Maintenance Of Corpus Luteum Research Articles

Changes in serum pregnancy-associated glycoprotein, pregnancy-specific protein B, and progesterone concentrations before and after induction of pregnancy loss in lactating dairy cows

Lactating crossbred dairy cows were synchronized to receive a timed artificial insemination (TAI), and blood samples were collected from all cows from TAI until pregnancy diagnosis 39 d after TAI (period 1), and from pregnant cows from onset of treatment until the end of the experiment (period 2). Cows diagnosed pregnant 39 d after TAI were randomly assigned to 1 of 3 treatments to receive (1) an i.m. injection of saline (CON, n=10); (2) an i.m. injection of PGF2α (PGF, n=10); or (3) an intrauterine infusion of 120mL of hypertonic saline (INF, n=9). During period 1, serum pregnancy-associated glycoprotein (PAG) concentrations began to increase in pregnant cows by 25 d after TAI and differed from those in nonpregnant cows by 27 d after TAI, whereas serum pregnancy-specific protein B (PSPB) concentrations in pregnant cows differed from those in nonpregnant cows by 22 d after TAI. During period 2, time from treatment to cessation of the embryonic heartbeat was greater for PGF than for INF cows (36.0±5.7 vs. 0.2±0.1h, respectively), and time from treatment to conceptus disappearance was greater for INF than for PGF cows (7.1±3.3 vs. 1.9±0.3 d, respectively). Overall, progesterone concentration was greater for CON and INF than for PGF cows (8.7±2.8, 8.2±3.1, and 1.0±2.3ng/mL, respectively) due to luteal regression for PGF cows and corpus luteum maintenance for CON and INF cows. Serum PAG and PSPB concentrations differed among CON cows and PGF and INF cows beginning 1 and 2.5 d after treatment for PAG and PSPB, respectively. By 9.5 d after treatment, PAG and PSPB concentrations were similar to those of nonpregnant cows. We conclude that although timing of conceptus expulsion occurred 5.2 d later for INF than for PGF cows, serum PAG and PSPB concentrations decreased at a similar rate from the onset of treatment for both models of pregnancy loss evaluated.

Gene Expressions in the Persistent Corpus Luteum of Postpartum Dairy Cows: Distinct Profiles from the Corpora Lutea of the Estrous Cycle and Pregnancy

Persistence of the corpus luteum (CL) in cattle usually occurs during the puerperium and is associated with interference of prostaglandin (PG) F(2α) release from the uterus. The objective of the present study was to determine for the first time the gene expressions in the persistent CL compared with the CL of pregnancy and cyclic CL. Three types of CL biopsy samples were collected from 32 lactating Holstein cows: (1) CL persisting for 29 to 33 days after the first ovulation postpartum (persistent CL, n=9), (2) CL between days 29 and 33 of early pregnancy (CL of pregnancy, n=8) and (3) CL between days 10 and 13 of the estrous cycle (cyclic CL, n=27). mRNA expression of 2',5'-oligoadenylate synthetase-1 was upregulated only in the CL of pregnancy, confirming exposure to interferon-τ (IFNT) produced by trophoblasts in pregnant cows. mRNA expressions of immune tolerance-related factors (PGES and forkhead/winged helix transcription factor 3) were upregulated in the CL of pregnancy but not in the persistent CL, suggesting that IFNT controls upregulation of these genes. mRNA expression relating to some of the major systems such as lymphangiogenesis, inflammation and apoptosis were similarly upregulated in the persistent CL and the CL of pregnancy but not in the cyclic CL. The results suggest that the persistent CL may survive for a long period without changes in local immune tolerance but develops several major systems required for CL maintenance similar to the CL of pregnancy.

Heme Oxygenase‐1 Expression in the Ovary Dictates a Proper Oocyte Ovulation, Fertilization, and Corpora Lutea Maintenance

Animals deficient in Heme oxygenase-1 (HO-1, Hmox1(-/-) mice) have impaired pregnancies, characterized by intrauterine fetal death. HO-1 expression has been shown to be essential for pregnancy by dictating placentation and intrauterine fetal development. Its absence leads to intrauterine fetal growth restriction and fetal loss, which is independent of the immune system. Defect in previous steps, e.g., ovulation, may, however, also count for their poor reproductive outcome. Here, we investigated ovulation after hormonal hyperstimulation in Hmox1 wild-type and knockout animals. We observed that animals lacking HO-1 produced significantly less oocytes after hormonal stimulation than wild type animals and this was mirrored by the number of corpora lutea in the ovary. Furthermore, ovulated oocytes from Hmox1(-/-) animals were poorly fertilized compared with those from wild-type animals. In conclusion, we demonstrate here that HO-1 plays a pivotal role in the process of oocyte ovulation as well as fertilization, bringing to light a new and unsuspected role for HO-1.

Effects of Post Insemination Flunixin Meglumine Injection on Corpus Luteum Maintenance, Plasma Progesterone Concentrations and Pregnancy Rate in Heat Stressed Holstein Dairy Cows

Effects of Post Insemination Flunixin Meglumine Injection on Corpus Luteum Maintenance, Plasma Progesterone Concentrations and Pregnancy Rate in Heat Stressed Holstein Dairy Cows

Ovine corpus luteum proteins, with functions including oxidative stress and lipid metabolism, show complex alterations during implantation

Progesterone (P(4)) secreted by the corpus luteum (CL) is critical for in utero embryo survival and development, although CL proteins are key regulatory factors during the luteal phase. We, therefore, characterised protein expression patterns in ovine CL of pregnancy (days 12, 16 and 20) compared with those of controls, CL of oestrous cycle (days 12 and 16), using two-dimensional gel electrophoresis (2DE) gel-based proteomics. Proteins in 24 significantly altered spots were identified by tandem mass spectroscopy. At the time of embryo implantation (day 16), 77 spots were up-regulated and 101 spots were down-regulated in CL of pregnancy compared with regressed CL. Vimentin, lamin A/C (LMNA), [Mn] superoxide dismutase (SOD2), isocitrate dehydrogenase 1, annexin A1 and elongation factor Tu, mitochondrial (TUFM) altered during CL regression, whereas glutathione S-transferase A1, apolipoprotein A-1, myxovirus resistance protein 1, ornithine aminotransferase and enoyl-CoA hydratase, mitochondrial (ECHS1) tended to be altered during CL maintenance. biliverdin reductase B (BLVRB), FDXR, guanine nucleotide-binding protein G(I)/G(S)/G(T) subunit beta-2 (GNB2) and cytochrome b-c1 complex subunit 1, mitochondrial (UQCRC1) showed divergent expression during CL regression and maintenance. The expression of two representative proteins, SOD2 and BLVRB, by western blot increased in CL of non-pregnant ewes on day 16 compared with that on day 12. SOD2 and BLVRB were localised in the large and small luteal cells and endothelial cells of CL over peri-implantation periods. 2DE gel and mass spectrometry have been used, for the first time, to study ovine CL function. We have identified proteins involved in key pathways, including oxidative stress, steroidogenesis, signal transduction and apoptosis, which have not previously been associated with changes occurring in the CL during the peri-implantation period. These proteins are most likely involved with mechanisms allowing the CL to produce P(4) during early pregnancy.

Regulation of corpus luteum development and maintenance: specific roles of angiogenesis and action of prostaglandin F<SUB>2α</SUB>

Regulation of corpus luteum development and maintenance: specific roles of angiogenesis and action of prostaglandin F<SUB>2α</SUB>

The effects of luteinizing hormone ablation/replacement versus steroid ablation/replacement on gene expression in the primate corpus luteum

This study was designed to provide a genome-wide analysis of the effects of luteinizing hormone (LH) versus steroid ablation/replacement on gene expression in the developed corpus luteum (CL) in primates during the menstrual cycle. On Days 9–11 of the luteal phase, female rhesus monkeys were left untreated (control) or received a GnRH antagonist Antide (A), A + LH, A + LH + the 3β-hydroxysteroid dehydrogenase inhibitor Trilostane (TRL) or A + LH + TRL + a progestin R5020. On Day 12 of the luteal phase, CL were removed and samples of RNA from individual CL were hybridized to Affymetrix™ rhesus macaque total genome microarrays. The greatest number of altered transcripts was associated with the ablation/replacement of LH, while steroid ablation/progestin replacement affected fewer transcripts. Replacement of LH during Antide treatment restored the expression of most transcripts to control levels. Validation of a subset of transcripts revealed that the expression patterns were similar between microarray and real-time PCR. Analyses of protein levels were subsequently determined for two transcripts. This is the first genome-wide analysis of LH and steroid regulation of gene transcription in the developed primate CL. Further analysis of novel transcripts identified in this data set can clarify the relative role for LH and steroids in CL maintenance and luteolysis.

Prostaglandin Synthesis, Metabolism, and Signaling Potential in the Rhesus Macaque Corpus Luteum throughout the Luteal Phase of the Menstrual Cycle

Prostaglandins in the corpus luteum (CL) reportedly serve as luteotropic and luteolytic agents. Based mainly on studies conducted in domesticated animals and rodents, prostaglandin E2 (PGE2) is generally considered a luteotropic factor, whereas uterine-derived prostaglandin F2alpha (PGF2alpha) initiates luteolysis. However, the role of prostaglandins in regulating primate luteal structure-function is poorly understood. Therefore, a comprehensive analysis of individual mRNA or proteins that are involved in PGE2 and PGF2alpha biosynthesis, metabolism, and signaling was performed using CL obtained at distinct stages of the luteal life span during the menstrual cycle in rhesus monkeys. Peak levels of proteins involved in PGE2 synthesis (prostaglandin-endoperoxide synthase 2, microsomal PGE2 synthase-1) and signaling (PGE2 receptor 3) occurred during periods corresponding to development and maintenance of the primate CL. Immunohistochemistry studies indicated that large luteal cells express PGE2 synthesizing and signaling proteins. Expression of PGE2 synthesizing and signaling proteins significantly decreased preceding the period of functional regression of the CL, which also coincided with increasing levels of PGF2alpha receptor protein expression within the large luteal cells. Moreover, significant levels of mRNA expression for several aldoketo reductase family members that synthesize PGF2alpha from other prostaglandins were observed throughout the rhesus macaque luteal phase, thus supporting the possibility of intraluteal PGF2alpha production. Collectively, our results indicate that there may be intraluteal synthesis and signaling of PGE2 during development and maintenance of the primate CL, followed by a shift to intraluteal PGF2alpha synthesis and signaling as the CL nears the time of luteolysis.

Regulation of Luteal Function and Corpus Luteum Regression in Cows: Hormonal Control, Immune Mechanisms and Intercellular Communication

The main function of the corpus luteum (CL) is production of progesterone (P4). Adequate luteal function to secrete P4 is crucial for determining the physiological duration of the oestrous cycle and for achieving a successful pregnancy. The bovine CL grows very fast and regresses within a few days at luteolysis. Mechanisms controlling development and secretory function of the bovine CL may involve many factors that are produced both within and outside the CL. Some of these regulators seem to be prostaglandins (PGs), oxytocin, growth and adrenergic factors. Moreover, there is evidence that P4 acts within the CL as an autocrine or paracrine regulator. Each of these factors may act on the CL independently or may modify the actions of others. Although uterine PGF(2 alpha) is known to be a principal luteolytic factor, its direct action on the CL is mediated by local factors: cytokines, endothelin-1, nitric oxide. The changes in ovarian blood flow have also been suggested to have some role in regulation of CL development, maintenance and regression.

Potential roles of transcription factor Elf‐1 during follicular development, corpus luteum formation, maintenance and degeneration in rat ovary

Potential roles of transcription factor Elf‐1 during follicular development, corpus luteum formation, maintenance and degeneration in rat ovary

Comparative profiles of different lipoprotein cholesterol parameters and Growth Hormone during hot humid and winter season in Murrah Buffaloes

Now, it is well known that in bovines HDL-C act as substrate for ovarian steroidogenesis. The restriction of entry of other lipoprotein parameters is due to ovarian blood barrier, which restricts the entry of other lipoproteins, which are bigger in size. In vitro studies have indicated their role in mediating proliferation of cells. Besides gonadotropin, Growth Hormone (GH) is also gaining importance in the field of reproduction. GH receptors have been localized on the ovaries and follicle of bovines. Further it has been suggested that it can be the direct role of the hormone or it can be mediated through IGF-I. It has been assigned various roles in mediating follicle development, ovulation and corpus luteum maintenance. The river buffaloes are capable of breeding throughout the year, but during certain period of time were found to be more favourable than the others. It has been found that, winter season and hot humid season exhibit two extreme conditions of temperature variation; Hot humid season being unfavourable than the winter season because of high humidity and reasonably high temperature. It has been observed that during June to August months, conception rate and exhibition of estrus behaviour is low. This study was undertaken to analyze different lipoprotein cholesterol parameters namely Total cholesterol (TC), High-density lipoprotein cholesterol (HDL-C), Triglycerides (TG) and Low density lipoprotein cholesterol (LDL-C) in the plasma of cyclic Murrah buffaloes throughout the estrous cycle. The mean plasma concentration (μg/ml) of different lipoproteins during hot humid season were TC 592±40, HDL-C 229±42, TG 345±95, LDL-C 285±94.Where as in winter season their concentrations were 1381.0±31.0, 1793.0±110.0, 511.0±21.0, 608.0±94.0 respectively.The mean±SEM circulatory level of GH was low during HH season than during winter (6±2 ng/ml vs. 17±2 ng/ml). During estrous cycle only one peak of GH was exhibited during hot humid season where as three peaks were exhibited during winter season. It can be concluded that winter season is favourable for maintaining physiological levels of hormones and metabolic parameters, which in turn may increase the reproductive efficiency of bovines. During winter season average temperature was 15±5 °C. During hot humid season average temperature was 34±3 °C. THI was more than 75%.

THE EFFECTS OF LUTEINIZING HORMONE ABLATION/REPLACEMENT VERSUS STEROID ABLATION/REPLACEMENT ON GENE EXPRESSION IN THE PRIMATE CORPUS LUTEUM

This study was designed to provide a genome-wide analysis of the effects of luteinizing hormone (LH) versus steroid ablation/replacement on gene expression in the developed corpus luteum (CL) in primates during the menstrual cycle. On Days 9–11 of the luteal phase, female rhesus monkeys were left untreated (control) or received a GnRH antagonist Antide (A), A + LH, A + LH + the 3β-hydroxysteroid dehydrogenase inhibitor Trilostane (TRL) or A + LH + TRL + a progestin R5020. On Day 12 of the luteal phase, CL were removed and samples of RNA from individual CL were hybridized to Affymetrix™ rhesus macaque total genome microarrays. The greatest number of altered transcripts was associated with the ablation/replacement of LH, while steroid ablation/progestin replacement affected fewer transcripts. Replacement of LH during Antide treatment restored the expression of most transcripts to control levels. Validation of a subset of transcripts revealed that the expression patterns were similar between microarray and real-time PCR. Analyses of protein levels were subsequently determined for two transcripts. This is the first genome-wide analysis of LH and steroid regulation of gene transcription in the developed primate CL. Further analysis of novel transcripts identified in this data set can clarify the relative role for LH and steroids in CL maintenance and luteolysis.

Expression of mRNA for Cell Adhesion Molecules in the Bovine Corpus Luteum During the Estrous Cycle and PGF2.ALPHA.-Induced Luteolysis

Cell-to-cell interaction via cell contact-dependent pathway is essentially important for maintenance and regulation of corpus luteum (CL) integrity and its physiological actions. The objective of the present study was to evaluate the mRNA expression of the cell adhesion molecules (CAMs) that are constituent factors of gap junctions [connexin (Cx) 43] and adherence junctions (VE-, E-, N-cadherin) in two types of endothelial cells from the mid CL and in CL tissue during the estrous cycle and PGF(2alpha)-induced luteolysis in the cow. Specific mRNA expression for Cx43 and N-cadherin was detected in cytokeratin-positive (CK+) and cytokeratin-negative (CK-) luteal endothelial cells (EC) and fully luteinized granulosa cells (LGC). E-cadherin mRNA was expressed in CK+EC and LGC, but not in CK-EC. VE-cadherin mRNA was expressed in both CK+ and CK-EC. During the estrous cycle, Cx43 mRNA expression was significantly lower in the regressing CL. VE-cadherin expression also tended to increase in the mid CL and increased significantly in the regressing CL. E-cadherin mRNA expression was higher in the early and late CL than in the mid- and regressing CL. N-cadherin mRNA expression gradually increased from the early to late CL followed by a decrease in the regressing CL. During PGF(2alpha)-induced luteolysis, Cx43 mRNA expression appeared to increase, and VE-cadherin and E-cadherin mRNA significantly increased at 24 h. N-cadherin mRNA expression decreased 2 and 4 h after PGF(2alpha) administration. Collectively, expression of the mRNAs for CAMs was different in the two types of luteal endothelial cells and fully luteinized granulosa cells and changed independently in the CL during the estrous cycle and PGF(2alpha)-induced luteolysis in the cow. The results suggest that CAMs play physiological roles in cell-to-cell communication to regulate both gap and adherence junctions during CL development and regression in the cow.

Effects of Zeranol ® upon luteal maintenance and fetal development in peripubertal gilts

Eighty gilts were utilized to determine whether zeranol implants could maintain hCG-induced corpora lutea (CL) in peripubertal gilts and to examine the effects of a Zeranol ® implant on fetal development. Crossbred gilts (171 ± 0.3 days of age, 109.1 + 1.4 kg) were blocked by weight and ancestry to control ( n = 40) or treatment ( n = 40) groups. To induce ovulation and CL maintenance, treated gilts received 500 IU of hCG i.m. and a Zeranol ® ear implant (Ralgro ®, 36 mg; day 0). All gilts were checked once daily for estrus with a mature boar from days 3–58 of the experiment. On day 42, treated gilts received two 10 mg injections of Lutalyse (PGF 2α) spaced 6 h apart. Treated gilts not displaying estrus within 7 days of PGF 2α received two additional 10 mg of PGF 2α spaced 6 h apart on day 49. On days 44–58, gilts detected in estrus were inseminated twice, 24 h apart with pooled semen via AI. Blood samples were obtained on days 0, 7, 18 and 42 and analyzed for serum progesterone (P 4). Bred gilts were slaughtered on days 58–62 of gestation. Ovulation, as determined by serum concentrations of P 4 on day 7 of the experiment, was induced by hCG in 79.5% of treated gilts. Zeranol ® implants, however, failed to increase ( P > 0.05) the proportion of gilts available for breeding (treated, 21/39; control, 18/40). Of gilts inseminated on days 44–58, 16/21 treated gilts and 16/18 control gilts were pregnant at slaughter on days 58–62 of gestation. Number of fetuses (7.5 versus 12), fetal weight (83 versus 121 g), fetal length (117 versus 132 mm) and fetal survival (45% versus 78%) were reduced ( P < 0.001) by Zeranol ® implants. These data indicate that treatment of peripubertal gilts with a 36 mg Zeranol ® implant did not increase the proportion of gilts available for breeding while causing deleterious effects upon the fetuses.

Immunohistochemical localization of VEGF and its receptors in the corpus luteum of the bitch during diestrus and anestrus

The corpus luteum (CL) is a temporary endocrine gland, whose life span depends on the interaction of luteotrophic and luteolytic factors. Since development and maintenance of CL is based on angiogenesis, angiogenic growth factors may play a role in CL-function of the bitch, as described for other species. The aim of this study was to detect the presence of the vascular endothelial growth factor (VEGF) system in the bitch CL throughout diestrus and early anestrus. For that purpose, blood samples from 24 bitches were collected and analyzed for progesterone to determine ovulation time and the animals were subjected to ovariosalpingohysterectomy 10, 20, 30, 40, 50, 60 or 70 days after ovulation. The corpora lutea were fixed in formalin and embedded in Paraplast ® resin. Five micrometers sections were submitted to standard immunohistochemistry protocol using three primary antibodies (SC-315, SC-316 and VG76e) for detection of kinase domain region (KDR), fms-like tyrosine kinase 1 (Flt-1) and VEGF, respectively. The VEGF system expression could be detected in all diestrus stages in endothelial as well as luteal cells (responsible for blood vessel formation and progesterone production, respectively), indicating time dependent changes: immunostaining tended to increase from Day 10 to 50 and to decrease until Day 70 post-ovulation. In the CL of the bitch, structure related cells, like pericytes and stroma cells, expressed it in determined time points of diestrus with little intensity variation. We concluded that VEGF might have a modulatory effect in the CL of the dog acting as paracrine and autocrine factor through its receptors, Flt-1 and KDR.

161 EFFECT OF MELOXICAM TREATMENT ON PREGNANCY RATES IN HOLSTEIN HEIFERS

We previously reported that administration of flunixin meglumine two times at a critical stage approaching pregnancy recognition associated with corpus luteum maintenance increased early embryo survival and pregnancy rate via an additive antiluteolytic effect with the conceptus (Guzeloglu et al. 2006 Reprod. Fertil. Dev. 18, 183). In this study, the objective was to determine if a single administration of meloxicam, a non-steroid anti-inflammatory drug (NSAID) with a longer half-life, could be used instead of flunixin meglumine to avoid repeated injections in heifers at a critical stage following insemination to increase pregnancy rate due to its inhibitory effect on PGF2� synthesis. Eighty-five 15-18-month-old Holstein heifers were synchronized; following insemination (Day 0), the heifers were randomly assigned to receive a subcutaneous meloxicam injection (0.5 mg kg-1; n = 37) in the afternoon of Day 15 or left untreated as controls (n = 48). Pregnancy rates were defined as the percentage of heifers diagnosed pregnant by ultrasound between Days 31 and 38 after AI. The effect of treatment on pregnancy rates was analyzed by chi-square test. Meloxicam treatment on Day 15 after insemination dramatically decreased the pregnancy rates in the heifers (25 of 48 (52%) in the control group vs. 9 of 37 (24.3%) in the meloxicam-treated group; P &amp;lt; 0.01). This result indicates that administration of meloxicam around a time associated with pregnancy recognition and corpus luteum maintenance was harmful to the pregnancy even though the drug is considered to be safe during pregnancy in cattle. It is concluded that direct or indirect effects of meloxicam on the uterine environment and/or embryo are not favorable at least during early pregnancy in cattle. How meloxicam exerted its detrimental effect on pregnancy warrants further investigation.

150 EFFECT OF TIMELY FLUNIXIN MEGLUMINE TREATMENT ON PREGNANCY RATES IN HOLSTEIN HEIFERS

The objective was to determine if administration of flunixin meglumine (FM) to heifers following insemination would increase pregnancy rate due to its inhibitory effect on prostaglandin F2� (PGF2�) synthesis. Fifty-two 15-month-old Holstein heifers were synchronized with single or double injections of PGF2� followed by an injection of gonadotropin-releasing hormone (GnRH) 48 h later and a timed artificial insemination at 12-14 h after injection of GnRH (Day 0). Heifers randomly assigned to the treatment group (FMG) were injected twice with FM (1.1 mg/kg BW; i.m.), given 12 h apart on the evening of Day 15 and the morning of Day 16. The control group (CG) was not treated. Pregnancy rates were defined as the percentage of heifers diagnosed pregnant by ultrasound at Days 29 and 65 after AI. Effects of treatment on pregnancy rates and pregnancy losses were analyzed by chi-square test and logistic regression analysis. Pregnancy rates in the heifers treated with FM were higher at Day 29 (76.9%; 20/26 [FMG] vs. 50%; 13/26 [CG]; P &lt; 0.04) and tended to be higher at Day 65 (69.2%; 18/26 [FMG] vs. 46.2%; 12/26 [CG]; P &lt; 0.09). Administration of FM two times at a critical stage leading up to pregnancy recognition, associated with corpus luteum maintenance, increased both early embryo survival and pregnancy rate via an additive antiluteolytic effect due to a delay in the luteolytic secretion of PGF2�; this provided conceptuses extra time to develop the capability to inhibit the luteolytic process.

The effect of embryonic death rates in cattle on the efficacy of estrus synchronization programs

Reproductive failure in inseminated cattle results from poor fertilization and embryo survival. Recent studies utilizing dairy and beef cattle indicate that fertilization rates are higher for nulliparous dairy and beef heifers and nonlactating beef cows than lactating beef and dairy cows and nonlactating dairy cows. Several factors affect fertilization rates, but the greatest impact was observed for high producing cows under heat stress, when fertilization was only 55%. Once fertilization has occurred, the fate of a successful pregnancy is then determined by the survival of the embryo and fetus. Losses of pregnancy are characterized by early embryonic death, which occurs prior to the period of corpus luteum (CL) maintenance in the cow at days 15–17 of the cycle, and late embryonic death, which occurs from CL maintenance to the end of the differentiation stage, at approximately 42 days of gestation. After 50 days of gestation, pregnancy losses are less frequent and characterize fetal death. Most pregnancy losses occur prior to the period of maintenance of the CL, but in high producing lactating dairy cattle, substantial losses continue to occur up to 42–56 days after insemination. Several factors affect pregnancy losses in cattle, such as compromised oocytes, which result in poorly developed embryos incapable of cross-talking with the endometrial epithelial cells, to inadequate uterine environment and infectious agents resulting in death of the embryo from undernourishment. Recently, studies have indicated that anovulation/anestrous, the metabolic status of the animal, some dietary ingredients, as well as occurrence of diseases, predispose the cow to experience embryonic and fetal death. Although some insemination protocols might impact embryo survival, when timed AI has been implemented properly, it has not influenced embryonic or fetal death in cattle. Improvements in reproductive programs in the future will have to focus on enhancing fertilization rates and minimizing embryonic losses to optimize conception rates in dairy and beef cattle.

Inhibition of nitric oxide synthesis potentiates apoptosis in the rabbit corpus luteum

To determine if nitric oxide (NO) plays a role in corpus luteum (CL) physiology by affecting progesterone secretion or luteal apoptosis, an in-vitro pseudopregnant rabbit ovarian perfusion system was used to measure the effects of an inhibitor of NO synthesis, N G-nitro- l-arginine methyl ester ( l-NAME), on progesterone secretion and corpus luteal apoptosis as measured by internucleosomal DNA breakdown. Pseudopregnant rabbit ovaries perfused in vitro with l-NAME did not demonstrate any significant differences compared with control ovaries in progesterone secretion. However, apoptosis, as measured by internucleosomal breakdown, was significantly increased in l-NAME-perfused CL compared with controls. While NO does not appear to directly affect progesterone secretion, there does appear to be a role for NO in CL maintenance, or a role for inhibition of NO production in CL regression.

Effect of human chorionic gonadotropin on luteal luteinizing hormone concentrations in natural cycles

Effect of human chorionic gonadotropin on luteal luteinizing hormone concentrations in natural cycles