The duration of prolactin secretory bursts from the pituitary is independent from both prolactin and gonadal steroid plasma levels in women and in men

The Mini-TRH Test

Thyrotropin-releasing hormone (TRH), at doses lower than those needed to stimulate prolactin secretion directly, can almost completely antagonize dopamine inhibition of prolactin release. In normal men, prolactin increases 15 min following an i. v. bolus of 12.5 µg TRH (the mini-TRH test), but not the maximal prolactin response to TRH or basal prolactin, positively correlated with prolactin response to haloperidol and negatively with 24-h urinary excretion of homovanillic acid (HVA). These results suggest that the mini-TRH test is a better estimate of dopamine inhibition of prolactin release than the maximal prolactin response or basal prolactin level. A recent neuroimaging study suggested that in schizophrenia, there is a widely distributed defect in extrastriatal dopamine release, but the patients were not in the most acute phase of psychosis. The evidence is reviewed that this defect extends to tuberoinfundibular dopamine (TIDA) and which symptoms are associated with the test. In patients with acute nonaffective psychosis, the mini-TRH test positively correlated with nonparanoid delusions and memory dysfunction, indicating decreased dopamine transmission in association with these symptoms. In patients with acute drug-naïve first-episode schizophrenia, the mini-TRH test negatively correlated with negative disorganization symptoms and with basal prolactin. The latter correlation suggests the contribution of factors related to maximal prolactin stimulation by TRH; therefore, an alternative dose of 6.25 μg TRH could be used for the mini-TRH test in first-episode patients, allowed by increased sensitivity of the present prolactin tests. Future studies are needed to investigate whether the mini-TRH test could help in finding the optimal antipsychotic medication.

Prolactin secretion in healthy adults is determined by gender, age and body mass index

Background

Prolactin (PRL) secretion is quantifiable as mean, peak and nadir PRL concentrations, degree of irregularity (ApEn, approximate entropy) and spikiness (brief staccato-like fluctuations).

Hypothesis

Distinct PRL dynamics reflect relatively distinct (combinations of) subject variables, such as gender, age, and BMI.

Location

Clinical Research Unit.

Subjects

Seventy-four healthy adults aged 22–77 yr (41 women and 33 men), with BMI 18.3–39.4 kg/m².

Measures

Immunofluorometric PRL assay of 10-min samples collected for 24 hours.

Results

Mean 24-h PRL concentration correlated jointly with gender (P<0.0001) and BMI (P = 0.01), but not with age (overall R² = 0.308, P<0.0001). Nadir PRL concentration correlated with gender only (P = 0.017) and peak PRL with gender (P<0.001) and negatively with age (P<0.003), overall R² = 0.325, P<0.0001. Forward-selection multivariate regression of PRL deconvolution results demonstrated that basal (nonpulsatile) PRL secretion tended to be associated with BMI (R² = 0.058, P = 0.03), pulsatile secretion with gender (R² = 0.152, P = 0.003), and total secretion with gender and BMI (R² = 0.204, P<0.0001). Pulse mass was associated with gender (P = 0.001) and with a negative tendency to age (P = 0.038). In male subjects older than 50 yr (but not in women) approximate entropy was increased (0.942±0.301 vs. 1.258±0.267, P = 0.007) compared with younger men, as well as spikiness (0.363±0.122 vs. 0463±2.12, P = 0.031). Cosinor analysis disclosed higher mesor and amplitude in females than in men, but the acrophase was gender-independent. The acrophase was determined by age and BMI (R² = 0.186, P = 0.001).

Conclusion

In healthy adults, selective combinations of gender, age, and BMI specify distinct PRL dynamics, thus requiring balanced representation of these variables in comparative PRL studies.

Abnormal LH pulsatility in women with hyperprolactinaemic amenorrhoea normalizes after bromocriptine treatment: deconvolution-based assessment

OBJECTIVE

The present study examines the LH secretory process in hyperprolactinaemic women before, during and after bromocriptine therapy, using restrictive clinical selection criteria as well as improved methodological tools.

PATIENTS AND DESIGN

Six women (aged 20-40 years) with microprolactinomas (mean ± SE prolactin, PRL: 2478 ± 427 mU/l, range: 1370-3800 mU/l) and four age- and sex-matched healthy controls were admitted to the study. After an overnight fast, all patients and controls had blood samples withdrawn at 10 minute intervals for 6 h (during saline infusion) from 0800 h to 1400 h to determine serum LH and PRL concentrations. After baseline evaluation, patients were treated with bromocriptine, which was started at a daily dose of 1.25 mg for 7 days; the dose was then increased to 2.5 mg daily for the next 7 days and subsequently to 2.5 mg twice daily. PRL levels were evaluated at weekly intervals after the beginning of bromocriptine therapy for the duration of the study. The 6 h pulsatility study was repeated on four patients during treatment at a time when PRL levels were decreased, although not normalized (PRL range: 450-1350 mU/l) and, on four patients, with the attainment of normal serum PRL levels (PRL < 450 mU/l) in the early follicular phase of the menstrual cycle (days 2-5). The LH instantaneous secretion rate was reconstructed by a nonparametric deconvolution method. In addition to pulse analysis made using the program DETECT, the evaluation of the secretion rate yielded the pulse frequency as well as the pulse amplitude distribution.

RESULTS

Each time series was submitted to deconvolution analysis using a nonparametric method in order to estimate the instantaneous secretion rate (ISR). Hyperprolactinaemic patients had very few high-amplitude LH pulses above 0.2 IU/(l minutes) before treatment (average frequency: 0.83 ± 0.40 pulses/6 h) and at the intermediate evaluation (0.25 ± 0.25 pulses/6 h). In both cases, the pulse frequency was significantly lower than in controls (P < 0.05 and P < 0.01, respectively). When PRL was normalized, the number of high-amplitude LH pulses (4.25 ± 1.03 pulses/6 h), became statistically different from the pulse number before (P < 0.01) and during (P < 0.01) therapy; in particular the pulse frequency after therapy rose to a level not statistically different from that in controls.

CONCLUSION

The present study shows the presence of reduced LH pulsatility in hyperprolactinaemic women that recovers completely to within the physiological distribution when PRL levels are normalized by bromocriptine therapy.