect pharmacological evidence still suggests a relative excess of dopaminergic activity being implicated in the pathogenesis of most of the schizophrenic symptoms, e.g. positive symptomatology. Synthesis and release of dopamine as well as firing rates of dopaminergic neurons are controlled by stimulation of autoreceptors via a negative feedback regulation. Investigations on therapeutic effects of autoreceptor-nonselective dopamine agonists in schizophrenia have yielded inconsistent results. Dopamine autoreceptor agonists like pramipexole, roxindole, talipexole and OPC-4392 as well as partial agonists like terguride and SDZ HDC 912 have been tested in positive schizophrenic symptomatology in order to reduce the postulated excess of central dopaminergic activity. However, administration of autoreceptor-'selective' agonists did not result in a significant improvement of positive symptoms. In predominantly negative schizophrenic symptomatology, a dopamine deficit rather than an excess has been hypothesized. Consequently, a nonselective dopamine agonistic action could be effective in some negative symptoms. Current evidence from several open and one placebo-controlled clinical trial suggests that some dopamine autoreceptor agonists like pramipexole, roxindole and talipexole may produce a mild improvement of symptoms like affective flattening, depressed mood, alogia and avolition. Nevertheless, these findings do not yet allow a reliable judgement and remain to be clarified by further double-blind placebo-controlled studies over a sufficient treatment duration.