Matteo Baldi

Acylated Ghrelin Inhibits Spontaneous Luteinizing Hormone Pulsatility and Responsiveness to Naloxone But Not That to Gonadotropin-Releasing Hormone in Young Men: Evidence for a Central Inhibitory Action of Ghrelin on the Gonadal Axis

CONTEXT Recent evidence suggests that ghrelin exerts a negative modulation on the gonadal axis. Ghrelin was reported to suppress LH secretion in both animal and human models. Moreover, acylated ghrelin (AG) also decreases the LH responsiveness to GnRH in vitro. OBJECTIVE The objective of the study was to evaluate the effects of AG infusion on spontaneous and stimulated gonadotropin secretion. DESIGN, PARTICIPANTS, AND INTERVENTION In seven young healthy male volunteers (age mean +/- sem 26.4 +/- 2.6 yr), we evaluated LH and FSH levels every 15 min during: 1) iv isotonic saline infusion; 2) iv saline followed by AG; LH and FSH response to GnRH (100 microg iv as a bolus), 3) alone and 4) during AG infusion; LH and FSH response to naloxone (0.1 mg/kg iv as a slow bolus), 5) alone and 6) during AG infusion. RESULTS Significant LH but not FSH pulses were recorded in all subjects under saline infusion. AG infusion inhibited LH levels [area under the curve((240-480)): 415.8 +/- 69.7 mIU/ml.min during AG vs. 744.6 +/- 120.0 mIU/ml.min during saline, P < 0.02] and abolished LH pulsatility. No change in FSH secretion was recorded. The LH and FSH responses to GnRH during saline were not affected by AG administration. However, AG inhibited the LH response to naloxone [area under the curve ((120-210)): 229.9 +/- 39.3 mIU/ml.min during AG vs. 401.1 +/- 44.6 mIU/ml.min during saline, P < 0.01]. FSH levels were not modified by naloxone alone or in combination with AG. CONCLUSIONS AG inhibits both spontaneous LH pulsatility and the LH response to naloxone. Because AG does not affect the LH response to GnRH, these findings indicate that the ghrelin system mediates central inhibition of the gonadal axis.

A novel mutation in the human aromatase gene: Insights on the relationship among serum estradiol, longitudinal growth and bone mineral density in an adult man under estrogen replacement treatment

OBJECTIVE Here we report on a new case of human aromatase deficiency in a man of 26 years of age and present the results of five year follow-up during trandermal estradiol (tE2) substitution, focusing on bone growth and mineralization. The lack of patients compliance to tE2 treatment, resulting in low but detectable serum estradiol levels, provides helpful information about the physiological estradiol needed in serum to guarantee a complete bone maturation and mineralization. DESIGN Clinical case report study. METHODS Genetic, biochemical and hormonal evaluations and the study of bone health were performed before and during estrogen treatment. RESULTS Eunuchoid body proportions, unfused epiphyses, tall stature, osteopenia, increase fasting insulin, mild astenozoospermia and a history of right cryptorchidism were present. Baseline serum FSH was slightly above the normal range and estradiol was undetectable. Genetic analysis revealed a pattern of compound heterozygosity due to 23 bp deletion in exon IV and a point mutation in the first nucleotide of intron IX of the CYP19A1 gene, respectively. The closure of epiphyseal cartilage, the normalization of bone BMD and bone turnover markers, and the improvement of insulin levels were reached during tE2 only when serum estradiol raised above 73 pmol/L. Sperm parameters and overweight did not improve with substitutive therapy. CONCLUSIONS This new case of aromatase deficiency underlines the role of estrogen on skeletal maturation, BMD, metabolic abnormalities and gonadal axis. It provides evidence on the need not only of a continuous estrogen replacement, but also of ensuring adequate estradiol levels in serum in order to ensure a complete bone maturation and mineralization and to prevent the worsening of body skeletal proportions. The comprehension of this physiological aspect has relevant clinical significance especially for the development of new therapeutic strategies useful to treat growth disorders by targeting serum estradiol in men.

Neuroendocrine Alterations in Obese Patients with Sleep Apnea Syndrome

Obstructive sleep apnea syndrome (OSAS) is a serious, prevalent condition that has significant morbidity and mortality when untreated. It is strongly associated with obesity and is characterized by changes in the serum levels or secretory patterns of several hormones. Obese patients with OSAS show a reduction of both spontaneous and stimulated growth hormone (GH) secretion coupled to reduced insulin-like growth factor-I (IGF-I) concentrations and impaired peripheral sensitivity to GH. Hypoxemia and chronic sleep fragmentation could affect the sleep-entrained prolactin (PRL) rhythm. A disrupted Hypothalamus-Pituitary-Adrenal (HPA) axis activity has been described in OSAS. Some derangement in Thyroid-Stimulating Hormone (TSH) secretion has been demonstrated by some authors, whereas a normal thyroid activity has been described by others. Changes of gonadal axis are common in patients with OSAS, who frequently show a hypogonadotropic hypogonadism. Altogether, hormonal abnormalities may be considered as adaptive changes which indicate how a local upper airway dysfunction induces systemic consequences. The understanding of the complex interactions between hormones and OSAS may allow a multi-disciplinary approach to obese patients with this disturbance and lead to an effective management that improves quality of life and prevents associated morbidity or death.

Ghrelin, Hypothalamus-Pituitary-Adrenal (HPA) Axis and Cushing's Syndrome

Ghrelin, a peptide predominantly produced by the stomach, has been discovered as a natural ligand of the GH Secretagogue receptor type 1a (GHS-R1a), known as specific for synthetic GHS. Ghrelin has recently attracted considerable interest as a new orexigenic factor. However, ghrelin exerts pleiotropic actions that are explained by the widespread distribution of ghrelin and GHS-R expression. Besides strong stimulation of GH secretion, the neuroendocrine ghrelin actions also include significant stimulation of both lactotroph and corticotroph secretion; all these actions depend on acylation of ghrelin in serine-3 that allows binding and activation of the GHS-R1a. However, GHS-R subtypes are likely to exist; they also bind unacylated ghrelin that is, in fact, the most abundant circulating form and exerts some biological actions. Ghrelin secretion is mainly regulated by metabolic signals, namely inhibited by feeding, glucose and insulin while stimulated by energy restriction. The role of glucocorticoids on ghrelin synthesis and secretion is still unclear although morning ghrelin levels have been found reduced in some patients with Cushings syndrome; this, however, would simply reflect its negative association to body mass. Ghrelin, like synthetic GHS, stimulates ACTH and cortisol secretion in normal subjects and this effect is generally sensitive to the negative glucocorticoid feedback. It is remarkable that, despite hypercortisolism, ghrelin as well as synthetic GHS display marked increase in their stimulatory effect on ACTH and cortisol secretion in patients with Cushings disease. This is even more intriguing considering that the GH response to ghrelin and GHS is markedly reduced by glucocorticoid excess. It has been demonstrated that the ACTH-releasing effect of ghrelin and GHS is purely mediated at the central level in physiological conditions; its enhancement in the presence of ACTH-secreting tumours is, instead, likely to reflect direct action on GHS receptors present on the neoplastic tissues. In fact, peculiar ACTH hyperresponsiveness to ghrelin and GHS has been observed also in ectopic ACTH-secreting tumours.

Corticotroph axis sensitivity after exercise: comparison between elite athletes and sedentary subjects

Strenuous exercise activates the hypothalamic-pituitary-adrenal (HPA) axis. Several reports showed that physical training is associated with a decreased efficiency of the feedback control of HPA axis. The aims of the present study were: 1) to evaluate the differences in the mechanical, hormonal, and lactate responses to a high-intensity isokinetic exercise among different groups of competitive athletes (CA, no.=20) of power and endurance disciplines and sedentary controls (SED, no.=10); 2) to determine the effects of the training status on the HPA axis responsiveness following exercise, as indirectly evaluated by the rates of ACTH, cortisol, and DHEA recovery after exercise. CA and SED fulfilled eight sets of twenty concentric contractions of the knee extensors at 180°/sec angular velocity throughout a constant range of motion (100°). There was a rest period of 30 sec between each set and a 3-min rest period between the two legs. Before, immediately after the isokinetic exercise and at different times in the subsequent 120 min of recovery, blood and saliva were sampled to determine plasma ACTH, salivary cortisol, serum DHEA, and serum lactate concentrations. CA showed a higher cortisol response to exercise than SED, whereas no differences were found in the responses of ACTH, DHEA and lactate. In the athlete group the exercise-induced increases of ACTH, cortisol, and lactate were higher in power athletes with respect to endurance athletes. No differences were observed between athletes and SED in the rates of hormonal recovery after exercise: this finding does not support the concept that a reduced feedback control of HPA axis can represent a feature of trained individuals.

Changes in awakening Cortisol response and midnight salivary Cortisol are sensitive markers of strenuous training-induced fatigue

The aim of the study was to examine the effects of strenuous training on the hypothalamic-pituitary-adrenal axis activity. Exercise tests and saliva collections for analysis of awakening cortisol response (ACR) and midnight cortisol were performed before and after a 7-day period of intensified training in a group of 15 soccer players. Intensified training resulted in a performancedecrement as shown by the pre-post-training changes in maximal values of counter movement jump (CMJ) height (p=0.008). Cortisol assessment during the first 30 min after awakening showed significant increases both before and after the 7-day period and post-training ACR higher than pre-training ACR (p<0.001). Midnight cortisol also significantly increased after training (mean±SD, before: 3.0±0.7 nmol/l vs after: 5.9±3.3 nmol/l; p=0.017). The analysis of individual data showed an important inter-individual variability in the pre-post-training changes: several subjects increased post-awakening peak of cortisol, rate of cortisol increase from awakening to peak, and area under the curve (AUC) values, whereas other subjects showed no training-related increases. Significant correlations were observed between pre-post-training change in CMJ and in the following variables: awakening cortisol (r=0.74), post-awakening peak of cortisol (r=0.81), rate of cortisol increase (r=0.75), and AUC (r=0.79). Briefly, the lower the performance decrease, the higher the training-associated ACR increase. These data could indicate that a dys-regulated adaptation to exercise occurred in athletes who experienced a higher performance decrease after training and lower (or absent) hormonal changes. Future studies are needed to elucidate the physiological determinants which underlie the exercise-elicited changes in ACR and in midnight cortisol levels and their value in predicting impaired adaptations to exercise.

Tall Stature without Growth Hormone: Four Male Patients with Aromatase Deficiency

CONTEXT From preliminary observations, GH-IGF-I seems to be compromised in men with aromatase deficiency. The GH deficiency (GHD) coexists paradoxically with tall stature, raising the question whether or not a true GHD is part of this rare syndrome. OBJECTIVE To evaluate the GH secretion in aromatase-deficient men, their GH response to the GHRH plus arginine (GHRH-ARG) test was compared with that of normal subjects. The effect of estrogen replacement treatment on the GH-IGF-I axis in aromatase-deficient men was evaluated before and during therapy. DESIGN AND SETTING A case-control study was conducted. PATIENTS Four adult men with aromatase deficiency were compared with 12 normal subjects. MAIN OUTCOME MEASURES We measured the GH response to GHRH-ARG in aromatase-deficient men (at baseline and during estrogen treatment) and in normal subjects. Basal serum IGF-I was measured in both patients and controls. RESULTS The response of GH to GHRH-ARG was severely impaired in men with aromatase deficiency and resulted in significantly lower (P < 0.001) levels than in normal subjects. Although normal, serum IGF-I levels were also significantly lower (P < 0.001) than in normal subjects. Both GH peak and IGF-I concentrations were not modified by estrogen therapy in men with aromatase deficiency. CONCLUSIONS In aromatase-deficient men, GH response to potent provocative stimuli is impaired and is not restored by exogenous estrogens. Furthermore, a tall stature may be reached, notwithstanding the coexistence of GHD, if a prolonged time for growth is available due to a delay in bone maturation, and other growth factors different from GH (mainly insulin) promote growth.

Ghrelin and Anterior Pituitary Function

Ghrelin, a 28-amino-acid octanoylated peptide predominantly produced by the stomach, was discovered to be the natural ligand of the type 1a GH secretagogue receptor. Thus, it was considered as a natural GH secretagogue (GHS) additional to GHRH, although later on ghrelin has mostly been considered a major orexigenic factor. The GH-releasing action of ghrelin takes place both directly on pituitary cells and through modulation of GHRH from the hypothalamus; some functional anti-somatostatin action has also been shown. However, even at the neuroendocrine level, ghrelin is much more than a natural GHS. In fact, it significantly stimulates prolactin secretion in humans, independent of both gender and age and probably involving a direct action on somatomammotroph cells. Above all, ghrelin and synthetic GHS possess an acute stimulatory effect on the activity of the hypothalamus-pituitary-adrenal axis in humans, which is, at least, similar to that of the opioid antagonist naloxone, arginine vasopressin and even corticotropin-releasing hormone. Also, ghrelin plays a relevant role in the modulation of the hypothalamic-pituitary-gonadal function, with a predominantly CNS-mediated inhibitory effect upon the gonadotropin pulsatility both in animals and in humans.

Ghrelin and prostate cancer.

Ghrelin, a 28-amino acid octanoylated peptide predominantly produced by the stomach, has been discovered to be a natural ligand of the type 1a growth hormone secretagogue receptor (GHSR1a). Ghrelin has recently attracted the interest as a new GH-releasing and orexigenic factor. However, ghrelin exerts several other activities, including regulation of tissue growth and development and control of neoplastic cell proliferation. Several endocrine and nonendocrine cancer cells (pituitary adenomas; gastroenteropancreatic and pulmonary carcinoids; colorectal neoplasms, thyroid tumors; lung, breast, and pancreatic carcinomas) as well as their related cell lines have been shown able to express ghrelin both at mRNA and at protein level. Many of the above-listed tumors express GHSR1a and/or alternative GHS receptor subtypes such as the type 1b GHSR, a truncated isoform of GHSR1a, and binding sites able to recognize ghrelin independently of its acylation. Evidence that ghrelin and multiple ghrelin/GHS receptors are coexpressed in cancer cell lines and tumoral tissues from organs, such as the breast, that do not express these receptors in physiological conditions suggests that the ghrelin system is likely to play an important autocrine/paracrine role in some cancers. This chapter highlights the evidence for the expression of ghrelin and its receptors in one of the most frequent human malignancies, the prostate cancer, and information regarding their potential functional role in related cell lines.

Muscle Fiber Conduction Slowing and Decreased Levels of Circulating Muscle Proteins after Short-Term Dexamethasone Administration in Healthy Subjects

CONTEXT Glucocorticoids are known to decrease protein synthesis and impair membrane excitability of muscle fibers. However, their short-term effects on muscle structure and function of healthy subjects remain poorly understood. OBJECTIVE Our objective was to investigate whether steroid administration could decrease the circulating levels of muscle proteins and modify myoelectric indexes of sarcolemmal excitability and fatigability. DESIGN We conducted a single-blind, placebo-controlled study in 20 men randomized to receive dexamethasone (8 mg/d) or placebo for 1 wk. Blood sampling, force measurements for knee extensors and elbow flexors, and electrophysiological tests for biceps brachii, vastus lateralis and medialis, and tibialis anterior muscles were performed before and after the intervention. RESULTS Dexamethasone administration improved force by 6.0 +/- 6.0% (P = 0.01) for elbow flexors and by 8.5 +/- 5.5% (P < 0.01) for knee extensors, decreased levels of creatine kinase by 50.5 +/- 30.0% (P < 0.01) and myoglobin by 41.8 +/- 17.5% (P < 0.01), and impaired sarcolemmal excitability, as shown by the decline of muscle fiber conduction velocity for the four muscles (range from -6 to -10.5%, P < 0.05). Moreover, significant reductions of the myoelectric manifestations of fatigue were observed for the four muscles; the decrease in the rate of change of the mean frequency of the electromyographic power spectrum ranged from -22.6 to -43.9% (P < 0.05). In contrast, no significant changes were observed in muscle excitability and fatigability in subjects who received the placebo. CONCLUSIONS The demonstration that glucocorticoid-induced muscle impairments can be unraveled by means of blood sampling and noninvasive electrophysiological tests has clinical implications for the early identification of subclinical or preclinical forms of myopathy in treated patients.