Interrelationships Between Pituitary Hormones as Assessed From 24-hour Serum Concentrations in Healthy Older Subjects

Perioperative fluctuation and overall evaluation of adenohypophyseal hormone secretion in patients with nonfunctioning pituitary adenoma

OBJECTIVE

Perioperative adenohypophyseal hormone assessment can improve therapeutic strategies and be used to evaluate the prognosis of pituitary adenomas. An individual hormone level does not entirely reflect the pituitary gland. Thus, this study aimed to analyze perioperative hormonal changes and propose a normalized method to facilitate overall assessment of the adenohypophysis.

METHODS

The authors retrospectively analyzed 89 male patients with nonfunctioning pituitary adenoma (NFPA) who underwent transsphenoidal surgery. Preoperative clinical data, imaging data, and perioperative hormone levels of the anterior pituitary gland were evaluated. Hormone values were rescaled using minimum-maximum normalization. The sum of the normalized hormone levels was defined as the total hormonal rate (THR).

RESULTS

Preoperative findings indicated correlations among different adenohypophyseal hormones. Luteinizing hormone (p = 0.62) and adrenocorticotropic hormone (p = 0.89) showed no significant changes after surgery, but growth hormone levels increased (p < 0.001). On the contrary, the levels of thyroid-stimulating hormone (p < 0.001), follicle-stimulating hormone (p = 0.02), and prolactin (p < 0.001) decreased. THR indicated a significant postoperative reduction in adenohypophyseal function (p = 0.04). Patients with postoperative hypopituitarism had significantly lower THR than those without (p = 0.003), with an area under the curve of 0.66. For NFPAs that presented with normal preoperative hormone levels, THR was a good clinical predictor of immediate postoperative hypopituitarism, with an area under the curve of 0.74.

CONCLUSIONS

The normalized synthesis index of hormones is a novel and clinically valuable method used to reflect adenohypophyseal secretion. Compared with individual hormones, these results indicated that THR can facilitate the analysis of general hormone levels despite various fluctuations in adenohypophyseal hormones. THR may also contribute to the effective prediction of short-term surgery-induced hypopituitarism.

Morphometric analysis of somatotropic and folliculostellate cells of human anterior pituitary during ageing

Introduction/Objective. In this study, we have pointed out the immunohistomorphometric characteristics of somatotropic (GH) and folliculo-stellate (FS) cells of the human pituitary gland during ageing. Methods. On histological sections of the pituitary gland of 14 male cadavers of different ages, the GH and FS cells were immunohistochemically labeled with corresponding antibodies, monoclonal anti-GH antibody and polyclonal anti-S100 antibody, respectively. Immunopositive GH- and FS-cells were further morphometrically analyzed using ImageJ software. Results. The obtained results of morphometric analysis showed that the surface area of GH cells increased significantly with age. In these cells, the nuclear-cytoplasmic ratio gradually decreased and became significantly higher after the age of 70 years. The volume density of GH cells has not changed during ageing, while in FS cells this parameter significantly increased in the cases older than 70 years. The nuclear-cytoplasmic ratio of GH cells is negatively correlated with the volume density of FS cells. Conclusions. Based on the obtained results, we concluded that hypertrophy of GH and FS cells occurs in men with ageing and that correlation between the morphometric parameters of these two cell types indicates their mutual interaction.

Relationships Between 24-hour LH and Testosterone Concentrations and With Other Pituitary Hormones in Healthy Older Men

Objective

To investigate the relationship between LH and testosterone (T), which characteristics associate with the strength of this relationship, and their interrelationships with GH, TSH, cortisol, and ACTH.

Design

Hormones were measured in serum samples collected every 10 minutes during 24 hours from 20 healthy men, comprising 10 offspring of long-lived families and 10 control subjects, with a mean (SD) age of 65.6 (5.3) years. We performed cross-correlation analyses to assess the relative strength between 2 timeseries for all possible time shifts.

Results

Mean (95% CI) maximal correlation was 0.21 (0.10-0.31) at lag time of 60 minutes between LH and total T concentrations. Results were comparable for calculated free, bioavailable, or secretion rates of T. Men with strong LH-T cross-correlations had, compared with men with no cross-correlation, lower fat mass (18.5 [14.9-19.7] vs. 22.3 [18.4-29.4] kg), waist circumference (93.6 [5.7] vs. 103.1 [12.0] cm), high-sensitivity C-reactive protein (0.7 [0.4-1.3] vs. 1.8 [0.8-12.3] mg/L), IL-6 (0.8 [0.6-1.0] vs. 1.2 [0.9-3.0] pg/mL), and 24-hour mean LH (4.3 [2.0] vs. 6.1 [1.5] U/L), and stronger LH-T feedforward synchrony (1.5 [0.3] vs. 1.9 [0.2]). Furthermore, T was positively cross-correlated with TSH (0.32 [0.21-0.43]), cortisol (0.26 [0.19-0.33]), and ACTH (0.26 [0.19-0.32]).

Conclusions

LH is followed by T with a delay of 60 minutes in healthy older men. Men with a strong LH-T relationship had more favorable body composition, inflammatory markers, LH levels, and LH-T feedforward synchrony. We observed positive correlations between T and TSH, cortisol, and ACTH.

T3 is linked to stress-associated reduction of prolactin in lactating women

The relationship between stress responses and lactation is bidirectional. Breastfeeding confers many benefits to maternal health, including attenuated hypothalamic-pituitary-adrenal axis responsiveness to stress. However, increased stress burden can impair lactation. The mechanisms that underlie these relationships are poorly understood. The present study aimed to compare breastfeeding habits, as well as subjective and objective measures of stress, in employed and non-employed lactating women and assess the relationships between these measures and prolactin (PRL), thyroid hormones (thyroid-stimulating hormone, triiodothyronine [T3] and thyroxine), vasopressin and cortisol levels. A dexamethasone suppression test was also administered to determine the sensitivity of the hypothalamic-pituitary-adrenal axis to negative-feedback. We report that lactating employed women had lower breastfeeding rates and lower PRL than lactating non-employed women. They also had a significantly higher stress burden, indicated by elevations in blood pressure and evening cortisol, relative to lactating non-employed women. In regression analyses that controlled for feeding modality and breastfeeding duration, we found these factors differentially affected PRL in the two groups and there were significant differences in PRL across groups that were not accounted for by these factors. A mediation regression analysis suggested that group differences in PRL were best explained by differences in T3 and income levels, rather than breastfeeding duration or other variables. Our data fit a speculative model in which elevated maternal stress increases cortisol, which suppresses T3, leading to decreased PRL. The decreases in PRL are associated with higher rates of bottlefeeding, which may further contribute to decreased PRL.

Within-Person Variation in Serum Thyrotropin Concentrations: Main Sources, Potential Underlying Biological Mechanisms, and Clinical Implications

BACKGROUND

Individuals exhibit fluctuations in the concentration of serum thyroid-stimulating hormone (TSH) over time. The scale of these variations ranges from minutes to hours, and from months to years. The main factors contributing to the observed within-person fluctuations in serum TSH comprise pulsatile secretion, circadian rhythm, seasonality, and ageing. In clinical practice and clinical research however, such within-person biological variation in serum TSH concentrations is often not considered. The aim of this review is to present an overview of the main sources of within-person variation in TSH levels, as well as the potential underlying biological mechanisms, and the clinical implications.

SUMMARY

In euthyroid individuals, the circadian rhythm, with a nocturnal surge around 02:00-04:00 h and a nadir during daytime has the greatest impact on variations in serum TSH concentrations. Another source of within-person variation in TSH levels is seasonality, with generally higher levels during the cold winter months. Since TSH is secreted in a pulsatile manner, TSH levels also fluctuate over minutes. Furthermore, elevated TSH levels have been observed with ageing. Other factors that affect TSH levels include thyroid peroxidase (TPO)-antibody positivity, BMI, obesity, smoking, critical illness, and many xenobiotics, including environmental pollutants and drugs. Potential underlying biological mechanisms of within-person variation in TSH levels can be safely concluded from the ability of TSH to respond quickly to changes in cues from the internal or external environment in order to maintain homeostasis. Such cues include the biological clock, environmental temperature, and length of day. The observed increase in TSH level with ageing can be explained at a population level and at an organism level. In clinical practice, the season for thyroid testing can influence a patient's test result and it occurs frequently that subclinical hypothyroid patients normalize to euthyroid levels over time without intervention.

CONCLUSIONS

Serum TSH concentrations vary over time within an individual, which is caused by multiple different internal and external factors. It is important to take the within-person variations in serum TSH concentrations into account when testing a patient in clinical practice, but also in performing clinical research.

Altered GH-IGF-1 Axis in Severe Obese Subjects is Reversed after Bariatric Surgery-Induced Weight Loss and Related with Low-Grade Chronic Inflammation

Endocrine disorders are common in obesity, including altered somatotropic axis. Obesity is characterized by reduced growth hormone (GH) secretion, although the insulin-like growth factor-1 (IGF-1) values are controversial. The aim of this study was to evaluate the effect of weight loss after bariatric surgery in the GH–IGF-1 axis in extreme obesity, in order to investigate IGF-1 values and the mechanism responsible for the alteration of the GH–IGF-1 axis in obesity. We performed an interventional trial in morbidly obese patients who underwent bariatric surgery. We included 116 patients (97 women) and 41 controls (30 women). The primary endpoint was circulating GH and IGF-1 values. Circulating IGF-1 values were lower in the obese patients than in the controls. Circulating GH and IGF-1 values increased significantly over time after surgery. Post-surgery changes in IGF-1 and GH values were significantly negatively correlated with changes in C-reactive protein (CRP) and free T4 values. After adjusting for preoperative body mass index (BMI), free T4 and CRP in a multivariate model, only CRP was independently associated with IGF-1 values in the follow-up. In summary, severe obesity is characterized by a functional hyposomatotropism at central and peripheral level that is progressively reversible with weight loss, and low-grade chronic inflammation could be the principal mediator.