Neonatal exposure to progesterone and estradiol alters uterine morphology and luminal protein content in adult beef heifers

Uterine histomorphological and immunohistochemical investigation during the follicular phase of estrous cycle in Saidi sheep

BACKGROUND

Saidi sheep are one of the most important farm animals in Upper Egypt, particularly in the Assiut governorate. Since they can provide meat, milk, fiber, and skins from low-quality roughages, sheep are among the most economically valuable animals bred for food in Egypt. Regarding breeding, relatively little is known about the Saidi breed. In mammals, the uterus is a crucial reproductive organ. Therefore, the purpose of this work was to provide further details on the histological, histochemical, and immunohistochemical analyses of superoxide dismutase 2 (SOD2), glutathione reductase (GR), and progesterone receptor alpha (PRA) as well as terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling assay (TUNEL) of the uterus during the follicular phase of estrous cycle in Saidi sheep. Thus, 11 healthy Saidi ewes (38.5 ± 2.03 kg weight) ranging in age from 2 to 5 years were used to examine the histological changes in the uterus.

RESULTS

In Saidi sheep, the uterine histological and immunological picture during the follicular phase of the estrous cycle was characterized by epithelial and stromal proliferation and apoptosis. Leucocytic recruitment (lymphocytes, plasma, and mast cells) was also observed. Uterine gland adenogenesis, vascular angiogenesis, oxidative marker expression, and PRA expression in the muscles, stroma, and epithelium were the most noticeable features of the follicular phase.

CONCLUSION

This study provides new evidence of the role of PRA, SOD2, GR, and mast cells in controlling uterine epithelial proliferation and apoptosis in the Saidi sheep during the follicular phase of the estrus cycle. These findings have growing significance in understanding the key mechanisms that characterize successful reproduction and enhancing the fertility and reproductive efficiency in Saidi Sheep.

Sex bias in utero alters ovarian reserve but not uterine capacity in female offspring†

Environmental stressors to which a fetus is exposed affect a range of physiological functions in postnatal offspring. We aimed to determine the in utero effect of steroid hormones on the reproductive potential of female offspring using a porcine model. Reproductive tracts of pigs from female-biased (>65% female, n = 15), non-biased (45-54.9% female, n = 15), and male-biased litters (<35% females, n = 9) were collected at slaughter (95-115 kg). Ovaries and uterine horns were processed for H&E or immunohistochemistry. Variability of data within groups was analyzed with a Levene's test, while data were analyzed using mixed linear models in R. In the ovarian reserve, there was a significant birth weight by sex ratio interaction (P = 0.015), with low birth weight pigs from male-biased litters having higher numbers of primordial follicles with opposite trends seen in pigs from female-biased litters. Sex bias held no effect on endometrial gland development. A lower birth weight decreased the proportion of glands found in the endometrium (P = 0.045) and was more variable in both male-biased and female-biased litters (P = 0.026). The variability of primordial follicles from male-biased litters was greater than non- and female-biased litters (P = 0.014). Similarly, endometrial stromal nuclei had a greater range in male- and female-biased litters than non-biased litters (P = 0.028). A crucial finding was the greater variability in primordial follicles in the ovaries from females derived from male-biased litters and stromal cell count in the endometrium of females from male- and female-biased litters. This could be inflating the variability of reproductive success seen in females from male-biased litters.

Effects of administration of a growth promoting implant during the suckling phase or at weaning on growth, reproduction, and ovarian development in replacement heifers grazing native range

Management strategies utilized during pre-breeding development of replacement heifers can impact fertility and the ovarian reserve. Angus-Hereford crossbred heifers (n = 233) were utilized over a three-year period to determine the effects of administration of a growth promoting implant at either branding or weaning on growth, reproduction, and ovarian development. Heifer calves were randomly assigned to one of three treatments: 1) non-implanted controls (CON; n = 79), 2) implanted at approximately 2 mo of age (average calf age = 58 d) with Synovex-C (BIMP, n = 82), or 3) implanted at approximately 7mo of age (average calf age = 210 d) with Synovex-C (WIMP; n = 72). In yr 2 and 3 a subset of heifers (yr 2 n = 16; yr 3 n = 14) were unilaterally ovariectomized. Heifers implanted at 2 mo of age were heavier at weaning, yearling (mid-February; average calf age = 332 d), and at the beginning of the breeding season (P < 0.01) compared to CON and WIMP heifers. Average daily gain (ADG) was similar among treatments from weaning to yearling and weaning to the start of the breeding season (P ≥ 0.61), however, WIMP heifers had increased (P = 0.05) ADG from yearling to the start of the breeding season compared to BIMP heifers. Antral follicle count and reproductive tract scores were not influenced by implant treatment (P ≥ 0.18). Response to synchronization of estrus was increased (P = 0.02) in WIMP compared to CON heifers, with BIMP heifers similar to all other treatments. First service conception rates tended to be increased (P = 0.09) in CON heifers compared to WIMP heifers, with BIMP heifers similar to CON and WIMP. Final pregnancy rates were similar (P = 0.54) among treatments. A treatment × yr interaction was detected (P = 0.01) for the number of primordial follicles/section with increased primordial follicles in WIMP heifers in yr 3 compared to BIMP and WIMP heifers in yr 2 and CON heifers in yr 3, as well as in BIMP compared to WIMP heifers in yr 2. Utilization of growth promoting implants did not negatively impact postweaning reproductive development or compromise pregnancy rates in beef heifers. Based on these results, administration of a growth promoting Synovex-C implant at 2 mo of age may allow for increased body weight at weaning, without hindering reproductive performance.

Uterine Glands: Developmental Biology and Functional Roles in Pregnancy

All mammalian uteri contain glands in the endometrium that develop only or primarily after birth. Gland development or adenogenesis in the postnatal uterus is intrinsically regulated by proliferation, cell-cell interactions, growth factors and their inhibitors, as well as transcription factors, including forkhead box A2 (FOXA2) and estrogen receptor α (ESR1). Extrinsic factors regulating adenogenesis originate from other organs, including the ovary, pituitary, and mammary gland. The infertility and recurrent pregnancy loss observed in uterine gland knockout sheep and mouse models support a primary role for secretions and products of the glands in pregnancy success. Recent studies in mice revealed that uterine glandular epithelia govern postimplantation pregnancy establishment through effects on stromal cell decidualization and placental development. In humans, uterine glands and, by inference, their secretions and products are hypothesized to be critical for blastocyst survival and implantation as well as embryo and placental development during the first trimester before the onset of fetal-maternal circulation. A variety of hormones and other factors from the ovary, placenta, and stromal cells impact secretory function of the uterine glands during pregnancy. This review summarizes new information related to the developmental biology of uterine glands and discusses novel perspectives on their functional roles in pregnancy establishment and success.

Partial ablation of endometrial glands in dogs after exposure to progestin during the neonatal period

Bitches with uteri devoid of endometrial glands should be sterile, and consequently could contribute to the population control of dogs. Considering that an inadequate exposure of the female reproductive system to steroids can lead to the formation of the uterine gland knock-out (UGKO) phenotype in some species, the aim of this study was to evaluate the effect of serial applications of medroxyprogesterone acetate (MPA) from birth until the age of six months on the development of endometrial glands in bitches. For this purpose, 16 female mongrel dogs from different litters were distributed into either an MPA group (n = 8), animals treated with 10 mg kg sc (Promone-E^®, Pfizer, Brasil) at 3-week intervals, from day one after birth until the age of six months, or a control group (n = 8), composed of animals that only received a 0.9% NaCl solution in place of MPA. At six months of age, ovariohysterectomy was performed and uterine horn samples were collected for histological and immunohistochemical examinations. The bitches from the MPA-treated group presented a 35% decrease in the number of endometrial glands, a larger diameter of the endometrial glands, a greater epithelial height, as well as a greater thickness of the uterine wall, endometrium, and myometrium. However, no significant differences were observed between the two groups in the expression of ER-α, ER-β, and PR on the surface epithelium and endometrial stroma. Therefore, the serial application of MPA from birth until the age of 6 months do not completely ablate the development of the endometrial glands in bitches, but impair it by 35%.

Beyond the brain-Peripheral kisspeptin signaling is essential for promoting endometrial gland development and function

Uterine growth and endometrial gland formation (adenogenesis) and function, are essential for fertility and are controlled by estrogens and other regulators, whose nature and physiological relevance are yet to be elucidated. Kisspeptin, which signals via Kiss1r, is essential for fertility, primarily through its central control of the hypothalamic-pituitary-ovarian axis, but also likely through peripheral actions. Using genetically modified mice, we addressed the contributions of central and peripheral kisspeptin signaling in regulating uterine growth and adenogenesis. Global ablation of Kiss1 or Kiss1r dramatically suppressed uterine growth and almost fully prevented adenogenesis. However, while uterine growth was fully rescued by E2 treatment of Kiss1^−/− mice and by genetic restoration of kisspeptin signaling in GnRH neurons in Kiss1r^−/− mice, functional adenogenesis was only marginally restored. Thus, while uterine growth is largely dependent on ovarian E2-output via central kisspeptin signaling, peripheral kisspeptin signaling is indispensable for endometrial adenogenesis and function, essential aspects of reproductive competence.

Age and Nursing Affect the Neonatal Porcine Uterine Transcriptome

The lactocrine hypothesis for maternal programming of neonatal development was proposed to describe a mechanism through which milk-borne bioactive factors, delivered from mother to nursing offspring, could affect development of tissues, including the uterus. Porcine uterine development, initiated before birth, is completed postnatally. However, age- and lactocrine-sensitive elements of the neonatal porcine uterine developmental program are undefined. Here, effects of age and nursing on the uterine transcriptome for 48 h from birth (Postnatal Day [PND] = 0) were identified using RNA sequencing (RNAseq). Uterine tissues were obtained from neonatal gilts (n = 4 per group) within 1 h of birth and before feeding (PND 0), or 48 h after nursing ad libitum (PND 2N) or feeding a commercial milk replacer (PND 2R). RNAseq analysis revealed differentially expressed genes (DEGs) associated with both age (PND 2N vs. PND 0; 3283 DEGs) and nursing on PND 2 (PND 2N vs PND 2R; 896 DEGs). Expression of selected uterine genes was validated using quantitative real-time PCR. Bioinformatic analyses revealed multiple biological processes enriched in response to both age and nursing, including cell adhesion, morphogenesis, and cell-cell signaling. Age-sensitive pathways also included estrogen receptor-alpha and hedgehog signaling cascades. Lactocrine-sensitive processes in nursed gilts included those involved in response to wounding, the plasminogen activator network and coagulation. Overall, RNAseq analysis revealed comprehensive age- and nursing-related transcriptomic differences in the neonatal porcine uterus and identified novel pathways and biological processes regulating uterine development.

Criteria for selecting replacements at weaning, before breeding, and after breeding

At weaning, heifers should be considered for replacements based on their dam's previous performance; heifer calving date, age, and weight; and previous exposure to implants. Before breeding, heifers should be selected as replacements based on whether they have attained puberty (determined by a prebreeding examination), do not have abnormal pelvic areas, or fail to meet temperament standards. After breeding, heifers should be selected as replacements if they conceive early in the breeding season, are capable of achieving 85% of their mature weight by calving, and calve at a body condition of 5.5 to 6.0.

Comparative developmental biology of the uterus: insights into mechanisms and developmental disruption

The uterus is an essential organ for reproduction in mammals that derives from the Müllerian duct. Despite the importance of the uterus for the fertility and health of women and their offspring, relatively little is known about the hormonal, cellular and molecular mechanisms that regulate development of the Müllerian duct and uterus. This review aims to summarize the hormonal, cellular and molecular mechanisms and pathways governing development of the Müllerian duct and uterus as well as highlight developmental programming effects of endocrine disruptor compounds. Organogenesis, morphogenesis, and functional differentiation of the uterus are complex, multifactorial processes. Disruption of uterine development in the fetus and neonate by genetic defects and exposure to endocrine disruptor compounds can cause infertility and cancer in the adult and their offspring via developmental programming. Clear conservation of some factors and pathways are observed between species; therefore, comparative biology is useful to identify candidate genes and pathways underlying congenital abnormalities in humans.

Uterine gland formation in mice is a continuous process, requiring the ovary after puberty, but not after parturition

Uterine gland formation occurs postnatally in an ovary- and steroid-independent manner in many species, including humans. Uterine glands secrete substances that are essential for embryo survival. Disruption of gland development during the postnatal period prevents gland formation, resulting in infertility. Interestingly, stabilization of beta-catenin (CTNNB1) in the uterine stroma causes a delay in gland formation rather than a complete absence of uterine glands. Thus, to determine if a critical postnatal window for gland development exists in mice, we tested the effects of extending the endocrine environment of pregnancy on uterine gland formation by treating neonatal mice with estradiol, progesterone, or oil for 5 days. One uterine horn was removed before puberty, and the other was collected at maturity. Some mice were also ovariectomized before puberty. The hormone-treated mice exhibited a delay in uterine gland formation. Hormone-treatment increased the abundance of uterine CTNNB1 and estrogen receptor alpha (ESR1) before puberty, indicating possible mechanisms for delayed gland formation. Despite having fewer glands, progesterone-treated mice were fertile, suggesting that a threshold number of glands is required for pregnancy. Mice that were ovariectomized before puberty did not undergo further uterine growth or gland development. Finally, to establish the role of the ovary in postpartum uterine gland regeneration, mice were either ovariectomized or given a sham surgery after parturition, and uteri were evaluated 1 wk later. We found that the ovary is not required for uterine growth or gland development following parturition. Thus, uterine gland development occurs continuously in mice and requires the ovary after puberty, but not after parturition.

Endometrial expression of progesterone-induced blocking factor and galectins-1, -3, -9, and -3 binding protein in the luteal phase and early pregnancy in cattle

Progesterone-induced blocking factor (PIBF) and galectins modulate the maternal immune response during pregnancy. We hypothesized that the relative transcript abundance of the above genes would be different during the luteal phase/early pregnancy and would be affected by progesterone supplementation. To further test this, hypothesis protein expression analyses were carried out to evaluate the abundance and localization of LGALS9 and PIBF. Following estrus synchronization, heifers were inseminated ( n = 140) or not ( n = 70). Half the heifers in each status (cyclic or potentially pregnant) were randomly assigned to receive a progesterone-releasing intravaginal device (PRID) on day 3 after estrus, which elevated progesterone concentrations from day 3.5 to 8 ( P < 0.05), resulting in four treatment groups: cyclic and pregnant heifers, each with normal and high progesterone. After confirmation of pregnancy status in inseminated animals, uterine tissue was collected on days 5, 7, 13, or 16 of the luteal phase of the cycle/pregnancy. Gene and protein expression was determined using Q-RT-PCR and IHC, respectively, on 5 heifers per treatment per time point (i.e., 80 in total). Progesterone concentrations did not affect expression of any of the genes ( P > 0.05). LGALS9 and LGALS3BP were expressed at low levels in both cyclic and pregnant endometria until day 13. On day 16, expression increased only in the pregnant heifers ( P < 0.0001). LGALS1 and LGALS3 decreased on day 7 ( P < 0.0001) and remained low until day 16. Pregnancy had no effect on the expression of LGALS1, LGALS3, and PIBF. Additionally, LGALS9 and PIBF proteins were expressed in distinct uterine cell types. These results indicate that the galectins may be involved in uterine receptivity and/or implantation in heifers.

Actions of progesterone on uterine immunosuppression and endometrial gland development in the uterine gland knockout (UGKO) ewe

In ewes, the uterine gland knockout (UGKO) phenotype is caused by neonatal exposure to norgestomet to arrest uterine gland development and produce an adult which has a uterus characterized by the lack of endometrial glands. Since endometrial glands in the sheep produce the lymphocyte-inhibitory protein, ovine uterine serpin (OvUS), an experiment was conducted with ewes of the UGKO phenotype to evaluate whether the inhibitory actions of progesterone on tissue rejection responses in utero are dependent upon the presence of endometrial glands. Control and UGKO ewes were ovariectomized and subsequently treated with either 100 mg/day progesterone or corn oil vehicle for 30 days. An autograft and allograft of skin were then placed in each uterine lumen and treatments were continued for an additional 30 days before grafts were examined for survival. All autografts survived and had a healthy appearance after histological analysis. Allografts were generally rejected in ewes treated with vehicle but were present for hormone-treated ewes, regardless of uterine phenotype. Analysis of the histoarchitecture and protein synthetic capacity of the uterus revealed that progesterone induced differentiation of endometrial glands and synthesis and secretion of OvUS in UGKO ewes. The UGKO ewes had reduced density of CD45R+ lymphocytes in the endometrial epithelium and there was a tendency for progesterone to reduce this effect in luminal epithelium. Taken together, results confirm the actions of progesterone to inhibit graft rejection response in utero. Responses of UGKO ewes to progesterone indicate that the hormone can induce de novo development and differentiation of endometrial glands, at least when skin grafts are in the uterus.

Comparative developmental biology of the mammalian uterus

The uterus is an essential organ for reproduction in mammals. Despite the importance of the uterus for the fertility and health of women and their offspring, relatively little is known about the hormonal, cellular, and molecular mechanisms that regulate development of the uterus in either the fetus or neonate. Disruption of uterine development in the fetus and neonate by genetic defects or exposure to endocrine disruptors can program the function of the uterus in the adult and lead to infertility, cancer, and even death. The intent of this chapter is to review the current knowledge of regulatory factors and pathways governing prenatal organogenesis and postnatal morphogenesis of the uterus in mammals, with a particular focus on laboratory and domestic animals. Prenatal organogenesis, postnatal morphogenesis, and adult functional differentiation of the uterus are complex, multifactorial processes. Although conservation of some factors and pathways are observed between species, it is clear that mutation of candidate genes in the mouse does not always recapitulate the same defects observed in the human. Therefore, comparative biology of the mechanisms regulating uterine development in other species may be useful to identify candidate genes and pathways to understand congenital abnormalities in humans. This knowledge is necessary to develop rational therapies to prevent and treat infertility and to enhance fertility in humans and domestic animals.

Neonatal estrogen exposure disrupts uterine development in the postnatal sheep

Postnatal development of the ovine uterus between birth and postnatal day (PND) 56 involves budding differentiation of the endometrial glandular epithelium from the luminal epithelium (LE) followed by extensive coiling and branching morphogenesis of the tubular glands. To determine the short- and long-term effects of estrogen on neonatal ovine uterine development after PND 14, neonatal sheep were randomly assigned at birth (PND 0) to be treated daily with estradiol-17beta benzoate (EB; 0, 0.01, 0.1, 1, or 10 microg/kg body weight.d) during one of two developmental periods (PND 14-27 or 42-55). All ewes were hemiovariohysterectomized at the end of EB treatment on either PND 28 or 56, and the remaining uterine horn and ovary removed on PND 112. Immediate responses to EB treatment included dose- and age-dependent increases in uterine wet weight, thickness of the endometrium, myometrium, and LE, but decreases in endometrial glands on PND 28 and 56. Transient exposure to EB decreased gland number and thickness of the endometrium and LE on PND 112 but did not affect extrauterine reproductive tract structures. The mechanism of estrogen inhibition of uterine development did not involve effects on cell proliferation. Real-time PCR analyses found that EB exposure disrupted normal patterns of growth factor (IGF-I, IGF-II, fibroblast growth factor-7, fibroblast growth factor-10, and hepatocyte growth factor) and receptor mRNA expression in the uterus. Transient exposure of the neonatal ewe to estrogens during critical periods specifically alters growth factor networks that perturb normal development of the uterus, leading to permanent alterations in uterine structure and function.

Estrogen-induced disruption of neonatal porcine uterine development alters adult uterine function

In the pig, estradiol-17beta valerate (EV) exposure from birth (Postnatal Day [PND] 0) disrupts estrogen receptor-alpha (ER)-dependent uterine development and increases embryo mortality in adults. To determine effects of neonatal EV exposure on adult uterine morphology and function, 36 gilts received corn oil (CO) or EV from PND 0 to PND 13. Cyclic and pregnant (PX) adults from each treatment group were hysterectomized on Day 12 after estrus/mating. Treatment and pregnancy effects were determined for uterine weight and horn volume, uterine luminal fluid (ULF) protein and estradiol content, endometrial incorporation of 3H-leucine (3H-Leu) into nondialyzable product, and endometrial mRNA levels for ER, progesterone receptor (PR), uteroferrin (UF), retinol-binding protein (RBP), and keratinocyte growth factor (KGF). Adults cycled normally and had similar numbers of corpora lutea. Uteri of PX gilts contained tubular/filamentous conceptuses, and ULF estradiol content was unaffected by treatment. However, pregnancy increased uterine weight and size only in CO gilts (Treatment x Status, P < 0.01). Treatment reduced ULF protein content (P < 0.01), endometrial 3H-Leu incorporation (P < 0.05), and the pregnancy-associated increase in ULF protein (Treatment x Status, P < 0.01). Treatment did not affect endometrial ER or PR mRNA levels but attenuated the pregnancy-associated increase in UF mRNA (Treatment x Status; P < 0.01), increased RBP (P < 0.10), and decreased KGF mRNA levels (P < 0.05). These results establish that transient postnatal estrogen exposure affects porcine uterine responsiveness to potentially embryotrophic signals and that estrogen-sensitive postnatal uterine organizational events are determinants of uterine size and functionality.

Developmental biology of uterine glands

All mammalian uteri contain endometrial glands that synthesize or transport and secrete substances essential for survival and development of the conceptus (embryo/fetus and associated extraembryonic membranes). In rodents, uterine secretory products of the endometrial glands are unequivocally required for establishment of uterine receptivity and conceptus implantation. Analyses of the ovine uterine gland knockout model support a primary role for endometrial glands and, by default, their secretions in peri-implantation conceptus survival and development. Uterine adenogenesis is the process whereby endometrial glands develop. In humans, this process begins in the fetus, continues postnatally, and is completed during puberty. In contrast, endometrial adenogenesis is primarily a postnatal event in sheep, pigs, and rodents. Typically, endometrial adenogenesis involves differentiation and budding of glandular epithelium from luminal epithelium, followed by invagination and extensive tubular coiling and branching morphogenesis throughout the uterine stroma to the myometrium. This process requires site-specific alterations in cell proliferation and extracellular matrix (ECM) remodeling as well as paracrine cell-cell and cell-ECM interactions that support the actions of specific hormones and growth factors. Studies of uterine development in neonatal ungulates implicate prolactin, estradiol-17 beta, and their receptors in mechanisms regulating endometrial adenogenesis. These same hormones appear to regulate endometrial gland morphogenesis in menstruating primates and humans during reconstruction of the functionalis from the basalis endometrium after menses. In sheep and pigs, extensive endometrial gland hyperplasia and hypertrophy occur during gestation, presumably to provide increasing histotrophic support for conceptus growth and development. In the rabbit, sheep, and pig, a servomechanism is proposed to regulate endometrial gland development and differentiated function during pregnancy that involves sequential actions of ovarian steroid hormones, pregnancy recognition signals, and lactogenic hormones from the pituitary or placenta. That disruption of uterine development during critical organizational periods can alter the functional capacity and embryotrophic potential of the adult uterus reinforces the importance of understanding the developmental biology of uterine glands. Unexplained high rates of peri-implantation embryonic loss in humans and livestock may reflect defects in endometrial gland morphogenesis due to genetic errors, epigenetic influences of endocrine disruptors, and pathological lesions.

Neonatal estradiol exposure alters uterine morphology and endometrial transcriptional activity in prepubertal gilts

Porcine endometrial development between birth (postnatal day = PND 0) and PND 56 involves differentiation of glandular epithelium (GE) from luminal epithelium (LE) and estrogen receptor-alpha (ER) expression. Juvenile ER architecture evolves after birth, as stroma and nascent GE first express ER. Mature ER architecture is evident after PND 30, when stroma, GE and LE are ER-positive. When administered during discrete periods between PND 0 and 56, effects of estradiol-17beta valerate (EV) on the neonatal porcine uterus relate to endometrial ER architecture. Transient EV exposure from birth reduces embryo survival in pregnant adult gilts. Effects of EV, administered as juvenile endometrial ER architecture develops (P1, PND 0-13), or after mature ER architecture is established (P2, PND 42-55), were evaluated in uteri from gilts treated with corn oil or EV in P1 or P2 and hysterectomized on PND 100 without additional steroids (NSt), on PND 102 after EV on PND100-101 (EV2), or on PND 117 after EV2 followed by progesterone on PND 102-116 (EP). Neonatal EV reduced uterine weight (P < 0.02), size (P < 0.01), luminal protein content (P < 0.07), and percent incorporation of 3H-leucine into nondialyzable endometrial products in vitro (P < 0.01). Group (NSt, EV2, EP) -specific treatment effects detected for endometrial ER, progesterone receptor, uteroferrin, and/or retinol binding protein mRNA levels were frequently related to period (P1,P2). Results support the idea that estrogen-sensitive postnatal organizational events, including those defined, in part, by endometrial ER architecture, are likely components of genetic and epigenetic programs governing uterine morphogenesis and ontogeny of endometrial function in the pig.

Effects of neonatal progestin exposure on female reproductive tract structure and function in the adult ewe

Endometrial glands are present in all mammalian uteri and produce secretions that are hypothesized to support conceptus (i.e., embryo/fetus and placental membranes) survival and development. In sheep, endometrial gland morphogenesis occurs postnatally and can be epigenetically ablated by chronic neonatal exposure to a progestin from birth, thereby producing an adult uterine gland knock-out (UGKO) phenotype. This study determined the long-term effects of neonatal progestin exposure on adult ovine reproductive tract structure and function. Neonatal ewes were exposed to norgestomet (Nor) from birth to 32 wk of age. Unexposed ewes served as controls. After puberty, adult Nor-treated (n = 6) and control (n = 6) ewes were repeatedly bred at estrus (Day 0) to intact rams of proven fertility. In contrast to a pregnancy rate of 80% for control ewes, pregnancy was never detected on Day 25 after mating (or thereafter) in bred UGKO ewes. Control and Nor-treated ewes were then bred and necropsied on Day 9. Similar numbers of hatched blastocysts were present in uterine flushings from control and Nor-treated ewes. Weights of the ovaries and cervices were not affected by treatment. No histoarchitectural differences between control and Nor-treated ewes were detected for ovaries, oviducts, cervices, or vaginae. However, uterocervical and uterine weight as well as uterine horn length were less for Nor-treated ewes. The uteri of Nor-treated ewes were devoid of endometrial glands and lacked the stromal delineation characteristic of intercaruncular endometrium in control ewes. Endometrial width, area, and lumenal epithelial length were decreased in uteri from Nor-treated ewes, but myometrial width and morphology were not affected. Expression of a number of mRNAs that are expressed predominantly in the endometrial epithelia was not different between uteri from control and from Nor-treated ewes. Collectively, these results indicate that neonatal exposure of ewes to a progestin from birth appears to only affect development of the uterus and not any extrauterine reproductive tract tissues. The infertility of the UGKO ewes appears to result from a lack of endometrial glands and, by extension, of their secretions that are required to support growth and development of peri-implantation conceptuses.

Ovine uterine gland knock-out model: effects of gland ablation on the estrous cycle

Ovine endometrial gland development is a postnatal event that can be inhibited epigenetically by chronic exposure of ewe lambs to a synthetic progestin from birth to puberty. As adults, these neonatally progestin-treated ewes lack endometrial glands and display a uterine gland knockout (UGKO) phenotype that is useful as a model for study of endometrial function. Here, objectives were to determine: 1) length of progestin exposure necessary from birth to produce the UGKO phenotype in ewes; 2) if UGKO ewes display normal estrous cycles; and 3) if UGKO ewes could establish and/or maintain pregnancy. Ewe lambs (n = 22) received a Norgestomet (Nor) implant at birth and every two weeks thereafter for 8 (Group I), 16 (Group II), or 32 (Groups III and IV) weeks. Control ewe lambs (n = 13) received no Nor treatment (Groups V and VI). Ewes in Groups I, II, III, and VI were hemihysterectomized (Hhx) at 16 weeks of age. After puberty, the remaining uterine horn in Hhx ewes was removed on either Day 9 or 15 of the estrous cycle (Day 0 = estrus). Histological analyses of uteri indicated that progestin exposure for 8, 16, or 32 weeks prevented endometrial adenogenesis and produced the UGKO phenotype in adult ewes. Three endometrial phenotypes were consistently observed in Nor-treated ewes: 1) no glands, 2) slight glandular invaginations into the stroma, and 3) limited numbers of cyst- or gland-like structures in the stroma. Overall patterns of uterine progesterone, estrogen, and oxytocin receptor expression were not different in uteri from adult cyclic control and UGKO ewes. However, receptor expression was variegated in the ruffled luminal epithelium of uteri from UGKO ewes. Intact UGKO ewes displayed altered estrous cycles with interestrous intervals of 17 to 43 days, and they responded to exogenous prostaglandin F(2 approximately ) (PGF) with luteolysis and behavioral estrus. During the estrous cycle, plasma concentrations of progesterone in intact control and UGKO ewes were not different during metestrus and diestrus, but levels did not decline in many UGKO ewes during late diestrus. Peak peripheral plasma concentrations of PGF metabolite, in response to an oxytocin challenge on Day 15, were threefold lower in UGKO compared to control ewes. Intact UGKO ewes bred repeatedly to intact rams did not display evidence of pregnancy based on results of ultrasound. Collectively, results indicate that 1) transient, progestin-induced disruption of ovine uterine development from birth alters both structural and functional integrity of the adult endometrium; 2) normal adult endometrial integrity, including uterine glands, is required to insure a luteolytic pattern of PGF production; and 3) the UGKO phenotype, characterized by the absence of endometrial glands and a compact, disorganized endometrial stroma, limits or inhibits the capacity of uterine tissues to support the establishment and/or maintenance of pregnancy.