Antenatal glucocorticoids and programming of the developing CNS

Glucocorticoids (GCs) are essential for many aspects of normal brain development. However, there is growing evidence from a number of species that exposure of the fetal brain to excess GC, at critical stages of development, can have life-long effects on behavior and neuroendocrine function. The hypothalamo-pituitary-adrenal axis, which is central to the integration of the individual's endocrine and behavioral response to stress, appears highly sensitive to excess GC exposure during development. A number of animal studies have shown that exposure to synthetic GCs in utero results in adult offspring that exhibit hyperactivity of the hypothalamo-pituitary-adrenal axis. This will have a long-term impact on health, inasmuch as increased life-long exposure to endogenous GC has been linked to the premature onset of diseases associated with aging. The mechanisms involved in the permanent programming of hypothalamo-pituitary-adrenal function and behavior are not well understood. Synthetic GCs are used extensively to promote pulmonary maturation in fetuses at risk of being delivered before term. Therefore, it is important that we understand the potential long-term consequences of prenatal GC exposure on brain development as well as the underlying mechanisms involved. This review will explore the current state of knowledge in this rapidly expanding field.

Endocrine and paracrine regulation of birth at term and preterm

We have examined factors concerned with the maintenance of uterine quiescence during pregnancy and the onset of uterine activity at term in an animal model, the sheep, and in primate species. We suggest that in both species the fetus exerts a critical role in the processes leading to birth, and that activation of the fetal hypothalamic-pituitary-adrenal axis is a central mechanism by which the fetal influence on gestation length is exerted. Increased cortisol output from the fetal adrenal gland is a common characteristic across animal species. In primates, there is, in addition, increased output of estrogen precursor from the adrenal in late gestation. The end result, however, in primates and in sheep is similar: an increase in estrogen production from the placenta and intrauterine tissues. We have revised the pathway by which endocrine events associated with parturition in the sheep come about and suggest that fetal cortisol directly affects placental PGHS expression. In human pregnancy we suggest that cortisol increases PGHS expression, activity, and PG output in human fetal membranes in a similar manner. Simultaneously, cortisol contributes to decreases in PG metabolism and to a feed-forward loop involving elevation of CRH production from intrauterine tissues. In human pregnancy, there is no systemic withdrawal of progesterone in late gestation. We have argued that high circulating progesterone concentrations are required to effect regionalization of uterine activity, with predominantly relaxation in the lower uterine segment, allowing contractions in the fundal region to precipitate delivery. This new information, arising from basic and clinical studies, should further the development of new methods of diagnosing the patient at risk of preterm labor, and the use of scientifically based strategies specifically for the management of this condition, which will improve the health of the newborn.

The fetal placental hypothalamic-pituitary-adrenal (HPA) axis, parturition and post natal health

A general characteristic of fetal endocrine maturation across different species is the enhanced activity of the fetal hypothalamic-pituitary-adrenal (HPA) axis during late gestation. Precocious activation of this axis may occur when the fetus is exposed to an adverse intra-uterine environment, such as hypoxemia. HPA development is associated with increased levels of ACTH(1-39) and adrenal corticosteroids (cortisol in sheep and human) in the fetal circulation, and increased expression of mRNA encoding corticotrophin releasing hormone (CRH) in the hypothalamus, proopiomelanocortin (POMC) in the pituitary, and key steroidogenic enzymes in the fetal adrenal. At term, increased levels of cortisol act on the placenta/trophoblast derived cells to increase expression of prostaglandin synthase Type II (PGHS-II). In human gestation, cortisol also decreases expression of 15-hydroxyprostaglandin dehydrogenase (PGDH) in chorionic trophoblast cells. Increased synthesis and decreased metabolism of prostaglandin (PG) results, during late gestation, in enhanced output of primary PG, which in turn increases the activity of 11 beta-hydroxysteroid dehydrogenase (11 beta HSD) in the human fetal membranes. Increased chorionic 11 beta HSD-1 results in increased local generation of cortisol from cortisone, with further paracrine/autocrine stimulation of PG output. Increased fetal cortisol contributes to the maturation of organ systems required for postnatal extra-uterine survival. However, excessive levels of feto-placental glucocorticoid, derived from maternal administration of synthetic corticosteroids or sustained endogenous fetal cortisol production, results in intrauterine growth restriction. Fetal sheep, exposed to maternal betamethasone in late gestation, develop insulin resistance and exaggerated adrenal responses to HPA stimulation by 6-12 months postnatal life. Thus, the level of fetal HPA activity is crucial not only for determining gestation length, but may also predict pathophysiologic adjustments in later life.

Expression of the multidrug resistance P-glycoprotein, (ABCB1 glycoprotein) in the human placenta decreases with advancing gestation

The multidrug resistance p-glycoprotein (P-gp), encoded by the ABCB1 gene, is a plasma membrane protein that actively extrudes a wide variety of substances from cells. Preliminary studies in mice have shown that the ABCB1/P-gp can protect the fetus from a number of toxic substances. ABCB1/P-gp is expressed in the human placenta and is potentially capable of protecting the fetus from a large number of drugs and toxins, including herbicides and pesticides. The protein can also extrude various steroids including certain glucocorticoids and may therefore play an important role in regulating fetal access of glucocorticoids. The aim of the present study was to examine the expression profile and cellular localization of ABCB1/P-gp in human placenta throughout gestation. We hypothesized that there would be gestational age-related changes in the expression of the protein. ABCB1/P-gp mRNA was measured by Real-Time PCR using specific probes in tissues obtained from 6 weeks gestation to term. ABCB1/P-gp mRNA levels in placental tissue obtained at 6-10 weeks (n=5) and 24-35 weeks (n=5) were significantly higher than in tissues obtained at term (38-41 weeks gestation) by elective C-section (n=6) or following labor (n=6). The profile of ABCB1/P-gp protein levels, quantified using Western analysis, demonstrated a similar decrease with advancing gestation. At all gestational ages ABCB1/P-gp was localized by immunohistochemistry to the syncytiotrophoblast. In term tissues, it appeared to be localized to some areas of the villi and not others. Together, these data indicate that with advancing gestation there is a decrease in the level of ABCB1/P-gp in the human placenta indicating that the fetus may be more susceptible to toxic insults in the latter part of gestation. Further, the reduction in ABCB1/P-gp expression may contribute to the increased transfer of maternal cortisol to the fetus that is known to occur in late gestation.

Maternal glucocorticoid treatment programs HPA regulation in adult offspring: sex-specific effects

Pregnant guinea pigs were treated with dexamethasone (1 mg/kg) or vehicle on days 40--41, days 50--51, and days 60--61 of gestation. Adult offspring were split into two groups. Group 1 guinea pigs were catheterized, and the hypothalamo-pituitary-adrenal (HPA) axis was tested in basal and activated states. Group 2 guinea pigs were euthanized with no further manipulation. In male offspring, prenatal dexamethasone exposure resulted in a significant reduction in brain-to-body weight ratio. Dexamethasone-exposed male offspring exhibited reduced basal and activated plasma cortisol levels, which was associated with elevated hippocampal mineralocorticoid receptor (MR) mRNA and increased plasma testosterone. In females exposed to glucocorticoids in utero, basal and stimulated plasma cortisol levels were higher in the follicular and early luteal phases of the cycle, but this effect was reversed in the late luteal phase, indicating a significant interaction of sex steroids. In female offspring (at estrus), glucocorticoid receptor mRNA levels were lower in the paraventricular nucleus and pars distalis but higher in the hippocampus in animals exposed to dexamethasone in utero. Hippocampal MR mRNA levels were significantly lower (approximately 50%) than in controls. In conclusion, repeated antenatal glucocorticoid treatment programs HPA function in a sex-specific manner, and these changes are associated with modification of corticosteroid receptor expression in the adult brain and pituitary.

Expression of breast cancer resistance protein (BCRP/ABCG2) in human placenta throughout gestation and at term before and after labor

Breast cancer resistance protein, BCRP, is a multidrug resistance protein that is highly expressed in the human placenta. In cancer tissues, this protein actively extrudes a wide variety of chemically and structurally unrelated chemotherapeutic drugs and other compounds. Studies in mice have shown that in the absence of BCRP activity in the placenta, there is a 2-fold increase in the uptake in BCRP substrates into fetus. This suggests that in the placenta, BCRP extrudes compounds that would otherwise cross the syncytiotrophoblast cells into fetal circulation. The purpose of this study was to examine the expression and localization of BCRP in the human placenta throughout gestation. Tissues from 6–13, 16–19, 24–29, 32–35, and 38–41 weeks of gestation were used. Real time RT-PCR analysis demonstrated that the mRNA levels of BCRP in the placenta do not change significantly as gestation progressed. However, Western blot analysis revealed that the protein levels increased towards the end of gestation. We demonstrated that BCRP is localized to the syncytiotrophoblast of the placenta and in some fetal blood vessels within the placenta. Tissues from the early stages of pregnancy (6–13 weeks) showed fewer BCRP positive blood vessels than term tissues (38–41 weeks).

Maternal dexamethasone treatment in late gestation alters glucocorticoid and mineralocorticoid receptor mRNA in the fetal guinea pig brain

Development of the fetal hypothalamo-pituitary-adrenocortical (HPA) axis is critical for fetal maturation and responses to stress. Guinea pigs, unlike rats, give birth to mature young, and peak brain growth occurs around days 48-52 (75%) of gestation. There is extensive development of the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) systems at the time of rapid brain growth in guinea pigs. Since approximately 10% of pregnant women are treated with synthetic glucocorticoids in late gestation, to promote fetal organ maturation, we tested the hypothesis that fetal exposure to glucocorticoids modifies developing GR and MR systems in the brain. Pregnant guinea pigs were subcutaneously injected with dexamethasone (dex; 1 mg/kg) or vehicle on days 50 and 51 of gestation (term=70 days). On day 52, guinea pigs were killed and the fetuses rapidly removed. Maternal dex treatment resulted in increased plasma cortisol concentrations in female fetuses, but decreased cortisol in male fetuses. Plasma thyroxine levels were increased in both female and male fetuses following maternal dex-treatment. Exposure to dex resulted in significant increases in MR and GR mRNA in the CA1-2 region of the hippocampus, and MR mRNA in the dentate gyrus in female fetuses. There was no effect of dex on GR or MR mRNA in the male fetuses. In conclusion, the effect of synthetic glucocorticoid on the developing brain GR and MR systems is sex-specific and is confined to very specific regions of the hippocampus. Since the hippocampus plays a central role in mediating glucocorticoid negative feedback of HPA function, alterations in the fetal development of corticosteroid receptors may form the basis of permanently modified HPA activity following fetal exposure to endogenous or synthetic glucocorticoid.

Antenatal glucocorticoids and the developing brain: mechanisms of action

Glucocorticoids are critical for normal brain development. There is no doubt that prenatal treatment with synthetic glucocorticoid affords great benefit to the preterm infant. However, animal studies, now carried out in many species, indicate that there may be some long-term physiological costs of early exposure to excess glucocorticoid, and that these appear sex-dependent. Further, the effects may not become apparent until later life. Given the dynamics of corticosteroid receptor systems in late gestation, it is likely that there are critical windows of development when specific regions of the brain are more sensitive to the influence of synthetic glucocorticoid. Once such windows have been identified it will be possible to target prenatal treatments, so as to maximize benefit and reduce risk of long-term effects. Notwithstanding, the data reviewed below indicate that caution should be exercised in the use of multiple course glucocorticoid therapy during pregnancy.

Dynamic changes in glucocorticoid and mineralocorticoid receptor mRNA in the developing guinea pig brain

The guinea pig has a high degree of neurological maturity at birth. Since glucocorticoid receptors (GR) and mineralocorticoid receptors (MR) are central to several aspects of brain and neuroendocrine development, we examined the hypothesis that development of central GR and MR systems takes place during fetal life, in species which give birth to mature young. Fetal guinea pigs were retrieved on gestational days (gd) 40-45, 50-55, 60-65. A group of 7-day old neonates was also euthanized. Levels of GR and MR mRNA were determined by in situ hybridization followed by computerized image analysis. MR mRNA was confined to limbic structures, and was present at high levels in the hippocampus and dentate gyrus by gd40. Hippocampal MR mRNA levels decreased with the progression of gestation. GR mRNA was more widely distributed, with highest levels being expressed in the cingulate cortex, hippocampus, amygdala and hypothalamic paraventricular nucleus (PVN). In the hippocampus, GR mRNA levels increased with progression of gestation, attaining highest levels near term. In contrast to the hippocampus, GR mRNA levels were highest in the PVN at gd40-45, but decreased dramatically in the last 25 days of gestation. In conclusion, there are dynamic site-specific changes in the expression of corticosteroid receptors in the brain of the fetal guinea pig, at the time of most rapid brain growth. The decreases in GR mRNA levels in the PVN in late gestation likely facilitate the simultaneous increases in ACTH and cortisol that occur near term, and which are critical for the delivery of viable young.

Current topic: the placental corticotrophin-releasing hormone-adrenocorticotrophin axis

In this review the factors regulating production of corticotrophin-releasing hormone (CRH) in intrauterine tissues are discussed and interactions of placental CRH with placental pro-opiomelanocortin (POMC)/adrenocorticotrophin (ACTH) and prostaglandins (PG) are examined. Discrepant results concerning localization of immunoreactive (IR-) CRH and its binding protein (CRH-BP) and their mRNAs in intrauterine tissues are described, and these issues require further resolution. It is suggested that the CRH-ACTH-PG axis in the placenta and choriodecidua may be important in relation to paracrine/autocrine regulation of uteroplacental blood flow, and in term and preterm labour. During the initial stages of preterm labour in the setting of infection, intrauterine cytokines and other factors may stimulate CRH output, implying a role for the immune-neuroendocrine axes in this process. With loss of chronic trophoblasts in advanced infection leading to preterm labour, a major intrauterine site of CRH production may be lost and the influence of this pathway becomes minimal. At this time increased intrauterine prostaglandin synthesis, together with loss of prostaglandin dehydrogenase activity in the fetal membranes, may become the primary route leading to myometrial activity and delivery.

Maternal nutrient restriction (48 h) modifies brain corticosteroid receptor expression and endocrine function in the fetal guinea pig

Modification of the fetal environment has been shown to program hypothalamo-pituitary-adrenal (HPA) development. Altered expression of brain corticosteroid receptors is thought to be central to this process. In the fetal guinea pig, rapid development of glucocorticoid receptors (GR) and mineralocorticoid receptors (MR) occurs in concert with rapid brain growth. Since nutrient availability has been associated with programming of endocrine function, we hypothesized that 48 h of maternal nutrient deprivation during rapid brain growth modifies the fetal endocrine environment and alters expression of GR and MR in the fetal brain. Pregnant guinea pigs were deprived of food (water available ad libitum) or fed normally on gestational days 50-51, and euthanized on gd52 (term=70 days). Nutrient deprivation caused intrauterine growth restriction (IUGR), though brain growth was protected. Fetal and maternal plasma cortisol was elevated in the deprived animals (p<0. 001), though plasma adrenocorticotrophin (ACTH) was only elevated in maternal blood. In deprived fetuses, plasma thyroxin levels were significantly (p<0.001) lower than control. GR mRNA levels were significantly decreased in the hypothalamic paraventricular nucleus (PVN; p<0.05) and CA1/2 (p<0.01) region of the hippocampus in female fetuses, and in the hippocampal CA1/2 in male fetuses (p<0.01). In contrast, MR mRNA levels were not changed by nutrient deprivation. In conclusion, 48 h of nutrient deprivation, activates the maternal, but not the fetal HPA axis, and decreases GR mRNA but not MR mRNA levels in the developing hypothalamus and limbic system. These developmental perturbations may have an important impact on the trajectory of corticosteroid receptor development and therefore central glucocorticoid feedback regulation.

A short period of maternal nutrient restriction in late gestation modifies pituitary-adrenal function in adult guinea pig offspring

Altered fetal environment can program the hypophyseal-pituitary-adrenal (HPA) axis development and thus affect endocrine function in later life. We hypothesized that 48 h of maternal nutrient restriction during the period of maximal fetal brain growth alters HPA function in adult offspring and leads to modified blood pressure regulation. Pregnant guinea pigs (n = 15) were deprived of food (water ad libitum) or fed normally (n = 13) on days 50 and 51 of gestation, after which they were all fed normally (birth = 68 days). Carotid artery and jugular vein catheters were implanted in adult guinea pig offspring (day 65). Animals were treated with corticotropin (ACTH(1-24); 0.5 microg/kg), corticotropin-releasing hormone (CRH; 0.5 microg/kg) and insulin (5 units/kg), and pituitary-adrenal responses were measured. Guinea pigs were then euthanized and pituitaries removed for analysis of pro-opiomelanocortin (POMC) and glucocorticoid receptor (GR) mRNA levels. There was no effect of prenatal treatment on body weight, blood pressure or heart rate. In male offspring, both basal ACTH (p < 0.007) and basal cortisol (p < 0.05) levels were significantly reduced in animals whose mothers had been nutrient restricted (NR). In contrast, in female offspring, basal plasma ACTH was not different between offspring from NR mothers and controls; however, basal plasma cortisol concentrations were significantly (p < 0.01) elevated at 13.00 h in females born to NR mothers. Responses to HPA challenge were different between offspring from NR mothers and control offspring, and these differences were consistent with alterations in basal adrenocortical function. There was no effect of prenatal treatment on POMC mRNA levels in the pars distalis or pars intermedia. However, GR mRNA levels were significantly (p < 0.05) reduced in adult female offspring born to NR mothers. In conclusion, 48 h of maternal nutrient restriction during pregnancy has a long-term effect on HPA function in adult offspring, and this effect is highly sex specific, but does not result in alteration of blood pressure.

Glucocorticoids, hypothalamo-pituitary-adrenal (HPA) development, and life after birth

Approximately 10% of women in North America are treated with synthetic glucocorticoid (sGC) between 24 and 32 weeks of pregnancy (term approximately 40 weeks), to promote lung maturation in fetuses at risk of preterm delivery. Such therapy is highly effective in reducing the frequency of respiratory complications, and as a result, repeated course treatment has become widespread. Nothing is known about the impact of repeated sGC treatment on neuroendocrine development in the human, or if specific time windows of increased sensitivity exist. Glucocorticoids are essential for many aspects of normal brain development. However, there is growing evidence from a number of species, that exposure of the fetal brain to excess glucocorticoid can have life-long effects on behaviour and neuroendocrine function. We have shown that exposure of fetuses to sGC in late gestation permanently alters HPA function in pre-pubertal, post-pubertal, and aging offspring, in a sex-dependent manner. These effects are linked to changes in central glucocorticoid feedback. Prenatal glucocorticoid exposure also leads to modification of HPA-associated behaviours and organ morphology, as well as altered regulation of other neuroendocrine systems. Permanent changes in HPA function will have a long-term impact on health, since elevated cumulative exposure to endogenous glucocorticoid has been linked to the premature onset of pathologies associated with aging.

Repeated antenatal glucocorticoid treatment decreases hypothalamic corticotropin releasing hormone mRNA but not corticosteroid receptor mRNA expression in the fetal guinea-pig brain

Approximately 10% of pregnant women are treated with synthetic glucocorticoids in late gestation, to promote fetal lung maturation. The effectiveness of this treatment has led to the use of repeated dose regimens, with little knowledge of the impact on neuroendocrine development. Animal studies have recently shown that repeated fetal glucocorticoid exposure can lead to permanent changes in hypothalamic-pituitary-adrenal (HPA) function in offspring. In this study, we hypothesized that such treatment modifies corticotropin releasing hormone (CRH), glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) systems in the developing limbic system and hypothalamus. Pregnant guinea-pigs were treated with dexamethasone, betamethasone or vehicle on days 40,41,50,51,60 and 61 of gestation (birth = 68 days). On day 62, guinea-pigs were killed and the fetuses rapidly removed. Glucocorticoid treatment resulted in a dose-dependent reduction in plasma cortisol concentrations in both male and female fetuses. There was also a significant reduction in CRH mRNA expression in the hypothalamic paraventricular nucleus. In contrast, exposure to glucocorticoid increased MR mRNA expression in the hippocampus (CA1/2 and CA3) and dentate gyrus of female fetuses. There was a small but significant increase in GR mRNA expression in limbic structures in male fetuses following treatment with 1 mg/kg dexamethasone. However, there was no significant effect of glucocorticoid exposure on hippocampal GR mRNA expression in female fetuses, or hypothalamic GR mRNA in either males or females. In conclusion, repeated maternal glucocorticoid treatment inhibits fetal HPA function. The fact that CRH mRNA levels were reduced indicates that synthetic glucocorticoids enter the fetal brain. By contrast, fetal glucocorticoid exposure does not downregulate GR mRNA, and increases MR mRNA expression. The latter likely reflects removal of circulating endogenous ligand (cortisol). These alterations may form the basis for permanently modified HPA activity in later life.

Serotonin transporter allelic variation in mothers predicts maternal sensitivity, behavior and attitudes toward 6-month-old infants

Maternal behavior in the new mother is a multidimensional set of responses to infant cues that are influenced by the mother's early life experiences. In this study, we wanted to test if mothers' early life experiences and mothers' genotype have interactive effects on maternal behaviors and attitudes, something which has not been previously explored. In a sample of 204 mothers, we assessed maternal genotype at the serotonin transporter-linked polymorphic region (5-HTTLPR) and an adjacent upstream polymorphism (rs25531), together giving rise to three alleles: short (S), L(G) and L(A). Controlling for maternal age and parity, we showed that this genotype can predict differences in maternal sensitivity at 6 months postpartum: mothers with an S (or the functionally similar L(G)) allele were more sensitive than mothers who lacked the allele during a 30-min recorded mother-infant interaction (F (4,140) = 3.43; P = 0.01). Furthermore, we found highly significant gene-environment interactions in association with maternal behavior, such that mothers with no S or L(G) alleles oriented away more frequently from their babies if they also reported more negative early care quality (F (5,138) = 3.28; P = 0.008). Finally, we found significant gene-environment associations with maternal attitudes; mothers with the S allele and with greater early care quality scored higher on ratings of their perceived attachment to their baby (F (5,125) = 3.27; P = 0.008). The regression results show significant interactions between the reported quality of care mothers received from their own parents and genotype on both their frequency of orienting away from the infant during the interaction (F(5, 138) = 3.28; P = 0.008, Fig. 1a) and their perceived attachment feelings to the infant (F(5, 125) = 3.27; P = 0.008, Fig. 1b); however the direction of the effects for these two outcome measures were different from one another. With increasing care quality, mothers with the L(A)L(A) genotype (no S or L(G) allele) oriented away less frequently, while S or L(G) allele carriers showed no significant change. In contrast, with increasing early care quality. L(A)L(A) (no S or L(G) allele) mothers scored lower on perceived attachment to their infants, whereas S or L(G) allele carrying mothers scored higher. [corrected].

ATP-binding cassette transporters in reproduction: a new frontier

BACKGROUND

The transmembrane ATP-binding cassette (ABC) transporters actively efflux an array of clinically relevant compounds across biological barriers, and modulate biodistribution of many physiological and pharmacological factors. To date, over 48 ABC transporters have been identified and shown to be directly and indirectly involved in peri-implantation events and fetal/placental development. They efflux cholesterol, steroid hormones, vitamins, cytokines, chemokines, prostaglandins, diverse xenobiotics and environmental toxins, playing a critical role in regulating drug disposition, immunological responses and lipid trafficking, as well as preventing fetal accumulation of drugs and environmental toxins.

METHODS

This review examines ABC transporters as important mediators of placental barrier functions and key reproductive processes. Expression, localization and function of all identified ABC transporters were systematically reviewed using PubMed and Google Scholar websites to identify relevant studies examining ABC transporters in reproductive tissues in physiological and pathophysiological states. Only reports written in English were incorporated with no restriction on year of publication. While a major focus has been placed on the human, extensive evidence from animal studies is utilized to describe current understanding of the regulation and function of ABC transporters relevant to human reproduction.

RESULTS

ABC transporters are modulators of steroidogenesis, fertilization, implantation, nutrient transport and immunological responses, and function as 'gatekeepers' at various barrier sites (i.e. blood-testes barrier and placenta) against potentially harmful xenobiotic factors, including drugs and environmental toxins. These roles appear to be species dependent and change as a function of gestation and development. The best-described ABC transporters in reproductive tissues (primarily in the placenta) are the multidrug transporters p-glycoprotein and breast cancer-related protein, the multidrug resistance proteins 1 through 5 and the cholesterol transporters ABCA1 and ABCG1.

CONCLUSIONS

The ABC transporters have various roles across multiple reproductive tissues. Knowledge of efflux direction, tissue distribution, substrate specificity and regulation of the ABC transporters in the placenta and other reproductive tissues is rapidly expanding. This will allow better understanding of the disposition of specific substrates within reproductive tissues, and facilitate development of novel treatments for reproductive disorders as well as improved approaches to protecting the developing fetus.

Molecular regulation of the hypothalamo-pituitary-adrenal axis in streptozotocin-induced diabetes: effects of insulin treatment

Increased hypothalamo-pituitary-adrenocortical (HPA) activity in diabetes is likely important in the development of some pathologies associated with the disorder. We hypothesized that central regulation of HPA activity differs among normal, streptozotocin (STZ)-diabetic, and insulin-treated diabetic rats. Blood glucose, ACTH, and corticosterone were elevated, 8 d after inducing diabetes. Insulin treatment normalized these parameters. Plasma norepinephrine was similar in all groups, but epinephrine was lower in STZ-diabetic and higher in insulin-treated rats vs. normals. Increased ACTH with diabetes corresponded with increased hypothalamic CRH mRNA, but no change in pituitary POMC mRNA. With insulin-treatment, CRH mRNA remained elevated, and POMC mRNA was unaltered. Hippocampal MR mRNA expression was dramatically increased with diabetes and, moreover, was not normalized by insulin. No differences in GR mRNA were detected between normal and STZ-diabetic rats. However, insulin treatment increased GR mRNA levels in the paraventricular nucleus and pituitary. We postulate that, in STZ-diabetes: 1) increased HPA activity is caused by increased central drive at and/or above the level of the paraventricular nucleus and is associated with decreased epinephrine; and 2) normalized pituitary-adrenal activity with insulin may be caused by the compensatory increase in GR mRNA allowing glucocorticoid-mediated suppression of ACTH secretion despite the residual increase in central HPA activity. Thus, insulin apparently restored HPA activity at and below the pituitary but, surprisingly, not above it.

Regulation of the hypothalamo-pituitary-adrenocortical axis in fetal sheep

Development of the fetal hypothalamo-pituitary-adrenal (HPA) axis is required for normal fetal life and subsequent neonatal health. Activation of the fetal pituitary gland results in the synthesis and release of glucocorticoids from the adrenal cortex. Glucocorticoids promote maturation of several organ systems, are important in responses of the fetus to stress, and are involved in the initiation of parturition in several species. The expression of hypothalamic and pituitary genes associated with HPA function is apparent early in gestation in fetal sheep, although the endocrine changes associated with maturation and parturition do not occur until the last fifth of gestation. In this connection, the fetal HPA axis can be activated by treatment with hypophysiotrophic factors or moderate stress throughout gestation. This review focuses on the development of neuroendocrine mechanisms controlling HPA function during fetal life.

Prenatal glucocorticoid modifies hypothalamo-pituitary-adrenal regulation in prepubertal guinea pigs

We hypothesized that exposure to synthetic glucocorticoid during rapid brain growth (d50-52, birth = 68 days) in fetal guinea pigs modifies hypothalamo-pituitary-adrenal (HPA) function after birth, and that this involves changes in central corticosteroid receptor regulation. On the basis of our previous studies, we proposed that this effect is sex-specific. Pregnant guinea pigs were treated with dexamethasone (1 mg/kg) or vehicle on d50-51 of gestation, and juvenile offspring were euthanized at rest or following isolation stress on postnatal day 18. Dexamethasone increased the length of gestation (1.5 days) and altered body and organ (brain, heart, adrenal) growth. Resting plasma cortisol concentrations were significantly elevated in young male, but not female guinea pigs exposed to dexamethasone as fetuses. In female offspring born to dexamethasone-treated mothers, cortisol responses to isolation stress were attenuated. In males, elevated basal cortisol levels were not increased further by isolation. In the brain, hippocampal glucocorticoid receptor (GR) mRNA levels were significantly lower (10-25%) in females exposed to dexamethasone in utero. In contrast, GR mRNA levels were elevated (10-20%) in males from this prenatal treatment group. Mineralocorticoid receptor mRNA in the limbic system and GR mRNA levels in the pars distalis were unaffected. Pro-opiomelanocortin mRNA was significantly lower (30%) in the male pars intermedia following dexamethasone exposure. In conclusion, prenatal glucocorticoid exposure affects growth and HPA function as well as limbic and hypothalamic GR expression in juvenile offspring, and these effects are highly sex-specific.

Maternal undernutrition in early gestation alters molecular regulation of the hypothalamic-pituitary-adrenal axis in the ovine fetus

We have demonstrated previously that plasma adrenocorticotropin hormone and cortisol responses to exogenous and endogenous stimuli are reduced in fetuses of mildly undernourished ewes. In the present study, we examined the molecular regulation of fetal hypothalamic-pituitary-adrenal (HPA) axis function at 127-130 days gestation (dGA) following 15% reduction in maternal nutrition between 0 and 70 dGA. Using in situ hybridization, we found that corticotropin releasing hormone (CRH) mRNA expression in the hypothalamic paraventricular nucleus (PVN) was lower in fetuses from nutrient restricted ewes than in controls. Restricted fetuses also had greater levels of mRNA encoding preproenkephalin (PENK) and magnocellular arginine vasopressin (AVP) in the PVN. Expression of oxytocin mRNA and parvocellular AVP mRNA in the PVN and pro-opiomelanocortin mRNA in the pituitary were unchanged. Glucocorticoid receptor mRNA expression was unaltered at the PVN, but was reduced (> 40%) in the anterior pituitary of restricted fetuses. Northern blot analysis demonstrated that levels of adrenal P450scc mRNA and P450(C17) mRNA were not different between the groups. We conclude that the reduction in HPA function reported previously is mediated, at least in part, by a decrease in expression of CRH mRNA and increase in PENK mRNA in the PVN.

Chorionic prostaglandin catabolism is decreased in the lower uterine segment with term labour

We have examined the hypothesis that regional differences in 15-hydroxyprostaglandin dehydrogenase (PGDH) activities occur within the human fetal membranes. Further, we reasoned that a specific reduction in PGDH in the fetal membranes at the lower uterine segment might occur with labour, providing a potential mechanism for local generation of primary prostaglandins (PG) that could contribute to cervical ripening. Full-thickness membranes were obtained from patients at caesarean section in the presence or absence of labour. Membranes were sampled from three regions: close to the site of placental attachment, in the region of the internal cervical os, and from a 'middle' area between these two. PGDH activities (sum of PGF2 alpha to 15-keto PGF2 alpha and 13, 14-dihydro 15-keto PGF2 alpha conversion) and immunoreactivity varied appreciably between the three regions. PGDH activity was highest in chorion in the cervical region of patients not in labour, but was significantly lower in the chorion from membranes taken closest to the internal os of patients in labour. Loss of PGDH activity was not attributable to a diminution in the number of trophoblast cells in this area. We conclude that regional loss of PGDH in the fetal membranes (chorion) at the lower uterine segment occurs with labour. Reduced PG catabolism could facilitate local generation of bioactive PG at this site for cervical effacement.

Immunoreactive 15-hydroxyprostaglandin dehydrogenase (PGDH) is reduced in fetal membranes from patients at preterm delivery in the presence of infection

Previously we reported that the proportion of trophoblast cells that were immunopositive for 15-OH prostaglandin dehydrogenase (PGDH) in the chorionic membranes was reduced in women in preterm labour without infection, compared with women at term, but was not altered in preterm labour patients with an underlying infective process. Subsequently, we found that PGDH activity and PGDH mRNA were significantly lower in membranes of this latter group of patients than in women at preterm labour without infection or at term. To resolve this issue we used immunohistochemistry to examine the distribution and frequency of immunoreactive (ir)-PGDH positive cells in full-thickness fetal membranes in patients at preterm labour in the presence or absence of infection. Trophoblast and decidual stromal cells were identified using antibodies against cytokeratin and vimentin, respectively. There was considerable variation in the number of chorionic trophoblast cells that were positive for ir-PGDH, but in some patients there was little or no ir-PGDH staining, and this was associated with loss of trophoblast cells from the tissue. The mean intensity and number of ir-PGDH positive cells was significantly lower in membranes from patients in preterm labour with infection than in idiopathic preterm labour at which the diagnosis of infection was not made. We conclude that in the setting of preterm labour with infection there may be loss of trophoblast cells from membranes, with corresponding reduction in the number of ir-PGDH positive cells. Loss of PGDH activity removes the initial step in activating primary prostaglandins, which are then able to pass unmetabolized to the decidua and myometrium, and contribute to the stimulus to preterm birth.

Child custody mediation and litigation: Further evidence on the differing views of mothers and fathers

An earlier study was replicated in which parents were randomly assigned to negotiate child custody disputes either in mediation or through the adversary system. In both the initial study (Emery & Wyer, 1987a) and the present replication, mediation greatly reduced the frequency of custody hearings, allowed settlements to be reached in half the time, and substantially improved the satisfaction reported by fathers. Considerably fewer differences were found for mothers who used the alternative forms of dispute resolution, however. Some differences found in both studies favored the women who litigated. No consistent differences in the psychological adjustment of mothers or fathers who mediated or litigated emerged across the two studies. Although careful consideration of findings argues against the conclusion that mediation is "good" for fathers and "bad" for mothers, findings point to the conflicting perspectives of men and women who contest child custody.

Breast Cancer Resistance Protein (Bcrp1/Abcg2) in Mouse Placenta and Yolk Sac: Ontogeny and its Regulation by Progesterone

Breast Cancer Resistance Protein (BCRP), a recently-discovered transporter belonging to ABC superfamily, is highly expressed within the labyrinth of the placenta, the primary site of exchange between the maternal and fetal circulation. It has been proposed to function as an efflux pump protecting the fetus from a wide range of xenobiotics. It has also been recently shown that the yolk sac, in addition to the placenta, may be involved in transport of certain substances to and from the fetus. We hypothesised that there are changes in placental Bcrp1 (the mouse orthologue of human BCRP) expression during pregnancy and that these correlate with changes in progesterone production that occur in late gestation. We also hypothesised that Bcrp1 is expressed in the yolk sac, and that levels change with advancing gestation. Either whole concepti, or placenta and yolk sac, were collected from pregnant mice and analysed at embryonic (E) day 9.5, 12.5, 15.5 and 18.5 (term approximately E19.5). Peak expression of Bcrp1 mRNA was detected using in situ hybridisation within the placenta at E9.5 and the yolk sac at E12.5. There was a significant decrease thereafter in both tissues (p<0.001). In contrast, expression of Bcrp1 protein as assessed by immunohistochemistry and Western immunoblots did not change significantly during gestation either in the placenta nor the yolk sac, and no sex difference in Bcrp1 protein expression in either tissue was observed at E12.5. Daily progesterone treatment starting at E14.5 and continuing until E18.5 significantly increased maternal progesterone levels, but did not elicit any changes in the Bcrp1 mRNA or Bcrp1 protein expression either in the placenta or the yolk sac. Significant expression of Bcrp1 protein in fetal tissue was evident at the end of gestation, while expression in the fetal brain endothelium was evident as early as E12.5. We suggest that the placenta and the yolk sac, both of which express Bcrp1, may limit fetal exposure to the potentially adverse effects of xenobiotics including therapeutic drugs which the mother may be exposed to during pregnancy. The significant decrease in Bcrp1 mRNA expression in both the yolk sac and the placenta from mid to late gestation may be counter-balanced by an increase in Bcrp1 expression in fetal organs involved in absorption, excretion and protection.