Pregnancy and Bovine Somatotropin in Nonlactating Dairy Cows: II. Endometrial Gene Expression Related to Maintenance of Pregnancy

Metabolic hormones are integral regulators of female reproductive health and function

The female reproductive system is strongly influenced by nutrition and energy balance. It is well known that food restriction or energy depletion can induce suppression of reproductive processes, while overnutrition is associated with reproductive dysfunction. However, the intricate mechanisms through which nutritional inputs and metabolic health are integrated into the coordination of reproduction are still being defined. In this review, we describe evidence for essential contributions by hormones that are responsive to food intake or fuel stores. Key metabolic hormones-including insulin, the incretins (glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1), growth hormone, ghrelin, leptin, and adiponectin-signal throughout the hypothalamic-pituitary-gonadal axis to support or suppress reproduction. We synthesize current knowledge on how these multifaceted hormones interact with the brain, pituitary, and ovaries to regulate functioning of the female reproductive system, incorporating in vitro and in vivo data from animal models and humans. Metabolic hormones are involved in orchestrating reproductive processes in healthy states, but some also play a significant role in the pathophysiology or treatment strategies of female reproductive disorders. Further understanding of the complex interrelationships between metabolic health and female reproductive function has important implications for improving women's health overall.

Growth hormone in fertility and infertility: Mechanisms of action and clinical applications

Secreted by the anterior pituitary gland, growth hormone (GH) is a peptide that plays a critical role in regulating cell growth, development, and metabolism in multiple targeted tissues. Studies have shown that GH and its functional receptor are also expressed in the female reproductive system, including the ovaries and uterus. The experimental data suggest putative roles for GH and insulin-like growth factor 1 (IGF-1, induced by GH activity) signaling in the direct control of multiple reproductive functions, including activation of primordial follicles, folliculogenesis, ovarian steroidogenesis, oocyte maturation, and embryo implantation. In addition, GH enhances granulosa cell responsiveness to gonadotropin by upregulating the expression of gonadotropin receptors (follicle-stimulating hormone receptor and luteinizing hormone receptor), indicating crosstalk between this ovarian regulator and the endocrine signaling system. Notably, natural gene mutation of GH and the age-related decline in GH levels may have a detrimental effect on female reproductive function, leading to several reproductive pathologies, such as diminished ovarian reserve, poor ovarian response during assisted reproductive technology (ART), and implantation failure. Association studies using clinical samples showed that mature GH peptide is present in human follicular fluid, and the concentration of GH in this fluid is positively correlated with oocyte quality and the subsequent embryo morphology and cleavage rate. Furthermore, the results obtained from animal experiments and human samples indicate that supplementation with GH in the in vitro culture system increases steroid hormone production, prevents cell apoptosis, and enhances oocyte maturation and embryo quality. The uterine endometrium is another GH target site, as GH promotes endometrial receptivity and pregnancy by facilitating the implantation process, and the targeted depletion of GH receptors in mice results in fewer uterine implantation sites. Although still controversial, the administration of GH during ovarian stimulation alleviates age-related decreases in ART efficiency, including the number of oocytes retrieved, fertilization rate, embryo quality, implantation rate, pregnancy rate, and live birth rate, especially in patients with poor ovarian response and recurrent implantation failure.

Estradiol cypionate administered at the end of a progesterone-based protocol for FTAI induces ovulation and improves postovulatory luteal function and uterine environment in anestrous beef cows

The objective of this study was to evaluate the effect of the administration of estradiol cypionate (ECP) at the end of an estradiol and progesterone-based protocol for fixed time artificial insemination (FTAI) on ovarian response and uterine function in postpartum anestrous beef cows. Multiparous suckled cows were randomly assigned to receive ECP at doses of 0 (control, n = 15), 0.5 (n = 15) or 1.0 mg (n = 15) im at the time of progesterone intravaginal insert removal. Serum 17β-estradiol concentrations at 24 h after insert removal were greater (P < 0.05) in both ECP treatments than in controls. No differences in estradiol were found between 0.5 mg and control cows (P > 0.1) from 48 h after insert removal until ovulation, although greater (P < 0.05) concentrations were maintained until ovulation in 1.0 mg ECP treated cows. Maximum 17β-estradiol concentration attained in each female was greater as ECP dose was greater (10.4 ± 0.4, 11.8 ± 0.5 and 13.5 ± 0.7, for control, 0.5 and 1.0 mg ECP treated cows, respectively; P < 005). Proportion of cows that ovulated tended to be greater (P = 0.06) in ECP treated than in control cows. Ovulation occurred earlier and the size of the ovulatory follicle was smaller (P < 0.05) for 1.0 mg but not for 0.5 mg (P > 0.1) when compared with control cows. After ovulation (Day 13 and 14), serum progesterone concentrations were greater (P < 0.05) in 0.5 and 1.0 mg ECP than control cows. Uterine environment on Day 6 after ovulation was affected by treatment; transcript expression of three of nine evaluated genes (i.e., estrogen, IGF-1 and insulin receptors genes) were upregulated (P < 0.05) after ECP treatment. In conclusion, ECP administration at progesterone insert removal in anestrous cows i) induces greater serum estradiol concentrations and tended to induce greater ovulation rate, ii) acts in a dose-dependent manner, as ECP dose increases ovulation occurs earlier and the size of the ovulatory follicle is smaller, iii) improves postovulatory luteal function and affects uterine gene expression. Altogether, this information contributes with the understanding of the effect of preovulatory estradiol exposure on ovulation and postovulatory ovarian and uterine function in anestrous beef cows.

The Potential Role of Growth Hormone on the Endometrium in Assisted Reproductive Technology

Growth hormone (GH) has been considered as an adjuvant treatment in human assisted reproductive technology (ART) for several years. Its action was largely attributed to an improvement of ovarian function and less emphasis was paid to its role in the uterus. However, there is increasing evidence that GH and its receptors are expressed and have actions in the endometrium and may play an important role in modifying endometrial receptivity. Thus, in this review, we firstly describe the existence of GH receptors in endometrium and then summarize the effects of GH on the endometrium in clinical situations and the underlying mechanisms of GH in the regulation of endometrial receptivity. Finally, we briefly review the potential risks of GH in ART and consider rationalized use of GH treatment in ART.

Effects of extending the length of pro-oestrus in an oestradiol- and progesterone-based oestrus synchronisation program on ovarian function, uterine environment and pregnancy establishment in beef heifers

The aim of the present study was to investigate the effects of a strategy for extending pro-oestrus (the interval between luteolysis and ovulation) in an oestrus synchronisation protocol (named J-Synch) in beef heifers on follicular growth, sexual steroid concentrations, the oestrogen receptor ERα and progesterone receptors (PR) in the uterus, insulin-like growth factor (IGF) 1 and pregnancy rates. In Experiment 1, heifers treated with the new J-Synch protocol had a longer pro-oestrus period than those treated with the conventional protocol (mean (± s.e.m.) 93.7 ± 12.9 vs 65.0 ± 13.7 h respectively; P < 0.05). The rate of dominant follicle growth from the time of progesterone device removal to ovulation was greater in heifers in the J-Synch than conventional group (P < 0.05). Luteal area and serum progesterone concentrations were greater in the J-Synch Group (P < 0.05) for the 12 days after ovulation. Progesterone receptor (PGR) staining on Day 6 after ovulation in the uterine stroma was lower in the J-Synch than conventional group (P < 0.05), and the expression of PR gene (PGR) and IGF1 gene tended to be lower in J-Synch-treated heifers (P < 0.1). In Experiment 2 (n = 2349), the pregnancy rate 30–35 days after fixed-time AI (FTAI) was greater for heifers in the J-Synch than conventional group (56.1% vs 50.7% respectively). In conclusion, our strategy for extending pro-oestrus (i.e. the J-Synch protocol) significantly improves pregnancy establishment in beef heifers. This improvement was related to an increased rate of growth of the dominant ovulatory follicle, greater progesterone concentrations during the ensuing luteal phase and different uterine patterns of PGR and IGF1, which may have favoured embryo development and pregnancy establishment.

Triennial Reproduction Symposium: deficiencies in the uterine environment and failure to support embryonic development

Pregnancy failure in livestock can result from failure to fertilize the oocyte or embryonic loss during gestation. The focus of this review is on cattle and factors affecting and mechanisms related to uterine insufficiency for pregnancy. A variety of factors contribute to embryonic loss and it may be exacerbated in certain animals, such as high-producing lactating dairy cows, and in some cattle in which estrous synchronization and timed AI was performed, due to reduced concentrations of reproductive steroids. Recent research in beef cattle induced to ovulate immature follicles and in lactating dairy cows indicates that deficient uterine function is a major factor responsible for infertility in these animals. Failure to provide adequate concentrations of estradiol before ovulation results in prolonged effects on expression and localization of uterine genes and proteins that participate in regulating uterine functions during early gestation. Furthermore, progesterone concentrations during early gestation affect embryonic growth, interferon-tau production, and uterine function. Therefore, an inadequate uterine environment induced by insufficient steroid concentrations before and after ovulation could cause early embryonic death either by failing to provide an adequate uterine environment for recognition of embryo signaling, adhesion, and implantation or by failing to support appropriate embryonic growth, which could lead to decreased conceptus size and failed maternal recognition of pregnancy.

Transcriptomic analysis of the bovine endometrium: What is required to establish uterine receptivity to implantation in cattle?

In cattle, the majority of pregnancy loss can be attributed to early embryonic loss which occurs prior maternal recognition of pregnancy on Day 16 (Day 0 = ovulation). During this time, carefully orchestrated spatio-temporal alterations in the transcriptomic profile of the endometrium are required to drive conceptus elongation, via secretions from the endometrium (termed histotroph) and establish uterine receptivity to implantation. The two main modulators of these processed are progesterone (P4) and the pregnancy recognition signal interferon tau (IFNT). Altered concentrations of P4 in circulation mediate its effects via the endometrium and have been associated with different rates of conceptus elongation in cattle. Transcriptomic analysis of the endometrium has shown that modulation of circulating P4 alters endometrial expression of genes that can contribute to histotroph composition, which is beneficial (when P4 is supplemented) or detrimental (when P4 is reduced) to the developing conceptus. In addition, down-regulation of the progesterone receptor, required to establish uterine receptivity, is altered in the endometrium of heifers with altered P4 concentrations. IFNT, a type 1 interferon, also significantly impacts on the endometrial transcriptome. It induces the expression of a large number of classical interferon stimulated genes as early as Day 15 of pregnancy. In summary, the successful establishment of pregnancy in cattle requires a sequence of key events to ensure appropriate maternally derived secretions, establish uterine receptivity to implantation as well as an adequate endometrial response to IFNT production.

Oxytocin receptor down-regulation is not necessary for reducing oxytocin-induced prostaglandin F(2alpha) accumulation by interferon-tau in a bovine endometrial epithelial cell line

Interferon-tau (IFNtau) is the embryonic signal responsible for pregnancy recognition in ruminants. The primary action of IFNtau is believed to be mediated through inhibition of prostaglandin F(2alpha) (PGF(2alpha)) released from the endometrial epithelial cells in response to oxytocin (OT). Our working hypothesis was that the antiluteolytic effect of IFNtau also involved modulation of PG production downstream of OT receptor (OTR) and/or cyclooxygenase 2 (COX2). There is currently no OT-sensitive endometrial cell line to study the molecular mechanisms underlying our hypotheses. Therefore, we established an immortalized bovine endometrial epithelial cell line (bEEL) exhibiting OT response. These cells were cytokeratin positive, expressed steroid receptors, and exhibited preferential accumulation of PGF(2alpha) over PGE(2). The bEEL cells were highly sensitive to OT, showing time- and concentration-dependent increase in COX2 transcript and protein and PGF(2alpha) accumulation. Interestingly, IFNtau (20 ng/ml) significantly reduced OT-induced PGF(2alpha) accumulation, but surprisingly, the effect was not mediated through down-regulation of either OTR or COX2. Rather, IFNtau up-regulated COX2 in a time- and concentration-dependent manner while decreasing OT-induced PG accumulation. This suggests that COX2 is not a primary target for the antiluteolytic effect of IFNtau. Because IFNtau reduced OT-stimulated PGF(2alpha) accumulation within 3 h, the mechanism likely involves a direct interference at the level of the OT signaling or transcription in addition to the down-regulation of OTR observed in vivo. In summary, bEEL cells offer a unique in vitro model for investigating the cellular and molecular mechanisms underlying OT and IFNtau response in relation with luteolysis and recognition of pregnancy in the bovine.

Effect of meloxicam treatment during early pregnancy in Holstein heifers

We previously reported that administration of flunixin meglumine two times at a critical stage approaching pregnancy recognition associated with maintenance of the corpus luteum (CL) increased early embryo survival and pregnancy rate via an additive antiluteolytic effect with the conceptus [Vet Rec 160 (2007) 404]. In this study, the objective was to determine if a single administration of meloxicam, a non-steroid anti-inflammatory drug with a longer half-life, could be used instead of flunixin meglumine. This would avoid repeated injections in heifers following insemination at a critical stage to increase pregnancy rate due to its inhibitory effect on prostaglandin F(2alpha) synthesis. Eighty-five, 15- to 18-month-old Holstein heifers were synchronized, and following insemination (day 0) heifers were assigned to receive subcutaneous meloxicam injection (0.5 mg/kg; n = 37) on the afternoon of day 15 or were untreated as a control (n = 48). Pregnancy rates were defined as the percentage of heifers inseminated that were diagnosed pregnant by ultrasound between days 31 and 38 after artificial insemination. Effect of the treatment on pregnancy rates was analysed by chi-square test. Meloxicam treatment on day 15 after insemination dramatically decreased pregnancy rates in the heifers (52%; 25 of 48 in the control group vs 24.3%; 9 of 37 in the meloxicam-treated group; p < 0.01). This result indicates that administration of meloxicam at the time associated with pregnancy recognition processes to maintain the CL was harmful to the pregnancy even though the drug is considered to be safe during pregnancy in cattle.

Development and characterization of a simian virus 40 immortalized bovine endometrial stromal cell line

In ruminants, interferon-tau (IFNtau) is the maternal recognition signal inhibiting prostaglandin (PG) F2alpha production by endometrial epithelial cells and stimulating interferon-stimulated genes in the stroma. Stromal cells mediate the action of progesterone on epithelial cells during pregnancy. Our working hypothesis is that IFNtau acts as a molecular switch that turns on PGE(2) production in endometrial stromal cells while suppressing PGF2alpha production from epithelial cells. In this report we document immortalization and functional characterization of a bovine stromal cell line from the caruncular region of the endometrium [caruncular stromal cell (CSC)]. Primary stromal cells were immortalized by nucleofection with simian virus 40 large T antigen and integrase. The resulting cell line, CSC, expresses stromal cell-specific vimentin, estrogen, and progesterone receptors, and is amenable for transient transfection. Basal and stimulated production of PGE2 is higher than PGF2alpha and associated with cyclooxygenase (COX) 2 expression. Phorbol myristate acetate (PMA) and IFNtau up-regulate COX2 and PG production in a dose-dependent manner. When added together, low concentrations of IFNtau inhibit PMA-induced COX2 expression; whereas this inhibition is lost at high concentrations. Expression of signal transducer and activator of transcription 1 is induced by IFNtau at all concentrations studied but is not modulated by PMA. Because expression of signal transducer and activator of transcription 1 does not exhibit the biphasic response to IFNtau, we investigated the p38 MAPK pathway using the selective inhibitor SB203580. Inhibition of the p38 MAPK pathway abolishes IFNtau action on PG production. In summary, CSC appears as a good stromal cell model for investigating the molecular mechanisms related to IFNtau action and PG production in the bovine.

Pregnancy, Bovine Somatotropin, and Dietary n-3 Fatty Acids in Lactating Dairy Cows: II. Endometrial Gene Expression Related to Maintenance of Pregnancy

The objectives were to examine the effects of bovine somatotropin (bST), pregnancy, and dietary fatty acids on expression of key endometrial genes and proteins regulating prostaglandin synthesis in lactating dairy cows. Two diets were fed, at about 17 d in milk (DIM), in which oil of whole cottonseed (control diet) was compared with calcium salts of fish oil-enriched lipid (FO). Ovulation was synchronized in cows with a presynchronization plus Ovsynch protocol and cows were inseminated artificially or not inseminated on d 0 (d 0 = time of synchronized ovulation; 77 +/- 12 DIM). On d 0 and 11, cows received bST (500 mg) or no bST, and were slaughtered on d 17 to recover uterine secretions and endometrial tissue. Number of cows in the control diet: 5 bST-treated cyclic (bST-C), 5 non-bST-treated cyclic (no bST-C), 4 bST-treated pregnant (bST-P), and 5 non-bST-treated pregnant (no bST-P) cows and in the FO diet: 4 bST-treated FO-cyclic (bST-FO-C) and 5 non-bST-treated cyclic (no bST-FO-C) cows. The FO diet increased progesterone receptor (PR) mRNA, and treatment with bST increased PR mRNA concentration in endometrium of no bST-C, but not in no bST-FO-C or no bST-P cows. Concentrations of estrogen receptor-alpha (ERalpha) mRNA and protein, and oxytocin receptor (OTR) mRNA were decreased in no bST-P cows compared with no bST-C cows. Treatment with bST tended to increase OTR and ERalpha mRNA concentrations in cyclic cows fed control or FO diets. Immunohistochemistry demonstrated effects of bST, FO, and pregnancy on distributions of ERalpha and PR proteins in endometrium. Pregnancy and FO feeding decreased ERalpha abundance in luminal epithelium. Prostaglandin H synthase-2 (PGHS-2) protein was elevated in pregnant cows and localized to the luminal epithelium. Both FO and bST treatments reduced staining intensity of PGHS-2 protein. Concentrations of prostaglandin E synthase mRNA were elevated in either cyclic or pregnant cows in response to bST, whereas bST decreased prostaglandin F synthase mRNA in pregnant cows. Uterine lumen fluids had more PGF2alpha and prostaglandin E2 in pregnant than cyclic cows. Uterine lumen fluids of bST-P cows contained more prostaglandin E2 than those from no bST-P cows. In summary, both pregnancy and bST altered endometrial gene expression, and cyclic cows responded differently to bST than pregnant cows. Feeding FO modulated PR, ERalpha, and PGHS-2 expression and distribution among endometrial cell types in a manner that may favor establishment and maintenance of pregnancy.

Effects of Bovine Somatotropin on Uterine Genes Related to the Prostaglandin Cascade in Lactating Dairy Cows

Multiparous Holstein cows, averaging 80 d in milk, were used to examine the effect of exogenous bovine somatotropin (bST) on uterine expression of estrogen receptor alpha (ERalpha), prostaglandin endoperoxide synthase-2 (PGHS-2), and peroxisome proliferator-activated receptor delta (PPARdelta). About 12 h before expected ovulation in a synchronization protocol, cows were assigned to receive bST (500 mg, n = 11) or serve as untreated controls (n = 10). Cows that ovulated (n = 9 bST, 8 control) were divided within treatment to be killed on d 3 or 7 postovulation. Samples of intercaruncular endometrial tissue from uterine horns ipsilateral to the corpus luteum were collected and stored at -80 degrees C for subsequent mRNA analyses. Endometrial concentrations of ERalpha and PGHS-2 mRNA transcripts were greater on d 7 than on d 3 of the estrous cycle, but did not differ between treatments. Compared with untreated cows, short-term bST treatment decreased PGHS-2 protein expression at d 7 of the estrous cycle. Concentration of PPARdelta mRNA transcript in the uterus decreased between d 3 and 7 of the estrous cycle and was negatively correlated with ERalpha and PGHS-2 mRNA concentrations. Short-term administration of bST to lactating dairy cows had minimal effects on uterine genes encoding ERalpha, PGHS-2, and PPARdelta at d 3 and 7 of the estrous cycle but there may be an inverse relationship between PPARdelta and uterine expression of ERalpha and PGHS-2 genes.

Pregnancy and Bovine Somatotropin in Nonlactating Dairy Cows: I. Ovarian, Conceptus, and Insulin-Like Growth Factor System Responses

Nonlactating dairy cows were used to examine effects of bovine somatotropin (bST) on components of the insulin-like growth factor (IGF) system. Estrus was synchronized in cows with a Presynch + Ovsynch protocol and timed AI (TAI; n = 55) or not TAI (cycling, C; n = 23) on d 0 (time of synchronized ovulation). On d 0 and 11, cows received bST (500 mg) or no bST, and were sacrificed on d 17. Pregnancy rates were less in bST cows (27.2%, 9 of 33) than in controls (63.6%; 14 of 22). In contrast, conceptuses were larger in bST-treated cows (39.2 +/- 4.8 cm) than in controls (20 +/- 4.3 cm). Total interferon-tau in uterine luminal flushings (ULF) was greater in bST-treated cows (7.15 > 2.36 microg). Number of class 2 follicles (6 to 9 mm) was less in bST-C cows on d 7 and 16. On d 17, corpus luteum (CL) weight tended to be greater in bST-treated cows. Concentrations of progesterone were greater after d 10 in C than in pregnant (P) cows. In the ULF, IGF-binding protein-3 was greater in bST-P cows than in pregnant cows. A tendency for an increase in IGF-I hormone concentrations in the ULF was detected on d 17 in bST-treated and cyclic cows. Endometrial mRNA for IGF-I, IGF-II, IGFBP-2, and IGFBP-3 increased in bST-C, but not in bST-P cows. Treatment with bST increased plasma concentrations of insulin, IGF-I, and growth hormone (GH). In conclusion, bST may have hyperstimulated plasma IGF-I and insulin to cause asynchrony between conceptus and uterus that was detrimental to pregnancy.