Time trend analysis of plasma unconjugated and sulfoconjugated estrone and 3 beta-delta 5-steroids in fetal and maternal sheep plasma in relation to spontaneous parturition at term

Steroid sulfates in domestic mammals and laboratory rodents

Historically steroid sulfates have been considered predominantly as inactive metabolites. It was later discovered that by cleavage of the sulfate residue by steroid sulfatase (STS), they can be (re-)converted into active forms or into precursors for the local production of active steroids. This sulfatase pathway is now a very active field of research, which has gained considerable interest particularly in connection with the steroid metabolism of human steroid hormone-dependent cancer tissue. In comparison, there is much less information available on the occurrence of the sulfatase pathway in physiological settings, where the targeted uptake of steroid sulfates by specific transporters and their hydrolysis could serve to limit steroid effects to a subgroup of potentially steroid responsive cells. In humans, steroid sulfates of adrenal origin circulate in intriguingly high concentrations throughout most of life. Thus, ample substrate is available for the sulfatase pathway regardless of sex. However, the abundant adrenal output of steroid sulfates is a specific feature of select primates. Compared to humans, in our domestic mammals (dogs, cats, domestic ungulates) and laboratory rodents (mouse, rat) research into the biology of steroid sulfates is still in its infancy and information on the subject has so far been largely limited to punctual observations, which indicate considerable species-specific peculiarities. The aim of this overview is to provide a summary of the relevant information available in the above-mentioned species, predominantly taking into account data on concentrations of steroid sulfates in blood as well as the expression patterns and activities of relevant sulfotransferases and STS.

Transcriptomics of the fetal hypothalamic response to brachiocephalic occlusion and estradiol treatment

Estradiol (E2) is a well-known modulator of fetal neuroendocrine activity and has been proposed as a critical endocrine signal readying the fetus for birth and postnatal life. To investigate the modulatory role of E2 on fetal stress responsiveness and the response of the fetal brain to asphyxic stress, we subjected chronically catheterized fetal sheep to a transient (10 min) brachiocephalic artery occlusion (BCO) or sham occlusion. Half of the fetuses received subcutaneous pellets that increased plasma E2 concentrations within the physiological range. Hypothalamic mRNA was analyzed using the Agilent 8x15k ovine array (019921), processed and annotated as previously reported by our laboratory. Analysis of the data by ANOVA revealed that E2 differentially regulated (DR) 561 genes, and BCO DR 894 genes compared with control and E2+BCO DR 1,153 genes compared with BCO alone (all P < 0.05). E2 upregulated epigenetic pathways and downregulated local steroid biosynthesis but did not significantly involve genes known to directly respond to the estrogen receptor. Brachiocephalic occlusion upregulated kinase pathways as well as genes associated with lymphocyte infiltration into the brain and downregulated neuropeptide synthesis. E2 upregulated immune- and apoptosis-related pathways after BCO and reduced kinase and epigenetic pathway responses to the BCO. Responses to BCO are different from responses to hypoxic hypoxia suggesting that mechanisms of responses to these two forms of brain hypoxia are distinct. We conclude that cerebral ischemia caused by BCO might stimulate lymphocyte infiltration into the brain and that this response appears to be modified by estradiol.

Estrogen in the fetus

Estradiol and other estrogens are important modulators of fetal and maternal physiology in pregnancy. Much is known about the biosynthesis of estrogens in fetus and mother, and much is known about the role that estrogen plays in labor and delivery. However, much less is known about the regulation of estrogen biosynthesis throughout the latter half of gestation, and the role that estrogen plays in homeostatic and neuroendocrine control in the fetus. This review focuses on the biosynthesis and actions of estrogen in the fetal circulation, the role that it plays in the development of the fetus in the latter half of gestation, and the role that is played by the estrogen milieu in the control of the timing of birth. Estrogen circulates in fetal blood in both unconjugated and conjugated molecular forms, with the conjugated steroids far more abundant than the unconjugated steroids. This review therefore also addresses the biological significance of the variety of molecular forms of estrogen circulating in fetal and maternal blood.

Pregnenolone sulfate: from steroid metabolite to TRP channel ligand

Pregnenolone sulfate is a steroid metabolite with a plethora of actions and functions. As a neurosteroid, pregnenolone sulfate modulates a variety of ion channels, transporters, and enzymes. Interestingly, as a sulfated steroid, pregnenolone sulfate is not the final- or waste-product of pregnenolone being sulfated via a phase II metabolism reaction and renally excreted, as one would presume from the pharmacology textbook knowledge. Pregnenolone sulfate is also the source and thereby the starting point for subsequent steroid synthesis pathways. Most recently, pregnenolone sulfate has been functionally “upgraded” from modulator of ion channels to an activating ion channel ligand. This review will focus on molecular aspects of the neurosteroid, pregnenolone sulfate, its metabolism, concentrations in serum and tissues and last not least will summarize the functional data.

Fetal hypothalamus-pituitary-adrenal responses to estradiol sulfate

Estradiol (E(2)) is an important modifier of the activity of the fetal hypothalamus-pituitary-adrenal axis. We have reported that estradiol-3-sulfate (E(2)SO(4)) circulates in fetal blood in far higher concentrations than E(2) and that the fetal brain expresses steroid sulfatase, required for local deconjugation of E(2)SO(4). We performed the present study to test the hypothesis that chronic infusion of E(2)SO(4) chronically increases ACTH and cortisol secretion and that it shortens gestation. Chronically catheterized fetal sheep were treated with E(2)SO(4) intracerebroventricular (n = 5), E(2)SO(4) iv (n = 4), or no steroid infusion (control group, n = 5). Fetuses were subjected to arterial blood sampling every other day until spontaneous birth for plasma hormone analysis. Treatment with E(2)SO(4) attenuated preparturient increases in ACTH secretion near term without affecting the ontogenetic rise in plasma cortisol. Infusion of E(2)SO(4) intracerebroventricularly significantly increased plasma E(2), plasma E(2)SO(4), and plasma progesterone and shortened gestation compared with all other groups. These results are consistent with the conclusion that E(2)SO(4): 1) interacts with the hypothalamus-pituitary-adrenal axis primarily by stimulating cortisol secretion and inhibiting ACTH and pro-ACTH secretion by negative feedback; and 2) stimulates the secretion of E(2) and E(2)SO(4). We conclude that the endocrine response to E(2)SO(4) in the fetus is not identical with the response to E(2).

Development of prostaglandin endoperoxide synthase expression in the ovine fetal central nervous system and pituitary

In this study, we tested the hypothesis that prostaglandin endoperoxide synthase-1 and -2 (PGHS-1 and PGHS-2) are expressed throughout the latter half of gestation in ovine fetal brain and pituitary. Hypothalamus, pituitary, hippocampus, brainstem, cortex and cerebellum were collected from fetal sheep at 80, 100, 120, 130, 145days of gestational age (DGA), 1 and 7days postpartum lambs, and from adult ewes (n=4-5 per group). mRNA and protein were isolated from each region, and expression of prostaglandin synthase-1 (PGHS-1) and -2 (PGHS-2) were evaluated using real-time RT-PCR and western blot. PGHS-1 and -2 were detected in every brain region at every age tested. Both enzymes were measured in highest abundance in hippocampus and cerebral cortex, and lowest in brainstem and pituitary. PGHS-1 and -2 mRNA's were upregulated in hypothalamus and pituitary after 100 DGA. The hippocampus exhibited decreases in PGHS-1 and increases in PGHS-2 mRNA after 80 DGA. Brainstem PGHS-1 and -2 and cortex PGHS-2 exhibited robust increases in mRNA postpartum, while cerebellar PGHS-1 and -2 mRNA's were upregulated at 120 DGA. Tissue concentrations of PGE(2) correlated with PGHS-2 mRNA, but not to other variables. We conclude that the regulation of expression of these enzymes is region-specific, suggesting that the activity of these enzymes is likely to be critical for brain development in the late-gestation ovine fetus.

Development of ER-alpha and ER-beta expression in the developing ovine brain and pituitary

Fetal neuroendocrine development in late gestation is critical for maintenance of fetal homeostasis, growth, and readiness for birth. We designed the present study to identify the regional patterns of expression of the two main isoforms of the estrogen receptor, ER-alpha and ER-beta, in the developing ovine fetal brain. Fetal (80, 100, 120, 130, and 145 days gestation), neonatal (1 and 7 days), and adult sheep were euthanized and the following tissues were collected: pituitary, hypothalamus, hippocampus, cerebral cortex, and brainstem. Both ER's are expressed in the ovine brain as early as 80 days gestation, and the expression of both receptors appears to be developmentally regulated. We conclude that both forms of the estrogen receptor are expressed in fetal brain and pituitary throughout the latter half of gestation.

Parallel changes between the percentage of fetal pituitary cells immunoreactive to oestrogen receptor alpha and the concentration of 17beta-oestradiol in fetal and maternal plasma during gestation in sheep

The present study was designed to investigate the relationship between fetal sheep pituitary oestrogen receptor (ER) alpha expression and changes in fetal and maternal plasma 17beta-oestradiol (E2) concentrations during gestation. The results revealed that immunoreactivity for ER was located in the nuclei and distributed throughout the fetal pituitary gland during gestation. The percentage of ERalpha-positive cells was approximately 2% of the total cell population in female fetuses at Day 60 of gestation, increased to approximately 7% and 13% of the total cell population at Days 90 and 120 of gestation, respectively, and then declined to approximately 10% at birth. The fetal plasma E2 concentrations were approximately 19 and 71 pg mL(-1) at Days 90 and 120 of gestation, respectively, and decreased to 22 pg mL(-1) after birth. In male fetuses, plasma E2 concentrations and the percentage of ERalpha-positive cells were similar to values in female fetuses throughout gestation, except on Day 120 when the plasma E2 level in female fetuses was significantly higher than in male fetuses. These data demonstrate that changes in the percentage of fetal pituitary ERalpha-positive cells parallel fetal plasma E2 concentrations throughout gestation.

Ontogeny of expression of organic anion transporters 1 and 3 in ovine fetal and neonatal kidney

Organic ions are excreted into the urine via the action of organic anion transporters (OATs). In adult kidney, both OAT1 and OAT3, both multispecific transporters, are abundant; OAT1 is a known transporter of para-aminohippurate (PAH) and OAT3 is a known transporter of sulfoconjugated estrogens. The present study was designed to test the hypotheses that the expression of both OAT1 and OAT3 are developmentally regulated and that the expression increases in late gestation. Fetal kidneys were collected at sacrifice of fetal sheep at 80, 100, 120, 130, and 145 days of gestation, as well as 1 day and 1 week after birth (n=4-5 per group). Renal tissue was separated into cortex and medulla and snap-frozen in liquid nitrogen for later extraction of mRNA. The expression levels of OAT1 and OAT3 were measured using real-time reverse transcriptase polymerase chain reaction (RT-PCR), with specific probes and primers designed in our laboratory. Cellular distribution of protein expression was identified using immunohistochemistry with commercially available antisera. The OAT1 and OAT3 mRNA in renal cortex was increased in the more mature animals. At 145 days of gestation, OAT1 mRNA abundance was increased and remained elevated postnatally. Compared with prenatal ages, OAT3 mRNA was increased postnatally. The expression of both transporters was not significantly changed as a function of development in the renal medulla. The protein expression of OAT1 and OAT3 was identified in tubular epithelium in renal cortex, although the immunoreactivity for OAT1 was greater than for OAT3. We conclude that there is a developmental pattern of expression of both OAT1 and OAT3 in ovine renal cortex, and that the pattern of expression suggests that the function of both transporters is likely to be greater starting in late gestation.

Regulation of alveolar epithelial cell phenotypes in fetal sheep: roles of cortisol and lung expansion

Our aim was to determine whether cortisol's effect on alveolar epithelial cell (AEC) phenotypes in the fetus is mediated via a sustained alteration in lung expansion. Chronically catheterized fetal sheep were exposed to 1) saline infusion, 2) cortisol infusion (122–131 days' gestation, 1.5–4.0 mg/day), 3) saline infusion plus reduced lung expansion, or 4) cortisol infusion plus reduced lung expansion. The proportions of type I and II AECs were determined by electron microscopy, and surfactant protein (SP)-A, -B, and -C mRNA levels were determined by Northern blot analysis. Cortisol infusions significantly increased type II AEC proportions (to 38.2 ± 2.2%), compared with saline-infused fetuses (23.8 ± 2.4%), and reduced type I AEC proportions (to 59.0 ± 2.2%), compared with saline-infused fetuses (70.4 ± 2.4%). Reduced lung expansion also increased type II AEC proportions (to 52.9 ± 3.5%) and decreased type I AEC proportions (to 34.2 ± 3.7%), compared with control, saline-infused fetuses. The infusion of cortisol into fetuses exposed to reduced lung expansion tended to further increase type II (to 60.3 ± 2.1%, P = 0.066) and reduce type I AEC (to 26.6 ± 2.3%, P = 0.07) proportions. SP-A, -B, and -C mRNA levels changed in parallel with the changes in type II AEC proportions. These results indicate that cortisol alters the proportion of type I and type II AECs via a mechanism unrelated to the degree of fetal lung expansion. However, reductions in fetal lung expansion appear to have a greater impact on the proportion of AECs than cortisol.

Fetal brain regional responses to cerebral hypoperfusion: modulation by estrogen

We have previously demonstrated that cerebral hypoperfusion stimulates several physiological and molecular responses which are components of homeostatic reflexes. Physiological increases in fetal plasma estradiol concentration modulate fetal brain responsiveness to hypotension. In the present study, we tested the effect of cerebral hypoperfusion and/or estradiol on the expression of Fos, the protein product of the gene c-fos in late-gestation fetal sheep. We hypothesized that estrogen and cerebral hypoperfusion alone would augment Fos abundance in various brain regions, including the hypothalamus and brainstem, and that estrogen would augment or otherwise modify the Fos response to cerebral hypoperfusion. Singleton or twin fetuses of time-dated pregnant ewes were chronically catheterized and fitted with an extravascular balloon occluder around the brachiocephalic artery using aseptic techniques. In one-half of the fetuses, we implanted a pellet subcutaneously which released estradiol at a rate of 5 mg in 21 days. Fetuses were studied at least 5 days after surgery (124-128 days' gestation, term is approximately 147 days). One-half of the fetuses were subjected to a 10-min period of brachiocephalic occlusion (BCO). One hour after the start of the experiment, the ewe and fetus were euthanized and the fetal brain was rapidly recovered, dissected, and frozen in a polypropylene tube in an acetone/dry ice bath. Brain tissue was homogenized in a boiling lysis buffer, and protein concentrations measured using the Bradford method. Extracted proteins were electrophoresed on 7.5% polyacrylamide gels, transferred to nitrocellulose membranes, and probed for Fos. In most brain regions, estradiol or BCO altered the expression of Fos. Analyzed by two-way analysis of variance, there was a statistically significant (p<0.05) interaction between estradiol and BCO in brainstem, cerebellum, and hippocampus, nearly significant in hypothalamus (p=0.07) and not statistically significant in cerebral cortex. In these regions with statistically significant interactions, the expression of Fos in response to the combined treatment of estradiol and BCO was less than the sum of responses to either treatment alone. We conclude that estradiol has a potent action on the fetal brain which is identifiable in the brainstem, cerebellum, and hippocampus and that it modulates the Fos response to cerebral hypoperfusion. The measurement of regional Fos responses using Western blot reveals a negative interaction between estrogen and BCO which might result from alterations in cerebral blood flow or metabolism.

Cortisol enhances structural maturation of the hypoplastic fetal lung in sheep

Although exogenous corticosteroids advance structural maturation of the fetal lung, they can adversely affect fetal lung and body growth. Our aim was to determine whether cortisol, at physiological doses, can enhance structural maturation of the hypoplastic fetal lung without affecting fetal lung growth. Fetal sheep were divided into four groups (n= 5 for each) and lung hypoplasia (LH) was induced in two groups. Increasing doses of cortisol (1.5-4.0 mg) were infused into one group of fetuses with LH and one group without LH; the other two groups received saline. LH retarded structural development, reduced tropoelastin mRNA levels, reduced hydroxyproline and elastin contents, and increased active matrix metalloproteinase-2 (MMP-2) levels in the fetal lung. Cortisol infusions had no effect on fetal lung growth or body weights. In fetuses with LH, cortisol increased the percentage airspace, reduced the interalveolar wall thickness, increased alveolar number and reduced the increase in active MMP-2 levels. Thus, relatively low doses of cortisol can enhance structural maturation of the fetal lung without adversely affecting fetal lung growth. However, cortisol did not correct the abnormal deposition of elastin within the alveolar parenchyma associated with LH, indicating that secondary septal crest formation remained abnormal.

Biological activity of 17beta-estradiol-3-sulfate in ovine fetal plasma and uptake in fetal brain

In sheep, the fetal hypothalamus-pituitary-adrenal axis plays a central role in the initiation of parturition. We have reported that estradiol dramatically increases the activity of the fetal hypothalamus-pituitary-adrenal (HPA) axis. Sulfoconjugated estrogens are known to circulate in high concentrations in fetal plasma. We have reported the expression and abundant activity of steroid sulfatase within the fetal brain regions important for HPA axis control, and we have proposed that sulfoconjugated estrogens in fetal plasma are deconjugated (and therefore converted to a biologically active form) in fetal brain. The present study was designed to test the hypothesis that exogenous estradiol-3-sulfate stimulates HPA axis activity in late gestation fetal sheep and that it is concentrated by fetal brain tissue. We infused estradiol-3-sulfate iv into fetal sheep (125-135 d gestation; term = 147 d) at rates of 0, 0.25, and 1.0 mg/d for 5 d and performed serial sampling of fetal blood before and at the end of the infusion periods. Infusions increased fetal plasma estradiol-3-sulfate concentrations and produced dose-related increases in HPA axis activity. The action of the steroid on the fetal brain was also demonstrated as dose-related increases in the abundance of Fos in fetal cerebellum. In a second study we measured the uptake of sulfoconjugated and unconjugated estrogen (estrone-3sulfate and estrone, respectively) into the fetal brain (124-128 d gestation) in vivo. Both forms of estrogen were concentrated in fetal brain, with the uptake of estrone greater than that of estrone-3-sulfate. We conclude that sulfoconjugated estrogens augment fetal HPA axis activity and that they can cross the fetal blood-brain barrier. We propose that in late gestation the large circulating pool of sulfoconjugated estrogen is a biologically important source of active hormone that might play a role in the timing of parturition in sheep.

Central nervous system regulation of reflex responses to hypotension during fetal life

The ability of the fetus to survive, grow, and successfully complete the transition from fetal to neonatal life is critically dependent on the appropriate regulation of fetal blood pressure, blood volume, and fluid dynamics. This is a short review of the physiological mechanisms controlling the fetal cardiovascular system, focusing mainly on the neural and endocrine elements in the schema of cardiovascular function and control. The fetal cardiovascular system is arranged anatomically to provide for perfusion of the umbilical-placental circulation, the organ of gas exchange of the fetus, and to largely bypass the lungs. Fetal blood volume and pressure, maintained at levels that are appropriate for this function, are influenced by neural and endocrine control mechanisms, which are similar to, but quantitatively different from, the adult animal. Baroreceptors and chemoreceptors located in the carotid sinuses and aortic arch sense changes in blood pressure and blood gases and comprise the afferent limb of the major reflexes that maintain normal fetal blood pressure and volume. Fetal hypotension stimulates reflex decreases in fetal heart rate, which are apparently mediated by chemoreceptor input. Arginine vasopressin responses to hypotension are most likely mediated by baroreceptor input. Recent evidence suggests that the reflex responses to hypotension in the fetus are modulated by paracrine or endocrine factors. For example, baroreceptor or chemoreceptor reflex pathways are modulated by the endogenous production of prostanoids and by the preparturient changes in fetal plasma estrogen concentration.

Ontogeny of estrogen sulfatase activity in ovine fetal hypothalamus, hippocampus, and brain stem

Ovine parturition is initiated by increases in fetal hypothalamus-pituitary-adrenal (HPA) axis activity, which in turn increase placental estrogen biosynthesis and ultimately increase uterine contractility. In addition to the action in the uterus, estrogens augment fetal ACTH secretion. In late gestation, estrone sulfate is more abundant in fetal plasma than is unconjugated estrone. We studied hypothalamus, hippocampus, and brain stem tissue from fetal, neonatal, and adult sheep to test the hypothesis that the ovine brain contains estrogen sulfatase activity. We found that the activity in the hippocampus was significantly increased in late-gestation fetuses compared with both younger and older animals. No significant change in either hypothalamus or brain stem was revealed; however, the activity in all brain areas was high. Immunohistochemistry revealed the presence of estrogen sulfatase in the paraventricular nucleus of the hypothalamus, the nucleus of the solitary tract, and the rostral ventrolateral medulla. We conclude that ovine fetal hypothalamus, hippocampus, and brain stem contain estrogen sulfatase activity and that the activity in the hippocampus is developmentally regulated.

Hypothalamic oxytocin in the developing ovine fetus: interaction with pituitary-adrenocortical function

Oxytocin (OT) stimulates corticotroph function in adult sheep, however, there is little information on OT synthesis and its potential involvement in hypothalamo-pituitary-adrenal (HPA) function in the fetus. The objectives of this study were to examine developmental changes in hypothalamic OT synthesis and to investigate the actions of OT on fetal corticotroph function. Hypothalami were removed at various stages of pre- and post-natal development. OT mRNA levels were measured using in situ hybridization. For in vitro studies, fetal pituitaries were removed on days 129 and 138 of gestation. Anterior pituitary cells were dispersed and cells were treated with different concentrations and combinations of OT, corticotrophin-releasing hormone (CRH), vasopressin (AVP) and cortisol. OT mRNA was present in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) by day 60 of gestation, and levels significantly increased at term. OT mRNA was present in parvocellular and magnocellular fields of the PVN. In vitro, OT stimulated adrenocorticotropin (ACTH) output in a dose-dependent fashion, but had no effect on cellular pro-opiomelanocortin (POMC) mRNA levels. There was no significant difference in corticotroph responsiveness to secretagogues between cells harvested at gestation day 129 or gestation day 138. Simultaneous exposure to CRH and OT stimulated increases in ACTH output that were significantly greater than for OT or CRH alone. However, no similar synergistic interaction existed between OT and AVP. Cortisol attenuated OT-stimulated ACTH output. In conclusion, hypothalamic OT mRNA increases at term and OT can stimulate ACTH output from fetal corticotrophs. Together, these data indicate that OT may be involved in the regulation of ACTH secretion in fetal sheep in late gestation.

Electrocortical activity in fetal sheep in the last seven days of gestation

1. Electrocorticogram (ECoG) and myometrial electromyogram (EMG) were recorded continuously in chronically instrumented late gestation sheep fetuses (n = 9) to analyse: (1) 24 h ECoG patterns, (2) relationships between ECoG and myometrial contractility, and (3) 24 h ECoG patterns at the spontaneous onset of labour. 2. Spontaneous onset of labour was determined from the myometrial EMG. ECoG signals were purified by a denoising procedure of wavelet decomposition. High-voltage slow ECoG activity (HV) and low-voltage fast ECoG activity (LV) were determined mathematically, and HV-LV cycle periodicity was calculated by periodogram analysis. 3. Twenty-four hour rhythms were present in fetal ECoG HV-LV cycles in the 3-5 days prior to spontaneous onset of labour (P < 0.01). Cycle frequency was lower at 08.00-12.00 h and higher at 16.00-20.00 h (lights on at 07.00 h, lights off at 21.00 h). LV duration was longer at 20.00-24.00 h, and HV was shorter at 16.00-20.00 h. No relationship was found between ECoG cycles and myometrial contracture cycles. Twenty-four hour ECoG rhythms disappeared 1 day before the spontaneous onset of labour. 4. ECoG patterns changed 7 to 4 h prior to spontaneous onset of labour, percentage of time spent and duration of HV ECoG increased, and percentage of time spent in LV decreased significantly. ECoG HV-LV cyclicity was reduced 4-5 h prior to spontaneous onset of labour, indicating that the altered fetal hormonal and blood gas environment around the spontaneous onset of labour alter fetal neural function.

Changes in the capacity of the vagina and the compliance of the vaginal wall in ovariectomized, normal cyclical and pregnant ewes, before and after treatment with exogenous oestradiol and progesterone

The 'capacity' of the vagina and the compliance of the vaginal wall was measured in bilaterally ovariectomized ewes (n = 7) before and after treatment with exogenous oestradiol and progesterone; in nulliparous ewes (n = 7) at oestrus (Day 0) and dioestrus (Day 10) and during pregnancy, and in another group of pregnant ewes (n = 15) treated with exogenous oestradiol and progesterone. Measurements were remarkably consistent within individual animals but there were considerable differences between individual animals. The 'vaginal capacity' and the compliance of the vaginal wall were greater at oestrus than during dioestrus. In the same seven ewes, which were studied during their first and second pregnancies, the 'capacity' of the vagina increased whereas the compliance of the vaginal wall declined; from 90 days to term both parameters remained fairly constant. For the first 2 months of gestation the vaginal capacity was greater in year 2 than year 1 but this was reversed during the last 3 months. The compliance of the vaginal wall was significantly greater (P < 0.0001) in year 2 than year 1 at all stages of pregnancy. In ovariectomized ewes, progesterone only significantly increased the vaginal capacity at the highest dose rate (viz. 100 mg); the compliance of the wall was reduced at the 25 and 50 mg dose rates. Oestradiol produced an inconsistent dose response effect; whilst 5 mg and 20 mg had no effect upon the vaginal capacity, the 10 mg dose rate significantly reduced it. Similarly, the highest and lowest dose rates reduced the compliance of the vaginal wall but the 10 mg dose rate increased it. At 90 and 120 days of gestation, both 5 mg oestradiol and 100 mg progesterone increased the vaginal capacity but reduced the compliance.

Inhibition of prostaglandin production by nimesulide is accompanied by changes in expression of the cassette of uterine labor-related genes in pregnant sheep

The present study was designed to characterize effects of inhibiting PG production by infusing nimesulide (CAS 51803-78-2) on PGE2 production and expression of uterine labor-related genes in pregnant sheep. Myometrium, endometrium, and placenta were collected following 6 h of i.v. nimesulide or vehicle infusion. Infusions were commenced 9 h after onset of spontaneous term labor. Tissues were also collected from term control ewes not in labor. PGE2 was measured in fetal plasma by RIA. ER, OTR, Hsp 70 and 90, cPLA2, and PGHS-2 messenger RNA (mRNA) abundance in myometrium, endometrium, and PGHS-2 in placenta were quantified by Northern blot analysis. Fetal plasma PGE2 decreased during nimesulide infusion (P < 0.05). ER, OTR, Hsp 70, and Hsp 90 mRNA increased during spontaneous term labor in vehicle infused ewes in both myometrium and endometrium. In myometrium after nimesulide infusion, OTR and Hsp 70 mRNA decreased significantly (P < 0.05) compared with vehicle infused animals, but the decrease in Hsp 90 and ER mRNA fell outside the level of significance. In the endometrium, nimesulide produced a decrease in ER and OTR mRNA (P < 0.05) compared with vehicle infused animals, but the changes in Hsp 90 and 70 mRNA fell outside the level of significance. Nimesulide reversed the up-regulation of PGHS-2 mRNA that occurred in myometrium, endometrium, and placenta during vehicle infusion (P < 0.05). cPLA2 was only elevated in the endometrium in vehicle infused ewes and did not change in either endometrium or myometrium after nimesulide infusion.

CONCLUSIONS

Inhibition of PG production resulted in decreased fetal plasma PGE2. The decreased abundance of mRNA for several of the well described cassette of utero-placental labor-related genes following nimesulide inhibition may result from altered PG production.

Local paracrine effects of estradiol are central to parturition in the rhesus monkey

The central biochemical mechanisms involved in primate parturition are still unclear. Studies in both humans and nonhuman primates such as the baboon and rhesus monkey indicate that many factors play a part in the cascade of interactive positive feedforward loops that progressively promote parturition: changes in maternal endocrinology, a nocturnal switch in myometrial activity from low amplitude, infrequent contractures to high amplitude, high frequency contractions (see Fig. 1), dilation of the cervix and biochemical changes in the fetal membranes that lead to rupture. Here we demonstrate that infusion of the aromatase inhibitor 4-hydroxyandrostenedione (4OHA) inhibits conversion of androgen to estrogen and prevents premature delivery caused by administration of androgen to pregnant rhesus monkeys at 0.8 of pregnancy term. 4OHA also inhibited the androstenedione induced maternal endocrine and fetal membrane biochemical changes, and alteration of myometrial activity patterns. Secondly, peripheral estrogen infusions increased myometrial activity but did not produce preterm delivery or fetal membrane changes. We conclude that paracrine functions of estrogen at its site of production play critical and central roles in delivery in the non-human primate.

Photoperiodic history and hypothalamic control of prolactin secretion before birth

We investigated whether the fetal lamb can construct a photoperiodic history in utero. We measured the fetal PRL response to a 12-h photoperiod in intact fetal sheep and in fetal sheep after hypothalamo-pituitary disconnection (HPD), following exposure of the ewe to either a long (16 h L) or short (8 h L) photoperiod for 50 days in early pregnancy. Ewes were maintained on either a long light (LL, n = 20) or a short light (SL, n = 19) regimen from 57 days gestation until fetal HPD (pre-LL, n = 7; pre-SL, n = 7) or sham surgery (pre-LL, n = 13; pre-SL, n = 12) was performed at 99-113 days gestation. All ewes were housed in a 12-h photoperiod from surgery until 140 days gestation. In HPD fetal sheep previously exposed to SL, fetal PRL concentrations were significantly higher (P < 0.05) after 20 days in the 12-h L regimen than previously (0-5 days, 3.2 +/- 0.6 ng/ml; 21-25 days, 5.6 +/- 1.4 ng/ml). In the HPD fetal sheep previously exposed to LL, however, fetal PRL concentrations significantly decreased (P < 0.05) after 5 days exposure to the 12-h L regimen (6.7 +/- 2.9 ng/ml) and remained low throughout the remaining study period (31-35 days, 1.7 +/- 0.5 ng/ml). In contrast, in the sham group there was no effect of photoperiodic history on the gestational age profile of fetal PRL, and PRL concentrations increased significantly (F = 22.4, P < 0.001) in fetal sheep previously exposed to either SL or LL. Fetal PRL concentrations were significantly higher (P < 0.05) after 121 days gestation in the 12-h L regimen in all sham fetal sheep (<110 days, pre-SL 6.4 +/- 0.3 ng/ml, pre-LL 12.0 +/- 3.3 ng/ml; 121-125 days, pre-SL 20.0 +/- 3.9 ng/ml, pre-LL 25.9 +/- 4.4 ng/ml). TRH (50 microg) was administered i.v. to all fetal sheep at 130-134 days gestation. There was a significant fetal PRL response to TRH in both the HPD (F = 20.9, P < 0.001) and sham (F = 31.3, P < 0.001) groups. There was no difference, however, in the PRL response to TRH in fetal sheep previously exposed to SL or LL in either the HPD or sham groups. The maximum percentage changes in PRL occurred at +10 min after TRH administration in the HPD (pre-SL, 421 +/- 75%; pre-LL, 555 +/- 76%) and sham groups (pre-SL, 394 +/- 68%; pre-LL, 369 +/- 59%). In summary, therefore, we have demonstrated that there is an effect of photoperiodic history on the PRL response to an intermediate photoperiod in utero in HPD fetal sheep. It appears, however, that the effect of photoperiodic history on PRL secretion in intact fetal sheep is either masked or suppressed by the stimulatory effect of factors associated with an increase in gestational age acting at the fetal hypothalamus.

The relative roles of the hypothalamus and cortisol in the control of prolactin gene expression in the anterior pituitary of the sheep fetus

The neuroendocrine control of prolactin synthesis and secretion before birth is not well understood. We have measured the changes in the level of prolactin mRNA in the anterior pituitary of the fetal sheep throughout the last 15 days of pregnancy (term = 147 +/- 3 days gestation). We have also investigated the effects of surgical disconnection of the fetal hypothalamus and pituitary (HPD) with or without long term cortisol infusion on pituitary prolactin mRNA levels and plasma prolactin concentrations in the late gestation sheep fetus. Prolactin mRNA levels were measured in anterior pituitaries collected from a series of fetal sheep (130-134 days, n = 6; 135-140 days, n = 6; 141-145 days, n = 6) in late gestation. HPD was carried out in ten fetal sheep at 105-115 days gestation and five intact fetal sheep were used as controls. In the HPD group, either saline (HPD + saline group, n = 5) or cortisol was infused (3.5 mg/24 h) for 5 days from 134-136 days gestation (HPD + cortisol group, n = 5). There was an increase in the ratio of prolactin mRNA: 18S rRNA in the fetal pituitary between 130-134 days (0.46 +/- 0.08, n = 6) and 135-140 days (1.27 +/- 0.17 n = 6) which was maintained after 141 days gestation, (1.27 +/- 0.11, n = 6). The mean prolactin mRNA: 18 S rRNA ratio was significantly higher (P < 0.05) in intact fetal sheep (1.41 +/- 0.16, n = 4) than in the HPD fetal sheep after either saline (0.54 +/- 0.14, n = 4) or cortisol (0.74 +/- 0.24, n = 5) administration. The mean plasma concentration of prolactin was also higher in the intact group (28.3 +/- 3.9 ng/ml) when compared with the HPD + saline group (8.0 +/- 3.3 ng/ml) or the HPD + cortisol group (5.6 +/- 1.9 ng/ml). We have demonstrated that there is a strong hypothalamic drive to prolactin synthesis and secretion in the fetus and that cortisol does not act directly at the fetal pituitary to stimulate prolactin synthesis and secretion in late gestation.

Changes in estrogen receptor messenger ribonucleic acid in sheep fetal and maternal tissues during late gestation and labor

OBJECTIVE

Our purpose was to investigate whether there is an increase in messenger ribonucleic acid for estrogen receptor in critical maternal or fetal tissues in the last third of pregnancy and during labor in sheep.

STUDY DESIGN

Estrogen receptor messenger ribonucleic acid was measured by Northern hybridization analysis in fetal-placental and maternal uterine tissues during the last third of pregnancy and during spontaneous or cortisol-induced labor in sheep. Statistical differences were assessed with two-way analysis of variance.

RESULTS

No estrogen receptor messenger ribonucleic acid was observed in amnion or chorion in any animal studied. There were no gestational age related changes in estrogen receptor messenger ribonucleic acid in any tissues between 100 and 145 days' gestation. During spontaneous and cortisol-induced labor estrogen receptor messenger ribonucleic acid increased significantly (p < 0.05) in myometrium, endometrium, and cervix. No increase was observed in the fetal placental cotyledon and mesometrium. Estrogen receptor messenger ribonucleic acid was markedly decreased (p < 0.05) in myometrium and endometrium after fetal adrenalectomy.

CONCLUSION

An increase in estrogen receptor messenger ribonucleic acid in association with labor may contribute part of the mechanism by which estrogens exert their influence on the process of parturition.

The influence of steroid hormones on the uterine cervix during pregnancy

This paper reviews the evidence concerning the actions of steroid hormones on the connective tissues of the pelvis. Most available data concern the effects of steroids on the cervix. The time course of cervical softening in rats, sheep and humans suggests the possibility that the changes in connective tissue biochemistry that underlie the physiological phenomenon of cervical softening are under hormonal control. Both oestrogens and progestogens have been implicated in the control of cervical softening. However, recent experiments using inhibitors of 3 beta-hydroxysteroid dehydrogenase suggest that cervical softening can be produced in both sheep and humans by progesterone withdrawal in the absence of high circulating concentrations of oestradiol-17 beta.

17 beta-Hydroxysteroid oxidoreductase: a ubiquitous enzyme. Interconversion of estrone and estradiol-17 beta in BALB/c mouse tissues

A survey was conducted to define the sites of 17 beta-hydroxysteroid oxidoreductase activity in organs and tissues of male and female BALB/c mice, as well as the favored direction of the oxidoreductase reaction in intact tissues. The enzyme activity was assayed by use of radiolabeled estrone and estradiol-17 beta as substrates. Estrone formation from estradiol-17 beta was demonstrated in all tissues. The formation of estradiol-17 beta from estrone was demonstrated in most tissues, however, it was barely detected or was undetectable in the glandular stomach, small intestine, cecum, and large intestine. Thus, 17 beta-hydroxysteroid oxidoreductase activity is expressed in all BALB/c mouse organs and tissues. Approximately two-thirds of the tissues and organs examined, including those of the reproductive tracts, favored the conversion of estrone to estradiol-17 beta rather than the reverse reaction. The results of this study, however, represent qualitative estimates of 17 beta-hydroxysteroid oxidoreductase activity in BALB/c mouse tissues that are uncorrected for conversion to hydroxylated metabolites. These in vitro findings suggest that the 17 beta-hydroxysteroid oxidoreductase catalyzed reduction of estrone may contribute to the maintenance of physiologic levels of estradiol-17 beta in estrogen responsive tissues.

Steroid sulfatase and 17 beta-hydroxysteroid oxidoreductase activities in mouse tissues

The metabolism of estrone sulfate and dehydroisoandrosterone sulfate to the free, unconjugated steroids, estrone and dehydroisoandrosterone, was demonstrated in more than thirty different tissues from male and female BALB/c mice. The activity of steroid sulfatase, when expressed per mg tissue, was greatest in both the pituitary gland and the adrenal glands. The pituitary gland, however, had the lowest capacity for hydrolysis of steroid sulfates while the liver had the greatest capacity. 17 beta-Hydroxysteroid oxidoreductase activity also was demonstrated in all mouse tissues by the formation of estradiol-17 beta when using estrone sulfate as the substrate. The highest apparent activity for 17 beta-hydroxysteroid oxidoreductase was found in lung tissue, and the greatest capacity to form estradiol-17 beta from estrone sulfate was found in liver, lungs, kidneys and testes. This study demonstrates that the majority of mouse tissues have steroid sulfatase and 17 beta-hydroxysteroid oxidoreductase activities.