A Crab Is Not a Fish: Unique Aspects of the Crustacean Endocrine System and Considerations for Endocrine Toxicology

Crustaceans-and arthropods in general-exhibit many unique aspects to their physiology. These include the requirement to moult (ecdysis) in order to grow and reproduce, the ability to change color, and multiple strategies for sexual differentiation. Accordingly, the endocrine regulation of these processes involves hormones, receptors, and enzymes that differ from those utilized by vertebrates and other non-arthropod invertebrates. As a result, environmental chemicals known to disrupt endocrine processes in vertebrates are often not endocrine disruptors in crustaceans; while, chemicals that disrupt endocrine processes in crustaceans are often not endocrine disruptors in vertebrates. In this review, we present an overview of the evolution of the endocrine system of crustaceans, highlight endocrine endpoints known to be a target of disruption by chemicals, and identify other components of endocrine signaling that may prove to be targets of disruption. This review highlights that crustaceans need to be evaluated for endocrine disruption with consideration of their unique endocrine system and not with consideration of the endocrine system of vertebrates.

Role of GH/IGF axis in arsenite-induced developmental toxicity in zebrafish embryos

Growth hormone (GH)/insulin-like growth factor (IGF) axis plays a critical role in fetal development. However, the effect of arsenite exposure on the GH/IGF axis and its toxic mechanism are still unclear. Zebrafish embryos were exposed to a range of NaAsO₂ concentrations (0.0-10.0 mM) between 4 and 120 h post-fertilization (hpf). Development indexes of survival, malformation, hatching rate, heart rate, body length and locomotor behavior were measured. Hormone levels, GH/IGF axis-related genes, and nerve-related genes were also tested. The results showed that survival rate, hatching rate, heart rate, body length and locomotor behavior all decreased, while deformity increased. At 120 hpf, the survival rate of zebrafish in 1.5 mM NaAsO₂ group was about 70%, the deformity rate exceeded 20%, and the body length shortened to 3.35 mm, the movement distance of zebrafish decreased approximately 63.6% under light condition and about 52.4% under dark condition. The level of GH increased and those of IGF did not change significantly, while the expression of GH/IGF axis related genes (ghra, ghrb, igf2r, igfbp3, igfbp2a, igfbp5b) and nerve related genes (dlx2, shha, ngn1, elavl3, gfap) decreased. In 1.5 mM NaAsO₂ group, the decrease of igfbp3 and igfbp5b was almost obvious, about 78.2% and 72.2%. The expression of nerve genes in 1.5 mM NaAsO₂ group all have declined by more than 50%. These findings suggested that arsenite exerted disruptive effects on the endocrine system by interfering with the GH/IGF axis, leading to zebrafish embryonic developmental toxicity.

Chronology of endocrine differentiation and beta-cell neogenesis

Diabetes is a chronic and incurable disease, which results from absolute or relative insulin insufficiency. Therefore, pancreatic beta cells, which are the only type of cell that expresses insulin, is considered to be a potential target for the cure of diabetes. Although the findings regarding beta-cell neogenesis during pancreas development have been exploited to induce insulin-producing cells from non-beta cells, there are still many hurdles towards generating fully functional beta cells that can produce high levels of insulin and respond to physiological signals. To overcome these problems, a solid understanding of pancreas development and beta-cell formation is required, and several mouse models have been developed to reveal the unique features of each endocrine cell type at distinct developmental time points. Here I review our understanding of pancreas development and endocrine differentiation focusing on recent progresses in improving temporal cell labeling in vivo.

Changes in the concentrations of four maternal steroids during embryonic development in the threespined stickleback (Gasterosteus aculeatus)

Embryonic exposure to steroids often leads to long-term phenotypic effects. It has been hypothesized that mothers may be able to create a steroid environment that adjusts the phenotypes of offspring to current environmental conditions. Complicating this hypothesis is the potential for developing embryos to modulate their early endocrine environment. This study utilized the threespined stickleback (Gasterosteus aculeatus) to characterize the early endocrine environment within eggs by measuring four steroids (progesterone, testosterone, estradiol, and cortisol) of maternal origin. We then examined how the concentrations of these four steroids changed over the first 12 days post fertilization (dpf). Progesterone, testosterone, estradiol, and cortisol of maternal origin could be detected within unfertilized eggs and levels of all four steroids declined in the first 3 days following fertilization. While levels of progesterone, testosterone, and estradiol remained low after the initial decline, levels of cortisol rose again by 8 dpf. These results demonstrate that G. aculeatus embryos begin development in the presence of a number of maternal steroids but levels begin to change quickly following fertilization. This suggests that embryonic processes change the early endocrine environment and hence influence the ability of maternal steroids to affect development. With these findings, G. aculeatus becomes an intriguing system in which to study how selection may act on both maternal and embryonic processes to shape the evolutionary consequence of steroid-mediated maternal effects.

Brain as an endocrine source of circulating 5-hydroxytryptamine in ontogenesis in rats

This study was aimed to test the authors' hypothesis stating that the developing brain before the closure of the blood brain barrier (BBB) operates as an endocrine organ that secretes classical neurotransmitters and neuropeptides into the general circulation. 5-Hydroxytryptamine (5-HT) was selected as a marker of brain endocrine activity though it is also secreted by peripheral organs. 5-HT was detected in blood of rats in a biologically active concentration at any studied age, from the 21st embryonic day till the 30th postnatal day. The brain was proven to be a source of circulating 5-HT before the BBB closure by showing that the 5-HT concentration in blood decreased significantly after the inhibition of 5-HT synthesis in the brain of neonates. The 5-HT concentration in blood was not diminished after the BBB closure, apparently due to compensatory increase of 5-HT secretion by peripheral sources. Thus, brain-derived 5-HT is delivered to the general circulation before the BBB closure being potentially capable of providing endocrine regulation of target organs.

Pancreas development in humans

PURPOSE OF REVIEW

We highlight some of the major recent advances in characterizing human pancreas development and endocrine cell differentiation.

RECENT FINDINGS

Extensive research efforts have helped to define crucial events in the mouse pancreas organogenesis. Information gained from these studies was used to develop human embryonic stem cell (hESC) differentiation protocols with the goal of generating functional glucose-responsive, insulin-producing human β-cells. In spite of remarkable progress in hESC differentiation, current protocols based on mouse developmental biology can produce human β-cells only in vivo. New differentiation markers and recently generated reagents may provide an unprecedented opportunity to develop a high-density expression map of human fetal pancreas and pancreatic islets that could serve as a reference point for in vitro hESC differentiation.

SUMMARY

Integrating an increased knowledge of human pancreas development into hESC differentiation protocols has the potential to greatly advance our ability to generate functional insulin-producing cells for β-cell replacement therapy.

Prenatal maternal stress exposure and immune function in the offspring

The intra-uterine environment provides the first regulatory connection for the developing fetus and shapes its physiological responses in preparation for postnatal life. Psychological stress acts as a programming determinant by setting functional parameters to abnormal levels, thus inducing postnatal maladaptation. The effects of prenatal maternal stress (PNMS) on the developing immune system have been documented mostly through animal studies, but inconsistent results and methodological differences have hampered the complete understanding of these findings. As the immune system follows a similar ontogenic pattern in all mammals, a translational framework based on the developmental windows of vulnerability proposed by immunotoxicology studies was created to integrate these findings. The objective of this review is to examine the available literature on PNMS and immune function in the offspring through the above framework and gain a better understanding of these results by elucidating the moderating influence of the stressor type, timing and duration, and the offspring species, sex and age at assessment. The evaluation of the literature through this framework showed that the effects of PNMS are parameter specific: the moderating effects of timing in gestation were relevant for lymphocyte population numbers, Natural Killer cell function and mitogen-induced proliferation. The presence of an important and directional sexual dimorphism was evident and the influence of the type or duration of PNMS paralleled that of stress in non-pregnant animals. In conclusion, PNMS is a relevant factor in the programming of immune function. Its consequences may be related to disorders with an important immune component such as allergies.

Development of the human pancreas from foregut to endocrine commitment

Knowledge of human pancreas development underpins our interpretation and exploitation of human pluripotent stem cell (PSC) differentiation toward a β-cell fate. However, almost no information exists on the early events of human pancreatic specification in the distal foregut, bud formation, and early development. Here, we have studied the expression profiles of key lineage-specific markers to understand differentiation and morphogenetic events during human pancreas development. The notochord was adjacent to the dorsal foregut endoderm during the fourth week of development before pancreatic duodenal homeobox-1 detection. In contrast to the published data from mouse embryos, during human pancreas development, we detected only a single-phase of Neurogenin 3 (NEUROG3) expression and endocrine differentiation from approximately 8 weeks, before which Nirenberg and Kim homeobox 2.2 (NKX2.2) was not observed in the pancreatic progenitor cell population. In addition to revealing a number of disparities in timing between human and mouse development, these data, directly assembled from human tissue, allow combinations of transcription factors to define sequential stages and differentiating pancreatic cell types. The data are anticipated to provide a useful reference point for stem cell researchers looking to differentiate human PSCs in vitro toward the pancreatic β-cell so as to model human development or enable drug discovery and potential cell therapy.

Sex and breed-dependent organ development and metabolic responses in foetuses from lean and obese/leptin resistant swine

The present study aimed to determine the effects of breed and sex on growth patterns and metabolic features of advanced-pregnancy foetuses exposed to the same environmental conditions. Thus, at Day 62 of pregnancy, swine foetuses from an obese breed with leptin resistance (Iberian breed) were compared to lean crossbred foetuses (25% Large White ×25% Landrace ×50% Pietrain). There were differential developmental patterns in foetuses with leptin resistance, mainly a higher relative weight of the brain resembling “brain-sparing effect”. Prioritization of brain growth may be protective for the adequate growth and postnatal survival of the Iberian individuals, an ancient breed reared in extensive semi-feral conditions for centuries. There were also clear sex-related differences in foetal development and metabolism in the Iberian breed. Female Iberian foetuses were similar in size and weight to male littermates but had a significantly higher relative liver to body weight ratio resembling “liver-sparing effect” and a trend for a higher relative intestine to body ratio. Moreover, the availability of triglycerides, cholesterol and IL-6 in female Iberian foetuses was similar to that of lean crossbred foetuses. Overall, these features may favour a better postnatal survival and development of females, the sex more critical for the species survival. These findings set the basis for future translational studies aimed at increasing the knowledge on the interaction between genetic and environmental factors in the early programming of the adult phenotype.

New findings in pancreatic and intestinal endocrine development to advance regenerative medicine

PURPOSE OF REVIEW

We highlight some of the major recent advances that have been made towards understanding the mechanisms that control endocrine differentiation and cell identity in the pancreas and intestine.

RECENT FINDINGS

Notch signaling plays a complex role in the fate choice between endocrine, duct, and acinar lineages in the developing pancreas. New approaches to dissecting the role of mesenchymal cells in the developing endocrine pancreas reveal inhibitory signals from the endothelium. Epigenetic mechanisms represent another layer of control over pancreatic development and β cell identity. Further details on the transcriptional control of enteroendocrine cell development have emerged and revealed a surprising role for FoxO1 in restraining insulin expression in the gut. Incremental progress is being made in the field of directed differentiation of embryonic stem cells to pancreatic β cells and the first reported differentiation of human embryonic stem cells into intestinal organoids containing enteroendocrine cells represents a major breakthrough.

SUMMARY

Greater knowledge of the fundamental processes controlling endocrine development in the pancreas and intestine has the potential to advance the field of regenerative medicine by providing a pathway to successfully create cell types of clinical interest.

[Novel concepts in biology of diffuse endocrine system: results and future investigations]

Diffuse endocrine system is a largest part of endocrine system of vertebrates. Recend findings showed that DES-cells are not neuroectodermal but have ectodermal, mesodermal, and entodermal ontogeny. The article reviews novel concept of diffuse endocrine system anatomy and physiology, functional role of DES hormones and poorly investigated aspects like DES-cell morphology, hormones secretion in normal and pathologic conditions. Further research of diffuse endocrine system has a great significance for biochemistry, morphology, and clinical medicine.

The origin of neuroendocrine tumors and the neural crest saga

In this essay, the role of the neural crest in the development of the vertebrate embryo is briefly described. The techniques used to document the neural crest origin of various cell types and the tumors arising from them are discussed, with emphasis on Le Douarin's quail-chick chimera model. The current dogma on the origin of the cells of the diffuse endocrine system is presented, and some personal conjectures based on the microscopic appearances of various types of normal, vestigial and neoplastic human tissues are offered to the reader as 'food for thought.'

[Cross-regulation in development of neuroendocrine and immune systems]

Cross-regulatory effects of immune and neuroendocrine systems on their appearance and functioning occur during a whole life period. At different stages of ontogenesis, the functions of these systems are diverse. In perinatal ontogenesis hormones, neuropeptides and neurotransmitters control the processes of growth and differentiation of various embryo tissues, particularly lymphoid. In the postnatal period, their functions are mostly in homeostasis maintaining of the immune system in response to changes of the environment. Conversely, transmitters of the immune system, such as cytokines, whose synthesis is increased in inflammation, and thymic peptides, program the development of the neuroendocrine system of the embryo. The perinatal period is crucial for final appearance of these systems. Changes in one of the interacting systems, caused by negative environmental factors at this stage, usually provoke changes in other developing systems for a long period. Plasticity of physiological systems in perinatal development allows the organism to adapt to changed conditions. However, these changes can limit physiological functions in interacting systems and induce the appearance of various pathologies in postnatal life.

The emergence of adipocytes

In mammals, the adipose organ is composed of white adipocytes (primary site in energy storage) and of brown adipocytes (specialized in thermogenesis). Adipocytes arise from mesenchymal stem cells (MSCs) by a sequential pathway of differentiation. MSCs develop either from ectoderm or mesoderm and commit into different undifferentiated precursors, which upon the expression of key transcription factors enter a differentiation program to acquire their specific functions. When triggered by appropriate developmental cues, MSCs become committed to the adipocyte lineage. White adipocytes differentiate from various types of vascular cell types, probably located within the white adipose tissue itself. Brown adipocytes arise from myogenic precursors. The differentiation between white adipocyte and brown adipocyte lineages occurs in the earliest steps of the fetal development, and both phenotypes are acquired independently. A better knowledge of these differentiation pathways allows new therapeutic strategies for reconstruction of damaged conjunctive tissues and for the control or prevention of risks associated with obesity in humans.

Review: the role of neural crest cells in the endocrine system

The neural crest is a pluripotent population of cells that arises at the junction of the neural tube and the dorsal ectoderm. These highly migratory cells form diverse derivatives including neurons and glia of the sensory, sympathetic, and enteric nervous systems, melanocytes, and the bones, cartilage, and connective tissues of the face. The neural crest has long been associated with the endocrine system, although not always correctly. According to current understanding, neural crest cells give rise to the chromaffin cells of the adrenal medulla, chief cells of the extra-adrenal paraganglia, and thyroid C cells. The endocrine tumors that correspond to these cell types are pheochromocytomas, extra-adrenal paragangliomas, and medullary thyroid carcinomas. Although controversies concerning embryological origin appear to have mostly been resolved, questions persist concerning the pathobiology of each tumor type and its basis in neural crest embryology. Here we present a brief history of the work on neural crest development, both in general and in application to the endocrine system. In particular, we present findings related to the plasticity and pluripotency of neural crest cells as well as a discussion of several different neural crest tumors in the endocrine system.

The chicken embryo as a model for developmental endocrinology: development of the thyrotropic, corticotropic, and somatotropic axes

The ease of in vivo experimental manipulation is one of the main factors that have made the chicken embryo an important animal model in developmental research, including developmental endocrinology. This review focuses on the development of the thyrotropic, corticotropic and somatotropic axes in the chicken, emphasizing the central role of the pituitary gland in these endocrine systems. Functional maturation of the endocrine axes entails the cellular differentiation and acquisition of cell function and responsiveness of the different glands involved, as well as the establishment of top-down and bottom-up anatomical and functional communication between the control levels. Extensive cross-talk between the above-mentioned axes accounts for the marked endocrine changes observed during the last third of embryonic development. In a final paragraph we shortly discuss how genomic resources and new transgenesis techniques can increase the power of the chicken embryo model in developmental endocrinology research.

Naturally occurring perinatal growth restriction in mice programs cardiovascular and endocrine function in a sex- and strain-dependent manner

Perinatal growth restriction (PGR) is associated with type 2 diabetes and hypertension. Identification of an isogenic mouse model of fetal programming will facilitate mechanistic understanding. We sought to test the hypotheses that 1) PGR impairs glucose tolerance and induces hypertension; and 2) the programming phenotype is more severe in an inbred mouse strain susceptible to diabetes (C57BL/6) than in a strain without such genetic predisposition (DBA/2). PGR pups were paired at weaning with same sex normally grown littermates. Glucose and insulin tolerance tests were performed at 17 wk, and systolic blood pressure (SBP) was measured at 20 wk. Impaired glucose tolerance was evident only among female PGR mice from both strains. While PGR did not alter insulin sensitivity in either strain, female DBA/2 mice had significantly decreased insulin levels during glucose tolerance testing. SBP was increased in PGR male C57BL/6 mice (p<0.01), while heart rate was decreased in PGR male DBA/2 mice (p<0.05). These studies indicate that in isogenic mice, PGR alters endocrine and cardiovascular physiology in female and male mice, respectively. Strain-and sex-specific genetic susceptibilities emphasize the need to consider genetic predisposition when evaluating the role of the perinatal environmental in the inception of adult disease.

Cell and molecular biology of Notch

Notch signalling is a cell-cell communication process, which allows the establishment of patterns of gene expression and differentiation, regulates binary cell fate choice and the maintenance of stem cell populations. So far, the data published has elucidated the main players in the Notch signalling pathway. However, its regulatory mechanisms are exhibiting an increasing complexity which could account for the multitude of roles it has during development and in adult organisms. In this review, we will describe the multiple roles of Notch and how various factors can regulate Notch signalling.

The menace of endocrine disruptors on thyroid hormone physiology and their impact on intrauterine development

The delivery of the appropriate thyroid hormones quantity to target tissues in euthyroidism is the result of unopposed synthesis, transport, metabolism, and excretion of these hormones. Thyroid hormones homeostasis depends on the maintenance of the circulating 'free' thyroid hormone reserves and on the development of a dynamic balance between the 'free' hormones reserves and those of the 'bound' hormones with the transport proteins. Disturbance of this hormone system, which is in constant interaction with other hormone systems, leads to an adaptational counter-response targeting to re-establish a new homeostatic equilibrium. An excessive disturbance is likely to result, however, in hypo- or hyper- thyroid clinical states. Endocrine disruptors are chemical substances forming part of 'natural' contaminating agents found in most ecosystems. There is abundant evidence that several key components of the thyroid hormones homeostasis are susceptible to the action of endocrine disruptors. These chemicals include some chlorinated organic compounds, polycyclic aromatic hydrocarbons, herbicides, and pharmaceutical agents. Intrauterine exposure to endocrine disruptors that either mimic or antagonize thyroid hormones can produce permanent developmental disorders in the structure and functioning of the brain, leading to behavioral changes. Steroid receptors are important determinants of the consequences of endocrine disruptors. Their interaction with thyroid hormones complicates the effect of endocrine disruptors. The aim of this review is to present the effect of endocrine disruptors on thyroid hormones physiology and their potential impact on intrauterine development.

Notch signaling in development and cancer

Notch is an evolutionarily conserved local cell signaling mechanism that participates in a variety of cellular processes: cell fate specification, differentiation, proliferation, apoptosis, adhesion, epithelial-mesenchymal transition, migration, and angiogenesis. These processes can be subverted in Notch-mediated pathological situations. In the first part of this review, we will discuss the role of Notch in vertebrate central nervous system development, somitogenesis, cardiovascular and endocrine development, with attention to the mechanisms by which Notch regulates cell fate specification and patterning in these tissues. In the second part, we will review the molecular aspects of Notch-mediated neoplasias, where Notch can act as an oncogene or as a tumor suppressor. From all these studies, it becomes evident that the outcome of Notch signaling is strictly context-dependent and differences in the strength, timing, cell type, and context of the signal may affect the final outcome. It is essential to understand how Notch integrates inputs from other signaling pathways and how specificity is achieved, because this knowledge may be relevant for future therapeutic applications.

Temporal control of neurogenin3 activity in pancreas progenitors reveals competence windows for the generation of different endocrine cell types

All pancreatic endocrine cells, producing glucagon, insulin, somatostatin, or PP, differentiate from Pdx1+ progenitors that transiently express Neurogenin3. To understand whether the competence of pancreatic progenitors changes over time, we generated transgenic mice expressing a tamoxifen-inducible Ngn3 fusion protein under the control of the pdx1 promoter and backcrossed the transgene into the ngn3(-/-) background, devoid of endogenous endocrine cells. Early activation of Ngn3-ER(TM) almost exclusively induced glucagon+ cells, while depleting the pool of pancreas progenitors. As from E11.5, Pdx1+ progenitors became competent to differentiate into insulin+ and PP+ cells. Somatostatin+ cells were generated from E14.5, while the competence to make glucagon+ cells was dramatically decreased. Hence, pancreas progenitors, similar to retinal or cortical progenitors, go through competence states that each allow the generation of a subset of cell types. We further show that the progenitors acquire competence to generate late-born cells in a mechanism that is intrinsic to the epithelium.

Calsenilin is required for endocrine pancreas development in zebrafish

Calsenilin/DREAM/Kchip3 is a neuronal calcium-binding protein. It is a multifunctional protein, mainly expressed in neural tissues and implicated in regulation of presenilin processing, repression of transcription, and modulation of A-type potassium channels. Here, we performed a search for new genes expressed during pancreatic development and have studied the spatiotemporal expression pattern and possible role of calsenilin in pancreatic development in zebrafish. We detected calsenilin transcripts in the pancreas from 21 somites to 39 hours postfertilization stages. Using double in situ hybridization, we found that the calsenilin gene was expressed in pancreatic endocrine cells. Loss-of-function experiments with anti-calsenilin morpholinos demonstrated that injected morphants have a significant decrease in the number of pancreatic endocrine cells. Furthermore, the knockdown of calsenilin leads to perturbation in islet morphogenesis, suggesting that calsenilin is required for early islet cell migration. Taken together, our results show that zebrafish calsenilin is involved in endocrine cell differentiation and morphogenesis within the pancreas.

The fringe molecules induce endocrine differentiation in embryonic endoderm by activating cMyt1/cMyt3

Endocrine differentiation in the early embryonic pancreas is regulated by Notch signaling. Activated Notch signaling maintains pancreatic progenitor cells in an undifferentiated state, whereas suppression of Notch leads to endocrine cell differentiation. Yet it is not known what mechanism is employed to inactivate Notch in a correct number of precursor cells to balance progenitor proliferation and differentiation. We report that an established Notch modifier, Manic Fringe (Mfng), is expressed in the putative endocrine progenitors, but not in exocrine pancreatic tissues, during early islet differentiation. Using chicken embryonic endoderm as an assaying system, we found that ectopic Mfng expression is sufficient to induce endodermal cells to differentiate towards an endocrine fate. This endocrine-inducing activity depends on inactivation of Notch. Furthermore, ectopic Mfng expression induces the expression of basic helix-loop-helix gene, Ngn3, and two zinc finger genes, cMyt1 and cMyt3. These results suggest that Mfng-mediated repression of Notch signaling could serve as a trigger for endocrine islet differentiation.

An amylase/Cre transgene marks the whole endoderm but the primordia of liver and ventral pancreas

Mice bearing a Cre-encoding transgene driven by a compound [SV40 small t antigen/mousealpha-amylase-2] promoter expressed the recombinase at early developmental stages broadly in the embryonic endoderm before the pancreas and lungs begin to outgrow, but not in other germ layers, as determined indirectly by beta-galactosidase and YFP reporter activity, indicating that the transgene is in fact an endodermic marker. Interestingly, the liver and ventral pancreas were excluded from this expression pattern, denoting that the chimerical alpha-amylase-2 promoter was not active in the anterior leading edge of the endoderm (the presumptive region from which liver and ventral pancreas form). These transgenics thus confirm, among other findings, that dorsal and ventral pancreatic primordia have different intrinsic transcriptional capabilities. In conclusion, we have generated a new transgenic mouse that should be useful to target endoderm at early stages, without affecting the liver or ventral pancreas before embryonic day E12.5.

The proneural gene ascl1a is required for endocrine differentiation and cell survival in the zebrafish adenohypophysis

Mammalian basic helix-loop-helix proteins of the achaete-scute family are proneural factors that, in addition to the central nervous system, are required for the differentiation of peripheral neurons and sensory cells, derivatives of the neural crest and placodal ectoderm. Here, in identifying the molecular nature of the pia mutation, we investigate the role of the zebrafish achaete-scute homologue ascl1a during development of the adenohypophysis, an endocrine derivative of the placodal ectoderm. Similar to mutants deficient in Fgf3 signaling from the adjacent ventral diencepahalon, pia mutants display failure of endocrine differentiation of all adenohypophyseal cell types. Shortly after the failed first phase of cell differentiation, the adenohypophysis of pia mutants displays a transient phase of cell death, which affects most, but not all adenohypophyseal cells. Surviving cells form a smaller pituitary rudiment, lack expression of specific adenohypophyseal marker genes (pit1, neurod), while expressing others (lim3, pitx3), and display an ultrastructure reminiscent of precursor cells. During normal development, ascl1a is expressed in the adenohypophysis and the adjacent diencephalon, the source of Fgf3 signals. However, chimera analyses show that ascl1a is required cell-autonomously in adenohypophyseal cells themselves. In fgf3 mutants, adenohypophyseal expression of ascl1a is absent, while implantation of Fgf3-soaked beads into pia mutants enhances ascl1a, but fails to rescue pit1 expression. Together, this suggests that Ascl1a might act downstream of diencephalic Fgf3 signaling to mediate some of the effects of Fgf3 on the developing adenohypophysis.

Members of the Plag gene family are expressed in complementary and overlapping regions in the developing murine nervous system

In the developing nervous system, cell fate specification and proliferation are tightly coupled events, ensuring the coordinated generation of the appropriate numbers and correct types of neuronal and glial cells. While it has become clear that tumor suppressor genes and oncogenes are key regulators of cell division in tumor cells, their role in normal cellular and developmental processes is less well understood. Here we present a comparative analysis of the expression profiles of the three members of the pleiomorphic adenoma gene (Plag) family, which encode zinc finger transcription factors previously characterized as tumor suppressors (Zac1) or oncogenes (Plag1, Plag-l2). We focused our analysis on the developing nervous system of mouse where we found that the Plag genes were expressed in both unique and overlapping patterns in the central and peripheral nervous systems, and in olfactory and neuroendocrine lineages. Based on their patterns of expression, we suggest that members of the Plag gene family might control cell fate and proliferation decisions in the developing nervous system and propose that deciphering these functions will help to explain why their inappropriate inactivation/activation leads to tumor formation.

Endocrine and metabolic programming during intrauterine development

In humans, low birth weight is associated with an increased risk of metabolic dysfunction in adult life. Many of these metabolic disorders have an endocrine origin and are accompanied by abnormal hormone concentrations. This has led to the hypothesis that adult metabolic disease arises in utero as a result of programming of key endocrine systems during suboptimal intrauterine conditions associated with fetal growth retardation. This review examines the experimental evidence for prenatal endocrine programming with particular emphasis on endocrine axes involved in growth and metabolism, namely, the hypothalamic-pituitary-adrenal axis, the endocrine pancreas and the somatotrophic axis. It also considers how changes in these endocrine systems contribute to the programming of metabolism in later life.

Macrophages in the murine pancreas and their involvement in fetal endocrine development in vitro

Macrophages are a heterogeneous population of cells that belong to the mononuclear phagocyte system. They play an important role in tissue homeostasis and remodeling and are also potent immune regulators. Pancreatic macrophages are critically involved in the development and pathogenesis of autoimmune diabetes. To elucidate the ontogeny of pancreatic macrophages, we characterized in this study the macrophages present in the adult and developing fetal pancreas of normal mice. We additionally examined the presence of local macrophage precursors and the involvement of macrophages in the growth of endocrine tissue in the fetal pancreas. We identified two phenotypically distinct macrophage subsets in the adult pancreas. The majority of macrophages was CD45(+)ER-MP23(+)MOMA-1(+). Under noninflammatory conditions, only a minority ( approximately 5%) of the pancreatic macrophages additionally expressed the macrophage marker F4/80. In contrast, in the fetal pancreas, phenotypically, mature macrophages were identified exclusively by their expression of F4/80 and lacked detectable staining with ER-MP23 and MOMA-1 antibodies. In fetal pancreas organ cultures, we could show that macrophages develop from pre-existing precursors, which are present in the fetal pancreas at embryonic age 12.5. Moreover, the number of macrophages increased significantly when macrophage-colony stimulating factor was added to these cultures. It is important that this increase of F4/80-positive cells was paralleled by an increase in the number of insulin-producing cells, suggesting that macrophages support the growth of these endocrine cells.

Hedgehog signaling regulates expansion of pancreatic epithelial cells

Embryonic Hedgehog signaling is essential for proper tissue morphogenesis and organ formation along the developing gastrointestinal tract. Hedgehog ligands are expressed throughout the endodermal epithelium at early embryonic stages but excluded from the region that will form the pancreas. Ectopic activation of Hedgehog signaling at the onset of pancreas development has been shown to inhibit organ morphogenesis. In contrast, Hedgehog signaling components are found within pancreatic tissue during subsequent stages of development as well as in the mature organ, indicating that a certain level of pathway activation is required for normal organ development and function. Here, we ectopically activate the Hedgehog pathway midway through pancreas development via expression of either Sonic (Shh) or Indian Hedgehog (Ihh) under control of the human Pax4-promoter. Similar pancreatic defects are observed in both Pax4-Shh and Pax4-Ihh transgenic lines, suggesting that regulation of the overall level of Hedgehog activity is critical for proper pancreas development. We also show that Hedgehog signaling controls mesenchymal vs. epithelial tissue differentiation and that pathway activation impairs formation of epithelial progenitors. Thus, tight control of Hedgehog pathway activity throughout embryonic development ensures proper pancreas organogenesis.

Relationship between ethinylestradiol-mediated changes in endocrine function and reproductive impairment in Japanese medaka (Oryzias latipes)

Many biochemical endpoints currently are used to describe endocrine function in fish; however, the sensitivity of these parameters as biomarkers of impaired reproduction or sexual development is not well understood. In the present study, adult Japanese medaka (Oryzias latipes) were assessed for reproductive output and endocrine function, including circulating steroid concentrations, ex vivo steroidogenesis from the gonads, aromatase activity, hepatic estrogen receptor (ER), and plasma vitellogenin (VTG) after exposure to 0, 0.2, 5, 500, and 2,000 ng/L of 17alpha-ethinylestradiol (EE) for 14 d. The EE altered these biochemical responses at various sites along the hypothalamus-pituitary-gonadal axis at concentrations as low as 0.2 ng/L, but it only depressed reproductive function at concentrations of 500 ng/L or greater. Offspring also had reduced ability to hatch at 500 ng/L of EE, but this concentration did not produce any other observed changes in development or sexual phenotype. The reproductive parameters correlated well with VTG, ER, and gonadosomatic index (GSI) in both sexes of adult medaka, which could be indicative of the ER-mediated mode of action for EE. Vitellogenin and ER were elevated at higher concentrations of EE in both sexes, whereas GSI was decreased. Overall, most biochemical endpoints were more sensitive than reproduction or development to exposure, indicating that reproductive function may be relatively protected.

The complex between urokinase-type plasminogen activator (uPA) and its type-1 inhibitor (PAI-I) independently predicts response to first-line endocrine therapy in advanced breast cancer

It has been shown that urokinase-type plasminogen activator (uPA) and its main inhibitor (PAI-I) have predictive value for therapy success in advanced breast cancer. Levels of the complex between uPA and PAI-I, formed when both molecules are in their active form, might have superior predictive power. Here, we investigate the association between levels of uPA:PAI-I complex and rate of response to first-line systemic therapy for advanced breast cancer. Tumor tissues of 170 patients with advanced breast cancer were analyzed for uPA:PAI-I complex concentrations using a quantitative enzyme-linked immunosorbent assay. The patients received either endocrine therapy (n=96) or chemotherapy (n=74) as first-line treatment after diagnosis of advanced disease. Of the endocrine treated patients, those with high levels of uPA:PAI-I complex showed a shorter progression-free survival (PFS) compared to patients with lower uPA:PAI-I complex levels (P=0.035). Furthermore, in the multivariate regression analysis a significant lower rate of response to first-line endocrine therapy was found in patients with high uPA:PAI-I complex levels compared to patients with low uPA:PAI-I complex levels (odds ratio (OR)=0.27, 95% CI, 0.09-0.59, P=0.018), in addition to the predictive impact of the steroid hormone receptor (ER/PgR) status (OR=2.68, 95% CI, 1.08-6.63, P=0.033). Complex levels did not predict efficacy of chemotherapy in patients with advanced breast cancer. The results show that the plasminogen activation system affects the response to endocrine therapy independent of steroid hormone receptor status and may be of help to further refine the indication for this treatment in individual patients. Further studies are warranted to explain this underlying resistance to endocrine therapy when uPA:PAI-I levels are high.

Development of pancreatic islets in pancreatic polypeptide-overexpressing mice

Recently we produced pancreatic polypeptide transgenic (PPTG) mice and found that PP was overexpressed in pancreatic islets. The present study examines development of four islet hormones in PPTG mice at embryonic days (ED) 15, 17, and 19, and in adult animals. Adult PPTG mice showed massive aggregation of PP-positive cells and glucagon-positive cells seen at the central area of the islets. Confocal laser microscopic study showed that three islet hormones (insulin, glucagon and PP) were completely overlapped in islets of PPTG mice. Overlapping of somatostatin/glucagon and somatostatin/PP were also increased at the peripheral area of the islets in adult PPTG mice compared to wild-type mice. In prenatal development of pancreatic islets of PPTG mice, somatostatin/glucagon overlapping cells appeared at ED 15, two days earlier than in wild-type mice. Differentiation of these somatostatin/glucagon double-positive cells into single-positive cells was disturbed in the PPTG mice during perinatal to postnatal periods. Differentiation of glucagon/insulin-double positive cells into single-positive cells was disturbed remarkably in postnatal development of the islets of PPTG mice. The present results suggest that early and overexpression of PP may engender the early appearance of somatostatin producing cells; however, that may disturb differentiation of multihormonal immature endocrine cells into single hormonal mature endocrine cells.

The diffuse endocrine system: from embryogenesis to carcinogenesis

In the present review we will summarise the current knowledge about the cells comprising the Diffuse Endocrine System (DES) in mammalian organs. We will describe the morphological, histochemical and functional traits of these cells in three major systems gastrointestinal, respiratory and prostatic. We will also focus on some aspects of their ontogeny and differentiation, as well as to their relevance in carcinogenesis, especially in neuroendocrine tumors. The first chapter describes the characteristics of DES cells and some of their specific biological and biochemical traits. The second chapter deals with DES in the gastrointestinal organs, with special reference to the new data on the differentiation mechanisms that leads to the appearance of endocrine cells from an undifferentiated stem cell. The third chapter is devoted to DES of the respiratory system and some aspects of its biological role, both, during development and adulthood. Neuroendocrine hyperplasia and neuroendocrine lung tumors are also addressed. Finally, the last chapter deals with the prostatic DES, discussing its probable functional role and its relevance in hormone-resistant prostatic carcinomas.

Endocrine and nutritional regulation of fetal adipose tissue development

In the fetus, adipose tIssue comprises both brown and white adipocytes for which brown fat is characterised as possessing the unique uncoupling protein (UCP)1. The dual characteristics of fetal fat reflect its critical role at birth in providing lipid that is mobilised rapidly following activation of UCP1 upon cold exposure to the extra-uterine environment. A key stage in the maturation of fetal fat is the gradual rise in the abundance of UCP1. For species with a mature hypothalamic-pituitary axis at birth there is a gradual increase in the amount and activity of UCP1 during late gestation, in conjunction with an increase in the plasma concentrations of catecholamines, thyroid hormones, cortisol, leptin and prolactin. These may act individually, or in combination, to promote UCP1 expression and, following the post-partum surge in each hormone, UCP1 abundance attains maximal amounts. Adipose tIssue grows in the fetus at a much lower rate than in the postnatal period. However, its growth is under marked nutritional constraints and, in contrast to many other fetal organs that are unaffected by nutritional manipulation, fat mass can be significantly altered by changes in maternal and, therefore, fetal nutrition. Fat deposition in the fetus is enhanced during late gestation following a previous period of nutrient restriction up to mid gestation. This is accompanied by increased mRNA abundance for the receptors of IGF-I and IGF-II. In contrast, increasing maternal nutrition in late gestation results in less adipose tIssue deposition but enhanced UCP1 abundance. The pronounced nutritional sensitivity of fetal adipose tIssue to both increased and decreased maternal nutrition may explain why the consequences of an adverse nutritional environment persist into later life.

Expression of VGF mRNA in developing neuroendocrine and endocrine tissues

Analysis of knockout mice suggests that the neurotropin-inducible secreted polypeptide VGF (non-acronymic) plays an important role in the regulation of energy balance. VGF is synthesized by neurons in the central and peripheral nervous systems (CNS, PNS), as well as in the adult pituitary, adrenal medulla, endocrine cells of the stomach and pancreatic beta cells. Thus VGF, like cholecystokinin, leptin, ghrelin and other peptide hormones that have been shown to regulate feeding and energy expenditure, is synthesized in both the gut and the brain. Although detailed developmental studies of VGF localization in the CNS and PNS have been completed, little is known about the ontogeny of VGF expression in endocrine and neuroendocrine tIssues. Here, we report that VGF mRNA is detectable as early as embryonic day 15.5 in the developing rat gastrointestinal and esophageal lumen, pancreas, adrenal, and pituitary, and we further demonstrate that VGF mRNA is synthesized in the gravid rat uterus, together supporting possible functional roles for this polypeptide outside the nervous system and in the enteric plexus.

Insulin-like growth factor I (IGF-I) regulates endocrine activity of the embryonic testis in the mouse

Insulin-like growth factor I (IGF-I) is important for gonadal and reproductive functions in mammals, although the physiological role of this growth factor during gonadal development in rodents remains largely unknown. Here, we examined the steady-state levels of IGF-I mRNA by the reverse transcriptase polymerase chain reaction (RT-PCR). IGF-I protein expression was also detected by Western blot. The effect of IGF-I as promoter of 17alpha-hydroxylase/C17-20 lyase and 17beta-hydroxysteroid dehydrogenase enzyme activity in vitro was evaluated by radioimmunoassay. Onset of IGF-I gene expression was on day E10 (urogenital ridge stage). IGF-I mRNA expression was markedly reduced on days E12 and E13 (testicular differentiation stage). IGF-I transcripts increased on day E14 and their transcription levels were maintained throughout the stages analyzed. Several IGF-I protein bands of 31-100 kDa were observed. Culture experiments demonstrated that 17alpha-hydroxyprogesterone and testosterone (T) secretion levels increased in the presence of IGF-I on days E11-E17. Additive effects of IGF-I plus (Bu)2cAMP were also seen during testicular development. It is proposed that IGF-I regulates the expression of key steroidogenic enzymes important for endocrine activity of the testis during prenatal development leading to establishment of the male phenotype and fertility.

The influence of various physiological challenges on permanent changes to the cardiovascular system

The concept of fetal programming provides an intellectual framework that links physiological adaptations that occur during development to permanent changes in postnatal regulatory systems. Recent research in the area of cardiovascular programming has highlighted the mechanisms by which these changes exert their effects. The aim of this review is to integrate some of the literature on nutritional changes, exposure to excess glucocorticoids and other challenges during development as they provide support for various mechanisms of programming of the cardiovascular system.

All-trans retinoic acid induces differentiation of ducts and endocrine cells by mesenchymal/epithelial interactions in embryonic pancreas

Retinoids during the embryonic period act as a mesenchymal inducer in many organs, including kidney, lung, central nervous system, and gut. Retinoic acid (RA) demonstrates insulinotropic effects in adult pancreas, but only a limited study has elucidated its role in pancreatic organogenesis. In this study, we have analyzed the existence of RA-signaling machinery in embryonic pancreas and evaluated its role using in vitro tissue culture experiments. Here we show the presence of endogenous retinaldehyde dehydrogenase 2 (RALDH2), the most effective RA-synthesizing enzyme, RA-binding proteins, and RA receptors (RARs) in embryonic pancreatic tissue. RALDH2 is expressed exclusively in the mesenchyme. Exogenously added all-trans-retinoic acid (atRA) in tissue culture experiments stimulated differentiation of endocrine and duct cells and promoted apoptotic cell death of acinar tissue. Furthermore, we demonstrate that atRA upregulates the PDX-1 expression. Taken together, our data suggest that atRA-mediated mesenchymal/epithelial interactions play an important role in determining the cell fate of epithelial cells via regulation of the PDX-1 gene, leading to the proper formation of the endocrine versus exocrine component during pancreatic organogenesis.

Mammalian development in a changing environment: exposure to endocrine disruptors reveals the developmental plasticity of steroid-hormone target organs

Recent findings in the field of environmental endocrine disruption have revealed that developmental exposure to estrogenic chemicals induces morphological, functional, and behavioral anomalies associated with reproduction. The aim of the present study was to determine the effects of in utero exposure to low doses of the estrogenic chemical bisphenol A (BPA) on the development of the female reproductive tissues and mammary glands in CD-1 mice. Humans are exposed to BPA, which leaches from dental materials and plastic food and beverage containers. Here we report that prenatal exposure to BPA induces alterations in tissue organization within the ovaries and mammary glands and disrupts estrous cyclicity in adulthood. Because estrogen receptors are expressed developmentally in these estrogen-target organs, we propose that BPA may directly affect the expression of genes involved in their morphogenesis. In addition, alterations in the sexual differentiation of the brain, and thus the hypothalamic-pituitary-gonadal axis, may further contribute to the observed phenotype. The emerging field of endocrine disruptors promises to provide new insights into the mechanisms underlying the development of hormone-target organs and demonstrates that the environment plays important roles in the making of phenotypes.

Influence of parental and developmental cadmium exposure on endocrine and reproductive function in Japanese medaka (Oryzias latipes)

Cadmium (Cd) is a ubiquitous element and an important anthropogenic metal contaminant. A series of assays were modified or developed for Japanese medaka (Oryzias latipes), and used to compare the effects of Cd exposure on indicators of endocrine function in adult animals previously exposed in ovo or as hatchlings. Adults were raised either from eggs produced during a 2 week exposure to 0-10 microg/l Cd or from fry exposed for 2 weeks beginning 2 days after hatching. The reproductive capacity of the resulting adults was determined during a 2 week period during which half of the animals were re-exposed to Cd. Two week Cd exposure did not result in reproductive impairment despite producing some changes in circulating steroid concentration. In addition, 1 microg/l cadmium exposure in ovo elevated male hepatic vitellogenin (VTG) relative to controls. Hence, steroid parameters were a better biomarker of cadmium exposure than changes in VTG. However, reproductive impairment was not correlated to change in VTG or plasma steroids.

Gene targeting reveals multiple essential functions of the neuregulin signaling system during development of the neuroendocrine and nervous systems

Mice harboring targeted mutations in neuregulin-1 and its receptors (erbB2, erbB3, and erbB4) have been invaluable tools for testing the roles of these genes in vivo as well as for identifying unexpected functions for this signaling system. This review summarizes the advances in understanding the myriad functions of neuregulins in the nervous and neuroendocrine systems that have been revealed by examining gene-targeted mice.

Transgenerational and developmental exposure of Japanese medaka (Oryzias latipes) to ethinylestradiol results in endocrine and reproductive differences in the response to ethinylestradiol as adults

17alpha-Ethinylestradiol (EE), a synthetic estrogen found in birth control pills, has been detected in the effluent of municipal wastewater treatment plants in several countries. Because EE was designed to be extremely potent at the estrogen receptor (ER), environmental exposure to low concentrations has the potential to disrupt the development of normal endocrine and reproductive function when exposure occurs during critical periods in development. Japanese medaka, Oryzias latipes, were used to evaluate the effect of exposure to EE during development on adult reproduction and endocrine function and the sensitivity of these animals to estrogen exposure as adults. To determine if the response to exogenous estrogen stimulation was diminished or sensitized, adults resulting from the developmental exposure groups were reexposed to EE at respectively higher concentrations. Hatchling exposure produced no changes in adult vitellogenin (VTG) content in the liver or circulating steroid concentrations, nor was reproduction affected. Reexposure of these adults inhibited reproduction, increased hepatic VTG and ER, and increased estrogen concentration measured in male plasma. Parental exposure produced permanent changes in hepatic content of ER and VTG in the adults resulting from exposure during gametogenesis and was related to a diminished response of males to subsequent estrogen exposure. The potential for this transgenerational exposure to decrease the responsiveness of males to EE is supported by comparing the concentration-response curves for hepatic VTG and ER in males exposed in ovo and as hatchlings. Our results indicate that the relationship between biomarkers and estrogen exposure will be altered by the timing and frequency of exposure.

Direct evidence for the pancreatic lineage: NGN3+ cells are islet progenitors and are distinct from duct progenitors

The location and lineage of cells that give rise to endocrine islets during embryogenesis has not been established nor has the origin or identity of adult islet stem cells. We have employed an inducible Cre-ERTM-LoxP system to indelibly mark the progeny of cells expressing either Ngn3 or Pdx1 at different stages of development. The results provide direct evidence that NGN3+ cells are islet progenitors during embryogenesis and in adult mice. In addition, we find that cells expressing Pdx1 give rise to all three types of pancreatic tissue: exocrine, endocrine and duct. Furthermore, exocrine and endocrine cells are derived from Pdx1-expressing progenitors throughout embryogenesis. By contrast, the pancreatic duct arises from PDX1+ progenitors that are set aside around embryonic day 10.5 (E9.5-E11.5). These findings suggest that lineages for exocrine, endocrine islet and duct progenitors are committed at mid-gestation.

Effects of prevailing hypoxaemia, acidaemia or hypoglycaemia upon the cardiovascular, endocrine and metabolic responses to acute hypoxaemia in the ovine fetus

Although it is established that the fetus can successfully withstand a single, acute hypoxaemic challenge during gestation, little is known about what effects prevailing adverse intrauterine conditions might have on the fetal response to acute hypoxaemia. The aims of this study were therefore: (1) to characterise the effects of prevailing and sustained hypoxaemia, acidaemia or hypoglycaemia on the fetal cardiovascular responses to an episode of acute hypoxaemia; and (2) to determine the effects of these adverse intrauterine conditions on mechanisms mediating these cardiovascular responses. Thirty-three Welsh Mountain sheep fetuses were chronically instrumented (1-2 % halothane) between 117 and 125 days of gestation (term is ca 145 days) with amniotic and vascular catheters and with a transit-time flow probe around a femoral artery. The animals were divided retrospectively into four groups based upon post-surgical, sustained, basal blood oxygen (chronically hypoxaemic; P(a,O2), 17.3 +/- 0.5 mmHg; n = 8), glucose (chronically hypoglycaemic; blood glucose, 0.49 +/- 0.03 mmol l(-1); n = 6) and acid-base (chronically acidaemic; pH(a), 7.25 +/- 0.01; n = 5) status. Values for compromised fetuses were -2 S.D. from a group of control (n = 14) fetuses. At 130 +/- 4 days, a 1 h episode of acute, isocapnic hypoxaemia (9 % O(2) in N(2), to reduce carotid P(a,O2) to 12 +/- 1 mmHg) was induced in all fetuses by reducing the maternal inspired O(2) fraction (F(I,O2)). Fetal cardiovascular variables were recorded at 1 s intervals throughout the experimental protocol and arterial blood samples taken at appropriate intervals for biophysical (blood gases, glucose, lactate) and endocrine (catecholamines, vasopressin, cortisol, ACTH) measures. During acute hypoxaemia all fetuses elicited hypertension, bradycardia and femoral vasoconstriction. However, prevailing fetal compromise altered the cardiovascular and endocrine responses to a further episode of acute hypoxaemia, including: (1) enhanced pressor and femoral vasoconstriction; (2) greater increments in plasma noradrenaline and vasopressin during hypoxaemia; and (3) basal upward resetting of hypothalamic-pituitary-adrenal axis function. Only chronically hypoxaemic fetuses had significantly elevated basal concentrations of noradrenaline and enhanced chemoreflex function during acute hypoxaemia. These data show that prevailing adverse intrauterine conditions alter the capacity of the fetus to respond to a subsequent episode of acute hypoxaemia; however, the partial contributions of hypoxaemia, acidaemia or hypoglycaemia to mediating these responses can vary.

Control of growth and development of the feto-placental unit

Classical gene targeting has identified many genes important for fetal and placental development. Null mutation of these genes may lead to fetal growth restriction, malformation or embryonic death. Growth restriction of epigenetic basis can predispose to adult-onset diseases. The mechanisms underlying this process, termed 'fetal programming', are beginning to be understood.

A novel method for controlled and reversible long term compression of the umbilical cord in fetal sheep

1. In fetal sheep during late gestation the aims of the present study were to (1) develop a technique for inducing prolonged but reversible periods of controlled compression of the umbilical cord and (2) characterise the cardiovascular, endocrine and metabolic responses to this challenge. 2. Under 1-2 % halothane anaesthesia, 16 Welsh Mountain sheep fetuses were chronically instrumented at 118 +/- 2 days of gestation (term is ca 145 days) with an inflatable occluder cuff around the umbilical cord, amniotic and femoral vascular catheters and with transit-time flow probes around the contra-lateral femoral artery and an umbilical artery. At 125 days, umbilical blood flow was reduced by 30 % from a pre-determined 24 h baseline for 3 days by automated servo-controlled inflation of the occluder cuff (n = 8). The occluder was then deflated allowing return of umbilical blood flow to baseline. The remaining eight fetuses were used as sham-operated controls in which the occluder was not inflated throughout the protocol. Fetal cardiovascular variables were recorded at 8 s intervals and arterial blood samples taken for measurement of blood gases, glucose and lactate and plasma adrenaline, noradrenaline and vasopressin concentration throughout the study. 3. Automated servo-controlled inflation of the occluder cuff, programmed to reduce umbilical blood flow by 30 % from baseline, reduced umbilical blood flow by 30.2 +/- 1.7 %, with a coefficient of variation during compression of 6.5 +/- 1.1 %. Sustained partial compression of the umbilical cord produced falls in fetal arterial pH, P(a,O2), percentage O(2) saturation of haemoglobin, and hindlimb oxygen delivery, and increases in P(a,CO2), haemoglobin concentration, arterial blood oxygen carrying capacity and in blood glucose and lactate concentrations. While the reductions in P(a,O2), percentage saturation of haemoglobin and hindlimb oxygen delivery and the increase in P(a,CO2) were sustained throughout compression, the reduction in arterial pH and the increase in arterial oxygen carrying capacity had returned towards baseline values by 48 h compression. Fetal blood lactate concentrations reached a peak at 8 h of compression and, thereafter, were maintained at an elevated level relative to baseline. 4. Partial compression of the umbilical cord produced fetal hypertension, a reduction in femoral blood flow and, consequently, an increase in calculated fetal femoral vascular resistance for the duration of the challenge. In addition, the fall in heart rate measured in sham control fetuses by the end of the study, did not occur in cord-compressed fetuses. Cosinor analysis on 24 h rhythms of cardiovascular data indicated a significant increase in the amplitude of the 24 h rhythm in heart rate in cord-compressed fetuses relative to sham controls during the period of compression or sham-compression. Furthermore, cord compression led to an increase in fetal plasma noradrenaline, but not adrenaline and vasopressin concentrations relative to sham control fetuses. 5. In conclusion, a novel reversible method for controlled, long-term compression of the umbilical cord in sheep has been developed. The data show that sustained, partial compression of the umbilical cord produced moderate but sustained asphyxia, which resolved after the end of the compression period, and induced changes in fetal cardiovascular, endocrine and metabolic functions.

The endocrine and metabolic profile of the growth-retarded fetus

Intrauterine growth retardation (IUGR) is characterized by the failure of the fetus to grow at a normal rate in utero and is associated with a number of endocrine and metabolic changes. Our knowledge of the placental nutrient supply and the endocrine status of the fetal-placental unit during pregnancies involving IUGR has greatly increased over the past decade as a result of the availability of fetal blood samples obtained under relatively steady state conditions. These studies have provided evidence that the supply of glucose is impaired only under severe conditions, whereas placental transfer of amino acids is reduced even in fetuses with normal oxygenation and feto-placental blood flow. Moreover, significant in utero relationships have been reported between fetal weight and circulating levels of growth factors such as insulin-like growth factor-I and leptin. When measured per kg fetal weight, however, levels of leptin are significantly higher in growth-retarded fetuses, with abnormal feto-placental blood flow and reduced oxygen content. The metabolic and endocrine changes observed should be interpreted in relation to the severity of the disease.