Effects of Leptin on Fetal Plasma Adrenocorticotropic Hormone and Cortisol Concentrations and the Timing of Parturition in the Sheep1

Minireview: Glucocorticoid-Leptin Crosstalk: Role of Glucocorticoid-Leptin Counterregulation in Metabolic Homeostasis and Normal Development

Glucocorticoids and leptin are two important hormones that regulate metabolic homeostasis by controlling appetite and energy expenditure in adult mammals. Also, glucocorticoids and leptin strongly counterregulate each other, such that chronic stress-induced glucocorticoids upregulate the production of leptin and leptin suppresses glucocorticoid production directly via action on endocrine organs and indirectly via action on food intake. Altered glucocorticoid or leptin levels during development can impair organ development and increase the risk of chronic diseases in adults, but there are limited studies depicting the significance of glucocorticoid-leptin interaction during development and its impact on developmental programming. In mammals, leptin-induced suppression of glucocorticoid production is critical during development, where leptin prevents stress-induced glucocorticoid production by inducing a period of short-hyporesponsiveness when the adrenal glands fail to respond to certain mild to moderate stressors. Conversely, reduced or absent leptin signaling increases glucocorticoid levels beyond what is appropriate for normal organogenesis. The counterregulatory interactions between leptin and glucocorticoids suggest the potential significant involvement of leptin in disorders that occur from stress during development.

Placenta DNA methylation levels of the promoter region of the leptin receptor gene are associated with infant cortisol

The intrauterine environment and early life stress regulation are widely recognized as an early foundation for lifelong physical and mental health. Methylation of CpG sites in the placenta represents an epigenetic modification that can potentially affect placental function, influence fetal development, and ultimately impact the health of offspring by programming the hypothalamic-pituitary-adrenal (HPA) axis stress response during prenatal development. Leptin, an adipokine produced by the placenta, is essential for energy homeostasis. It is also epigenetically regulated by promoter DNA methylation. Mounting evidence suggests that leptin also affects the stress response system. Though heterogeneity in the early stress response system may influence life-long mental and physical health, few studies explicitly examine the heterogeneity in the newborn stress response system. Less is known about leptin's association with the human hypothalamic-pituitary-adrenocortical (HPA) axis early in life. This study sought to serve as a proof of concept study investigating the relationship between newborn cortisol output trajectories and placental leptin DNA methylation in 117 healthy newborns from socioeconomically and racially- and ethnically-diverse families. We characterized heterogeneity in newborn cortisol output during the NICU Network Neurobehavioral Scales exam in the first week of life with latent growth mixture models. We then evaluated whether leptin promoter (LEP) methylation in placental samples was associated with newborn cortisol trajectories. Our findings suggest that increased placental LEP methylation, which corresponds to decreased leptin production, is associated with infant cortisol trajectories marked by increased cortisol output in the NNNS exam. These results provide important insights into the role of placental leptin DNA methylation in human newborn HPA axis development and subsequent developmental origins of health and disease processes.

[Development of clinically relevant vital signs of goat lambs of different breeds between birth and 28th day of life post natum]

Monitoring caprine neonates is of great importance to minimize losses of valuable offspring potential. In addition to experience and ethological knowledge, it requires clinically relevant basic values for vitality assessment. Therefore, the aim of the study was to register appropriate basic parameters in healthy caprine lambs.

MATERIAL AND METHODS

Included in the study were 46 healthy, vital born lambs from 28 dams of the breeds White German Edel goat (WGE, n=15), Boer goat (n=7); Toggenburg goat (n=6). The three groups of subjects included 26 WGE, 9 Boer goat and 11 Toggenburg goat lambs. From birth, they were under intensive veterinary control. Vital signs respiratory rate, heart rate, and rectal temperature were measured immediately p.n.; 3rd, 12th, 24th h p.n.; 2nd, 3rd, 5th, 7th, 9th, 14th, 21st, and 28th d p.n. Furthermore, crown-rump length (CRL), birth weight, and weight development until 28th d p.n. Statistical analysis of the data was performed using BMDP/Dynamic Release 7.0 and two-factorial analysis of variance.

RESULTS

Vital signs showed a typical course in the first 4 weeks p.n. with a significant decrease in values from the 5th d. p.n. Time as well as breed had significant influence on the development of the respective profiles (covariance analysis; p<0.001). There was a linear correlation for SSL and birth weight (y=0.0037 ×28969; r value 0.7805). Daily weight gain was independent of race and diet type. In contrast, there was a significant dependence between birth type (singleton or multiple birth) and weight gain with p<0.01 and between birth weight and sex (p<0.05).

CONCLUSION

The presented typical, breed-dependent postnatal changes of vital parameters in goat lambs in the period 0-28 days p.n. allow a more specific differentiation between clinically healthy and abnormal individuals in herd management using the physiological value tables. The age-correlated weight gain serves as a further evaluation parameter.

Endocrine regulation of fetal metabolism towards term

Hormones have an important role in regulating fetal metabolism in relation to the prevailing nutritional conditions both in late gestation and during the prepartum period as the fetus prepares for birth. In particular, the pancreatic, thyroid and adrenal hormones all affect fetal uptake and utilization of nutrients for oxidative metabolism, tissue accretion and fuel storage. These hormones also influence the fetal metabolic preparations for the nutritional transition from intra- to extra-uterine life. This review discusses the role of insulin, glucagon, thyroxine, tri-iodothyronine, cortisol and the catecholamines in these processes during normal intrauterine conditions and in response to maternal undernutrition with particular emphasis on the sheep fetus. It also considers the metabolic interactions between these hormones and their role in the maturation of key tissues, such as the liver, skeletal muscle and adipose tissue, in readiness for their new metabolic functions after birth. Endocrine regulation of fetal metabolism is shown to be multifactorial and dynamic with a central role in optimizing metabolic fitness for survival both in utero and at birth.

Thyroid Hormone Deficiency Suppresses Fetal Pituitary-Adrenal Function Near Term: Implications for the Control of Fetal Maturation and Parturition

Background: The fetal hypothalamic-pituitary-adrenal (HPA) axis plays a key role in the control of parturition and maturation of organ systems in preparation for birth. In hypothyroid fetuses, gestational length may be prolonged and maturational processes delayed. The extent to which the effects of thyroid hormone deficiency in utero on the timing of fetal maturation and parturition are mediated by changes to the structure and function of the fetal HPA axis is unknown. Methods: In twin sheep pregnancies where one fetus was thyroidectomized and the other sham-operated, this study investigated the effect of hypothyroidism on circulating concentrations of adrenocorticotrophic hormone (ACTH) and cortisol, and the structure and secretory capacity of the anterior pituitary and adrenal glands. The relative population of pituitary corticotrophs and the masses of the adrenal zones were assessed by immunohistochemical and stereological techniques. Adrenal mRNA abundances of key steroidogenic enzymes and growth factors were examined by quantitative polymerase chain reaction. Results: Hypothyroidism in utero reduced plasma concentrations of ACTH and cortisol. In thyroid-deficient fetuses, the mass of corticotrophs in the anterior pituitary gland was unexpectedly increased, while the mass of the zona fasciculata and its proportion of the adrenal gland were decreased. These structural changes were associated with lower adrenocortical mRNA abundances of insulin-like growth factor (IGF)-I and its receptor, and key steroidogenic enzymes responsible for glucocorticoid synthesis. The relative mass of the adrenal medulla and its proportion of the adrenal gland were increased by thyroid hormone deficiency in utero, without any change in expression of phenylethanolamine N-methyltransferase or the IGF system. Conclusions: Thyroid hormones are important regulators of the structure and secretory capacity of the pituitary-adrenal axis before birth. In hypothyroid fetuses, low plasma cortisol may be due to impaired adrenocortical growth and steroidogenic enzyme expression, secondary to low circulating ACTH concentration. Greater corticotroph population in the anterior pituitary gland of the hypothyroid fetus indicates compensatory cell proliferation and that there may be abnormal corticotroph capacity for ACTH synthesis and/or impaired hypothalamic input. Suppression of the development of the fetal HPA axis by thyroid hormone deficiency may contribute to the delay in fetal maturation and delivery observed in hypothyroid offspring.

C-Peptide and leptin system in dichorionic, small and appropriate for gestational age twins-possible link to metabolic programming?

Children born small for gestational age (SGA) are at increased risk of future glucose intolerance and type 2 diabetes, possibly after due intrauterine metabolic programming. Soluble leptin receptor (SLR) limits leptin access to signal-transducing membrane receptors. The present study examines whether SGA and appropriate for gestational age (AGA) twins differ with regard to their C-peptide, glucose and leptin systems. The markers C-peptide, glucose, fetal leptin, and SLR in cord blood were assessed in children from dichorionic twin pregnancies at delivery. In 32 cases, weight differed by >15% between twins: one demonstrated Intrauterine Growth Retardation (IUGR) (<10th percentile-SGA), while the other did not (AGA_I). The other 67 pairs presented appropriate weight for gestational age (AGA_II). Placental leptin and placental leptin receptor content were also assessed. Despite the same concentrations of glucose, the SGA twins maintained a higher level of C-peptide [44.48 pmol/l vs. 20.91 pmol/l, p < 0.05] than the AGA_I co-twins, higher HOMA index, calculated as [C-peptide] x [Glucose] (p = 0.045), in cord blood, and a higher level of SLR [SGA vs AGA_I—mean: 28.63 ng/ml vs. 19.91 ng/ml, p < 0.01], without any differences in total leptin (p = 0.37). However, SGA placentas demonstrated higher leptin level [130.1 pg/100 g total protein vs 83.8 pg/100 g total protein, p = 0.03], without differences in placental leptin receptor (p = 0.66). SGA/IUGR twins demonstrate relative insulin resistance accompanied by decreased fetal and increased placental leptin signaling. We speculate that relative insulin resistance and changes in the leptin system might be the first evidence of processes promoting deleterious metabolic programming for post-natal life.

Gestational Hypoxia and Developmental Plasticity

Hypoxia is one of the most common and severe challenges to the maintenance of homeostasis. Oxygen sensing is a property of all tissues, and the response to hypoxia is multidimensional involving complicated intracellular networks concerned with the transduction of hypoxia-induced responses. Of all the stresses to which the fetus and newborn infant are subjected, perhaps the most important and clinically relevant is that of hypoxia. Hypoxia during gestation impacts both the mother and fetal development through interactions with an individual's genetic traits acquired over multiple generations by natural selection and changes in gene expression patterns by altering the epigenetic code. Changes in the epigenome determine "genomic plasticity," i.e., the ability of genes to be differentially expressed according to environmental cues. The genomic plasticity defined by epigenomic mechanisms including DNA methylation, histone modifications, and noncoding RNAs during development is the mechanistic substrate for phenotypic programming that determines physiological response and risk for healthy or deleterious outcomes. This review explores the impact of gestational hypoxia on maternal health and fetal development, and epigenetic mechanisms of developmental plasticity with emphasis on the uteroplacental circulation, heart development, cerebral circulation, pulmonary development, and the hypothalamic-pituitary-adrenal axis and adipose tissue. The complex molecular and epigenetic interactions that may impact an individual's physiology and developmental programming of health and disease later in life are discussed.

Developmental programming, adiposity, and reproduction in ruminants

Although sheep have been widely adopted as an animal model for examining the timing of nutritional interventions through pregnancy on the short- and long-term outcomes, only modest programming effects have been seen. This is due in part to the mismatch in numbers of twins and singletons between study groups as well as unequal numbers of males and females. Placental growth differs between singleton and twin pregnancies which can result in different body composition in the offspring. One tissue that is especially affected is adipose tissue which in the sheep fetus is primarily located around the kidneys and heart plus the sternal/neck region. Its main role is the rapid generation of heat due to activation of the brown adipose tissue-specific uncoupling protein 1 at birth. The fetal adipose tissue response to suboptimal maternal food intake at defined stages of development differs between the perirenal abdominal and pericardial depots, with the latter being more sensitive. Fetal adipose tissue growth may be mediated in part by changes in leptin status of the mother which are paralleled in the fetus. Then, over the first month of life plasma leptin is higher in females than males despite similar adiposity, when fat is the fastest growing tissue with the sternal/neck depot retaining uncoupling protein 1, whereas other depots do not. Future studies should take into account the respective effects of fetal number and sex to provide more detailed insights into the mechanisms by which adipose and related tissues can be programmed in utero.

Preeclampsia As Modulator of Offspring Health

A balanced intrauterine homeostasis during pregnancy is crucial for optimal growth and development of the fetus. The intrauterine environment is extremely vulnerable to multisystem pregnancy disorders such as preeclampsia, which can be triggered by various pathophysiological factors, such as angiogenic imbalance, immune responses, and inflammation. The fetus adapts to these conditions by a mechanism known as developmental programming that can lead to increased risk of chronic noncommunicable diseases in later life. This is shown in a substantial number of epidemiological studies that associate preeclampsia with increased onset of cardiovascular and metabolic diseases in the later life of the offspring. Furthermore, animal models based predominantly on one of the pathophysiological mechanism of preeclampsia, for example, angiogenic imbalance, immune response, or inflammation, do address the susceptibility of the preeclamptic offspring to increased maternal blood pressure and disrupted metabolic homeostasis. Accordingly, we extensively reviewed the latest research on the role of preeclampsia on the offspring's metabolism and cardiovascular phenotype. We conclude that future research on the pathophysiological changes during preeclampsia and methods to intervene in the harsh intrauterine environment will be essential for effective therapies.

Fetal endocrine and metabolic adaptations to hypoxia: the role of the hypothalamic-pituitary-adrenal axis

In utero, hypoxia is a significant yet common stress that perturbs homeostasis and can occur due to preeclampsia, preterm labor, maternal smoking, heart or lung disease, obesity, and high altitude. The fetus has the extraordinary capacity to respond to stress during development. This is mediated in part by the hypothalamic-pituitary-adrenal (HPA) axis and more recently explored changes in perirenal adipose tissue (PAT) in response to hypoxia. Obvious ethical considerations limit studies of the human fetus, and fetal studies in the rodent model are limited due to size considerations and major differences in developmental landmarks. The sheep is a common model that has been used extensively to study the effects of both acute and chronic hypoxia on fetal development. In response to high-altitude-induced, moderate long-term hypoxia (LTH), both the HPA axis and PAT adapt to preserve normal fetal growth and development while allowing for responses to acute stress. Although these adaptations appear beneficial during fetal development, they may become deleterious postnatally and into adulthood. The goal of this review is to examine the role of the HPA axis in the convergence of endocrine and metabolic adaptive responses to hypoxia in the fetus.

Leptin receptor antagonist treatment ameliorates the effects of long-term maternal hypoxia on adrenal expression of key steroidogenic genes in the ovine fetus

We previously reported elevated adipose leptin expression, plasma leptin concentrations, and adrenocortical leptin receptor expression in the long-term hypoxic (LTH) ovine fetus. This study addressed whether leptin antagonist (LA) administration to LTH fetal sheep altered expression of key genes governing cortisol synthesis. Ewes were maintained at high altitude (3,820 meters) from 40 to 130 days gestation (dG), returned to Loma Linda University, and implanted with a maternal tracheal catheter. Reduced Po2 was maintained by nitrogen infusion. On 132 dG, LTH (n = 11) and age-matched, normoxic control (n = 11) fetuses underwent vascular catheter implantation. At 138 dG, fetuses were continuously infused with either saline or the LA (1.5 mg·kg(-1)·day(-1)) for 4 days and samples collected for blood gases, ACTH, and cortisol. Fetal adrenal cortex was collected for determination of steriodogenic acute regulatory protein (StAR), ACTH, and leptin receptor, cholesterol side-chain cleavage (CYP11A1), cytochrome P-450 11β-hydroxylase (CYP11B1), 17α-hydroxylase (CYP17), 21-hydroxylase (CYP21), signal transducer and activator of transcription 3 (STAT3), pSTAT3, and 17β-hydroxysteroid dehydrogenase (HSD3B) expression. In the saline-infused LTH fetuses, StAR, ACTH receptor, CYP11A1, and CYP17 expression was significantly lower compared with control (P < 0.05), whereas levels of CYP11B1, CYP21, and HSD3B mRNA were similar between groups. LA infusion restored expression of StAR, pSTAT3, CYP11A1, and CYP17, but not ACTH receptor, to normal ontogenic levels in the LTH group while having no effect on control fetuses. Neither fetal plasma ACTH nor cortisol concentrations were altered by LA infusion. We speculate that while leptin plays a role in governing expression of key enzymes and StAR in response to LTH, other factors play a role in modulating cortisol synthesis in these fetuses.

Adrenocortical and adipose responses to high-altitude-induced, long-term hypoxia in the ovine fetus

By late gestation, the maturing hypothalamo-pituitary-adrenal (HPA) axis aids the fetus in responding to stress. Hypoxia represents a significant threat to the fetus accompanying situations such as preeclampsia, smoking, high altitude, and preterm labor. We developed a model of high-altitude (3,820 m), long-term hypoxia (LTH) in pregnant sheep. We describe the impact of LTH on the fetal HPA axis at the level of the hypothalamic paraventricular nucleus (PVN), anterior pituitary corticotrope, and adrenal cortex. At the PVN and anterior pituitary, the responses to LTH are consistent with hypoxia being a potent activator of the HPA axis and potentially maladaptive, while the adrenocortical response to LTH appears to be primarily adaptive. We discuss mechanisms involved in the delicate balance between these seemingly opposing responses that preserve the normal ontogenic rise in fetal plasma cortisol essential for organ maturation and in this species, birth. Further, we examine the response to, and ramifications of, an acute secondary stressor in the LTH fetus. We provide an integrative model on the potential role of adipose in modulating these responses to LTH. Integration of these adaptive responses to LTH plays a key role in promoting normal fetal growth and development under conditions of a chronic stress.

Leptin alters adrenal responsiveness by decreasing expression of ACTH-R, StAR, and P450c21 in hypoxemic fetal sheep

The late gestation increase in adrenal responsiveness to adrenocorticotropin (ACTH) is dependent upon the upregulation of the ACTH receptor (ACTH-R), steroidogenic acute regulatory protein (StAR), and steroidogenic enzymes in the fetal adrenal. Long-term hypoxia decreases the expression of these and adrenal responsiveness to ACTH in vivo. Leptin, an adipocyte-derived hormone which attenuates the peripartum increase in fetal plasma cortisol is elevated in hypoxic fetuses. Therefore, we hypothesized that increases in plasma leptin will inhibit the expression of the ACTH-R, StAR, and steroidogenic enzymes and attenuate adrenal responsiveness in hypoxic fetuses. Spontaneously hypoxemic fetal sheep (132 days of gestation, PO(2) ≈ 15 mm Hg) were infused with recombinant human leptin (n = 8) or saline (n = 7) for 96 hours. An ACTH challenge was performed at 72 hours of infusion to assess adrenal responsiveness. Plasma cortisol and ACTH were measured daily and adrenals were collected after 96 hours infusion for messenger RNA (mRNA) and protein expression measurement. Plasma cortisol concentrations were lower in leptin- compared with saline-infused fetuses (14.8 ± 3.2 vs 42.3 ± 9.6 ng/mL, P < .05), as was the cortisol:ACTH ratio (0.9 ± 0.074 vs 46 ± 1.49, P < .05). Increases in cortisol concentrations were blunted in the leptin-treated group after ACTH(1-24) challenge (F = 12.2, P < .0001). Adrenal ACTH-R, StAR, and P450c21 expression levels were reduced in leptin-treated fetuses (P < .05), whereas the expression of Ob-Ra and Ob-Rb leptin receptor isoforms remained unchanged. Our results indicate that leptin blunts adrenal responsiveness in the late gestation hypoxemic fetus, and this effect appears mediated by decreased adrenal ACTH-R, StAR, and P450c21 expression.

Adipokines, an adipose tissue and placental product with biological functions during pregnancy

Latter half of pregnancy is characterized by a "physiological diabetogenic state" since changes in insulin-sensitivity have been well documented. These changes ensure continuous supply of nutrients to the growing fetus. In the last years the role of adipocyte-derived signaling molecules, collectively known as adipokines has been object of different in vitro and in vivo studies. Of interest, adipokines and/or their receptors are expressed in the placental tissue which, therefore, can contribute to development of maternal insulin-resistance and, as a consequence, fetal growth. Leptin, adiponectin, and resistin represent the most well studied adipokines and, with the exception of adiponectin, their serum and placental levels increase as pregnancy progresses. High levels of adipokines have also been detected in umbilical plasma hence suggesting a possible role on fetal development and metabolism; however, it remains still unclear if such adipokines can directly stimulate fetal tissues development acting as growth factors. In addition to their well known metabolic effects, we also reported studies describing the role of adipokines in promoting proliferation and invasiveness of trophoblast cells and affecting local angiogenic processes. These observations strongly suggest that adipokines, by alternatively interfering with placental development, may affect pregnancy outcome and fetal growth. However, further studies are needed to better understand the local regulation of their expression. © 2012 International Union of Biochemistry and Molecular Biology, Inc.

Impact of intrauterine balloon aortic valvuloplasty on gestational outcome in a fetal goat model

OBJECTIVE

Intrauterine balloon aortic valvuloplasty (IUBAV) has been used to correct critical aortic valve stenosis. Evaluation of the intervention-related risk is necessary. The purpose of this study was to establish an experimental goat model for ultrasound-guided IUBAV intervention and investigate the immediate and long-term effects of IUBAV on the fetus, gestational outcome and mother's safety.

STUDY DESIGN

Fifteen pregnant goats with twin gestation in the 2nd and 3rd trimester were anesthetized to establish the surgical procedure. One fetus of the twins received IUBAV intervention, the other served as a control. The data were collected at three time points: immediately before and after IUBAV, and 24 h after birth. Critical organs including the heart, brain, lung and liver from the fetuses/newborns were collected after IUBAV or 24 h after birth.

RESULTS

IUBAV intervention immediately induced a significant decrease of pH and Ca(2+), as well as an increase of blood glucose and lactic acid levels (p < 0.05). IUBAV also caused an increase in stress hormones (epinephrine 1-fold, norepinephrine 4-fold, and cortisol 1-fold; p < 0.05). Following the operation, all of the mother goats recovered, but in 60% (6/10) preterm delivery occurred. Neither pathological changes in fetal critical organs nor a significant difference in metabolism or growth parameters were detected between IUBAV and control kids.

CONCLUSIONS

Ultrasound-guided IUBAV intervention induced a strong but transient stress response in the operated fetus, which did not result in irreversible histological changes in the fetus or the mother, but may disrupt the continuation of normal gestation in the long term. Preterm delivery is the major risk in this goat IUBAV model.

Long-term hypoxia enhances cortisol biosynthesis in near-term ovine fetal adrenal cortical cells

This study was designed to determine the potential mechanism/mechanisms of previously observed enhanced fetal cortisol secretion following exposure to long-term hypoxia (LTH). Pregnant ewes were maintained at high altitude (3820 m) for approximately the last 100 days of gestation. Between the gestation days of 138 and 141, adrenal glands were collected from LTH and age-matched normoxic control fetuses. Cyclic adenosine monophosphate (cAMP), cortisol, and steroidogenic acute regulatory (StAR) protein were measured in response to adrenocorticotropic hormone (ACTH) stimulation. Cortisol responses to ACTH were also measured in the presence of the protein kinase (PKA) inhibitor H-89, proopiomelanocortin (POMC), or 22-kDa pro-ACTH. Cortisol output was higher in the LTH group compared to the control (P < .05), following ACTH treatment while the cAMP response was similar in both groups. Although PKA inhibition decreased cortisol production in both groups, however no differences were observed between groups. Western analysis revealed a significant increase in protein expression for StAR in the LTH group (P < .05, compared to control). Proopiomelanocortin and 22-kDa pro-ACTH did not alter the cortisol response to ACTH treatment. Results from the present study taken together with those of previous in vivo studies suggest that the enhanced cortisol output in the LTH group is not the result of differences in cAMP generation or PKA. We conclude that enhanced cortisol production in LTH adrenals is the result of enhanced protein expression of StAR and potential downstream signaling pathways.

Molecular cloning and gene expression analysis of the leptin receptor in the Chinese mitten crab Eriocheir sinensis

Background

Leptin is an adipocyte-derived hormone with multiple functions that regulates energy homeostasis and reproductive functions. Increased knowledge of leptin receptor function will enhance our understanding of the physiological roles of leptin in animals.

Methodology/Principal Findings

In the present study, a full-length leptin receptor (lepr) cDNA, consisting of 1,353 nucleotides, was cloned from Chinese mitten crab (Eriocheir sinensis) using rapid amplification of cDNA ends (RACE) following the identification of a single expressed sequence tag (EST) clone in a cDNA library. The lepr cDNA consisted of a 22-nucleotide 5′-untranslated region (5′ UTR), a 402-nucleotide open reading frame (ORF) and a 929-nucleotide 3′ UTR. Multiple sequence alignments revealed that Chinese mitten crab lepr shared a conserved vacuolar protein sorting 55 (Vps55) domain with other species. Chinese mitten crab lepr expression was determined in various tissues and at three different reproductive stages using quantitative real-time RT-PCR. Lepr expression was highest in the intestine, thoracic ganglia, gonad, and accessory gonad, moderate in hepatopancreas and cranial ganglia, and low in muscle, gill, heart, haemocytes, and stomach. Furthermore, lepr expression was significantly higher in the intestine, gonad and thoracic ganglia in immature crabs relative to precocious and mature crabs. In contrast, lepr expression was significantly lower in the hepatopancreas of immature crabs relative to mature crabs.

Conclusions/Significance

We are the first to identify the lepr gene and to determine its gene expression patterns in various tissues and at three different reproductive stages in Chinese mitten crab. Taken together, our results suggest that lepr may be involved in the nutritional regulation of metabolism and reproduction in Chinese mitten crabs.

An Investigation of Hair Cortisol Concentration Across Body Sites and within Hair Shaft

Cortisol concentrations in hair collected from young male and female adults were assayed and compared for differences along shaft length and between body sites. No significant differences were found between hair shaft sites, supporting a model of the hair shaft as "alive" and responsive to environmental demand in terms of cortisol production. Hair taken from forearms had significantly higher concentrations of cortisol than hair from lower legs, suggesting a localized hair cortisol response and verifying previous findings. Issues of the link between central and peripheral HPA axes are raised for discussion and further investigation.

Diurnal Variation in Peripheral (Hair) vs Central (Saliva) HPA Axis Cortisol Concentrations

Cortisol concentrations in hair and saliva collected from male and female adults over a 15-hour period were compared for differences in overall level and cyclic pattern. Typical diurnal fluctuations were noted for both salivary and hair cortisol, with some individual differences that are congruent with the previous literature. Issues of the link between central and peripheral HPA axes are raised for discussion and further investigation, and hypothetical explanations for the diurnal variability shown in these two sets of cortisol secretion patterns are discussed from an evolutionary advantage perspective.

The hungry fetus? Role of leptin as a nutritional signal before birth

In adult animals, leptin is an adipose-derived hormone that is important primarily in the regulation of energy balance during short- and long-term changes in nutritional state. Expression of leptin and its receptors is widespread in fetal and placental tissues, although the role of leptin as a nutritional signal in utero is unclear. Before birth, leptin concentration correlates with several indices of fetal growth, and may be an endocrine marker of fetal size and energy stores in the control of metabolism and maturation of fetal tissues. In addition, leptin synthesis and plasma concentration can be modified by insulin, glucocorticoids, thyroid hormones and oxygen availability in utero, and therefore, leptin may be part of the hormonal response to changes in the intrauterine environment. Evidence is emerging to show that leptin has actions before birth that are tissue-specific and may occur in critical periods of development. Some of these actions are involved in the growth and development of the fetus and others have long-term consequences for the control of energy balance in adult life.

Leptin and the regulation of the hypothalamic-pituitary-adrenal axis

Leptin, the product of the obesity gene (ob) predominantly secreted from adipocytes, plays a major role in the negative control of feeding and acts via a specific receptor (Ob-R), six isoforms of which are known at present. Evidence has been accumulated that leptin, like other peptides involved in the central regulation of food intake, controls the function of the hypothalamic-pituitary-adrenal (HPA) axis, acting on both its central and peripheral branches. Leptin, along with Ob-R, is expressed in the hypothalamus and pituitary gland, where it modulates corticotropin-releasing hormone and ACTH secretion, probably acting in an autocrine-paracrine manner. Only Ob-R is expressed in the adrenal gland, thereby making it likely that leptin affects it by acting as a circulating hormone. Although in vitro and in vivo findings could suggest a glucocorticoid secretagogue action in the rat, the bulk of evidence indicates that leptin inhibits steroid-hormone secretion from the adrenal cortex. In keeping with this, leptin was found to dampen the HPA axis response to many kinds of stress. In contrast, leptin enhances catecolamine release from the adrenal medulla. This observation suggests that leptin activates the sympathoadrenal axis and does not appear to agree with its above-mentioned antistress action. Leptin and/or Ob-R are also expressed in pituitary and adrenal tumors, but little is known about the role of this cytokine in the pathophysiology.

Regulation of leptin synthesis and secretion before birth: implications for the early programming of adult obesity

A series of epidemiological, clinical and experimental studies have shown that there are associations between the fetal and neonatal nutritional environment and the amount and distribution of adipose tissue in adult life. This review considers the evidence for these relationships and discusses the potential impact of the prenatal nutritional experience on the development of the endocrine and neuroendocrine systems that regulate energy balance, with a particular emphasis on the role of the adipocyte-derived hormone, leptin. In the rodent, leptin derived from the mother may exert an important influence on the development of the appetite regulatory neural network and on the subsequent regulation of leptin synthesis and the risk for obesity in the offspring. In species such as the human and sheep, there is also recent evidence that the synthesis and secretion of adipocyte-derived hormones, such as leptin, are regulated in fetal life. Furthermore, the hypothalamic neuropeptides that regulate energy intake and expenditure in adult life are also present within the fetal brain and may be regulated by the prevailing level of maternal and hence fetal nutrient and hormonal signals, including leptin. This work is important in determining those initiating mechanisms within the 'fat-brain' axis in early life that precede the development of adult obesity.

Infusion of ACTH stimulates expression of adrenal ACTH receptor and steroidogenic acute regulatory protein mRNA in fetal sheep

The late-gestation plasma cortisol surge in the sheep fetus is critical for stimulating organ development and parturition. Increased adrenal responsiveness is one of the key reasons for the surge; however, the underlying mechanisms are not fully understood. Our recent studies suggest that ACTH-mediated increased expression of ACTH receptor (ACTH-R) and steroid acute regulatory protein (StAR) may play a role in enhancing responsiveness. Hence, we examined effects of ACTH infusion in fetal sheep on mRNA expression of these two mediators of adrenal responsiveness and assessed the functional consequences of this treatment in vitro. Fetuses of approximately 118 and 138 days of gestational age (dGA) were infused with ACTH-(1-24) for 24 h. Controls received saline infusion. Arterial blood was sampled throughout the infusion. Adrenals were isolated and analyzed for ACTH-R and StAR mRNA, or cells were cultured for 48 h. Cells were stimulated with ACTH, and medium was collected for cortisol measurement. Fetal plasma ACTH and cortisol concentrations increased over the infusion period in both groups. ACTH-R mRNA levels were significantly higher in ACTH-infused fetuses in both the 118 and 138 dGA groups. StAR mRNA increased significantly in both the 118 and 138 dGA groups. Adrenal cells from ACTH-infused fetuses were significantly more responsive to ACTH stimulation in terms of cortisol secretion than those from saline-infused controls. These findings demonstrate that increases in circulating ACTH levels promote increased expression of ACTH-R and StAR mRNA and are coupled to heightened adrenal responsiveness.

Long-term hypoxia increases leptin receptors and plasma leptin concentrations in the late-gestation ovine fetus

This study was designed to test the hypothesis that long-term hypoxia (LTH) increases fetal plasma leptin and fetal adipose or placental leptin expression and alters hypothalamic and adrenocortical leptin receptor (OB-R) expression. Pregnant ewes were maintained at high altitude (3,820 m) from day 30 to approximately 130 days of gestation. Reduced Po2 was maintained in the laboratory by nitrogen infusion through a maternal tracheal catheter. On day 132, normoxic control and LTH fetuses underwent surgical implantation of vascular catheters (n=6 for each group). Five days after surgery, maternal and fetal arterial blood samples were collected for leptin, insulin, and glucose analysis. Placental tissue, periadrenal fat, and fetal hypothalami and adrenal glands were collected from additional control (n=7) and LTH (n=8) fetuses for analysis of leptin mRNA by quantitative, real-time, RT-PCR (qRT-PCR). There was a significant (P<0.03) elevation in fetal plasma leptin in the LTH fetuses (3.5+/-0.7 ng/ml) vs. control (1.1+/-0.1 ng/ml). There were no differences in either glucose or insulin concentrations between the two groups. Periadrenal adipose leptin mRNA was significantly higher in the LTH group compared with control, as was placental leptin expression. The levels of leptin mRNA in adipose were approximately 70 times higher vs. placenta. LTH significantly reduced expression of OB-Ra (short-isoform) in the hypothalamus (P=0.0156), while resulting in a significant increase in adrenal OB-Rb (long-form) expression (P<0.03). Our data suggest that leptin is a hypoxia-inducible gene in the ovine fetus and OB-R expression is altered by LTH. These changes may be responsible in part, for our previously observed alterations in fetal hypothalamic-pituitary-adrenal function following LTH.

Pregnancy stage and number of fetuses may influence maternal plasma leptin in ewes

Maternal plasma leptin is elevated in ewes during pregnancy. The authors studied whether there was any relation between maternal plasma leptin and insulin concentrations, the number of fetuses and the circulating and faecal levels of gestagens. At the end of the breeding season in January the ovarian activity of Prolific Merino ewes was induced/synchronised with gestagen + eCG treatment. Ewes were inseminated artificially (AI) by laparoscopy. Blood and faecal samples were collected before AI (day 0) and again 41, 81 and 101 days later. The plasma levels of leptin (pL), insulin and progesterone (pP4), and the faecal P4 metabolite (P4-met) content were determined. The day 0 level of pL was significantly higher in pregnant (n = 24) than in non-pregnant ewes (n = 32). By day 41 the pL of pregnant animals had doubled, it showed a further moderate increase on day 81, and decreased slightly thereafter. During pregnancy pP4 and faecal P4-met rose continuously and were positively correlated at all stages. The mean levels of pL and pP4 and the faecal content of P4-met were lower in ewes bearing single (n = 12) than in those with 2 (n = 6) or 3-5 fetuses (n = 6). Analysis of variance demonstrated significant differences according to the number of fetuses in the pL and pP4, but not in P4-met (p = 0.042, 0.044, and 0.051, respectively). Leptin showed positive correlation with insulin before the AI but not during pregnancy. On days 41 and 81 pL showed a slight positive correlation with P4 and P4-met, which decreased slightly by day 101. This study shows that although leptinaemia is affected by the number of fetuses and the level of P4, pregnancy stage is a more important regulator than these additional factors.

Effects of central and systemic administration of leptin on neurotransmitter concentrations in specific areas of the hypothalamus

Leptin, a hormone produced by adipocytes, has been shown to affect a number of central functions, such as regulation of the hypothalamo-pituitary-adrenal axis, feeding, and body weight regulation. Because hypothalamic monoamines are intricately involved in the regulation of these functions, we hypothesized that leptin may produce its effects by altering the activity of these neurotransmitters. To test this hypothesis, male rats received peripheral (0, 100, or 500 μg ip), or central (0 or 5 μg icv) injections of leptin. The animals were killed 5 h later, and their brains were removed, frozen, and sectioned. Serum was collected to measure leptin and corticosterone by RIA. The paraventricular nucleus (PVN), arcuate nucleus (AN), ventromedial hypothalamus (VMH), dorsomedial dorsal nucleus (DMD), median eminence (ME), and medial preoptic area (MPA) were obtained using Palkovits' microdissection technique, and monoamine concentrations in these areas were determined using HPLC-EC. Intraperitoneal administration of leptin increased serum leptin concentrations in a dose-dependent manner ( P < 0.05). Both intraperitoneal and intracerebroventricular administration of leptin decreased serum corticosterone significantly ( P < 0.05). Norepinephrine (NE) concentration decreased significantly in the PVN, AN, and VMH after both intraperitoneal and intracerebroventricular administration of leptin ( P < 0.05). NE concentrations decreased significantly in the DMN after intracerebroventricular administration of leptin ( P < 0.05). Leptin treatment (both ip and icv) decreased dopamine concentrations significantly in the PVN. Serotonin (5-HT) concentration decreased significantly in the PVN after both intraperitoneal and intracerebroventricular injections of leptin and decreased in the VMH only with intracerebroventricular treatment of leptin. Leptin did not affect any of the monoamines in the ME and MPA. These results indicate that both central and systemic administration of leptin can affect hypothalamic monoamines in a region-specific manner, which, in turn, could mediate many of leptin's central and neuroendocrine effects.

Leptin in pregnancy: an update

Leptin influences satiety, adiposity, and metabolism and is associated with mechanisms regulating puberty onset, fertility, and pregnancy in various species. Maternal hyperleptinemia is a hallmark of mammalian pregnancy, although both the roles of leptin and the mechanisms regulating its synthesis appear to be taxa specific. In pregnant humans and nonhuman primates, leptin is produced by both maternal and fetal adipose tissues, as well as by the placental trophoblast. Specific receptors in the uterine endometrium, trophoblast, and fetus facilitate direct effects of the polypeptide on implantation, placental endocrine function, and conceptus development. A soluble isoform of the receptor may be responsible for inducing maternal leptin resistance during pregnancy and/or may facilitate the transplacental passage of leptin for the purpose of directly regulating fetal development. The steroid hormones are linked to the regulation of leptin and the leptin receptor and probably interact with other pregnancy-specific, serum-borne factors to regulate leptin dynamics during pregnancy. In addition to its effects on normal conceptus development, leptin is linked to mechanisms affecting a diverse array of pregnancy-specific pathologies that include preeclampsia, gestational diabetes, and intrauterine growth restriction. Association with these anomalies and with mechanisms pointing to a fetal origin for a range of conditions affecting the individual's health in adult life, such as obesity, diabetes mellitus, and cardiovascular disease, reiterate the need for continued research dedicated to elucidating leptin's roles and regulation throughout gestation.