Subpopulations of corticotrophs in the sheep pituitary during late gestation: effects of development and placental restriction

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.

Dietary ractopamine supplementation of pregnant sows: what are the impacts on the neonate?

The use of additives such as ractopamine (Rac) in pregnant sows during early-mid pregnancy is an alternative to increase foetal and progeny growth and development. However, Rac supplementation in finishing pigs can lead to behavioural and physiological changes similar to the typical stress responses. The objective of this study was to evaluate the effects of dietary supplementation with Rac in pregnant sows from day 25 to 50 of gestation (pre-hyperplastic stage) on piglet's vitality, blood parameters, number, diameter and perimeter of muscle fibres in semitendinosus muscle and developmental characteristics of piglets at birth to weaning. Forty-one hybrid sows were divided into three dietary treatments: (1) control diet without Rac (control), (2) addition of 10 mg/kg of Rac (Rac10) and (3) addition of 20 mg/kg of Rac (Rac20). Higher numbers of low-vitality piglets (P<0.05) were observed in Rac-fed sows, regardless of dose, compared with the control group. Very low-density lipoprotein levels were lower in the Rac10 group when compared with the Rac20 group at day 21. Haematocrit was greater, and the mean corpuscular haemoglobin concentration was lower in piglets from Rac-fed sows. No significant statistical differences were detected regarding piglets body weight, average daily gain, blood gasometry, complete blood count and muscle fibre measurements in semitendinosus muscle. The use of Rac in pregnant sows reduced the vitality parameters of piglets but did not improve the performance from birth until weaning and did not negatively influence the haematological parameter and lipid metabolism.

Evaluation of neonatal vitality and blood glucose, lactate and cortisol concentrations in foals of the Paint Horse breed

ABSTRACT: Clinical evaluations of newborns, as well as defining the therapeutic decision, represent significant challenges to the veterinarian. This study aimed to evaluate neonatal vitality using the modified Apgar score and blood glucose, lactate, and cortisol concentrations in newborn equines. Twenty foals of the Paint Horse breed born by normal delivery were evaluated during the first 48 hours of life. The modified Apgar score was determined at birth and 10 minutes later, with values ranging from 0 to 10. Blood samples for the laboratory tests were collected at birth and at 4, 8, 12, 16, 20, 24, 36, and 48 hours. The mean Apgar score was significantly lower at birth than at 10 minutes (p < 0.001). Blood glucose concentrations increased significantly between birth (98.90 ± 35.97 mg/dL) and 8 hours (127.90 ± 27.15 mg/dL), stabilizing after the first 12 hours (148.95 ± 29.59 mg/dL). Serum lactate concentrations showed a significant decrease across the time points tested, with the highest value occurring at birth (5.48 ± 2.17 mmol/L) and stabilizing after 24 hours (2.76 ± 1.31 mmol/L). Cortisol concentrations significantly decreased (p < 0.01) between 4 (10.46 ± 7.46 μg/dL) and 48 hours (5.21 ± 3.35 μg/dL), with the highest value occurring 4 hours after birth. The common occurrence of laboratory abnormalities in healthy newborn foals reinforces the need to conduct regular clinical examinations and to develop laboratory reference values for different breeds and ages.

Early and late analysis of postpartum stress in newborn foals

ABSTRACT The aim of this study was to evaluate newborn foals stress in the first 48 hours of life. Heart rate (HR), heart rate variability (HRV) and serum cortisol concentrations, blood glucose, and lactate were determined in foals (n = 20, Paint Horse). Cortisol concentrations decreased significantly between four and 48 hours, with the highest concentration at 4 hours after birth. Positive correlations between cortisol and lactate occurred between 12 and 16 hours. And there was a negative correlation between cortisol and lactate 4 hours after birth. Among the values obtained for HR, there was significantly difference between the the value obtained at twelve hours of life moment and all the other moments measured, the highest values were at birth, 24 and 48 hours of life. Among HRV indexes, there were no statistical differences between the variables analysed. The cortisol, HR and HRV alterations were consistent to neonatal stress, but might be related to extrauterine environment adaptation associated to sympathoadrenal response, since those foals were healthy.

Heterogeneity of Calcium Responses to Secretagogues in Corticotrophs From Male Rats

Heterogeneity in homotypic cellular responses is an important feature of many biological systems, and it has been shown to be prominent in most anterior pituitary hormonal cell types. In this study, we analyze heterogeneity in the responses to hypothalamic secretagogues in the corticotroph cell population of adult male rats. Using the genetically encoded calcium indicator GCaMP6s, we determined the intracellular calcium responses of these cells to corticotropin-releasing hormone and arginine-vasopressin. Our experiments revealed marked population heterogeneity in the response to these peptides, in terms of amplitude and dynamics of the responses, as well as the sensitivity to different concentrations and duration of stimuli. However, repeated stimuli to the same cell produced remarkably consistent responses, indicating that these are deterministic on a cell-by-cell level. We also describe similar heterogeneity in the sensitivity of cells to inhibition by corticosterone. In summary, our results highlight a large degree of heterogeneity in the cellular mechanisms that govern corticotroph responses to their physiological stimuli; this could provide a mechanism to extend the dynamic range of the responses at the population level to allow adaptation to different physiological challenges.

Ontogenic development of corticotrophs in fetal buffalo (Bubalus bubalis) pituitary gland

To evaluate the subpopulation of corticotrophs in developing buffalo (Bubalus bubalis) fetus, pituitary glands were recovered (n=6 per group) from late first, second and third gestational female buffalo dams. The corticotrophs were identified by using specific antibodies against proopiomelanocortin (POMC) and adrenocorticotrophic hormone (ACTH) through immunohistochemistry. There was a significant (P≤0.05) increase of immunoreactive (ir) ir-ACTH cells during late 2^nd trimester while, ir-POMC cells were more (P≤0.05) at late 3^rd trimester of gestation as compared to other age groups. The quantity of co-localized cells for POMC and ACTH was significantly (P≤0.05) greater at the end of 1^st gestation rather than 2^nd and 3^rd gestational fetal adenohypophyseal cells. This study is the first to demonstrate co-localization of POMC+ACTH and the affect of gestational age on the expression of these cells in buffalo fetus adenohypophysis.

Maternal undernutrition during the first week after conception results in decreased expression of glucocorticoid receptor mRNA in the absence of GR exon 17 hypermethylation in the fetal pituitary in late gestation

Exposure to maternal undernutrition during the periconceptional period results in an earlier prepartum activation of the fetal hypothalamo–pituitary–adrenal (HPA) axis and altered stress responsiveness in the offspring. It is not known whether such changes are a consequence of exposure of the oocyte and/or the early embryo to maternal undernutrition in the periconceptional period. We have compared the effects of ‘periconceptional’ undernutrition (PCUN: maternal undernutrition imposed from at least 45 days before until 6 days after conception), and ‘early preimplantation’ undernutrition (PIUN: maternal undernutrition imposed for only 6 days after conception) on the expression of genes in the fetal anterior pituitary that regulate adrenal growth and steroidogenesis, proopiomelanorcortin (POMC), prohormone convertase 1 (PC1), 11β-hydroxysteroid dehydrogenase type 1 and 2 (11βHSD1 and 2) and the glucocorticoid receptor (GR) in fetal sheep at 136–138 days of gestation. Pituitary GR mRNA expression was significantly lower in the PCUN and PIUN groups in both singletons and twins compared with controls, although this suppression of GR expression was not associated with hypermethylation of the exon 17 region of the GR gene. In twin fetuses, the pituitary 11βHSD1 mRNA expression was significantly higher in the PIUN group compared with the PCUN but not the control group. Thus, exposure of the single or twin embryo to maternal undernutrition for only 1 week after conception is sufficient to cause a suppression of the pituitary GR expression in late gestation. These changes may contribute to the increased stress responsiveness of the HPA axis in the offspring after exposure to poor nutrition during the periconceptional period.

Effects of twinning and periconceptional undernutrition on late-gestation hypothalamic-pituitary-adrenal axis function in ovine pregnancy

The relationships between reduced size at birth, increased activity of the hypothalamic-pituitary-adrenal (HPA) axis, and increased risk of disease in adulthood are well described in singletons but are much less clear in twins. This may be because the physiological processes underlying reduced size at birth are different in singletons and twins. Periconceptional undernutrition can cause altered activity of the fetal and postnatal HPA axis without altering size at birth. However, the independent effects of periconceptional undernutrition and twinning on activity of the maternal and fetal HPA axes are not well described. We therefore studied maternal and fetal HPA axis function during late gestation in twin and singleton sheep pregnancies, either undernourished around conception or fed ad libitum. We found that twinning led to suppressed baseline HPA axis function and decreased adrenal sensitivity to ACTH stimulation but increased fetal pituitary ACTH response both to direct stimulation by CRH (ACTH area under the curve response: 29.7 +/- 2.2 vs. 17.1 +/- 1.6 ng/min x ml, P < 0.01) and to decreased cortisol negative feedback. In contrast, periconceptional undernutrition resulted in a decreased pituitary response (ACTH area under the curve response: 19.4 +/- 1.6 vs. 26.1 +/- 2.2 ng/min x ml, P = 0.02) but no difference in adrenal response. Thus, the HPA axis function of twin sheep fetuses in late gestation is very different from that of control and undernourished singletons. If the HPA axis is an important mediator between fetal adaptations and adult disease, these data may help explain why the relationship between fetal growth and postnatal physiology and disease risk is inconsistent in twins.

Hypothalamic input is required for development of normal numbers of thyrotrophs and gonadotrophs, but not other anterior pituitary cells in late gestation sheep

To evaluate the hypothalamic contribution to the development of anterior pituitary (AP) cells we surgically disconnected the hypothalamus from the pituitary (hypothalamo-pituitary disconnection, HPD) in fetal sheep and collected pituitaries 31 days later. Pituitaries (n = 6 per group) were obtained from fetal sheep (term = 147 +/- 3 days) at 110 days (unoperated group) of gestation and at 141 days from animals that had undergone HPD or sham surgery at 110 days. Cells were identified by labelling pituitary sections with antisera against the six AP hormones. Additionally, we investigated the colocalization of glycoprotein hormones. The proportions of somatotrophs and corticotrophs were unchanged by age or HPD. Lactotrophs increased 80% over time, but the proportion was unaffected by HPD. Thyrotrophs, which were unaffected by age, increased 70% following HPD. Gonadotrophs increased with gestational age (LH+ cells 55%; FSH+ cells 19-fold), but this was severely attenuated by HPD. We investigated the possible existence of a reciprocal effect of HPD on multipotential glycoprotein-expressing cells. Co-expression of LH and TSH was extremely rare (< 1%) and unchanged over the last month of gestation or HPD. The increase of gonadotrophs expressing FSH only or LH and FSH was attenuated by HPD. Therefore, the proportions of somatotrophs, lactotrophs and corticotrophs are regulated independently of hypothalamic input in the late gestation fetal pituitary. In marked contrast, the determination of the thyrotroph and gonadotroph lineages over the same time period is subject to complex mechanisms involving hypothalamic factors, which inhibit differentiation and/or proliferation of thyrotrophs, but stimulate gonadotrophs down the FSH lineage. Development of a distinct population of gonadotrophs, expressing only LH, appears to be subject to alternative mechanisms.