Dapagliflozin partially restores reproductive function in MC4R KO obese female mice

Obese women often have certain degree of reproductive dysfunction with infertility. Although the clinical impact of obesity on female infertility has been extensively studied, the effective and targeted treatment is still lacking. Melanocortin-4-receptor knock-out (MC4R KO) mouse is an over-eating obese model with hyperphagia, hyperinsulinemia, reduced growth hormone (GH), and insulin resistance. Dapagliflozin improved the metabolic and hormonal parameters in MC4R KO mice. MC4R KO female mice were treated with dapagliflozin for 14 weeks from 14-week age. Age-matched WT littermates and non-treated MC4R KO mice were used as control groups. Food intake was measured daily. Body weight was measured twice a week. Estrous cycles, GH, and luteinizing hormone (LH) profiles were measured. Selected tissues were collected at the end of experiments for gene expression profiles and hematoxylin-eosin staining. Regularity and mode of hormonal profiles were restored by the dapagliflozin treatment. Estrous cycle was partially normalized, number of CL was significantly increased, and the expression of Kiss1 and Gnrh1 in the hypothalamus and LH in the pituitary was markedly increased by the dapagliflozin treatment. It is conclsuded that dapagliflozin may recover LH and GH profiles partially through modification of relevant gene expression in the hypothalamus and pituitary, and result in an improved ovulation rate in obese mouse model. Dapagliflozin may therefore improve fertility in obese patients.

Effect of Growth Hormone Secretagogue Receptor Deletion on Growth, Pulsatile Growth Hormone Secretion, and Meal Pattern in Male and Female Mice

INTRODUCTION

While the vast majority of research investigating the role of ghrelin or its receptor, GHS-R1a, in growth, feeding, and metabolism has been conducted in male rodents, very little is known about sex differences in this system. Furthermore, the role of GHS-R1a signaling in the control of pulsatile GH secretion and its link with growth or metabolic parameters has never been characterized.

METHODS

We assessed the sex-specific contribution of GHS-R1a signaling in the activity of the GH/IGF-1 axis, metabolic parameters, and feeding behavior in adolescent (5-6 weeks old) or adult (10-19 weeks old) GHS-R KO (Ghsr-/-) and WT (Ghsr+/+) male and female mice.

RESULTS

Adult Ghsr-/- male and female mice displayed deficits in weight and linear growth that were correlated with reduced GH pituitary contents in males only. GHS-R1a deletion was associated with reduced meal frequency and increased meal intervals, as well as reduced hypothalamic GHRH and NPY mRNA in males, not females. In adult, GH release from Ghsr-/- mice pituitary explants ex vivo was reduced independently of the sex. However, in vivo pulsatile GH secretion decreased in adult but not adolescent Ghsr-/- females, while in males, GHS-R1a deletion was associated with reduction in pulsatile GH secretion during adolescence exclusively. In males, linear growth did not correlate with pulsatile GH secretion, but rather with ApEn, a measure that reflects irregularity of the rhythmic secretion. Fat mass, plasma leptin concentrations, or ambulatory activity did not predict differences in GH secretion.

DISCUSSION/CONCLUSION

These results point to a sex-dependent dimorphic effect of GHS-R1a signaling to modulate pulsatile GH secretion and meal pattern in mice with different compensatory mechanisms occurring in the hypothalamus of adult males and females after GHS-R1a deletion. Altogether, we show that GHS-R1a signaling plays a more critical role in the regulation of pulsatile GH secretion during adolescence in males and adulthood in females.

Rotating Day and Night Disturb Growth Hormone Secretion Profiles, Body Energy Metabolism, and Insulin Levels in Mice

BACKGROUND

Insulin and growth hormone (GH) - 2 vital metabolic regulatory hormones - regulate glucose, lipid, and energy metabolism. These 2 hormones determine substrate and energy metabolism under different living conditions. Shift of day and night affects the clock system and metabolism probably through altered insulin and GH secretion.

METHODS

Five-week-old male mice were randomly assigned to a rotating light (RL) group (3-day normal light/dark cycle followed by 4-day reversed light/dark cycle per week) and normal light (NL) group. Body weight and food intake were recorded every week. Series of blood samples were collected for pulsatile GH analysis, glucose tolerance test, and insulin tolerance test at 9, 10, and 11 weeks from the start of intervention, respectively. Indirect calorimetric measurement was performed, and body composition was tested at 12 weeks. Expressions of energy and substrate metabolism-related genes were evaluated in pituitary and liver tissues at the end of 12-week intervention.

RESULTS

The RL group had an increased number of GH pulsatile bursts and reduced GH mass/burst. RL also disturbed the GH secretion regularity and mode. It suppressed insulin secretion, which led to a disturbed insulin/GH balance. It was accompanied by the reduced metabolic flexibility and modified gene expression involved in energy balance and substrate metabolism. Indirect calorimeter recording revealed that RL decreased the respiratory exchange ratio (RER) and oxygen consumption at the dark phase, which resulted in an increase in fat mass and free fatty acid levels in circulation.

CONCLUSION

RL disturbed pulsatile GH secretion and decreased insulin secretion in male mice with significant impairment in energy, substrate metabolism, and body composition.

Addition of a carboxy terminal tail to the normally tailless gonadotropin-releasing hormone receptor impairs fertility in female mice

Gonadotropin-releasing hormone (GnRH) is the primary neuropeptide controlling reproduction in vertebrates. GnRH stimulates follicle-stimulating hormone (FSH) and luteinizing hormone (LH) synthesis via a G-protein-coupled receptor, GnRHR, in the pituitary gland. In mammals, GnRHR lacks a C-terminal cytosolic tail (Ctail) and does not exhibit homologous desensitization. This might be an evolutionary adaptation that enables LH surge generation and ovulation. To test this idea, we fused the chicken GnRHR Ctail to the endogenous murine GnRHR in a transgenic model. The LH surge was blunted, but not blocked in these mice. In contrast, they showed reductions in FSH production, ovarian follicle development, and fertility. Addition of the Ctail altered the nature of agonist-induced calcium signaling required for normal FSH production. The loss of the GnRHR Ctail during mammalian evolution is unlikely to have conferred a selective advantage by enabling the LH surge. The adaptive significance of this specialization remains to be determined.

Ghrelin Gene Deletion Alters Pulsatile Growth Hormone Secretion in Adult Female Mice

Using preproghrelin-deficient mice (Ghrl-/-), we previously observed that preproghrelin modulates pulsatile growth hormone (GH) secretion in post-pubertal male mice. However, the role of ghrelin and its derived peptides in the regulation of growth parameters or feeding in females is unknown. We measured pulsatile GH secretion, growth, metabolic parameters and feeding behavior in adult Ghrl-/- and Ghrl+/+ male and female mice. We also assessed GH release from pituitary explants and hypothalamic growth hormone-releasing hormone (GHRH) expression and immunoreactivity. Body weight and body fat mass, linear growth, spontaneous food intake and food intake following a 48-h fast, GH pituitary contents and GH release from pituitary explants ex vivo, fasting glucose and glucose tolerance were not different among adult Ghrl-/- and Ghrl+/+ male or female mice. In vivo, pulsatile GH secretion was decreased, while approximate entropy, that quantified orderliness of secretion, was increased in adult Ghrl-/- females only, defining more irregular GH pattern. The number of neurons immunoreactive for GHRH visualized in the hypothalamic arcuate nucleus was increased in adult Ghrl-/- females, as compared to Ghrl+/+ females, whereas the expression of GHRH was not different amongst groups. Thus, these results point to sex-specific effects of preproghrelin gene deletion on pulsatile GH secretion, but not feeding, growth or metabolic parameters, in adult mice.

Interleukin-2 Transiently Inhibits Pulsatile Growth Hormone Secretion in Young but not Older Healthy Men

CONTEXT

Interleukin-2 (IL-2), a proinflammatory cytokine, has been used to treat malignancies. Increased cortisol and adrenocorticotropin (ACTH) were noted, but growth hormone (GH) secretion was not investigated in detail.

OBJECTIVE

We quantified GH secretion after a single subcutaneous injection of IL-2 in 17 young and 18 older healthy men in relation to dose, age, and body composition.

METHODS

This was a placebo-controlled, blinded, prospectively randomized, crossover study. At 20:00 hours IL-2 (3 or 6 million units/m2) or saline was injected subcutaneously. Lights were off between 23:00 and 07:00 hours. Blood was sampled at 10-minute intervals for 24 hours. Outcome measures included convolution analysis of GH secretion.

RESULTS

GH profiles were pulsatile under both experimental conditions and lower in older than young volunteers. Since the effect of IL-2 might be time limited, GH analyses were performed on the complete 24-hour series and the 6 hours after IL-2 administration. Total and pulsatile 24-hour GH secretion decreased nonsignificantly. Pulsatile secretion fell over the first 6 hours after IL-2 (P = .03), with visceral fat as a covariate (P = .003), but not age (P = .10). Plots of cumulative 2-hour bins of GH pulse mass showed a distinction by treatment and age groups: A temporary GH decrease of 32% and 28% occurred in the first 2-hour bins after midnight (P = .02 and .04) in young participants, whereas in older individuals no differences were present at any time point.

CONCLUSION

This study demonstrates that IL-2 temporarily diminishes GH secretion in young, but not older, men.

Familial longevity is associated with lower baseline bone turnover but not differences in bone turnover in response to rhTSH

Context: Offspring from long-lived families have a different thyroid status than controls, characterised by higher circulating levels of thyroid stimulating hormone (TSH) and similar levels of thyroid hormone. Expression of the TSH receptor has previously been observed on various extrathyroidal tissues, including bone. However, potential physiological consequences of differences in circulating TSH as observed in familial longevity on bone tissue remain unclear.

Objective: Based on the hypothesis that TSH may inhibit bone resorption, we explored whether offspring of long-lived families have lower bone turnover than controls at baseline as well as following a challenge with recombinant human TSH (rhTSH).

Methods: Bone turnover markers CTX and P1NP were measured in fasted morning samples from 14 offspring and 12 controls at baseline and at 24 hour intervals following 0.1 mg rhTSH i.m. administration for four consecutive days.

Results: At baseline, mean (SEM) CTX was 0.32 (0.03) ng/ml in offspring and 0.50 (0.04) ng/ml in controls, p < 0.01, whereas mean (SEM) P1NP was 39.6 (3.2) ng/ml in offspring and 61.8 (6.6) ng/ml in controls, p < 0.01. Following rhTSH administration, both CTX and P1NP levels transiently increased over time and normalized towards baseline after 72 h (general linear modelling: CTX time p = 0.01, P1NP time p < 0.01); the response was similar between offspring and controls.

Conclusions: Bone turnover markers were lower at baseline in offspring from long-lived families than in controls but increased similarly following an rhTSH challenge.

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.

Growth Hormone Secretion Does Not Increase After Interleukin-2 Administration in Healthy Men

Context: Interleukin-2 (IL2), a proinflammatory cytokine, is used for treatment of malignancies. Increased cortisol and ACTH were noted, but GH secretion was not investigated in detail. This is the first study in healthy men which uses moderate high IL2 doses as used in cancer treatment. Objective: The goal of this study was to quantify GH secretion after a single sc injection of IL2 in young and older healthy men in relation to dose, age and body composition. Design: This was a placebo-controlled, blinded, prospectively randomized cross-over study in 17 young subjects (mean age 24.1 yr) and 18 older subjects (mean age 63.9 yr). The subjects underwent 24 h of blood sampling at 10-min intervals, starting at 1800 h. At 2000 h IL2 (3 or 6 million units per m² body surface) or saline was injected sc. Lights were off between 2300 and 0700 h. Outcome Measures: Deconvolution analysis of GH. Abdominal visceral fat (AVF) was calculated from single slice CT. Results: GH secretion (pulsatile and total) was negatively related to AVF (R=0.67, P<0.0001) and to age (R=0.56, P=0.001). These relations were maintained after IL2 administration. GH profiles were pulsatile under both experimental conditions. Since the effect of IL2 might be limited in time, GH deconvolution analyses were performed on the complete 24 h data series, the period with lights off and 6 h after IL2 administration. Total 24 h GH secretion decreased non-significantly from 74.6 ±10.2 to 67.5±7.4 µg/L (P=0.25) and pulsatile secretion from 69.4±9.8 to 62.2±7.4 µg/L (P=0.23). In the GLM procedure the effect of IL2 treatment was borderline significant (P=0.08), no interaction with age (P=0.28), but borderline with IL2 dose (P=0.07), and caused by decreased GH secretion (88 to 67 µg/L) at a low dose IL2. In a sub-analysis of the two age groups no effect on GH secretion in the older group was noted, in contrast to young subjects, especially on low dose IL2 (P=0.07). The analysis was refined further by calculating cumulative pulse masses in 2-h bins. By this approach it could be demonstrated that the cumulative GH pulse mass in older subjects across the 24 h was unchanged, while that in young subjects was temporarily inhibited in the bins between midnight and 0400 h (P=0.019 and 0.038). Conclusion: This study demonstrated that IL2 temporarily diminished GH secretion in young but not elderly volunteers. Pituitary hormone secretion by IL2 has not been studied as extensively as other cytokines, including IL1, IL6 and TNF. IL2 stimulates ACTH and TSH, inhibits LH and has no effect on GH secretion by rat pituitary (PNAS 58:185,1993). In patients with renal cancer IL2 infusion has no effect on GH levels (Anti-Cancer Res 10:753,1990. The present findings extend these observations to a large group of healthy volunteers, in whom we demonstrated previously suppression of the gonadal axis and activation of the HPA-axis (JCEM 101:539,2016, Endocr Connect 9:637,2010).

Relationship Between 24-Hour Serum LH and Testosterone Concentrations and Their Interrelationships With Other Pituitary Hormones in Healthy Older Men

Background: With ageing, LH levels rise while T levels decline in men, although this decline in T levels could also be caused by a change in health status, including body composition, inflammation, and comorbidities. Not only levels of LH and T change with age, but levels of other pituitary hormones also change concomitantly with age. It could be hypothesized that these hormonal changes are synchronized with each other.

Objective: In this study, we aimed to determine the relationship between 24-h serum LH and T concentrations in healthy older men. Besides, we aimed to determine which health factors, including body composition, metabolic and inflammatory markers, and LH-T related markers are associated with the strength of this LH-T relationship. Furthermore, we explored the interrelationships between LH and T with 24-h serum concentrations of GH, TSH, cortisol, and ACTH.

Design: Hormones were measured in serum samples collected every 10 min during 24 h 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 two 24-h hormone concentration series for all possible time shifts.

Results: A mean (95% confidence interval) maximal correlation coefficient of 0.21 (0.10 – 0.31) at lag time 60 min was found 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 to men with no LH-T relationship, 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), hsCRP levels (0.7 (0.4 – 1.3) vs. 1.8 (0.8 – 12.3) mg/L), IL-6 levels (0.8 (0.6 – 1.0) vs. 1.2 (0.9 – 3.0) pg/mL), and 24-h mean LH levels (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 concentrations (0.26 (0.19 – 0.32)).

Conclusions: LH concentrations were followed by T concentrations/secretion with a delay of 60 min in healthy older men, which is in line with literature. Men with a strong LH-T relationship had more favorable body composition, inflammatory markers, 24-h mean LH levels, and LH-T feedforward synchrony. In contrast, chronological age and 24-h mean T levels were not associated with the strength of the LH-T relationship. This observation could indicate that LH and health markers play a bigger role in determining the strength of LH-T cross-correlations than T and chronological age. Furthermore, we observed positive correlations between T and TSH, cortisol, and ACTH concentrations. These exploratory analyses could indicate that T and other hormones are driven by a common regulator or that there is crosstalk between these hormones.

Bone Markers Are Diminished in Offspring of Long-Lived Families Compared With Matched Controls, but Respond Equally to T3 and rhTSH

Objective: We explored the effects of T3 and rhTSH administration on bone turnover in subjects of the Leiden Longevity Study. Design: Twenty-six subjects (13 offspring and 13 matched controls), mean age 68 y, underwent a rhTSH (0.1 mg i.m) and a T3 challenge (100 µg orally) with an interval of at least 3 m. Bone markers were measured at baseline and hereafter once daily for 3–4 days. Outcome Measures: Bone markers and changes after T3 and rhTSH. The influence of sex, group and time, and relations with incremental changes in TSH, fT4 and T3. Results: CTX (bone resorption) was lower in offspring than controls (mean ± SEM), 0.324±0.026 vs 0.443±0.036 ng/mL, P= 0.02. P1NP (bone formation) was also lower in offspring than in controls (40.3±2.2 vs 59.0± 4.7 ng/mL, P=0.004). No sex differences were found. In offspring, CTX but not P1NP was positively related to TSH and fT4 (R=0.48, P=0.001 and R=0.55, P=0.005). In controls, CTX was negatively related to TSH (R=-0.50, P=0.009), while P1NP was positively related with fT4 (R=0.52, P=0.006). TSH administration increased bone resorption and formation (P<0.0001 and 0.005, respectively). CTX was maximal at 48 h, increasing from 0.415±0.032 to 0.470 ±0.037 ng/mL, P=0.001. P1NP increased from 51.1±4.09 to a maximum of 56.2±3.9 ng/mL at 24 h (P=0.005). T3 also increased bone resorption (P=0.049) and formation (P=0.001). CTX increased from 0.386±0.034 to 0.410± 0.041 ng/mL, P=0.05, and P1NP from 48.9± 4.3 to 55.5±4.2 ng/mL, P=0.007), with maximal values at 48 h. Offspring and controls had similar responses and sex had generally no statistical impact. Significant linear regressions were found between the incremental changes of CTX and TSH at 24 h (R=0.44, P=0.003), but not later. Here, significant linear relation were found for the incremental fT4 and CTX (R=0.60, P=0.001 at 48 h, and R=0.49, P=0.013 at 72 h). For P1NP such relations were not present (R values between from 0.002 to 0.14). T3 changes did not correlate with bone markers at any time point. Conclusion: This study demonstrates that bone turnover is diminished in members of long-lived families where bone resorption was positively related to serum TSH and fT4. Nevertheless, the responses to TSH (and fT4) and T3 were similar in offspring and controls. Interestingly, the maximal effect of TSH increment on bone resorption preceded that of fT4, suggesting that TSH may have an independent stimulatory effect on bone resorption. At physiological TSH concentrations such stimulatory effect on bone resorption may be postulated in offspring, along with many other factors, e.g PTH, vitamin D, GH, sex hormones and cytokines.

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.

Circulating Thyroid Hormone Profile in Response to a Triiodothyronine Challenge in Familial Longevity

Context

Familial longevity is associated with higher circulating levels of thyrotropin (TSH), in the absence of differences in circulating thyroid hormones, and a lower thyroid responsivity to TSH, as previously observed in the Leiden Longevity Study (LLS). Further mechanisms underlying these observations remain unknown.

Objective

We hypothesized that members from long-lived families (offspring) have higher thyroid hormone turnover or less negative feedback effect on TSH secretion compared to controls.

Methods

In a case-control intervention study, 14 offspring and 13 similarly aged controls received 100 µg 3,5,3′-triiodothyronine (T3) orally. Their circulating T3, free T3 (fT3), and TSH levels were measured during 5 consecutive days. We compared profiles of circulating T3, fT3, and TSH between offspring and controls using general linear modeling (GLM) and calculated the percentage decline in TSH following T3 administration.

Results

Circulating T3 and fT3 levels increased to supraphysiologic values and normalized over the course of 5 days. There were no serious adverse events. T3 and fT3 concentration profiles over 5 days were similar between offspring and controls (T3 GLM P = .11, fT3 GLM P = .46). TSH levels decreased in a biphasic manner and started returning to baseline by day 5. The TSH concentration profile over 5 days was similar between offspring and controls (GLM P = .08), as was the relative TSH decline (%).

Conclusions

Members of long-lived families have neither higher T3 turnover nor diminished negative feedback of T3 on TSH secretion. The cause and biological role of elevated TSH levels in familial longevity remain to be elucidated.

Interleukin-2 drives cortisol secretion in an age-, dose-, and body composition-dependent way

BACKGROUND

Interleukin-2 (IL-2), one of the proinflammatory cytokines, is used in the treatment of certain malignancies. In some studies, transient increases in cortisol and ACTH secretion occurred. Thus, this agent may be used as an experimental probe of adrenal cortisol secretion.

OBJECTIVE

This study quantifies the effects of low and moderate doses of IL-2 on cortisol secretion and assesses the modulation by age, dose and body composition.

SITE

Mayo Clinical Translational Research Unit.

SUBJECTS

Study comprised 35 healthy men, 17 young and 18 older.

METHODS

Randomized prospective double-blind saline-controlled study of IL-2 administration in two doses with concurrent 10-min blood sampling for 24 h.

OUTCOME MEASURES

Deconvolution analysis and approximate entropy of cortisol secretion.

RESULTS

Low-dose IL-2 administration increased nocturnal pulsatile cortisol secretion from 1460 ± 160 to 2120 ± 220 nmol/L/8 h in young subjects and from 1680 ± 105 to 1960 ± 125 nmol/L/8 h (treatment P < 0.0001, but more in young than older, P = 0.02). Comparable results were obtained for total cortisol secretion (P treatment <0.0001, age effect P = 0.005). The higher IL-2 dose caused a large increase in young (P < 0.0001), but not in older (P = 0.90) subjects. This dose also increased approximate entropy from 0.877 ± 0.041 to 1.024 ± 0.049 (P = 0.008), pointing to reduced secretory orderliness. Incremental cortisol (nocturnal) secretion correlated negatively with visceral fat mass (R = -0.41, P = 0.019).

CONCLUSION

In healthy men, IL-2 injection drives pulsatile cortisol secretion in a dose-dependent way in young, but not older, individuals and erodes cortisol secretory orderliness at a higher dose in young subjects. Cortisol responses are diminished with increasing abdominal visceral fat mass.

Familial Longevity is Associated with an Attenuated Thyroidal Response to Recombinant Human Thyroid Stimulating Hormone

CONTEXT

Longevity is associated with higher circulating levels of TSH in the absence of differences in circulating thyroid hormones (TH), as previously observed in F2 members of long-lived families (F2-LLS) and their partners (F2-Con). The mechanism underlying this observed difference remains unknown.

OBJECTIVE

We hypothesized that the thyroid gland of members from long-lived families are less responsive to TSH stimulation, thereby requiring higher circulating TSH levels to maintain adequate TH levels.

METHODS

We performed a case-control intervention study with a single intramuscular (gluteal) injection with 0.1 mg recombinant human TSH in a subgroup of 14 F2-LLS and 15 similarly aged F2-Con. They were followed for 4 days. No serious adverse events were reported. For analyses, we compared time trajectories of TSH and TH, and the ratio of TH to TSH using area under the curve (AUC) calculations.

RESULTS

The AUC free T4/AUC TSH ratio was significantly lower in F2-LLS than in F2-Con (estimated mean [95% confidence interval] 1.6 [1.2-1.9] and 2.2 [1.9-2.6], respectively, P = 0.01). The AUC thyroglobulin/AUC TSH ratio was also lower in F2-LLS than in F2-Con (median [interquartile range] 2.1 [1.4-3.6] and 3.2 [2.7-7.4], respectively, P = 0.04). We observed the same trend with the AUC free T3/AUC TSH ratio, although the difference was not statistically significant (estimated mean [95% confidence interval] 0.6 [0.4-0.7] and 0.7 [0.6-0.8], respectively, P = 0.07).

CONCLUSIONS

The present findings show that members of long-living families have a lower thyroid responsivity to TSH compared with their partners.

OR32-04 Dynamic Interactions Between Luteinizing Hormone and Testosterone in Healthy Community-Dwelling Men: Impact by Age and Body Composition

Context. Aging is associated with diminished testosterone (Te) secretion, which could be attributed to Leydig cell dysfunction, decreased pituitary stimulation and altered Te feedback. Objective. The goal was to quantify all three regulatory nodes of the GnRH-LH-Leydig cell- axis in the same cohort of healthy men, by measuring (1) indirectly the strength of the endogenous GnRH signal on the gonadotrope, (2) the strength of Te feedback on LH by ketoconazole (KTCZ), and (3) the effect of LH infusions on Te secretion, in relation to age and body composition.

Design. This was a placebo-controlled, blinded, prospectively randomized cross-over study in 40 men, age 19–73 yr, BMI 20–34.3 kg/m2. A submaximal dose of ganirelix (GnRH antagonist) was used to assess outflow of GnRH, by calculating the difference between LH output during the control and ganirelix arm. Ketoconazole (steroidogenic inhibitor) was used to estimate feedback, by the difference in LH output during ketoconazole and control arm. High-dose ganirelix and repeated 6-min LH (18.75 IU) infusions were used to measure testicular responsivity. Blood sampling was at 10-min intervals. The 4 sessions were concluded with, a single submaximally GnRH stimulus to assess the responsiveness of the gonadotrope during ganirelix inhibition.

Setting. The study was performed in a Clinical Translational Research Unit.

Interventions. In 3 of the 4 experiments subjects underwent 5 h of blood sampling at 10-min intervals, starting at 0800 h. At 1100 h GnRH was injected and sampling was continued for another 2 h. Admission was at 1700 h the day before. At 2000 h they received KTCZ, dexamethasone or ganirelix and/or placebo. KTCZ and dexamethasone (or placebo) were administered again at 0700 when the IV catheter was placed. High-dose ganirelix was used to test the testicular responsiveness, and 7 LH pulses (90 min intervals) were given., with blood sampling from 1500 till 1300 h next day.

Outcome measures. Mean concentrations of LH and (bio)Te, deconvolution analysis, endogenous dose-response LH-bioTe relation, and approximate entropy. Abdominal visceral fat (AVF) was calculated from single slice CT.

Results. There were age-, but not body composition-related decreases in estimated endogenous GnRH secretion, Te’s feedback strength on LH, and Leydig cell responsivity to LH, accompanied by changes in approximate entropy. Bioavailable Te levels were negatively related to both age and AVF, without interaction between these variables. The LH response to a submaximal dose of GnRH was independent of age and AVF.

Conclusion. Advancing age is associated with 1) attenuated bioavailable Te secretion caused by diminished GnRH outflow and not by decreased GnRH responsivity of the gonadotrope, 2) diminished testicular responsivity to infused LH pulses, and 3) partial compensation by diminished Te feedback on central gonadotropic regulation.

SUN-309 Interleukin-2 Administration in Healthy Men Activates Cortisol Secretion in an Age-, Dose-, and Body Composition-Dependent Way

Context. Interleukin-2 (IL2), a proinflammatory cytokine, is used for treatment of malignancies. Increased cortisol and ACTH were noted, but not investigated in detail. This is the first study in healthy men which uses moderate high IL2 doses as used in cancer treatment.

Objective. The goal of this study was to quantify cortisol secretion after a single sc injection of IL2 at 1900 h in young and older healthy men in relation to dose, age and body composition. Design. This was a placebo-controlled, blinded, prospectively randomized cross-over study in 17 young subjects (mean age 24.1 yr, range 19–30 yr) and 18 older subjects (mean age 63.9 yr, range 60–75 yr). The subjects underwent 24 h of blood sampling at 10-min intervals, starting at 1800 h. At 2000 h IL2 (3 or 6 million units per m² body surface) or saline was injected sc. Lights were off between 2300 and 0700 h.

Setting. The study was performed in a Clinical Translational Research Unit.

Outcome measures. Mean concentrations of cortisol, deconvolution analysis, and approximate entropy. Abdominal visceral fat (AVF) and total abdominal fat (TAF) were calculated from single slice CT.

Results. Cortisol concentrations started to rise at 2300 h. The AUC’s during the lights-on periods were unchanged by IL2. Therefore, most analyses were restricted to the 8 h lights-off period. In young volunteers pulsatile cortisol secretion increased from 52.9±5.8 to 77.0±8.0 µg/L/8h and in older subjects from 60.6±3.8 to 70.6±4.6 µg/L/8h (GLM: treatment P <0.0001, treatment x age: P=0.02, mean ± SEM). Thus, the effect was smaller in older subjects. Increasing the IL2 dose increased cortisol secretion in young subjects (P= 0.001), but not in older subjects (P=0.90). In addition, the slopes (mean ± SE) of the linear part of the concentration curves after IL-2 were steeper than after placebo, pointing to accelerated release (young 1.40±0.13 to 3.76±0.11, P<0.0001, in older 1.27±0.04 to 3.28±0.15, P<0.0001).The incremental nocturnal pulsatile cortisol secretion after IL2 was negatively related to body composition (AVF: R= – 0.41, P=0.019; TAF R= – 0.41, P=0.043). Nocturnal ApEn-cortisol did not increase after low dose IL2 (0.981± 0.099 to 0.991±0.046, P=0.92). After high-dose, ApEn increased from 0.877±0.041 to 1.024±0.049, P=0.008, not correlated with body composition, nor with age. The ApEn increase points to decreased secretory regularity imposed by enhanced CRF signaling, rather than diminished cortisol feedback, which leads to greater secretory regularity.

Conclusion. Il2, a paradigm for inflammation, increased pulsatile cortisol secretion, more in young than in older subjects. Higher IL2 doses in young subjects amplified cortisol secretion, but not in older subjects. Cortisol secretion exhibited an advance (earlier) time shift, accompanied by accelerated secretion. Incremental nocturnal cortisol secretion was negatively related to fat mass.

Dynamic Pituitary-Adrenal Interactions in the Critically Ill after Cardiac Surgery

CONTEXT

Patients with critical illness are thought to be at risk of adrenal insufficiency. There are no models of dynamic hypothalamic-pituitary-adrenal (HPA) axis function in this group of patients and thus current methods of diagnosis are based on aggregated, static models.

OBJECTIVE

To characterize the secretory dynamics of the HPA axis in the critically ill (CI) after cardiac surgery.

DESIGN

Mathematical modeling of cohorts.

SETTING

Cardiac critical care unit.

PATIENTS

20 male patients CI at least 48 hours after cardiac surgery and 19 healthy (H) male volunteers.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Measures of hormone secretory dynamics were generated from serum adrenocorticotrophic hormone (ACTH) sampled every hour and total cortisol every 10 min for 24 h.

RESULTS

All CI patients had pulsatile ACTH and cortisol profiles. CI patients had similar ACTH secretion (1036.4 [737.6] pg/mL/24 h) compared to the H volunteers (1502.3 [1152.2] pg/mL/24 h; P = .20), but increased cortisol secretion (CI: 14 447.0 [5709.3] vs H: 5915.5 [1686.7)] nmol/L/24 h; P < .0001). This increase in cortisol was due to nonpulsatile (CI: 9253.4 [3348.8] vs H: 960 [589.0] nmol/L/24 h, P < .0001), rather than pulsatile cortisol secretion (CI: 5193.1 [3018.5] vs H: 4955.1 [1753.6] nmol/L/24 h; P = .43). Seven (35%) of the 20 CI patients had cortisol pulse nadirs below the current international guideline threshold for critical illness-related corticosteroid insufficiency, but an overall secretion that would not be considered deficient.

CONCLUSIONS

This study supports the premise that current tests of HPA axis function are unhelpful in the diagnosis of adrenal insufficiency in the CI. The reduced ACTH and increase in nonpulsatile cortisol secretion imply that the secretion of cortisol is driven by factors outside the HPA axis in critical illness.

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

CONTEXT

Hormones of the hypothalamic-pituitary-target gland axes are mostly investigated separately, whereas the interplay between hormones might be as important as each separate hormonal axis.

OBJECTIVE

Our aim is to determine the interrelationships between GH, TSH, ACTH, and cortisol in healthy older individuals.

DESIGN

We made use of 24-hour hormone serum concentrations assessed with intervals of 10 minutes from 38 healthy older individuals with a mean age (SD) of 65.1 (5.1) years from the Leiden Longevity Study. Cross-correlation analyses were performed to assess the relative strength between 2 24-hour hormone serum concentration series for all possible time shifts. Cross-approximate entropy was used to assess pattern synchronicity between 2 24-hour hormone serum concentration series.

RESULTS

Within an interlinked hormonal axis, ACTH and cortisol were positively correlated with a mean (95% confidence interval) correlation coefficient of 0.78 (0.74-0.81) with cortisol following ACTH concentrations with a delay of 10 minutes. Between different hormonal axes, we observed a negative correlation coefficient between cortisol and TSH of -0.30 (-0.36 to -0.25) with TSH following cortisol concentrations with a delay of 170 minutes. Furthermore, a positive mean (95% confidence interval) correlation coefficient of 0.29 (0.22-0.37) was found between TSH and GH concentrations without any delay. Moreover, cross-approximate entropy analyses showed that GH and cortisol exhibit synchronous serum concentration patterns.

CONCLUSIONS

This study demonstrates that interrelations between hormones from interlinked as well as different hypothalamic-pituitary-target gland axes are observed in healthy older individuals. More research is needed to determine the biological meaning and clinical consequences of these observations.

Dynamic Interactions Between LH and Testosterone in Healthy Community-Dwelling Men: Impact of Age and Body Composition

BACKGROUND

Aging is associated with diminished testosterone (Te) secretion, which may be attributed to Leydig cell dysfunction, decreased pituitary stimulation, and altered Te feedback.

OBJECTIVE

To study all regulatory nodes-gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH) and Leydig cell-in the same cohort of healthy men.

STUDY DESIGN

This was a placebo-controlled, blinded, prospectively randomized cross-over study in 40 men, age range 19 to 73 years, and body mass index (BMI) range 20 to 34.3 kg/m2. A submaximal dose of the GnRH antagonist ganirelix was used to assess outflow of GnRH, by calculating the difference between LH output during the control arm and ganirelix arm. Ketoconazole (a steroidogenic inhibitor) was used to estimate feedback, by the difference in LH output during the ketoconazole and control arm. High-dose ganirelix and repeated LH infusions were used to measure testicular responsivity. Blood sampling was performed at 10-minute intervals.

RESULTS

There were age-related, but not body composition-related decreases in estimated GnRH secretion, the feedback strength of Te on LH, and Leydig cell responsivity to LH, accompanied by changes in approximate entropy. Bioavailable Te levels were negatively related to both age and computed tomography (CT)-estimated abdominal visceral mass (AVF), without interaction between these variables. The LH response to a submaximal dose of GnRH was independent of age and AVF.

CONCLUSION

Advancing age is associated with (1) attenuated bioavailable Te secretion caused by diminished GnRH outflow and not by decreased GnRH responsivity of the gonadotrope, (2) diminished testicular responsivity to infused LH pulses, and (3) partial compensation by diminished Te feedback on central gonadotropic regulation.

IGSF1 Deficiency Results in Human and Murine Somatotrope Neurosecretory Hyperfunction

CONTEXT

The X-linked immunoglobulin superfamily, member 1 (IGSF1), gene is highly expressed in the hypothalamus and in pituitary cells of the POU1F1 lineage. Human loss-of-function mutations in IGSF1 cause central hypothyroidism, hypoprolactinemia, and macroorchidism. Additionally, most affected adults exhibit higher than average IGF-1 levels and anecdotal reports describe acromegaloid features in older subjects. However, somatotrope function has not yet been formally evaluated in this condition.

OBJECTIVE

We aimed to evaluate the role of IGSF1 in human and murine somatotrope function.

PATIENTS, DESIGN, AND SETTING

We evaluated 21 adult males harboring hemizygous IGSF1 loss-of-function mutations for features of GH excess, in an academic clinical setting.

MAIN OUTCOME MEASURES

We compared biochemical and tissue markers of GH excess in patients and controls, including 24-hour GH profile studies in 7 patients. Parallel studies were undertaken in male Igsf1-deficient mice and wild-type littermates.

RESULTS

IGSF1-deficient adult male patients demonstrated acromegaloid facial features with increased head circumference as well as increased finger soft-tissue thickness. Median serum IGF-1 concentrations were elevated, and 24-hour GH profile studies confirmed 2- to 3-fold increased median basal, pulsatile, and total GH secretion. Male Igsf1-deficient mice also demonstrated features of GH excess with increased lean mass, organ size, and skeletal dimensions and elevated mean circulating IGF-1 and pituitary GH levels.

CONCLUSIONS

We demonstrate somatotrope neurosecretory hyperfunction in IGSF1-deficient humans and mice. These observations define a hitherto uncharacterized role for IGSF1 in somatotropes and indicate that patients with IGSF1 mutations should be evaluated for long-term consequences of increased GH exposure.

Impaired LH surge amplitude in gonadotrope-specific progesterone receptor knockout mice

The progesterone receptor (PR, encoded by Pgr) plays essential roles in reproduction. Female mice lacking the PR are infertile, due to the loss of the protein's functions in the brain, ovary, and uterus. PR is also expressed in pituitary gonadotrope cells, but its specific role therein has not been assessed in vivo. We therefore generated gonadotrope-specific Pgr conditional knockout mice (cKO) using the Cre-LoxP system. Overall, both female and male cKO mice appeared phenotypically normal. cKO females displayed regular estrous cycles (vaginal cytology) and normal fertility (litter size and frequency). Reproductive organ weights were comparable between wild-type and cKO mice of both sexes, as were production and secretion of the gonadotropins, LH and FSH, with one exception. On the afternoon of proestrus, the amplitude of the LH surge was blunted in cKO females relative to controls. Contrary to predictions of earlier models, this did not appear to derive from impaired GnRH self-priming. Collectively, these data indicate that PR function in gonadotropes may be limited to regulation of LH surge amplitude in female mice via a currently unknown mechanism.

Comparing Methods for Measurement Error Detection in Serial 24-h Hormonal Data

Measurement errors commonly occur in 24-h hormonal data and may affect the outcomes of such studies. Measurement errors often appear as outliers in such data sets; however, no well-established method is available for their automatic detection. In this study, we aimed to compare performances of different methods for outlier detection in hormonal serial data. Hormones (glucose, insulin, thyroid-stimulating hormone, cortisol, and growth hormone) were measured in blood sampled every 10 min for 24 h in 38 participants of the Leiden Longevity Study. Four methods for detecting outliers were compared: (1) eyeballing, (2) Tukey’s fences, (3) stepwise approach, and (4) the expectation-maximization (EM) algorithm. Eyeballing detects outliers based on experts’ knowledge, and the stepwise approach incorporates physiological knowledge with a statistical algorithm. Tukey’s fences and the EM algorithm are data-driven methods, using interquartile range and a mathematical algorithm to identify the underlying distribution, respectively. The performance of the methods was evaluated based on the number of outliers detected and the change in statistical outcomes after removing detected outliers. Eyeballing resulted in the lowest number of outliers detected (1.0% of all data points), followed by Tukey’s fences (2.3%), the stepwise approach (2.7%), and the EM algorithm (11.0%). In all methods, the mean hormone levels did not change materially after removing outliers. However, their minima were affected by outlier removal. Although removing outliers affected the correlation between glucose and insulin on the individual level, when averaged over all participants, none of the 4 methods influenced the correlation. Based on our results, the EM algorithm is not recommended given the high number of outliers detected, even where data points are physiologically plausible. Since Tukey’s fences is not suitable for all types of data and eyeballing is time-consuming, we recommend the stepwise approach for outlier detection, which combines physiological knowledge and an automated process.

Modulating Effects of Progesterone on Spontaneous Nocturnal and Ghrelin-Induced GH Secretion in Postmenopausal Women

BACKGROUND

Oral administration of estradiol (E2) generally increases GH secretion in postmenopausal women. Oral administration of E2 is associated with a decrease in IGF-1, whereas parenteral or transdermally administered E2 may have no effect on GH. The effect of progesterone (P4) on GH secretion has rarely been studied. We hypothesized that moderately increased serum E2 levels stimulate GH and that P4 modulates E2-stimulated GH secretion.

STUDY DESIGN

Four parallel groups of randomly assigned postmenopausal women (n = 40). Treatments were saline placebo and oral placebo, saline placebo and oral micronized P4 (3 × 200 mg/d IM), E2 (5 mg IM) and oral placebo, and E2 IM and oral micronized P4. Outcome measures were overnight GH secretion (10 hours), stimulated (ghrelin, 0.3 µg/kg IV bolus) GH secretion, and CT-estimated visceral fat.

RESULTS

Intramuscular E2 administration did not alter nocturnal and ghrelin-stimulated GH secretion. Nocturnal GH secretion was not changed by P4 administration. However, P4 diminished ghrelin-stimulated pulsatile GH release with or without E2 (average, 7.20 ± 2.14 and 9.58 ± 1.97 µg/L/2 h, respectively; P = 0.045). Respective outcomes for mean GH concentrations and GH peak amplitudes were 0.97 ± 0.31 and 1.52 μg/L ± 0.29 (P = 0.025) and 2.76 ± 1.04 and 3.95 μg/L ± 0.90 (P = 0.031). Ghrelin-stimulated GH secretion correlated negatively with P4 concentration with or without correction for visceral fat area in the regression equation (R = 0.49, P = 0.04, β = -0.040 ± 0.016).

CONCLUSIONS

Low-range physiological E2 concentrations do not affect spontaneous or ghrelin-stimulated pulsatile GH secretion. Conversely, P4 inhibits ghrelin-stimulated GH secretion in a concentration-dependent fashion. The mechanistic aspects and physiological significance of natural P4's regulation of ghrelin-evoked GH secretion require further study.

SAT-440 Modulating Effects of Progesterone on Spontaneous and Ghrelin-Induced GH Secretion in Postmenopausal Women

Introduction. GH secretion is regulated by hypothalamic neuropeptides, sex steroids, and negative feedback signals across the lifespan. GH secretion in premenopausal women is higher than that in age-matched men, and can be amplified by oral estradiol (E2) in postmenopausal (PM) women. In contrast, the effect of progesterone (P) on GH secretion has rarely been studied in the presence or absence of estrogen repletion. Study design: Four parallel groups of PM women (total 40) received (1) im saline and oral placebo, (2) im saline and oral micronized P (3x200mg/day), (3) E2 im (5 mg) and oral placebo, and (4) E2 im and oral P, respectively. Study parameters were overnight (10 h) and ghrelin-stimulated (0.3 µg/kg) GH secretion. Results: Mean E2 levels increased to 88 and 99 pg/mL and mean P to 10.1 and 20.3 ng/dL. Whereas E2 at this dose did not change GH, P vs placebo reduced pulsatile GH secretion to 7.20±2.14 µg/L/10h vs 9.58±1.97 (P=0.045). Mean GH concentrations and burst amplitudes were respectively 0.97±0.31 and 1.52±0.29 (P=0.025), and 2.76±1.04 and 3.95±0.90 (P=0.031). Visceral fat area, determined by CT, was a strongly negative GH predictor of pulsatile GH secretion, R=-0.53 (P=0.001, β=-0.096±0.026). P levels correlated negatively with GH secretion, with or without AVF or E2 in the regression equation (e.g. pulsatile GH secretion: R=-0.69, P=0.005, β=0.693±0.246). P administration also reduced ghrelin-stimulated GH release (9.6±1.9 vs 7.2±2.1 µg/L, P=0.046). Restricting this analysis to estrogen-treated subjects, P decreased ghrelin-stimulated GH secretion from 10.7±2.7 to 2.6±1.3 µg/L/2 h (P=0.002) in a P concentration-dependent manner, viz., R=-0.49 (P=0.04, β=-0.040±0.018). Conclusions. Early follicular phase E2 levels did not impact spontaneous or ghrelin-stimulated GH concentrations, whereas P inhibited 10-h overnight and 2-h ghrelin-stimulated GH secretion a concentration-dependent fashion. Accordingly, the physiological significance of P on GH regulation requires further studies.

OR16-5 Feedback on LH in Testosterone-Clamped Men Depends on the Mode of Testosterone Administration and Body Composition

Context. Investigations of testosterone (T)-mediated feedback on LH secretion are few and contradictory. Discrepancies may reflect the choice of androgen, as well as dose, route and/or pattern (continuous vspulsatile) of administration. Moreover, for controlled T feedback studies, endogenous T secretion must be shut down and replaced by iv T infusion. Objective. The goal of this study was to quantify feedback in relation to the infused T pattern (pulsatile vs nonpulsatile) with the hypotheses that: 1) feedback by T pulses is less inhibitory, 2) T feedback operates partly at the pituitary level, 3) T feedback is controlled in part by body composition. Design. This was a placebo-controlled, blinded, and prospectively randomized crossover study comprising 16 men (age range 23-54 yr and BMI between 22.3-34.2 kg/m²). Subjects received ketoconazole (1600 mg over 22 h to block endogenous T secretion: serum T below 85 ng/dL) followed by pulsatile or continuous iv T addback (total T dose 5 mg/22 h). Cortisol inhibition was treated with low-dose dexamethasone. &nbsp; Setting. The study was performed in a Clinical Translational Research Unit. Interventions. Subjects underwent 14 h of blood sampling at 10-min intervals, starting at 0600 h. T was given continuously starting at 0900 h or as 45-min squarewave pulses every 90 min. To test pituitary feedback, a bolus iv injection of 33 ng/kg GnRH was given at 1630 h. Outcome measures. Log-transformed LH and T concentration ratios before and after GnRH administration. In addition, a four-parameter logistic regression between serum T concentration and LH secretion rate (calculated by deconvolution analysis) was used to independently estimate feedback of T on LH. Results. Despite higher T (total, bioavailable and free T) concentrations during pulsatile feedback, LH concentrations and secretion rates, whether driven by endogenous or exogenous GnRH, were similar to those during continuous infusion, indicating diminished pulsatile T feedback. This interpretation was corroborated by the right-shift (i.e. towards higher T concentrations) of the T-LH inhibitory dose-response curve. During continuous and pulsatile T infusion, LH concentrations and LH:T ratios depended positively on BMI to a similar extent before and after GnRH administration.&nbsp; Under both feedback regimens, basal but not pulsatile LH secretion correlated negatively with CT-estimated abdominal visceral fat mass. Age was not a significant covariate over the limited range explored. Conclusion. In summary, pulsatile T is less effective as a negative feedback signal on LH secretion than continuous T administration, as demonstrated by two independent methods. This difference in feedback strength was evident for exogenous GnRH-stimulated LH release as well, and thus occurs probably in part at the pituitary level, while not excluding additional hypothalamic involvement.

The 24-hour serum profiles of bone markers in healthy older men and women

The process of bone turnover displays variations over 24 h, with C-terminal cross-linked telopeptide of type 1 collagen (CTX) and osteocalcin exhibiting a nadir in the afternoon and a peak in the night. In contrast, N-terminal propeptide of type 1 procollagen (P1NP) did not display an apparent 24-hour rhythm. Other emerging novel biomarkers of bone, sclerostin and Dickkopf-related protein 1 (DKK1), are markers of osteocyte activity with limited data available regarding their 24-hour profiles. In this study, we aimed to extend available data on 24-hour profiles of CTX, osteocalcin, and P1NP and to assess the 24-hour profiles of sclerostin and DKK1 in healthy older men and women and to compare these between men and women. We measured these five bone markers in EDTA plasma collected every 4 h during 24 h in 37 healthy older men and women (range 52-76 years). Differences between time points were determined using repeated measures ANOVA and cosinor analyses were performed to determine circadian rhythmicity. The circadian rhythm of CTX was confirmed by the cosinor model, with women showing larger amplitude compared to men. Osteocalcin showed higher levels during nighttime compared to daytime in both men and women. For P1NP levels we observed a small but significant increase in the night in men. Sclerostin and DKK1 did not show a circadian rhythm, but sclerostin levels differed between time points. Because of the large intraindividual variation, DKK1 as measured in this study cannot be considered a reliable marker for diagnostic or research purposes. In conclusion, when measuring CTX, osteocalcin, P1NP, or sclerostin either in clinical practice or in a research setting, one should consider the 24-hour profiles of these bone markers.

Aromatized Estrogens Amplify Nocturnal Growth Hormone Secretion in Testosterone-Replaced Older Hypogonadal Men

CONTEXT

Testosterone (T) increases GH secretion in older men with a relative lack of T, in hypogonadal men of all ages, and in patients undergoing sex reassignment. The role of estradiol (E2) in men is less well defined.

OBJECTIVE

To assess the contribution of aromatization of T to spontaneous nocturnal and stimulated GH secretion.

PARTICIPANTS

Four groups of healthy older men (N = 74, age range 57 to 77 years) were studied. The gonadotropic axis was clamped with the gonadotropin-releasing hormone antagonist degarelix. Three groups received T and one group placebo addback. Two T-replaced groups were treated with anastrozole (an aromatase inhibitor) and either placebo or E2 addback.

MAIN OUTCOME MEASURES

Ten-minute GH concentration profiles were quantified by deconvolution analysis, after overnight (2200 to 0800 hours) sampling, and after combined IV injection of GHRH (0.3 µg/kg) and GHRH-2 (0.3 µg/kg) and withdrawal of a 2-hour somatostatin infusion (1 µg/kg/h).

RESULTS

E2 addback during aromatase inhibition increased basal (P = 0.046), pulsatile (P = 0.020), and total (P = 0.018) GH secretion by 60% to 70%. E2 did not potentiate GH secretory stimuli. Logarithmically transformed pulsatile GH secretion correlated strongly and positively with concurrent E2 concentrations overall (P = 0.028) and under anastrozole treatment (P = 0.005).

CONCLUSION

E2 administration in older men transdermally stimulates overnight pulsatile GH secretion. The exact site of E2 action cannot be ascertained from these experiments but may include hypothalamic loci involved in GH regulation, especially because GH secretagogue effects on somatotrope pituitary cells were not affected.

Feedback on LH in Testosterone-Clamped Men Depends on the Mode of Testosterone Administration and Body Composition

Context

Quantitative studies of the short-term feedback of testosterone (T) on luteinizing hormone (LH) secretion in healthy men are relatively rare. Such studies require the shutting down of endogenous T secretion and the imposition of experimentally controlled IV T addback.

Objective

To evaluate whether pulsatile and continuous T delivery confers equivalent negative feedback on LH secretion.

Design

This was a placebo-controlled, blinded, and prospectively randomized crossover study comprising 16 healthy men [age range 23 to 54 years and a body mass index (BMI) between 22.3 and 34.2 kg/m²]. Subjects received ketoconazole to block endogenous T secretion and received continuous or 90-minute pulses of IV T addback.

Setting

The study was performed in a Clinical Translational Research Unit.

Interventions

Subjects underwent 14 hours of blood sampling at 10-minute intervals, with a bolus IV injection of 33 ng/kg gonadotropin-releasing hormone (GnRH).

Main Outcome Measures

Log-transformed LH and T concentration ratios before and after GnRH administration.

Results

Despite higher T concentrations during pulsatile T feedback, LH concentrations and secretion rates, whether driven by endogenous or exogenous GnRH, were similar to those during continuous T infusion, indicating diminished pulsatile T feedback. Feedback correlated negatively with BMI. Under controlled T feedback, basal but not pulsatile LH secretion correlated negatively with CT-estimated visceral fat mass.

Conclusion

Feedback by pulsatile T delivery has diminished inhibitory strength compared with continuous infusion. Feedback is negatively correlated with BMI.

Estradiol Does Not Influence Lipid Measures and Inflammatory Markers in Testosterone-Clamped Healthy Men

Context

Experimentally controlled studies of estrogenic regulation of lipid measures and inflammatory cytokines in men are rare.

Objective

To delineate the effect of estradiol (E₂) on lipids and inflammatory markers.

Design

This was a placebo-controlled, single-masked, prospectively randomized study comprising experimentally degarelix-downregulated healthy men [n = 74; age 65 years (range, 57 to 77)] assigned to four treatment groups: (1) IM saline and oral placebo; (2) IM testosterone and oral placebo; (3) IM testosterone and oral anastrozole (aromatase inhibitor); and (4) IM testosterone, oral anastrozole, and transdermal E₂ for 22 (±1) days.

Results

Mean mass spectrometry–quantified serum E₂ concentrations ranged from 1.2 to 82 pg/mL in the four treatment groups. E₂ extremes did not alter total cholesterol, triglyceride, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein cholesterol (HDL-C) , non–HDL-C, apolipoprotein B, lipoprotein (a), IL-6, or high-sensitivity C-reactive protein (hsCRP) concentrations. Higher E₂ concentrations elevated both sex hormone-binding globulin and prolactin as positive controls. LDL cholesterol, adiponectin, and leptin were higher in hypogonadal subjects without testosterone or E₂ addback (P = 0.018, 0.039, and 0.023, respectively). Abdominal visceral fat area by CT (independent variable) correlated negatively with HDL-C (P = 0.017), and positively with triglycerides (P = 0.004), hsCRP (P = 0.005), and leptin (P < 0.0001).

Conclusion

In this placebo-controlled prospectively randomized study, wide variations in circulating E₂ did not influence lipid measures and inflammatory markers when testosterone concentrations were controlled experimentally. However, medically induced central hypogonadism in older men was accompanied by increased LDL cholesterol and metabolic cytokines, adiponectin and leptin. Abdominal visceral fat correlated strongly and positively with triglycerides, hsCRP, and leptin, but negatively with HDL.

Mutations in IRS4 are associated with central hypothyroidism

BACKGROUND

Four genetic causes of isolated congenital central hypothyroidism (CeH) have been identified, but many cases remain unexplained. We hypothesised the existence of other genetic causes of CeH with a Mendelian inheritance pattern.

METHODS

We performed exome sequencing in two families with unexplained isolated CeH and subsequently Sanger sequenced unrelated idiopathic CeH cases. We performed clinical and biochemical characterisation of the probands and carriers identified by family screening. We investigated IRS4 mRNA expression in human hypothalamus and pituitary tissue, and measured serum thyroid hormones and Trh and Tshb mRNA expression in hypothalamus and pituitary tissue of Irs4 knockout mice.

RESULTS

We found mutations in the insulin receptor substrate 4 (IRS4) gene in two pairs of brothers with CeH (one nonsense, one frameshift). Sequencing of IRS4 in 12 unrelated CeH cases negative for variants in known genes yielded three frameshift mutations (two novel) in three patients and one male sibling. All male carriers (n=8) had CeH with plasma free thyroxine concentrations below the reference interval. MRI of the hypothalamus and pituitary showed no structural abnormalities (n=12). 24-hour thyroid-stimulating hormone (TSH) secretion profiles in two adult male patients showed decreased basal, pulsatile and total TSH secretion. IRS4 mRNA was expressed in human hypothalamic nuclei, including the paraventricular nucleus, and in the pituitary gland. Female knockout mice showed decreased pituitary Tshb mRNA levels but had unchanged serum thyroid hormone concentrations.

CONCLUSIONS

Mutations in IRS4 are associated with isolated CeH in male carriers. As IRS4 is involved in leptin signalling, the phenotype may be related to disrupted leptin signalling.

Differential Effects of Estradiol and Progesterone on Cardiovascular Risk Factors in Postmenopausal Women

Context

Controlled, blinded studies of sex-hormone replacement in postmenopausal women using natural estradiol (E₂) and native progesterone (P) are few.

Objective

To delineate the effect of E₂ alone or with P on lipids and inflammatory markers.

Design

A placebo-controlled, double-masked, prospectively randomized study of 40 healthy, postmenopausal volunteers assigned to four treatment groups: placebo, intramuscular E₂, and/or micronized oral P for 23 (±2) days.

Results

Treatment with E₂ alone compared with placebo lowered total cholesterol (TC; P = 0.006), non-high-density lipoprotein cholesterol (nonHDL-C; P = 0.004), low-density lipoprotein cholesterol (LDL-C; P = 0.012), and apolipoprotein B (Apo B; P = 0.02) levels, and raised HDL-C levels (P = 0.03 vs the 3 other groups). Conversely, addition of P to E₂ reduced HDL-C levels (P = 0.015). Triglyceride concentrations manifested no effect on E₂ or P. High-sensitivity C-reactive protein (hsCRP) level was highest in women with E₂ and P replacement (P = 0.018 vs placebo). Leptin and IL-6 concentrations did not vary. P treatment decreased adiponectin levels (P = 0.019). Serum E₂ levels correlated linearly with TC, LDL-C, nonHDL-C, Apo B (all negatively), and SHBG (positively) concentrations. P level correlated negatively with TC (P = 0.029), HDL-C (P = 0.002), and adiponectin (P = 0.002) levels.

Conclusion

In this study, there were individual and interactive effects of E₂ and P on key lipids in postmenopausal individuals.

How are growth hormone and insulin-like growth factor-1 reported as markers for drug effectiveness in clinical acromegaly research? A comprehensive methodologic review

OBJECTIVE

In rare disease research, most randomized prospective clinical trials can only use limited number of patients and are comprised of highly heterogeneous populations. Therefore, it is crucial to report the results in such a manner that it allows for comparison of treatment effectiveness and biochemical control between studies. The aim of this review was to investigate the current methods that are being applied to measure and report growth hormone (GH) and insulin-like growth factor-1 (IGF-1) as markers for drug effectiveness in clinical acromegaly research.

SEARCH STRATEGY

A systematic search of recent prospective and retrospective studies, published between 2012 and 2017, that studied the effects of somatostatin analogues or dopamine agonists in acromegaly patients was performed. The markers of interest were GH, IGF-1, and the suppression of GH after an oral glucose tolerance test (OGTT). Additionally, the use of pharmacokinetic (PK) measurements in these studies was analyzed. The sampling design, cut-off for biochemical control, reported units, and used summary statistics were summarized.

RESULTS

A total of 49 articles were selected out of the 263 screened abstracts. IGF-1 concentrations were measured in all 49 studies, GH in 45 studies, and an OGTT was performed in 11 studies. A wide range of different cut-off values and sampling designs were used to determine biochemical control in acromegaly patients. The summary statistics were reported in various ways, with the percentage of biochemical control most frequently used. Nine studies sampled the PK at one or more time points. Non-compartmental analyses were commonly performed on the available PK data.

CONCLUSIONS

The way GH and IGF-1 are measured and reported in acromegaly research varies considerably. A consensus on how to report study results would enable better comparisons between studies, thereby improving evidence based decision making to optimize treatment in acromegaly.

Effects of Toremifene, a Selective Estrogen Receptor Modulator, on Spontaneous and Stimulated GH Secretion, IGF-I, and IGF-Binding Proteins in Healthy Elderly Subjects

Context:

Estrogens amplify spontaneous and stimulated growth hormone (GH) secretion, whereas they diminish GH-dependent insulin-like growth factor (IGF)-I in a dose-dependent manner. Selective estrogen receptor modulators (SERMs), including tamoxifen and toremifene, are widely adjunctively used in breast and prostate cancer. Although some endocrine effects of tamoxifen are known, few data are available for toremifene.

Objective:

To explore sex-dependent effects of toremifene on spontaneous 10-hour overnight GH secretion, followed by GH-releasing hormone–ghrelin stimulation. Additionally, effects on IGF-I, its binding proteins, and sex hormone–binding globulin (SHBG) were quantified.

Participants and Design:

Twenty men and 20 women, within an allowable age range of 50 to 80 years, volunteered for this double-blind, placebo-controlled prospective crossover study. Ten-minute blood sampling was done for 10 hours overnight and then for 2 hours after combined GH-releasing hormone–ghrelin injection.

Main Outcome Measures:

Pulsatile GH and stimulated GH secretion, and fasting levels of IGF-I, IGF-binding protein (IGFBP)1, IGFBP3, and SHBG.

Results:

Toremifene did not enhance pulsatile or stimulated GH secretion, but decreased IGF-I by 20% in men and women. IGFBP3 was unchanged, whereas while IGFBP1 and SHBG increased in both sexes to a similar extent.

Conclusions:

The expected rise in spontaneous and stimulated GH secretion under the diminished negative feedback restraint of powered IGF-I favors a central inhibitory antiestrogenic effect of toremifene. Estrogenic effects of toremifene on the liver were present, as evidenced by increased IGFBP1 and SHBG levels. Men and women responded to this SERM comparably.

Impact of age, sex and body mass index on cortisol secretion in 143 healthy adults

CONTEXT

Studies on 24-h cortisol secretion are rare. The impact of sex, age and adiposity on cortisol levels, often restricted to one or a few samples, are well recognized, but conflicting.

OBJECTIVE

To investigate cortisol dynamics in 143 healthy men and women, spanning 7 decades and with a 2-fold body mass index (BMI) range with different analytic tools.

SETTING

Clinical Research Unit.

DESIGN

Cortisol concentrations in 10-min samples collected for 24 h. Outcomes were mean levels, deconvolution parameters, approximate entropy (ApEn, regularity statistic) and 24-h rhythms.

RESULTS

Total 24-h cortisol secretion rates estimated by deconvolution analysis were sex, age and BMI independent. Mean 24-h cortisol concentrations were lower in premenopausal women than those in men of comparable age (176 ± 8.2 vs 217 ± 9.4 nmol/L, P = 0.02), but not in subjects older than 50 years. This was due to lower daytime levels in women, albeit similar in the quiescent overnight period. Aging increased mean cortisol by 10 nmol/L per decade during the quiescent secretory phase and advanced the acrophase of the diurnal rhythm by 24 min/decade. However, total 24-h cortisol secretion rates estimated by deconvolution analysis were sex, age and BMI independent. ApEn of 24-h profiles was higher (more random) in premenopausal women than those in men (1.048 ± 0.025 vs 0.933 ± 0.023, P = 0.001), but not in subjects older than 50 years. ApEn peaked during the daytime.

CONCLUSION

Sex and age jointly determine the 24-h cortisol secretory profile. Sex effects are largely restricted to age <50 years, whereas age effects elevate concentrations in the late evening and early night and advance the timing of the peak diurnal rhythm.

Regulatory aspects of the human hypothalamus-pituitary-thyroid axis

Thyroid hormones are essential for growth, differentiation and metabolism during prenatal and postnatal life. The hypothalamus-pituitary-thyroid (HPT)-axis is optimized for these actions. Knowledge of this hormonal axis is derived from decades of experiments in animals and man, and more recently from spontaneous mutations in man and constructed mutations in mice. This review examines the HPT-axis in relation to 24 h TSH profiles in men in various physiological and pathophysiological conditions, including obesity, age, longevity, and primary as well as central hypothyroidism. Hormone rhythms can be analyzed by quantitative methods, e.g. operator-independent deconvolution, approximate entropy and fitting the 24-h component by Cosinor analysis or related procedures. These approaches have identified some of the regulatory components in (patho)physiological conditions.

Regulation of Pulsatile and Entropic ACTH Secretion Under Fixed Exogenous Secretagogue Clamps

BACKGROUND

Adrenocorticotropic hormone (ACTH) secretion is controlled by unobservable hypothalamic corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) pulses. Clamping exogenous CRH or AVP input could allow indirect quantification of the impact of the endogenous heterotypic hormone.

METHODS

We conducted a randomized, double-blind, placebo-controlled, crossover study in 28 healthy adults (16 men). Volunteers underwent a sex-steroid clamp and a cortisol clamp. ACTH was measured over 10 hours by 10-minute sampling during each of four randomized intravenous (IV) secretagogue clamps (i.e., continuous IV CRH, AVP, both peptides, or saline). Desensitization was tested by bolus injection of the noninfused peptide.

RESULTS

Mean ± standard error of the mean 10-hour ACTH concentrations (ng/L) in the sex-combined analysis were: saline, 32 ± 4.6; AVP, 29 ± 4.6; CRH, 67 ± 6.2; and CRH-AVP, 67 ± 8.8 (any CRH vs AVP or saline, P < 0.0001). CRH and AVP increased approximate entropy (relative randomness) of ACTH release (P < 0.0001). Bolus AVP injection after CRH infusion yielded a 2.5-hour ACTH concentration of 46 ± 4.3, exceeding that seen after bolus CRH or saline injection (26 ± 3.3 and 24 ± 3.6, respectively; P = 0.002 and 0.001). Sex hormone clamps did not influence ACTH levels.

CONCLUSIONS

A CRH, but not AVP, clamp yields sustained pulsatile ACTH secretion with high ACTH secretory-burst mass and randomness. After 10-hour CRH infusion, bolus AVP but not CRH, evoked marked ACTH release, likely caused by heterotypic sensitization of corticotropes by CRH. Similar interactions might underlie chronic stress states.

Enhanced Coupling Within Gonadotropic and Adrenocorticotropic Axes by Moderate Exercise in Healthy Men

CONTEXT

Exercise elicits incompletely defined adaptations of metabolic and endocrine milieu, including the gonadotropic and corticotropic axes.

OBJECTIVE

To quantify the impact of acute exercise on coordinate luteinizing hormone (LH) and testosterone (T) and adrenocorticotropic hormone (ACTH) and cortisol secretion in healthy men in relation to age.

PARTICIPANTS AND DESIGN

Prospectively randomized, within-subject crossover study in 23 men aged 19 to 77 years old. Subjects underwent rest and 30 minutes of mixed exercise at 65% of maximal aerobic capacity with 10-minute blood sampling between 7:00 am and 1:00 pm, 2 weeks apart.

MAIN OUTCOME MEASURES

Incremental changes in LH, T, ACTH, and cortisol concentrations, the feedforward and feedback strength between exercise and rest, quantified by approximate entropy (ApEn), and bihormonal synchrony, quantitated by cross-ApEn.

RESULTS

Mean hourly exercise-minus-rest LH and ACTH increments increased from -0.055 ± 0.187 to 0.755 ± 0.245 IU/L (P = 0.003) and from 2.9 ± 2.2 to 71.2 ± 16.1 ng/L (P < 0.0001), respectively, during exercise. T and cortisol increments increased concurrently from -9.6 ± 16.7 to 47.6 ± 17.1 ng/dL (P < 0.0001) and 0.45 ± 0.76 to 7.27 ± 0.64 µg/dL (P < 0.0001), respectively. During exercise, feedforward and feedback LH-T and ACTH-cortisol cross-ApEn decreased markedly quantifying enhanced hormonal coupling.

CONCLUSIONS

Acute moderate mixed exercise in healthy men rapidly enhances feedforward LH-T and ACTH-cortisol coordination and reciprocal feedback within the gonadotropic and corticotropic axes. In principle, enhancement of both LH-T and ACTH-cortisol secretory synchrony by exercise could reflect augmented coupling between brain-testicular and brain-adrenal neural outflow.

Growth hormone secretion is diminished and tightly controlled in humans enriched for familial longevity

Reduced growth hormone (GH) signaling has been consistently associated with increased health and lifespan in various mouse models. Here, we assessed GH secretion and its control in relation with human familial longevity. We frequently sampled blood over 24 h in 19 middle‐aged offspring of long‐living families from the Leiden Longevity Study together with 18 of their partners as controls. Circulating GH concentrations were measured every 10 min and insulin‐like growth factor 1 (IGF‐1) and insulin‐like growth factor binding protein 3 (IGFBP3) every 4 h. Using deconvolution analysis, we found that 24‐h total GH secretion was 28% lower (P = 0.04) in offspring [172 (128–216) mU L⁻¹] compared with controls [238 (193–284) mU L⁻¹]. We used approximate entropy (ApEn) to quantify the strength of feedback/feedforward control of GH secretion. ApEn was lower (P = 0.001) in offspring [0.45 (0.39–0.53)] compared with controls [0.66 (0.56–0.77)], indicating tighter control of GH secretion. No significant differences were observed in circulating levels of IGF‐1 and IGFBP3 between offspring and controls. In conclusion, GH secretion in human familial longevity is characterized by diminished secretion rate and more tight control. These data imply that the highly conserved GH signaling pathway, which has been linked to longevity in animal models, is also associated with human longevity.

Pulsatile Cortisol Feedback on ACTH Secretion Is Mediated by the Glucocorticoid Receptor and Modulated by Gender

CONTEXT

Factors that regulate physiological feedback by pulses of glucocorticoids on the hypothalamic-pituitary unit are sparsely defined in humans in relation to gluco- or mineralocorticoid receptor pathways, gender, age, and the sex steroid milieu.

OBJECTIVE

The objective of the study was to test (the clinical hypothesis) that glucocorticoid (GR) and mineralocorticoid (MR) receptor-selective mechanisms differentially govern pulsatile cortisol-dependent negative feedback on ACTH output (by the hypothalamo-pituitary unit) in men and women studied under experimentally defined T and estradiol depletion and repletion, respectively.

SETTING

The study was conducted at the Mayo Center for Translational Science Activities.

SUBJECTS

Healthy middle-aged men (n = 16) and women (n = 25) participated in the study.

INTERVENTIONS

This was a randomized, prospective, double-blind, placebo- and saline-controlled study of pulsatile cortisol infusions in low cortisol-clamped volunteers with and without eplerenone (MR blocker) and mifepristone (GR blocker) administration under a low and normal T and estradiol clamp. During frequent sampling, a bolus of CRH-arginine vasopressin was infused to assess corticotrope responsiveness. Analytical Methods and Outcomes: Deconvolution and approximate entropy of ACTH profiles were measured.

RESULTS

Infusion of cortisol (but not saline) pulses diminished ACTH secretion. The GR antagonist, mifepristone, interfered with negative feedback on both ACTH burst mass and secretion regularity. Eplerenone, an MR antagonist, exerted no detectable effect on the same parameters. Despite feedback imposition, CRH-arginine vasopressin-stimulated ACTH secretion was also increased by mifepristone and not by eplerenone. Withdrawal vs addback of sex steroids had no effect on ACTH secretion parameters. Nonetheless, ACTH secretion was greater (P = .006) and more regular (P = .004) in men than women.

CONCLUSION

Pulsatile cortisol feedback on ACTH secretion in this paradigm is mediated by the glucocorticoid receptor, in part acting at the level of the pituitary, and influenced by sex.

Optimizing Blood Sampling Protocols in Patients With Acromegaly for the Estimation of Growth Hormone Secretion

CONTEXT

Optimal blood sampling schemas of GH for the estimation of the 24-hour secretion rate have not been established in acromegalic patients.

OBJECTIVE

By censoring available 24-hour GH serum profiles, we investigated the reliability of such simplified schemas. Design, Subjects, and Methods: We used 24-hour serum GH concentration profiles obtained with 10-minute sampling in a large cohort of healthy subjects (n = 130; mean age, 42; range, 18-77 years) and acromegalic patients (n = 87; mean age, 48; range 18-72 years). Patient categories were active disease, surgically cured, and somatostatin analog-treated individuals. The regression coefficients of determination (R(2)) and the linear slopes (β) between 24-hour secretion rates or mean concentrations (144 samples) on the one hand and mean values with less frequent sampling on the other, decreased in controls and in patients a short (1-2 weeks) or long (2-5 years) time after successful surgery. By contrast, the regression parameters remained essentially unchanged in patients with active acromegaly and those under GH suppressive treatment. Excellent correlations (R(2) ≥ 0.90) without GH underestimation existed between mean GH of daytime profiles and mean GH of 24-hour profiles and GH secretion rates estimated by deconvolution in patients with active acromegaly and patients treated with somatostatin analogs.

CONCLUSION

Simplified sampling schemes, particularly a day profile, can be used for the estimation of GH secretion in patients with active acromegaly and under medical treatment. However, in healthy controls and patients after successful surgery, prolonged and frequent sampling schemes, at least at 2-hour intervals, reliably reflect 24-hour secretion.

Proinflammatory Cytokine Infusion Attenuates LH's Feedforward on Testosterone Secretion: Modulation by Age

CONTEXT

In the experimental animal, inflammatory signals quench LH's feedforward drive of testosterone (T) secretion and appear to impair GnRH-LH output. The degree to which such suppressive effects operate in the human is not known.

OBJECTIVE

To test the hypothesis that IL-2 impairs LH's feedforward drive on T and T's feedback inhibition of LH secretion in healthy men.

SETTING

Mayo Center for Translational Science Activities.

PATIENTS OR OTHER PARTICIPANTS

A total of 35 healthy men, 17 young and 18 older.

INTERVENTIONS

Randomized prospective double-blind saline-controlled study of IL-2 infusion in 2 doses with concurrent 10-minute blood sampling for 24 hours.

MAIN OUTCOME MEASURES

Deconvolution analysis of LH and T secretion.

RESULTS

After saline injection, older compared with young men exhibited reduced LH feedforward drive on T secretion (P < .001), and decreased T feedback inhibition of LH secretion (P < .01). After IL-2 injection, LH's feedforward onto T secretion declined markedly especially in young subjects (P < .001). Concomitantly, IL-2 potentiated T's proportional feedback on LH secretion especially in older volunteers.

CONCLUSION

This investigation confirms combined feedforward and feedback deficits in older relative to young men given saline and demonstrates 1) joint mechanisms by which IL-2 enforces biochemical hypogonadism, viz, combined feedforward block and feedback amplification; and 2) unequal absolute inhibition of T and LH secretion by IL-2 in young and older men. These outcomes establish that the male gonadal axis is susceptible to dual-site suppression by a prototypic inflammatory mediator. Thus, we postulate that selected ILs might also enforce male hypogonadism in chronic systemic inflammation.

Growth Hormone Dynamics in Healthy Adults Are Related to Age and Sex and Strongly Dependent on Body Mass Index

BACKGROUND

Studies on 24-hour growth hormone (GH) secretion are rare. The influences of sex, age, and adiposity are well recognized but generally derived from specific, selected subject groups, not spanning sexes, many age decades, and a range of body weights.

OBJECTIVE

Our goal was to investigate GH dynamics in a group of 130 healthy adult subjects, both men and women, across 5 age decades as well as a 2.5-fold range of body mass index (BMI) values.

METHODS

GH was measured by a sensitive immunofluorometric assay. Secretion parameters were quantified by automated deconvolution and relative pattern randomness by approximate entropy (ApEn).

RESULTS

The median age was 40 years (range 20-77). The median BMI was 26 (range 18.3-49.8). Pulsatile 24-hour GH secretion was negatively correlated with age (p = 0.002) and BMI (p < 0.0001). Basal GH secretion negatively correlated with BMI (p = 0.003) but not with age. The sex- dependent GH secretion (greater in women) was no longer detectable after 50 years of age. Insulin-like growth factor (IGF)-1 levels were lower in women over 50 years of age compared with men of a similar age. ApEn showed an age-related increase in both sexes and was higher in premenopausal and postmenopausal women than in men of comparable age (p < 0.0001). A single fasting GH measurement is not informative of 24-hour GH secretion.

CONCLUSIONS

BMI dominates the negative regulation of 24-hour GH secretion across 5 decades of age in this up till now largest cohort of healthy adults who underwent 24-hour blood sampling. Sex also impacts GH secretion before the age of 50 years as well as its regularity at all ages. Differences in serum IGF-1 partly depend on the pre- or postmenopausal state. Finally, a single GH measurement is not informative of 24-hour GH secretion.

Familial Longevity Is Not Associated with Major Differences in the Hypothalamic-Pituitary-Gonadal Axis in Healthy Middle-Aged Men

CONTEXT

A trade-off between fertility and longevity possibly exists. The association of the male hypothalamic-pituitary-gonadal (HPG) axis with familial longevity has not yet been investigated.

OBJECTIVE

To study 24-h hormone concentration profiles of the HPG axis in men enriched for familial longevity and controls.

DESIGN

We frequently sampled blood over 24 h in 10 healthy middle-aged male offspring of nonagenarian participants from the Leiden Longevity Study together with 10 male age-matched controls. Individual 24-h luteinizing hormone (LH) and testosterone concentration profiles were analyzed by deconvolution analyses to estimate secretion parameters. Furthermore, the temporal relationship between LH and testosterone was assessed by cross-correlation analysis. We used (cross-)approximate entropy to quantify the strength of feedback and/or feedforward control of LH and testosterone secretion.

RESULTS

Mean [95% confidence interval (CI)] total LH secretion of the offspring was 212 (156-268) U/L/24 h, which did not differ significantly (p = 0.51) from the total LH secretion of controls [186 (130-242) U/L/24 h]. Likewise, mean (95% CI) total testosterone secretion of the offspring [806 (671-941) nmol/L/24 h] and controls [811 (676-947) nmol/L/24 h] were similar (p = 0.95). Other parameters of LH and testosterone secretion were also not significantly different between offspring and controls. The temporal relationship between LH and testosterone and the strength of feedforward/feedback regulation within the HPG axis were similar between offspring of long-lived families and controls.

CONCLUSION

This relatively small study suggests that in healthy male middle-aged participants, familial longevity is not associated with major differences in the HPG axis. Selection on both fertility and health may in part explain the results.

Pituitary Hormone Secretion Profiles in IGSF1 Deficiency Syndrome

BACKGROUND

Loss-of-function mutations in immunoglobulin superfamily member 1 (IGSF1) cause an X-linked syndrome of central hypothyroidism, macroorchidism, delayed pubertal testosterone rise, variable prolactin deficiency and variable partial GH deficiency in childhood. The clinical features and gene expression pattern suggest a pivotal role for IGSF1 in the pituitary, but detailed knowledge on pituitary hormone secretion in this syndrome is lacking. We therefore aimed to study the 24-hour pituitary hormone secretion in male patients with IGSF1 deficiency.

METHODS

We collected blood samples every 10 min for 24 h in eight adult male IGSF1-deficient patients and measured circulating TSH, prolactin and gonadotropins. Deconvolution, modified cosinor and approximate entropy analyses were applied to quantify secretion rates, diurnal rhythmicity and regularity of hormone release. Results were compared to healthy controls matched for age and body mass index.

RESULTS

Compared to healthy controls, IGSF1-deficient patients showed decreased pulsatile secretion of TSH with decreased disorderliness and reduced diurnal variation. Basal and pulsatile secretion of FSH was increased by over 200%, while LH secretion did not differ from healthy controls. We observed a bimodal distribution of prolactin secretion, i.e. severe deficiency in three and increased basal and total secretion in the other five patients.

CONCLUSION

The altered TSH secretion pattern is consistent with the previously hypothesized defect in thyrotropin-releasing hormone signaling in IGSF1 deficiency. However, the phenotype is more extensive and includes increased FSH secretion without altered LH secretion as well as either undetectable or increased prolactin secretion.

Diagnosis, treatment and clinical perspectives of acromegaly

Acromegaly is an insidious disease of the pituitary caused by a growth hormone-secreting adenoma. Generally, the diagnosis is made rather late in the course of the disease. Currently, acromegaly can be cured in about half of the patients with the disease by expert surgery. The remainder of non-surgically cured patients often can be effectively treated with somatostatin analogs; either with the new generation of dopaminergic drugs or with Pegvisomant, a GH-receptor blocking agent. However, at the time of diagnosis many patients suffer from serious comorbidities, including hypertension, heart disease, arthrosis, sleep apnea and diabetes mellitus. Recent reports have shown that mortality risk can be normalized. Nevertheless, all efforts should be undertaken to treat comorbidities. New strategies for surgery and medical treatment are discussed.

Familial Longevity Is Associated With Higher TSH Secretion and Strong TSH-fT3 Relationship

CONTEXT

Longevity is associated with changes in circulating levels of thyroid hormone (TH) and/or TSH in animals and humans, but underlying mechanisms remain elusive.

OBJECTIVE

We explored in 38 offspring of nonagenarian participants from the Leiden Longevity Study, who are enriched for longevity and in their partners, ultradian and circadian rhythmicity of TSH, temporal relationship, and feedback and forward interplay between TSH and TH.

METHODS

We collected blood samples every 10 minutes for 24 hours for TSH and TH profiles. We used a deconvolution analysis to estimate basal (nonpulsatile), pulsatile, and other secretion parameters to characterize ultradian rhythmicity and locally weighted polynomial regression of TSH to assess circadian rhythmicity. A cross-correlation analysis was used to investigate the temporal relationship between TSH and TH and cross-approximate entropy to assess feedback and forward interplay between TSH and TH.

RESULTS

Compared with partners, offspring displayed higher mean (95% confidence interval [CI]) basal TSH secretion (34.3 [95% CI 27.2-43.1] mU/L per 24 hours vs 18.5 [95% CI 14.4-23.7] mU/L per 24 hours, P = .001) but no differences in ultradian or circadian properties of TSH. The temporal relationship between TSH and free T3 at zero delay was higher in offspring (0.48 ± 0.2) compared with partners (0.26 ± 0.4) (P = .05), but the feedback and forward interplay between TSH and TH did not differ.

CONCLUSIONS

Familial longevity is associated with increased basal TSH secretion and a strong temporal relationship between TSH and free T3 but not with differences in ultradian or circadian TSH rhythmicity or feedback and forward interplay between TSH and TH.