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.

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.

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.

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.

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.

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.

Clinical factors involved in the recurrence of pituitary adenomas after surgical remission: a structured review and meta-analysis.

To study the currently available data of recurrence rates of functioning and nonfunctioning pituitary adenomas following surgical cure and to analyze associated predisposing factors, which are not well established. A systematic literature search was conducted using Medline, Embase, Web of Science and the Cochran Library for studies reporting data on recurrence of pituitary adenoma after surgery, in nonfunctioning adenoma (NF), prolactinoma (PRL) acromegaly (ACRO) and Cushing's disease (CUSH). Of 557 initially retrieved potential relevant studies 143 were selected. Recurrence in NFA was defined as reappearance of tumor on MRI or CT. Increase of hormone levels above normal limits as set by the authors after initial remission was used to indicate recurrence in the functioning tumor types. Remission percentage was lowest in NFA compared with other tumor types (P < 0.001). Surgery-related hypopituitarism was more frequent in CUSH than in the other tumors (P < 0.001). Recurrence, expressed as percentage of the cured population or as ratio of recurrence and total patient years of follow-up was highest in PRL (P < 0.001). The remission percentage did not improve over 3 decades of publications, but there was a modest decrease in recurrence rate (P = 0.04). Recurrences peaked between 1 and 5 years after surgery. Most of the studies with a sufficient number of recurrences did not apply multivariate statistics, and mentioned at best associated factors. Age, gender, tumor size and invasion were generally unrelated to recurrence. For functioning adenomas a low postoperative hormone concentration was a prognostically favorable factor. In NFA no specific factor predicted recurrence. Recurrence rate differs between pituitary adenomas, being highest in patients with prolactinoma, with the highest incidence of recurrence between 1 and 5 years after surgery in all adenomas. Patients with NFA have a lower chance of remission than patients with functioning adenomas. The postoperative basal hormone level is the most important predictor for recurrence in functioning adenomas, while in NFA no single convincing factor could be identified.

The use of an early postoperative CRH test to assess adrenal function after transsphenoidal surgery for pituitary adenomas.

Transsphenoidal surgery (TS) is the treatment of choice for many pituitary tumors. Because TS may cause pituitary insufficiency in some of these patients, early postoperative assessment of pituitary function is essential for appropriate endocrine management. The aim of our study was to evaluate the clinical relevance of the CRH-stimulation test in assessing postoperative pituitary-adrenal function. We performed a retrospective analysis of 144 patients treated by TS between January 1990 and November 2009, in whom a CRH-test and a second stimulation test was performed to assess adrenal function during follow-up. Patients with Cushing's disease were excluded. Hydrocortisone substitution was started if peak cortisol levels were <550 nmol/L. The cortisol response was insufficient in 42(29%) and sufficient in 102 patients at the postoperative CRH-test. Thirteen of 42(30%) demonstrated a normal cortisol response during a second cortisol stimulation test. In 75 of the 102 patients with a sufficient response to CRH repeat testing revealed an insufficient cortisol response in 14 patients (14%). All but one had concomitant pituitary hormone deficits. There were no cases of adrenal crises during follow-up. Additional pituitary insufficiency was significantly more present (P < 0.001) in the group of patients with an abnormal response to CRH directly after surgery. In this study a substitution strategy of hydrocortisone guided by the postoperative cortisol response to CRH appeared safe and did not result in any case of adrenal crises. However, the early postoperative CRH-test does not reliably predict adrenal function after TS for pituitary adenomas in all patients and retesting is mandatory.

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 sodium oxybate on growth hormone secretion in narcolepsy patients and healthy controls.

Hypocretin deficiency causes narcolepsy and may affect neuroendocrine systems and body composition. Additionally, growth hormone (GH) alterations my influence weight in narcolepsy. Symptoms can be treated effectively with sodium oxybate (SXB; γ-hydroxybutyrate) in many patients. This study compared growth hormone secretion in patients and matched controls and established the effect of SXB administration on GH and sleep in both groups. Eight male hypocretin-deficient patients with narcolepsy and cataplexy and eight controls matched for sex, age, BMI, waist-to-hip ratio, and fat percentage were enrolled. Blood was sampled before and on the 5th day of SXB administration. SXB was taken two times 3 g/night for 5 consecutive nights. Both groups underwent 24-h blood sampling at 10-min intervals for measurement of GH concentrations. The GH concentration time series were analyzed with AutoDecon and approximate entropy (ApEn). Basal and pulsatile GH secretion, pulse regularity, and frequency, as well as ApEn values, were similar in patients and controls. Administration of SXB caused a significant increase in total 24-h GH secretion rate in narcolepsy patients, but not in controls. After SXB, slow-wave sleep (SWS) and, importantly, the cross-correlation between GH levels and SWS more than doubled in both groups. In conclusion, SXB leads to a consistent increase in nocturnal GH secretion and strengthens the temporal relation between GH secretion and SWS. These data suggest that SXB may alter somatotropic tone in addition to its consolidating effect on nighttime sleep in narcolepsy. This could explain the suggested nonsleep effects of SXB, including body weight reduction.

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.

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.

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.

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.

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.

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.

Endocrine pulse identification using penalized methods and a minimum set of assumptions.

The detection of hormone secretion episodes is important for understanding normal and abnormal endocrine functioning, but pulse identification from hormones measured with short interval sampling is challenging. Furthermore, to obtain useable results, the model underlying hormone secretion and clearance must be augmented with restrictions based on biologically acceptable assumptions. Here, using the assumption that there are only a few time points at which a hormone is secreted, we used a modern penalized nonlinear least-squares setup to select the number of secretion events. We did not assume a particular shape or frequency distribution for the secretion pulses. Our pulse identfication method, VisPulse, worked well with luteinizing hormone (LH), cortisol, growth hormone, or testosterone. In particular, applying our modeling strategy to previous LH data revealed a good correlation between the modeled and measured LH hormone concentrations, the estimated secretion pattern was sparse, and the small and structureless residuals indicated a proper model with a good fit. We benchmarked our method to AutoDecon, a commonly used hormone secretion model, and performed releasing hormone infusion experiments. The results of these experiments confirmed that our method is accurate and outperforms AutoDecon, especially for detecting silent periods and small secretion events, suggesting a high-secretion event resolution. Method validation using (releasing hormone) infusion data revealed sensitivities and selectivities of 0.88 and 0.95 and of 0.69 and 0.91 for VisPulse and AutoDecon, respectively.

Dose-response downregulation within the span of single interpulse intervals.

Pituitary ACTH drives adrenal glucocorticoid (cortisol) pulses via a time-delayed asymptotic dose-response process. To test the postulate that ACTH stimulates cortisol secretion dynamically (unequally during the initiation and termination of a cortisol secretory burst), a mathematical formalism was developed in which dose-response hysteretic shifts were allowed, but not required, within the time evolution of ACTH-cortisol pulse pairs. A dual-waveform deconvolution model was used to quantify cortisol secretion rates and reconstruct ACTH concentration profiles in 28 healthy adults previously sampled every 10 min for 24 h in the unstressed state (8,120 measurements). ACTH concentration-cortisol secretion dose-response functions were then estimated in each subject 1) without hysteresis (base model) and with allowances for possible hysteresis in 2) ACTH potency, 3) adrenal sensitivity, and 4) ACTH efficacy. Model residual error was 40% lower in the potency and sensitivity models and 20% lower in the efficacy model than in the base model (P < 0.001). Mean time shifts for inferable hysteretic inflection were model-independent, i.e., grand mean (95% confidence interval) 22 (12-39) min after the onset of a cortisol secretory burst. Half-maximally effective ACTH concentrations (EC(50)) differed before and after hysteretic inflection within individual pulses: 1) 9.4 and 54 ng/l in the potency model (P < 0.001) and 2) 8.9 and 123 ng/l in the sensitivity model (P < 0.001) compared with 16 ng/l in the no-hysteresis model (P < 0.001). In the efficacy-shift model, estimated maximal ACTH drive varied by 17-fold within cortisol secretory bursts (from 22 to 1.3 nmol.l(-1).min cortisol secretion(-1), P < 0.001). The collective results introduce the basis for modeling the dynamics of rapid, reversible physiological downregulation within the span of single interpulse intervals in vivo. This construct should have utility in parsing mechanisms of physiological regulation in other integrative systems.

Altered thyrotropic and lactotropic axes regulation in Huntington's disease.

BACKGROUND: Recently, a loss of hypothalamic dopamine D(2) receptors was demonstrated in Huntington's disease (HD). Activation of dopamine D(2) receptors is known to inhibit the function of both thyrotropic and lactotropic axes. OBJECTIVE: To assess whether the activity of the thyrotropic and lactotropic axes is disturbed in patients with HD, contributing to symptoms such as unintended weight loss. PARTICIPANTS AND METHODS: In nine medication-free patients with early-stage HD (six men, three women) and nine age-, sex- and body mass index-matched controls, we measured serum levels of thyroid-stimulating hormone (TSH) and prolactin (men only) every 10 min for 24 h. Multiparameter auto-deconvolution and approximate entropy analysis were applied to quantify basal, pulsatile and total TSH and prolactin secretion rates as well as the regularity of hormone release. RESULTS: Compared with controls, TSH and prolactin secretion tended to be slightly, but not significantly, higher in patients with HD (TSH: 1.13 ± 0.14 vs 0.91 ± 0.19 mU/l, P = 0.40; prolactin: 213 ± 18 vs 209 ± 11 pmol/l, P = 0.87). However, in patients with HD, total T(3) levels were significantly higher (1.60 ± 0.05 vs 1.35 ± 0.09, P = 0.045), while T(4) levels tended to be higher as well (91.9 ± 3.9 vs 81.3 ± 3.1, P = 0.085). Prolactin secretion was significantly more irregular in patients with HD (Approximate entropy (ApEn): 1.06 ± 0.08 vs 0.80 ± 0.09, P = 0.037). Total T(3) levels were negatively associated with motor impairment (r = -0.72, P = 0.030), whereas increasing free T(4) levels were associated with a larger mutant cytosine-adenine-guanine (CAG) repeat size (r = +0.68, P = 0.044). CONCLUSION: Our findings indicate a mild hyperactivity of the thyrotropic axis and a disturbed regulation of the lactotropic axis in patients with early-stage HD.

Leptin secretion rate increases with higher CAG repeat number in Huntington's disease patients.

BACKGROUND: Huntington's disease (HD) is a hereditary neurodegenerative disorder caused by an increased number of CAG repeats in the huntingtin gene. A hallmark of HD is unintended weight loss, the cause of which is unknown. OBJECTIVE: To perform a detailed analysis of adipose tissue function in HD patients as abnormal fat tissue function could contribute to the weight loss. DESIGN, SETTING AND PARTICIPANTS: In a clinical research laboratory, 24-h plasma concentrations of leptin, adiponectin and resistin were studied in nine early-stage, medication-free HD patients and nine age-, gender- and body mass index (BMI)-matched controls. MEASUREMENTS: Leptin was measured every 20 min whereas adiponectin and resistin were measured hourly. Autodeconvolution and cosinor regression were applied to quantify secretion characteristics of leptin and diurnal variations in leptin, adiponectin and resistin levels. RESULTS: Plasma levels and diurnal rhythmicity of leptin, adiponectin and resistin were not significantly different between HD patients and controls. However, although leptin production increased with higher BMI and fat mass in controls, no such relation was present in HD patients. Moreover, when corrected for fat mass, mean plasma leptin concentration as well as basal, pulsatile and total secretion rates increased with the size of the CAG repeat mutation (r = +0.72 to r = +0.80; all P < 0.05). Both higher pulsatile leptin secretion and higher mean adiponectin levels were associated with a greater degree of motor and functional impairment in HD patients. CONCLUSIONS: CAG-repeat size-dependent interference of the HD mutation with adipose tissue function may contribute to weight loss in HD patients.