Prolactin bioassay in schizophrenia before and after neuroleptics

Different neuroendocrine profiles of remitted and nonremitted schizophrenic patients

BACKGROUND

Thyrotropin-releasing hormone (TRH) test and Dexamethasone Suppression Test (DST) are two neuroendocrine tests that have been extensively used in an attempt to predict treatment response and outcome in schizophrenia. The objectives of this study were to investigate (1) the relationship between TRH test and DST and various psychiatric symptoms and (2) the potential value of these tests in prediction of short-term outcome in schizophrenic patients.

METHODS

TRH test and DST were administered to 58 patients with schizophrenia. All patients were evaluated with a battery of rating scales before neuroendocrine test procedures and at regular intervals for 1 year. Patients were divided into two groups as remitted (RP; n = 30) and nonremitted patients (NRP; n = 28). Baseline results of these two groups were compared with each other and 30 healthy controls.

RESULTS

Basal levels of total T3 (T3T) and free T3 (T3F) were higher in RP group than controls. Basal prolactin (PRL) level was higher in RP group, but not in NRP, compared to controls. Basal growth hormone (GH) and thyroid-stimulating hormone (TSH) levels of NRP were significantly higher than those of RP. DST nonsuppression was observed at a significantly higher rate in RP than NRP and control group. Blunted TSH response rate in RP group was higher significantly compared to other two groups.

CONCLUSIONS

The data implicate that higher basal TSH and GH levels may be associated with a poorer treatment response, whereas higher total and free T3 levels, a blunted TSH response to TRH and nonsuppression on the DST may indicate a better response in schizophrenics.

Dopamine as a prolactin (PRL) inhibitor

Dopamine is a small and relatively simple molecule that fulfills diverse functions. Within the brain, it acts as a classical neurotransmitter whose attenuation or overactivity can result in disorders such as Parkinson's disease and schizophrenia. Major advances in the cloning and characterization of biosynthetic enzymes, transporters, and receptors have increased our knowledge regarding the metabolism, release, reuptake, and mechanism of action of dopamine. Dopamine reaches the pituitary via hypophysial portal blood from several hypothalamic nerve tracts that are regulated by PRL itself, estrogens, and several neuropeptides and neurotransmitters. Dopamine binds to type-2 dopamine receptors that are functionally linked to membrane channels and G proteins and suppresses the high intrinsic secretory activity of the pituitary lactotrophs. In addition to inhibiting PRL release by controlling calcium fluxes, dopamine activates several interacting intracellular signaling pathways and suppresses PRL gene expression and lactotroph proliferation. Thus, PRL homeostasis should be viewed in the context of a fine balance between the action of dopamine as an inhibitor and the many hypothalamic, systemic, and local factors acting as stimulators, none of which has yet emerged as a primary PRL releasing factor. The generation of transgenic animals with overexpressed or mutated genes expanded our understanding of dopamine-PRL interactions and the physiological consequences of their perturbations. PRL release in humans, which differs in many respects from that in laboratory animals, is affected by several drugs used in clinical practice. Hyperprolactinemia is a major neuroendocrine-related cause of reproductive disturbances in both men and women. The treatment of hyperprolactinemia has greatly benefited from the generation of progressively more effective and selective dopaminergic drugs.

Lower prolactin bioactivity in unmedicated schizophrenic patients

In previous work, prolactin (PRL) abnormalities of a lower bioassay (BA) to radioimmunoassay (RIA) ratio were found in schizophrenic patients. This line of research was extended in seven male patients with schizophrenia who were neuroleptic-free; seven male control subjects were also studied. PRL values were assessed by RIA and Nb(2) BA techniques. The schizophrenic group had a significantly lower PRL BA as compared to normal controls and a lower PRL ratio of BA/RIA. The lower ratio is consistent with an earlier finding and suggests that schizophrenic patients have different molecular forms of PRL than control subjects. This difference could be due to a disordered tuberoinfundibular dopamine system or the long-term effects of neuroleptic medications.

Psychoneuroendocrinology of schizophrenia

The study of psychoneuroendocrinology of schizophrenia has yielded an extensive but inconclusive body of data. Investigations to date have been limited by several factors, including the confounding effects of neuroleptic drugs, methodological limitations, and lack of appreciation for the heterogeneity of the illness. Previously, the focus of research has been on the measurement of anterior pituitary hormones, guided by the assumptions that these hormones are regulated by the central nervous system (CNS) to a significant degree and that the unique anatomic relationship of the pituitary gland to the hypothalamus and the CNS is potentially relevant. Patients with schizophrenia do appear to have distinct endocrinologic profiles. However, although the hormonal differences between patients with schizophrenia and the general population appear to be subtle in magnitude. Nonetheless, investigation, and the exploration of the possible effect of gonadal and posterior pituitary hormones merits particular attention.