LH and FSH secretory responses to GnRH in normal individuals: a non-parametric deconvolution approach

Short-term estriol administration modulates hypothalamo-pituitary function in patients with functional hypothalamic amenorrhea (FHA)

OBJECTIVE

To evaluate the influence of short-term estriol administration (10 d) on the hypothalamus-pituitary function and gonadotropins secretion in patients affected by functional hypothalamic amenorrhea (FHA).

STUDY DESIGN

Controlled clinical study on patients with FHA (n = 12) in a clinical research environment.

INTERVENTION(S)

Hormonal determinations and gonadotropin (luteinizing hormone [LH] and FSH) response to a gonadotropin-releasing hormone (GnRH) bolus (10 μg) at baseline condition and after 10 d of therapy with 2 mg/d of estriol per os.

MAIN OUTCOME MEASURE(S)

Measurements of plasma LH, FSH, prolactin, estradiol, androstenedione, 17α-hydroxyprogesterone, insulin, cortisol, thyroid-stimulating hormone, free triiodothyronine, and free thyroxine.

RESULT(S)

After treatment, the FHA patients showed a statistically significant increase of both LH and FSH plasma levels and the significant increase of their responses to the GnRH bolus.

CONCLUSION(S)

Estriol short-term therapy modulates within 10 d of administration the neuroendocrine control of the hypothalamus-pituitary unit and induces the recovery of both gonadotropins synthesis and secretion in hypogonadotropic patients with FHA.

The GHRH + arginine stimulated pituitary GH secretion in children and adults with Prader-Willi syndrome shows age- and BMI-dependent and genotype-related differences

OBJECTIVE

The quantitative and qualitative aspects of the pituitary response in children and adults with Prader-Willi syndrome (PWS) are compared in order to verify the possible age-dependent and genotype-related differences in terms of GH secretion.

DESIGN

29 young subjects (21 males and 8 females) and 65 adults (24 males and 41 females) with PWS were studied. All subjects underwent a standard GH Releasing Hormone (GHRH 1-29, 1 μg/kg as i.v. bolus at 0 minutes)+arginine (0.5 g/kg) test. Peak GH values, standard GH area under the curve (AUC), AUC of the instantaneous secretion rate (ISR), and secretion response analysis (i.e. half-secretion time) were evaluated. A regression analysis was performed to investigate which are the patient characteristics that affect the amplitude and shape of the GH secretion response.

RESULTS

Peak GH values and AUCGH were significantly higher in PWS children than in PWS adults, these differences being also significant both in PWS DEL15 (only peak GH value) and PWS UPD15. Moreover, PWS children showed significantly lower half secretion time than PWS adults, this delayed response being present both in PWS DEL15 and PWS UPD15. Significant negative correlations between AUCGH and BMISDS were observed in the two groups (adults and children), as well as in adults and children DEL15, but not in adults and children PWS UPD15. A regression analysis performed on the whole dataset showed that for PWS DEL15 the statistically significant variable explaining GH responsiveness was BMISDS (p<0.0001), while for UPD15 no statistically significant covariate was found. Conversely, when the delay of the secretion response was considered, the regression model yielding the best performances was the one with only age as a regressor (p<0.001).

CONCLUSIONS

The quantitative and qualitative analyses of GH responsiveness to GHRH+arginine highlight relevant differences between PWS children and PWS adults and genotype-related traits. The negative influence of BMISDS on GH secretion reinforces the need for an early start of life-long weight management in PWS subjects.

Deconvolution-based assessment of pituitary GH secretion stimulated with GHRH+arginine in Prader-Willi adults and obese controls

OBJECTIVE

The assessment of GH deficiency in adult patients with Prader-Willi syndrome (PWS) has been previously assessed through the evaluation of quantitative parameters, such as the peak value of GH response to exogenous stimuli. A comprehensive description of the pattern of secretory response obtainable by deconvolution analysis is still lacking. The aim of our study was to characterize the time evolution of responses of PWS subjects compared with obese controls.

DESIGN AND SUBJECTS

GH responsiveness was measured following the combined administration of GHRH+arginine to 65 PWS adults (24 males, 41 females) aged 18-41·2 years, and 17 age-, gender- and body mass index-matched obese controls. PWS subjects were analysed considering the stratification on different genotypes.

MEASUREMENTS

GH response to GHRH+arginine was analysed in terms of peak values, standard area under the curves (AUCs), AUCs due to the stimulus, AUCs of the Instantaneous Secretion Rate signal and Secretion Response Analysis.

RESULTS

In terms of both peak values and AUC, GH responses were statistically different between PWS UPD15 and PWS DEL15 subjects as well as between PWS UPD15 and obese controls. PWS subjects showed a lower and a more delayed GH response compared with obese controls. Moreover, PWS UPD15 subjects had the most delayed GH response.

CONCLUSIONS

Our findings demonstrate that impaired GH secretion in PWS subjects compared with obese controls regards not only amplitude parameters such as peak value and AUC, but also the shape of the secretory response, which is more delayed, especially for UPD15 subjects.

Endogenous circannual rhythm in luteinizing hormone secretion: insight from signal analysis coupled with mathematical modelling

In sheep, as in many vertebrates, the seasonal pattern of reproduction is timed by the annual photoperiodic cycle, characterized by seasonal changes in the day length. The photoperiodic information is translated into a circadian profile of melatonin secretion. After multiple neuronal relays (within the hypothalamus), melatonin affects gonadotrophin-releasing hormone (GnRH) secretion, which in turn controls ovarian cyclicity. The pattern of GnRH secretion is mirrored by that of luteinizing hormone (LH) secretion, whose plasmatic level can be easily measured. We addressed the question of whether there exists an endogenous circannual rhythm in a tropical sheep (Blackbelly) population that exhibits clear seasonal ovarian activity when ewes are subject to temperate latitudes. We based our analysis on LH time series collected in the course of 3 years from ewes subject to a constant photoperiodic regime. Owing to intra- and interanimal variability and unequal sampling times, the existence of an endogenous rhythm is not straightforward. We have used time-frequency signal processing methods, and especially the smooth pseudo-Wigner-Ville distribution, to extract possible hidden rhythms from the data. To further investigate the low-frequency (LF) and high-frequency (HF) components of the signals, we have designed a simple mathematical model of the LH plasmatic level accounting for the effect of experimental sampling times. The model enables us to (i) confirm the existence of an endogenous circannual rhythm as detected by the LF signal component, (ii) investigate the action mechanism of the photoperiod on the pulsatile pattern of LH secretion (control of the interpulse interval), and (iii) conclude that the HF component is mainly due to the experimental sampling protocol.

Recent neuroendocrine facets of male reproductive aging

We recently identified consistent attenuation of LH and testosterone secretory pulse amplitude and associated disruption of their orderly patterns of release in healthy older men. These dynamic changes emerge despite young-adult concentrations of LH and total testosterone. Moreover, we could document disruption of synchrony between LH secretion and oscillations in FSH, prolactin, sleep-stage and NPT (nocturnal penile tumescence), thus pointing to loss of coordinate neurohormone outflow. Such data suggest that CNS-hypothalamically based regulatory defects may be important in aging, as inferred indirectly in the old male rat and mouse more than 15 years ago. How such alterations are related to specific hypothalamic neurotransmitter changes in aging will be critical to unravel.