Local regulation of corpus luteum development and regression in the cow: Impact of angiogenic and vasoactive factors

CRISPR/Cas genome editing revealed non-angiogenic role of VEGFA gene in porcine luteal cells: a preliminary report

BACKGROUND

The angiogenic cytokine vascular endothelial growth factor A (VEGFA) also exerts non-angiogenic effects on endocrine functionality of porcine luteal cells critical for progesterone (P4) production.

METHOD AND RESULTS

The expression dynamics of VEGFA-FLT/KDR system were investigated using RT-qPCR during luteal stages and VEGFA gene knock out (KO) porcine luteal cells were generated using CRISPR/Cas9 technology. The downstream effects of VEGFA ablation were studied using RT-qPCR, Annexin V, MTT, ELISA for P4 estimation and scratch wound assay. Bioinformatics analysis of RNA-Seq data of porcine mid-luteal stage was conducted for exploring protein-protein interaction network, KEGG pathways, transcription factors and kinase mapping for VEGFA-FLT/KDR interactomes. The VEGFA-FLT/KDR system expressed throughout the luteal stages with highest expression during mid- luteal stage. Cellular morphology, structure and oil-red-o staining for lipid droplets did not differ significantly between VEGFA KO and wild type cells, however, VEGFA KO significantly decreased (p < 0.05) viability and proliferation efficiency of edited cells on subsequent passages. Expression of apoptotic gene, CASP3 and hypoxia related gene, HIF1A were significantly (p < 0.05) upregulated in KO cells. The relative mRNA expression of VEGFA and steroidogenic genes STAR, CYP11A1 and HSD3B1 decreased significantly (p < 0.05) upon KO, which was further validated by the significant (p < 0.05) decrease in P4 output from KO cells. Bioinformatics analysis mapped VEGFA-FLT/KDR system to signalling pathways associated with steroidogenic cell functionality and survival, which complemented the findings of the study.

CONCLUSION

The ablation of VEGFA gene resulted in decreased steroidogenic capability of luteal cells, which suggests that VEGFA exerts additional non-angiogenic regulatory effects in luteal cell functionality.

Immunoexpression of vascular endothelial growth factor and vWF-regulating angiogenesis in cyclic corpus luteum of Indian buffalo

The present study was conducted to localize the immunoexpression of VEGF-A (Vascular Endothelial Growth Factor) and von Willebrand factor (vWF) in corpora lutea of healthy buffaloes (24) collected from local slaughterhouses. CL collected were categorized into early (stage I, 1-5 days, n = 6), mid (stage II, 6-11 days, n = 6), late luteal phase (stage III, 12 to 16 days, n = 6) and regressing phase (stage IV, 17 to 20 days, n = 6). The percent positive immunostaining for VEGF-A was significantly (p < 0.05) higher in mid-luteal phase than the other three stages of CL. However, it was higher in early luteal phase as well indicated intense angiogenesis in both early and mid-luteal phases. The number of capillary endothelium expressing vWF was significantly (p < 0.05) highest in mid-luteal phase among all the phases. However, in late luteal phase, the percent area positive for VEGF-A immunostaining was reduced but it was significantly (p < 0.05) higher than corpus albicans phase. Thus, in regressing phase or corpus albicans, it was lowest and reduced considerably. However, in late luteal phase, the number of capillaries with vWF immunoexpression reduced significantly (p < 0.05) but it was lowest in corpus albicans phase. Therefore, the immunotaining pattern for VEGF-A and vWF concluded that there was a spositive linear correlation between the two, that is, as the VEGF-A expression was increased, the number of vWF positive capillaries also increased and vice versa. The VEGF-A expressed by the luteal parenchyma in different stages of development and regression of corpus luteum was thus observed to be involved in promoting the angiogenesis and luteal cell proliferation as supported by vWF expressed by endothelium of proliferating capillaries in buffalo corpus luteum throughout the estrous cycle.

Local Expression Dynamics of Various Adipokines during Induced Luteal Regression (Luteolysis) in the Bovine Corpus Luteum

The study aimed to evaluate the mRNA expression levels of various local novel adipokines, including vaspin, adiponectin, visfatin, and resistin, along with their associated receptors, heat shock 70 protein 5, adiponectin receptor 1, and adiponectin receptor 2, in the corpus luteum (CL) during luteal regression, also known as luteolysis, in dairy cows. We selected Fleckvieh cows in the mid-luteal phase (days 8-12, control group) and administered cloprostenol (PGF analog) to experimentally induce luteolysis. We collected CL samples at different time points following PGF application: before treatment (days 8-12, control group) and at 0.5, 2, 4, 12, 24, 48, and 64 h post-treatment (n = 5) per group. The mRNA expression was measured via real-time reverse transcription polymerase chain reaction (RT-qPCR). Vaspin was characterized by high mRNA levels at the beginning of the regression stage, followed by a significant decrease 48 h and 64 h after PGF treatment. Adiponectin mRNA levels were elevated 48 h after PGF. Resistin showed upregulation 4 h post PGF application. In summary, the alterations observed in the adipokine family within experimentally induced regressing CL tissue potentially play an integral role in the local regulatory processes governing the sequence of events culminating in functional luteolysis and subsequent structural changes in the bovine ovary.

Review: Luteal prostaglandins: mechanisms regulating luteal survival and demise in ruminants

The corpus luteum (CL) is critical for establishment and maintenance of pregnancy in all mammals. However, the fate of the CL in ruminants is dependent on the presence of a functional uterus or signals from a developing embryo to modify uterine function to ensure its own survival. The key molecule secreted by the uterus that must be modified is prostaglandin F2alpha (PGF2A). At the same time, there is evidence that mechanisms within the CL may influence the ability of PGF2A to cause luteolysis. This review focuses on prostaglandins and steroidogenic capacity as endogenous modulators of the sensitivity of the CL to exogenous PGF2A. Early luteal development and early pregnancy are two different luteal stages in which sensitivity of the CL to PGF2A renders it incapable, or less capable, respectively, of undergoing luteolysis in response to PGF2A compared to a midcycle CL. An analysis of molecular changes that occur during these two stages provides some novel insight into molecules and pathways worth exploring to explain the regulation of luteolytic capacity in corpora lutea of ruminants.

Effects of two protocols of ovulation synchronization on corpus luteum size and blood flow, progesterone concentration, and pregnancy rate in beef heifers

The objective of this study was to evaluate the effect of 7-day estradiol-progesterone-based [Treat_(C)] and 5-day Co-Synch plus progesterone [Treat_(Co-Sy)] protocols on ovulation time, pre-ovulatory follicle diameter, corpus luteum (CL) size and blood flow, progesterone (P4) concentration and pregnancy rate (PR) in beef heifers. In Experiment 1, a crossover design was applied (n = 9). For Treat_(C), a progesterone intravaginal (PI) device was inserted, plus 2 mg of estradiol benzoate (day 0). On day 7, 500 µg of cloprostenol plus 0.5 mg of estradiol cypionate were administered, and PI was removed. For Treat_(Co-Sy), on day 0, a PI was inserted plus 100 µg gonadotropin-releasing hormone (GnRH). On day 5, PI was removed, plus 500 µg of cloprostenol and 100 µg of GnRH were administered at 69-70 h later. From day one to ovulation day, dominant follicle was evaluated by ultrasonography. On days 4 and 8 post-ovulation, CL was evaluated by color Doppler, and P4 concentration was determined by chemiluminescence. In Experiment 2, a split-plot experimental design was used. Protocols followed were the same as in Experiment 1 [Treat_(C); n = 310 and Treat_(Co-Sy); n = 314]. Heifers were fixed-time artificially inseminated. Pregnancy was determined on day 41. In Experiment 1, the interval between PI removal and ovulation time was different between protocols (P < 0.01). In addition, P4 concentration was related to the CL size (P < 0.001), CL blood flow (P < 0.01) and protocols (P < 0.03). In Experiment 2, PR did not differ between protocols.

Effect of increased serum progesterone on luteal morphology and function, pregnancy, and gestational loss in Nelore cows

The aim of the present study was to determine the impact of different strategies for increasing the level of serum progesterone (P4) on luteal morphology and function in bovine females. The effects of increasing P4 on pregnancy rate and gestational loss (GL) in Nelore cows subjected to timed artificial insemination (TAI) were also evaluated. A total of 939 cows were divided into three groups: P4LA (n = 305), 150 mg of long-acting injectable P4 7 days after TAI; GnRH (n = 306), 10 μg of buserelin acetate 7 days after TAI; and control (n = 328), no hormone treatment after TAI. Doppler ultrasound assessments and P4 measurements were performed on days 7 and 16 after TAI. The pregnancy rate and GL as a function of treatment were compared using the SAS GLIMMIX procedure. Corpus luteum (CL) vascular perfusion, volume, and plasma P4 concentration were analysed using the SAS PROC MIXED procedure. No significant difference was found among the treatments in terms of volume, number of pixels, and CL intensity or in the serum P4 concentration at 7 days after ovulation. The CL blood flow at 16 days after ovulation was lower in the P4LA and GnRH groups than that in the control group (p < .01). Serum concentrations of P4 at 16 days after ovulation were higher in the P4LA and GnRH groups than those in the control group (p = .04). A difference in the pregnancy rate (p = .003) and a trend in GL (p = .07) as a function of treatment were found. Overall, long-acting injectable P4 supplementation on day 7 after TAI or GnRH administration affected CL vascularization and increased the serum concentrations of P4 16 days after ovulation, promoting better pregnancy rates than the control.

Pregnancy maintenance following sequential induced prostaglandin pulses in beef cows

The relationship between the maternal endocrine environment and late embryonic mortality (> 28 d of gestation) in cattle is poorly defined. A definitive rise and alterations in secretion patterns of prostaglandin F_2α (PGF_2α) concentration without luteal regression is a trademark of this period. The objective was to evaluate whether consecutively induced PGF_2α pulses would alter steroid hormone production and luteal blood perfusion potentially influencing pregnancy success. Pregnant beef cows (n = 12) were selected to receive either an oxytocin injection (OT, n = 8) or saline injection (CON, n = 4) on d 30 and 31 of gestation to stimulate sequential prostaglandin releases 24 h apart. Blood samples were collected every 30 min for 1 h before and continuing for 4 h post oxytocin administration. Luteal blood perfusion was measured via Doppler ultrasound at the beginning and end of the OT challenge. Concentrations of prostaglandin F_2α metabolite (PGFM) were quantified to show effectiveness of the treatment while concentrations of progesterone, estradiol and pregnancy-associated glycoproteins (PAG) were measured to examine the effect of PGF_2α release. Control animals exhibited no changes in any quantified hormone and an expected numerical increase in circulating PAG concentrations. Peak concentrations of PGFM in OT cows were observed 2 h post OT administration and concentrations returned to basal levels by the end of the sampling period. Peak concentrations of PGFM were decreased on d 31 compared to d 30. Following OT administration, progesterone and estradiol concentrations did not change in response to PGF_2α release but were decreased on d 31 compared to d 30. There were no changes in luteal blood perfusion in response to PGF release on d 30 or d 31. Repeated PGF_2α release may alter steroid hormone production; however, it does not negatively affect pregnancy status during the transition between early and late embryonic development.

The effect of a double dose of cloprostenol sodium on luteal blood flow and pregnancy rates per artificial insemination in lactating dairy cows

Inadequate luteolysis in fertility programs is a problem for lactating dairy cows treated with a single dose of PGF_2α. The proportion of cows with complete luteolysis can be increased by administering 2 doses of PGF_2α 24 h apart. This study hypothesized that a double dose of cloprostenol sodium (1.0 mg) could take the place of 2 doses 24 h apart due to its enhanced half-life. Cows were allocated to receive 1 of 3 treatments: negative controls: 0.5 mg of cloprostenol sodium (single; n = 337); positive controls: two 0.5-mg doses of cloprostenol sodium 24 h apart (two/24; n = 313); and treated: 1.0 mg of cloprostenol sodium (double; n = 298) at the final PGF_2α of Double-Ovsynch. Cows received artificial insemination (AI) 16 h after final GnRH of Double-Ovsynch. Pregnancy diagnosis was determined at 24, 34, 62, and 184 d post-AI. Pregnancy loss was categorized in the following periods: between 24 to 34, 34 to 62, and 62 to 184 d post-AI. Ultrasonography (B-mode and color Doppler) was used to assess luteal function pre- and posttreatment with various doses of cloprostenol sodium. Luteal volume and luteal blood flow (LBF) from d 7 and 14 corpora lutea were determined before treatment (d -1), and 2 and 4 d after treatment. No evidence was observed of an effect of treatment on pregnancy rates per AI at 24, 34, or 62 d post-AI. No effect was observed of treatment on pregnancy losses occurring between d 24 and 34, 34, and 62, and between 62 and 184 d post-AI. However, third-plus parity cows treated with the single treatment had greater pregnancy loss compared with two/24 and double between d 24 and 34 post-AI. Third-plus parity cows that received the double treatment had lower LBF 2 and 4 d after treatment compared with cows treated with single. Amount of LBF present 4 d after treatment was not a predictor of pregnancy or pregnancy loss. A double dose (1.0 mg) of cloprostenol sodium may be a feasible alternative for fertility programs based on nondifferent outcomes to the two/24 treatment, lower pregnancy losses, and reduced LBF disappearance following treatment in third-plus parity cows in comparison with the single treatment.

Effect of cloprostenol sodium dose on luteal blood flow and volume measurements in Holstein heifers with both day-4 and day-10 corpora lutea

Establishment of a vascular system within the corpus luteum (CL) is critical for progesterone (P₄) secretion. Measurement of luteal blood flow (LBF) may be a feasible way to determine luteolysis induced with cloprostenol sodium (CLO). Our overall objective was to establish timelines to assess luteolysis via Doppler ultrasonography. Estrous cycles were synchronized in 11- to 12-mo-old Holstein heifers (n = 37). Heifers were injected CLO at a random stage of the estrous cycle 12 d from treatment. Gonadotropin-releasing hormone (GnRH) was administered 2 (d -10) and 8 d (d -4) after the initial CLO. This satisfied the study objective of inducing simultaneous presence of CL at d 4 of development (D4 CL) and CL at d 10 of development (D10 CL) on the day of treatment with different CLO doses (hereafter referred to as d 0). Heifers were randomly assigned to 1 of 5 treatments on d 0: negative control (NC) consisting of no treatment with CLO (n = 8); a quarter dose of CLO (0.125 mg; n = 8); half dose of CLO (0.25 mg; n = 8); full dose of CLO (0.5 mg; n = 8); or positive control (PC) consisting of 4 doses of 0.5 mg of CLO at 24-h intervals starting at d 0 (n = 5). Data collection was performed at d 0 (before and 1 h after treatment) and 2, 4, 6, and 8 d following treatment, to determine luteal volume (LV), LBF, and circulating concentrations of P₄. Both NC and PC were efficient in mimicking physiological scenarios that occur during normal luteal development and luteolysis. Heifers that received PC had complete LBF disappearance of both D4 and D10 CL between d 2 and 4 after the first of 4 CLO treatments given 24 h apart (average 4.0 ± 0.0 and 3.2 ± 0.7 d, respectively). Complete LBF disappearance was used as a luteolysis marker. Treatment with different doses of CLO did not impair luteal development of the D4 CL. However, concurrent complete LBF disappearance for D10 CL in heifers treated with half (5/8 heifers) and full doses of CLO (8/8 heifers) resulted in less LBF in the half dose, and less LV and LBF in the full-dose treatment, in D4 CL at d 8 post-treatment, compared with NC. Treatment with various doses of CLO induced an acute increase in LBF 1 h after treatment, regardless of dose in D10 but not in D4 CL. We found a lack of dose response in LV reduction of D4 and D10 CL. Interestingly, LV of the D10 CL decreased in untreated NC between d 0 and 8 after treatment (d 10-18 of luteal development). Assessment with color Doppler ultrasound was sensitive enough to identify dose-response patterns in Holstein heifers (absence, partial, or complete luteolysis) following various doses of CLO. Variability in time to complete LBF disappearance of mature D10 CL following a full dose of CLO limits the use of Doppler ultrasonography to detect luteolysis at a single time point following treatment.

Partial luteolysis during early diestrus in cattle downregulates VEGFA expression and reduces large luteal cell and corpus luteum sizes and plasma progesterone concentration

Our objectives were to investigate potential changes in the size of steroidogenic large luteal cells (LLC) during partial luteolysis induced by a sub-dose of cloprostenol in early diestrus and to determine transcriptional variations in genes involved in corpus luteum (CL) functions. Cows were subjected to an Ovsynch protocol, with the time of the second GnRH treatment defined as Day 0 (D0). On D6, cows were randomly allocated into three treatments: Control (2 mL saline, im; n = 10), 2XPGF (two doses of 500 μg of cloprostenol, im, 2 h apart; n = 8) or 1/6PGF (single dose of 83.3 μg of cloprostenol, im; n = 10). Before treatments and every 8 h during the 48-h experimental period, blood samples were collected and CL volumes measured. Furthermore, two CL biopsies were obtained at 24 and 40 h post-treatment. The 1/6PGF treatment caused partial luteolysis, characterized by sudden decreases in plasma progesterone (P₄) concentrations, luteal volume and LLC size, followed by increases (to pretreatment values) in P₄ and luteal volume at 24 and 40 h post-treatment, respectively. However, at the end of the study, P4, luteal volume and LLC size were all significantly smaller than in Control cows. Temporally associated with these phenotypes, there was a lower mRNA abundance of VEGFA at 24 and 40 h, and ABCA1 at 24 h (P < 0.05). In conclusion, a sudden reduction in CL size during partial luteolysis induced by a sub-dose of PGF_2α analog on day 6 of the estrous cycle was attributed to a reduction in LLC size, although these changes did not account for the entire phenomenon. In addition to its involvement in reducing CL size, decreased VEGFA mRNA abundance impaired CL development, resulting in a smaller luteal gland and lower plasma P₄ concentrations compared to Control cows.

Early pregnancy-induced transcripts in peripheral blood immune cells in Bos indicus heifers

Immune cells play a central role in early pregnancy establishment in cattle. We aimed to: (1) discover novel early-pregnancy-induced genes in peripheral blood mononuclear cells (PBMC); and (2) characterize the temporal pattern of early-pregnancy-induced transcription of select genes in PBMC and peripheral blood polymorphonuclear cells (PMN). Beef heifers were artificially inseminated on D0 and pregnancies were diagnosed on D28. On D10, 14, 16, 18, and 20, blood was collected for isolation of PBMC and PMN from heifers that were retrospectively classified as pregnant (P) or non-pregnant (NP). PBMC samples from D18 were submitted to RNAseq and 220 genes were differentially expressed between pregnant (P) and non-pregnant (NP) heifers. The temporal abundance of 20 transcripts was compared between P and NP, both in PBMC and PMN. In PBMC, pregnancy stimulated transcription of IFI6, RSAD2, IFI44, IFITM2, CLEC3B, OAS2, TNFSF13B, DMKN and LGALS3BP as early as D18. Expression of IFI44, RSAD2, OAS2, LGALS3BP, IFI6 and C1R in PMN was stimulated in the P group from D18. The novel early-pregnancy induced genes discovered in beef heifers will allow both the understanding of the role of immune cells during the pre-attachment period and the development of technologies to detect early pregnancies in beef cattle.

Intraovarian influence of bovine corpus luteum on oocyte morphometry and developmental competence, embryo production and cryotolerance

Three experiments were conducted to determine influence of the bovine corpus luteum (CL) on morphometric and functional characteristics of oocytes, and subsequent embryonic development. Cumulus-oocyte complexes were aspirated from two types of cows: 1) with a CL in one ovary (CL+) and without a CL in the contralateral ovary (CL-), 2) and from cows without CL in either ovary (C). Intracellular activity of the enzyme glucose-6-phosphate dehydrogenase (G6PDH), oocyte diameter and thickness of the zona pellucida were determined (Experiment 1). Then, the rate of in vitro oocyte maturation for each ovarian category was evaluated and oocyte diameter and zona pellucida thickness were measured after maturation (Experiment 2). In Experiment 3, in vitro embryo production and cryotolerance were assessed. The oocyte diameter was greater (P < 0.01) and the zona pellucida was thinner in CL+ than in CL- (P > 0.05) or C (P = 0.0131) ovaries. Activity of G6PDH was lower in oocytes from CL+ than CL- (P < 0.01) and C (P = 0.0148) ovaries. Rate of oocyte maturation, oocyte diameter and thickness of the zona pellucida after maturation did not differ among groups. Rate of cleavage was greater in zygotes from CL+ than from CL- or C (P < 0.01); and CL+ ovaries produced more total embryos on day 7 (P < 0.05) and more blastocysts (P < 0.01) than CL- and C ovaries. Rate of expansion and hatching of day-7 vitrified-warmed blastocysts at 24 and 48 h of culture did not differ among groups. In conclusion, oocytes collected from CL+ ovaries were larger and metabolically more prepared to continue maturation than those from ovaries lacking a CL. Also, rates of cleavage and yield of blastocysts were greater for oocytes from CL+ ovaries than from CL- and C ovaries. These findings indicate that a CL influenced oocyte developmental competence and embryonic development, presumably through intraovarian interactions.

Human chorionic gonadotropin (hCG)-induced ovulation occurs later but with equal occurrence in lactating dairy cows: comparing hCG and gonadotropin-releasing hormone protocols

This study assessed the effects of two hormones, human chorionic gonadotropin (hCG) and gonadotropin-releasing hormone (GnRH), on ovulatory responses during different diestrous stages in lactating dairy cows. Estrous cycles of 21 cows were synchronized and were enrolled in stage 1 of the experiment. The cows were treated with a prostaglandin (PG) F2α analog either 9 to 10 days [mid-diestrus (MD) group] or 5.5 to 6.5 days [early-diestrus (ED) group] after synchronized ovulation (day 0 = first PGF2α administration). On day 2, the cows were administrated 250 μg GnRH or 3000 IU hCG. Ovulation was determined every 2 h from 24 to 36 h after GnRH or hCG administration, and then every 4 h up to 72 h until ovulation. Cows in stage 2 were administered these treatments in the reverse order. The results indicated that average ovulation times in cows treated with GnRH in the MD group (GnRH-MD group) and cows treated with GnRH in the ED group (GnRH-ED group) were 30.0 ± 1.0 h and 28.8 ± 0.4 h, respectively. However, ovulation times for cows treated with hCG in the MD group (hCG-MD group) and cows treated with hCG in the ED group (hCG-ED group) were 35.8 ± 4.6 h and 32.8 ± 2.2 h, respectively, and ovulation occurred significantly later in the hCG-treated groups than in the GnRH-treated groups. In summary, we found that hCG-induced ovulation occurred later than GnRH-induced ovulation regardless of different diestrous peroids; however, the two treatments did not differ in terms of percentage of ovulation.

Transforming growth factor-beta family members are regulated during induced luteolysis in cattle

The transforming growth factors beta (TGFβ) are local factors produced by ovarian cells which, after binding to their receptors, regulate follicular deviation and ovulation. However, their regulation and function during corpus luteum (CL) regression has been poorly investigated. The present study evaluated the mRNA regulation of some TGFβ family ligands and their receptors in the bovine CL during induced luteolysis in vivo. On day 10 of the estrous cycle, cows received an injection of prostaglandin F2α (PGF) and luteal samples were obtained from separate groups of cows (n= 4-5 cows per time-point) at 0, 2, 12, 24 or 48 h after treatment. Since TGF beta family comprises more than 30 ligands, we focused in some candidates genes such as activin receptors (ACVR-1A, -1B, -2A, -2B) AMH, AMHR2, BMPs (BMP-1, -2, -3, -4, -6 and -7), BMP receptors (BMPR-1A, -1B and -2), inhibin subunits (INH-A, -BA, -BB) and betaglycan (TGFBR3). The mRNA levels of BMP4, BMP6 and INHBA were higher at 2 h after PGF administration (P<0.05) in comparison to 0 h. The relative mRNA abundance of BMP1, BMP2, BMP3, BMP4, BMP6, ACVR1B, INHBA and INHBB was upregulated up to 12 h post PGF (P<0.05). On the other hand, TGFBR3 mRNA that codes for a reservoir of ligands that bind to TGF-beta receptors, was lower at 48 h. In conclusion, findings from this study demonstrated that genes encoding several TGFβ family members are expressed in a time-specific manner after PGF administration.

Luteal Blood Flow and progesterone concentration during first and second postpartum estrous cycle in lactating dairy cows

The aim of the present study was to determine the differences in corpus luteum (CL) functionality between the first postpartum estrous cycle and the following cycle in lactating dairy cows. Luteal blood flow (LBF), luteal size and blood progesterone (P4) concentration were monitored during the first and second postpartum estrous cycle. During the first and second postpartum estrous cycle, the mean LBF value increased (p < .05) from early to late dioestrus, while it decreased rapidly in proestrus, resulting statistically lower (p < .05) than those registered in all previous phases. Statistically significant differences were not observed between overall LBF during first and second postpartum estrous cycle (p > .05). During the first postpartum estrous cycle, P4 blood concentrations showed a significant reduction (p < .05) from dioestrus to proestrus. A different trend of P4 concentrations was observed during the second postpartum estrous cycle, where mean P4 value registered in proestrus resulted statistically lower than those registered in the previous cycle phases (p < .05). The mean P4 concentration registered over the first postpartum estrous cycle resulted statistically lower (p < .05) than that registered during the second one. A significant correlation between P4 concentrations and LBF was registered only during the second postpartum estrous cycle. Results indicate that during the first postpartum estrous cycle, P4 concentration was independent of luteal blood flow and luteal size.

Angiopoietin expression in ovine corpora lutea during the luteal phase: Effects of nutrition, arginine and follicle stimulating hormone

The aim of this study was to evaluate angiopoietin (ANGPT) 1 and 2, and tyrosine-protein kinase receptor 2 (TIE2) expression in the corpora lutea (CL) of FSH-treated, or non-treated sheep administered arginine (Arg) or vehicle (saline, Sal), and fed a control (C), excess (O) or restricted (U) diet. Ewes from each dietary group were treated with Arg or Sal (experiment 1), and with FSH (experiment 2). Luteal tissues were collected at the early-, mid- and/or late-luteal phases of the estrous cycle. Protein and mRNA expression was determined using immunohistochemistry followed by image analysis, and quantitative RT-PCR, respectively. The results demonstrated that ANGPT1 and TIE2 proteins were localized to luteal capillaries and endothelial cells of larger blood vessels, and ANGPT2 was localized to tunica media of larger blood vessels. TIE2 protein was also present in luteal cells. In experiment 1, ANGPT1 protein expression was greater in O than C during early- and mid-luteal phases, and was greatest during late-luteal phase, less at the mid- and least at the early-luteal phase; 2) TIE2 protein expression was greatest at the mid-, less at the early- and least at the late-luteal phase; 3) ANGPT1 and 2 mRNA expression was greater at the mid- and late- than the early-luteal phase, and TIE2 mRNA expression was greatest at the late-, less at the mid- and least at the early-luteal phase. The ANGPT1/2 ratio was less at the early- than mid- or late-luteal phases. In experiment 2, ANGPT1 protein expression was greater in O during the mid-luteal phase than in other groups, and was greater at the mid- than early-luteal phase. TIE2 protein expression was highest at the mid-, less at the early- and least during the late-luteal phase. ANGPT1 and 2, and TIE2 mRNA expression was higher at the mid- than the early-luteal phase. During mid-luteal phase, ANGPT1 mRNA expression was greater in C than O and U, ANGPT2 was greatest in C, less in O and least in U, and TIE2 mRNA expression was greater in C than O and U. The ANGPT1/2 ratio was higher in U than in any other group. Comparison of FSH vs. Sal treatment effects (experiment 2 vs. experiment 1) demonstrated that FSH affected ANGPT1 and/or -2, and TIE2 protein and mRNA expression depending on luteal phase and/or diet. Thus, expression of ANGPTs and TIE2 in the CL changes during the luteal lifespan, indicating their involvement in luteal vascular formation, stabilization and degradation. Moreover, this study has demonstrated that plane of nutrition and/or FSH treatment affect the ANGPT system, and may alter luteal vascularity and luteal function in sheep.

Follicle vascularity coordinates corpus luteum blood flow and progesterone production

Colour Doppler ultrasonography was used to compare the ability of preovulatory follicle (POF) blood flow and its dimensions to predict the size, blood flow and progesterone production capability of the subsequent corpus luteum (CL). Cows (n=30) were submitted to a synchronisation protocol. Follicles ≥7mm were measured and follicular wall blood flow evaluated every 12h for approximately 3.5 days until ovulation. After ovulation, cows were scanned daily for 8 days and similar parameters were evaluated for the CL. Blood samples were collected and plasma progesterone concentrations quantified. All parameters were positively correlated. Correlation values ranged from 0.26 to 0.74 on data normalised to ovulation and from 0.31 to 0.74 on data normalised to maximum values. Correlations between calculated ratios of both POF and CL in data normalised to ovulation and to maximum values ranged from moderate (0.57) to strong (0.87). Significant (P<0.0001) linear regression analyses were seen in all comparisons. In conclusion, higher correlations were observed between the dimensions of POF and/or CL and blood flow of both structures, as well as POF and/or CL blood flow with plasma progesterone concentrations of the resultant CL. These findings indicate that follicle vascularity coordinates CL blood flow and progesterone production in synchronised beef cows.

Activation of P2X7 receptors decreases the proliferation of murine luteal cells

Extracellular ATP regulates cellular function in an autocrine or paracrine manner through activating purinergic signalling. Studies have shown that purinergic receptors were expressed in mammalian ovaries and they have been proposed as an intra-ovarian regulatory mechanism. P2X7 was expressed in porcine ovarian theca cells and murine and human ovarian surface epithelium and is involved in ATP-induced apoptotic cell death. However, the role of P2X7 in corpus luteum is still unclear. The aim of this study was to investigate the role of ATP signalling in murine luteal cells and the possible mechanism(s) involved. We found that P2X7 was highly expressed in murine small luteal cells. The agonists of P2X7, ATP and BzATP, inhibited the proliferation of luteal cells. P2X7 antagonist BBG reversed the inhibition induced by ATP and BzATP. Further studies showed that ATP and BzATP inhibited the expression of cell cycle regulators cyclinD2 and cyclinE2. ATP and BzATP also inhibited the p38-mitogen-activated protein kinase (MAPK) signalling pathway. These results reveal that P2X7 receptor activation is involved in corpus luteum formation and function.

Lipid droplets in cultured luteal cells in non-pregnant sheep fed different planes of nutrition

Accumulation of lipid droplets (LD) in luteal cells likely is important for energy storage and steroidogenesis in the highly metabolically active corpus luteum (CL). The objective of this study was to determine the effect of plane of nutrition on progesterone (P4) secretion, and lipid droplet number and size in cultured ovine luteal cells. Ewes were randomly assigned to one of three nutritional groups: control (C; 100% NRC requirements, n=9), overfed (O; 2×C, n=12), or underfed (U; 0.6×C, n=10). Superovulation was induced by follicle stimulating hormone injections. At the early and mid-luteal phases of the estrous cycle, CL were dissected from ovaries, and luteal cells isolated enzymatically. Luteal cells were incubated overnight in medium containing serum in chamber slides. Media were then changed to serum-free and after 24h incubation, media were collected for P4 analysis, and cells were fixed in formalin and stained with BODIPY followed by DAPI staining. Z-stacks of optical sections of large and small luteal cells (LLC and SLC, respectively) were obtained using a laser-scanning microscope. Rendered 3D images of individual LLC and SLC were analyzed for cell volume, and total and individual LD volume, number and percentage of cellular volume occupied by LD by using Imaris software. Concentrations of P4 in serum and media were greater (P<0.05) at the mid than early-luteal phase, and were not affected by nutritional plane. LD total volume and number were greater (P<0.001) in LLC than SLC; however, mean volume of individual LD was greater (P<0.02) in SLC than LLC. In LLC, total LD volume was greater (P<0.02) in O than C and U ewes. In SLC, total LD volume and number was greater (P<0.003) at the mid than early-luteal phase, and percentage of cell volume occupied by LD was greater (P<0.002) in U than C and O ewes. These data demonstrate that both stage of luteal development and nutritional plane affect selected LD measurements and thus may affect luteal functions. Furthermore, these data confirm that LD dynamics differ among parenchymal steroidogenic luteal cell types.

The role of adrenergic activation on murine luteal cell viability and progesterone production

Sympathetic innervations exist in mammalian CL. The action of catecholaminergic system on luteal cells has been the focus of a variety of studies. Norepinephrine (NE) increased progesterone secretion of cattle luteal cells by activating β-adrenoceptors. In this study, murine luteal cells were treated with NE and isoprenaline (ISO). We found that NE increased the viability of murine luteal cells and ISO decreased the viability of luteal cells. Both NE and ISO promoted the progesterone production. Nonselective β-adrenergic antagonist, propranolol reversed the effect of ISO on cell viability but did not reverse the effect of NE on cell viability. Propranolol blocked the influence of NE and ISO on progesterone production. These results reveal that the increase of luteal cell viability induced by NE is not dependent on β-adrenergic activation. α-Adrenergic activation possibly contributes to it. Both NE and ISO increased progesterone production through activating β-adrenergic receptor. Further study showed that CyclinD2 is involved in the increase of luteal cell induced by NE. 3β-Hydroxysteroid dehydrogenase, LHR, steroidogenic acute regulatory protein (StAR), and PGF2α contribute to the progesterone production induced by NE and ISO.

Lipopolysaccharide enhances apoptosis of corpus luteum in isolated perfused bovine ovaries in vitro

Lipopolysaccharide (LPS), the endotoxin of Gram-negative bacteria, has detrimental effects on the structure and function of bovine corpus luteum (CL)in vivo. The objective was to investigate whether these effects were mediated directly by LPS orviaLPS-induced release of PGF2α. Bovine ovaries with a mid-cycle CL were collected immediately after slaughter and isolated perfused for 240 min. After 60 min of equilibration, LPS (0.5 μg/ml) was added to the medium of five ovaries, whereas an additional six ovaries were not treated with LPS (control). After 210 min of perfusion, all ovaries were treated with 500 iu of hCG. In the effluent perfusate, concentrations of progesterone (P4) and PGF2αwere measured every 10 and 30 min, respectively. Punch biopsies of the CL were collected every 60 min and used for RT-qPCR to evaluate mRNA expression of receptors for LPS (TLR2,-4) and LH (LHCGR); the cytokineTNFA; steroidogenic (STAR,HSD3B), angiogenic (VEGFA121,FGF2), and vasoactive (EDN1) factors; and factors of prostaglandin synthesis (PGES,PGFS,PTGFR) and apoptosis (CASP3,-8,-9). Treatment with LPS abolished the hCG-induced increase in P4(P≤0.05); however, there was a tendency (P=0.10) for increased release of PGF2αat 70 min after LPS challenge. Furthermore, mRNA abundance ofTLR2,TNFA,CASP3,CASP8,PGES,PGFS, andVEGFA121increased (P≤0.05) after LPS treatment, whereas all other factors remained unchanged (P>0.05). In conclusion, reduced P4responsiveness to hCG in LPS-treated ovariesin vitrowas not due to reduced steroidogenesis, but was attributed to enhanced apoptosis. However, an impact of luteal PGF2αcould not be excluded.

Effects of intraluteal implants of prostaglandin E1 or E2 on angiogenic growth factors in luteal tissue of Angus and Brahman cows

Previously, it was reported that intraluteal implants containing prostaglandin E1 or E2 (PGE1 and PGE2) in Angus or Brahman cows prevented luteolysis by preventing loss of mRNA expression for luteal LH receptors and luteal unoccupied and occupied LH receptors. In addition, intraluteal implants containing PGE1 or PGE2 upregulated mRNA expression for FP prostanoid receptors and downregulated mRNA expression for EP2 and EP4 prostanoid receptors. Luteal weight during the estrous cycle of Brahman cows was reported to be lesser than that of Angus cows but not during pregnancy. The objective of this experiment was to determine whether intraluteal implants containing PGE1 or PGE2 alter vascular endothelial growth factor (VEGF), fibroblast growth factor-2 (FGF-2), angiopoietin-1 (ANG-1), and angiopoietin-2 (ANG-2) protein in Brahman or Angus cows. On Day 13 of the estrous cycle, Angus cows received no intraluteal implant and corpora lutea were retrieved, or Angus and Brahman cows received intraluteal silastic implants containing vehicle, PGE1, or PGE2 on Day 13 and corpora lutea were retrieved on Day 19. Corpora lutea slices were analyzed for VEGF, FGF-2, ANG-1, and ANG-2 angiogenic proteins via Western blot. Day-13 Angus cow luteal tissue served as preluteolytic controls. Data for VEGF were not affected (P > 0.05) by day, breed, or treatment. PGE1 or PGE2 increased (P < 0.05) FGF-2 in luteal tissue of Angus cows compared with Day-13 and Day-19 Angus controls but decreased (P < 0.05) FGF-2 in luteal tissue of Brahman cows when compared w Day-13 or Day-19 Angus controls. There was no effect (P > 0.05) of PGE1 or PGE2 on ANG-1 in Angus luteal tissue when compared with Day-13 or Day-19 controls, but ANG-1 was decreased (P < 0.05) by PGE1 or PGE2 in Brahman cows when compared with Day-19 Brahman controls. ANG-2 was increased (P < 0.05) on Day 19 in Angus Vehicle controls when compared with Day-13 Angus controls, which was prevented (P < 0.05) by PGE1 but not by PGE2 in Angus cows. There was no effect (P > 0.05) of PGE1 or PGE2 on ANG-2 in Brahman cows. PGE1 or PGE2 may alter cow luteal FGF-2, ANG-1, or ANG-2 but not VEGF to prevent luteolysis; however, species or breed differences may exist.

Luteal activity of pregnant rats with hypo-and hyperthyroidism

Background

Luteal activity is dependent on the interaction of various growth factors, cytokines and hormones, including the thyroid hormones, being that hypo- and hyperthyroidism alter the gestational period and are also a cause of miscarriage and stillbirth. Because of that, we evaluated the proliferation, apoptosis and expression of angiogenic factors and COX-2 in the corpus luteum of hypo- and hyperthyroid pregnant rats.

Methods

Seventy-two adult female rats were equally distributed into three groups: hypothyroid, hyperthyroid and control. Hypo- and hyperthyroidism were induced by the daily administration of propylthiouracil and L-thyroxine, respectively. The administration began five days before becoming pregnant and the animals were sacrificed at days 10, 14, and 19 of gestation. We performed an immunohistochemical analysis to evaluate the expression of CDC-47, VEGF, Flk-1 (VEGF receptor) and COX-2. Apoptosis was evaluated by the TUNEL assay. We assessed the gene expression of VEGF, Flk-1, caspase 3, COX-2 and PGF2α receptor using real time RT-PCR. The data were analyzed by SNK test.

Results

Hypothyroidism reduced COX-2 expression on day 10 and 19 (P < 0.05), endothelial/pericyte and luteal cell proliferation on day 10 and 14 (p < 0.05), apoptotic cell numbers on day 19 (p < 0.05) and the expression of Flk-1 and VEGF on day 14 and 19, respectively (p < 0.05). Hyperthyroidism increased the expression of COX-2 on day 19 (P < 0.05) and the proliferative activity of endothelial/pericytes cells on day 14 (p <0.05), as well as the expression of VEGF and Flk-1 on day 19 (P < 0.05).

Conclusions

Hypothyroidism reduces the proliferation, apoptosis and expression of angiogenic factors and COX-2in the corpus luteum of pregnant rats, contrary to what is observed in hyperthyroid animals, being this effect dependent of the gestational period.

Expression and localization of ghrelin and its functional receptor in corpus luteum during different stages of estrous cycle and the modulatory role of ghrelin on progesterone production in cultured luteal cells in buffalo

Evidence obtained during recent years provided has insight into the regulation of corpus luteum (CL) development, function, and regression by locally produced ghrelin. The present study was carried out to evaluate the expression and localization of ghrelin and its receptor (GHS-R1a) in bubaline CL during different stages of the estrous cycle and investigate the role of ghrelin on progesterone (P4) production along with messenger RNA (mRNA) expression of P4 synthesis intermediates. The mRNA and protein expression of ghrelin and GHS-R1a was significantly greater in mid- and late luteal phases. Both factors were localized in luteal cells, exclusively in the cytoplasm. Immunoreactivity of ghrelin and GHS-R1a was greater during mid- and late luteal phases. Luteal cells were cultured in vitro and treated with ghrelin each at 1, 10, and 100 ng/mL concentrations for 48 h after obtaining 75% to 80% confluence. At a dose of 1 ng/mL, there was no significant difference in P4 secretion between control and treatment group. At 10 and 100 ng/mL, there was a decrease (P < 0.05) in P4 concentration, cytochrome P45011A1 (CYP11A1), and 3-beta-hydroxysteroid dehydrogenase mRNA expression and localization. There was no difference in mRNA expression of steroidogenic acute regulatory protein between control and treatment group. In summary, the present study provided evidence that ghrelin and its receptor are expressed in bubaline CL and are localized exclusively in the cell cytoplasm and ghrelin has an inhibitory effect on P4 production in buffalo.

ATF3 expression in the corpus luteum: possible role in luteal regression

The present study investigated the induction and possible role of activating transcription factor 3 (ATF3) in the corpus luteum. Postpubertal cattle were treated at midcycle with prostaglandin F2α(PGF) for 0-4 hours. Luteal tissue was processed for immunohistochemistry, in situ hybridization, and isolation of protein and RNA. Ovaries were also collected from midluteal phase and first-trimester pregnant cows. Luteal cells were prepared and sorted by centrifugal elutriation to obtain purified small (SLCs) and large luteal cells (LLCs). Real-time PCR and in situ hybridization showed that ATF3 mRNA increased within 1 hour of PGF treatment in vivo. Western blot and immunohistochemistry demonstrated that ATF3 protein was expressed in the nuclei of LLC within 1 hour and was maintained for at least 4 hours. PGF treatment in vitro increased ATF3 expression only in LLC, whereas TNF induced ATF3 in both SLCs and LLCs. PGF stimulated concentration- and time-dependent increases in ATF3 and phosphorylation of MAPKs in LLCs. Combinations of MAPK inhibitors suppressed ATF3 expression in LLCs. Adenoviral-mediated expression of ATF3 inhibited LH-stimulated cAMP response element reporter luciferase activity and progesterone production in LLCs and SLCs but did not alter cell viability or change the expression or activity of key regulators of progesterone synthesis. In conclusion, the action of PGF in LLCs is associated with the rapid activation of stress-activated protein kinases and the induction of ATF3, which may contribute to the reduction in steroid synthesis during luteal regression. ATF3 appears to affect gonadotropin-stimulated progesterone secretion at a step or steps downstream of PKA signaling and before cholesterol conversion to progesterone.

Local Renin-Angiotensin system in the reproductive system

The renin-angiotensin system (RAS) is well known as regulator of electrolytes and blood pressure. Besides this function, there are numerous studies supporting the idea of a local tissue RAS. This system controls the local activity of the different RAS family members, especially of the functional proteins Angiotensin II and Angiotensin (1-7). Those antagonistically acting proteins have been described to be expressed in different organ systems including the human reproductive tract. Therefore, this local RAS has been suspected to be involved in the control and regulation of physiological and pathological conditions in the female reproduction tract. This review of the available literature summarizes the physiological influence of the RAS on the follicular development, ovarian angiogenesis, and placental- and uterine function. In addition, in the second part the role of the RAS concerning ovarian- and endometrial cancer becomes elucidated. This section includes possible novel therapeutic strategies via inhibition of RAS-mediated tumor growth and angiogenesis. Looking at a very complex system of agonistic and antagonistic tissue factors, it may be supposed that the RAS in the female reproduction tract will be of rising scientific interest in the upcoming years.

Impact of angiogenic and innate immune systems on the corpus luteum function during its formation and maintenance in ruminants

The corpus luteum (CL) is formed from an ovulated follicle, and grows rapidly to secrete progesterone (P4) thereby supporting implantation and maintenance of pregnancy. It is now evident that angiogenesis is necessary to form the structure of the developing CL as well as to acquire the steroidogenic capacity to secrete large amounts of P4. It is of interest that the increases in CL size, plasma P4 concentration and luteal blood flow are occurring in parallel during the first seven days after ovulation. Angiogenic factors, such as vascular endothelial growth factor-A (VEGFA) and basic fibroblast growth factor (FGF2), play a central role in promoting cell proliferation and angiogenesis in the developing CL. Angiopoietins regulate the stability of blood vessels, which directly affects angiogenesis or angiolysis via angiogenic factors. Vasohibin-1 is a novel negative feedback regulator, which inhibits VEGF-based vasculogenesis. It became evident that the immune cells, i.e., macrophages, eosinophils and neutrophils are recruited into the CL - using the innate immune system - just after ovulation which is accompanied by bleeding. The immune cells support active angiogenesis and thus the growth of the CL. In cows, the lymphatic system, but not blood vascular system, is reconstituted during early pregnancy, and embryonic trophoblast-derived interferon tau could play a crucial role in inducing lymphangiogenesis. This novel phenomenon may support a maternal recognition of pregnancy in shifting the local systems in such a way that they ensure a long-term supply of P4 over the period of pregnancy. Overall, the current findings support the concept that several major components involved in the regulation of the CL development and maintenance overlap in stimulating steroidogenesis, angiogenesis, vascular function and the innate immune system.

Blood and lymphatic vasculature in the ovary: development, function and disease

BACKGROUND

The remodelling of the blood vasculature has been the subject of much research while rapid progress in the understanding of the factors controlling lymphangiogenesis in the ovary has only been reported more recently. The ovary undergoes cyclic remodelling throughout each menstrual/estrous cycle. This process requires significant vascular remodelling to supply each new cohort of growing follicles.

METHODS

Literature searches were performed to review studies on the ovarian lymphatic vasculature that described spatial, temporal and functional data in human or animal species. The role of ovarian blood and lymphatic vasculature in the pathogenesis of ovarian disease and dysfunction was also explored.

RESULTS

Research in a number of species including zebrafish, rodents and primates has described the lymphatic vasculature within the remodelling ovary, while recent research in mouse has confirmed hormonal regulation of lymphangiogenic growth factors, their receptors and also a role for the protease, ADAMTS1 in the development of the lymphatic vasculature. With a critical role in the maintenence of fluid homeostasis, the ovarian lymphatic vasculature is important for normal ovarian function and has been linked to syndromes involving ovarian fluid imbalance, including ovarian hyperstimulation syndrome and massive ovarian edema. The lymphatic vasculature has also been heavily implicated in the metastatic cancer process.

CONCLUSION

The spatial and temporal regulation of the ovarian lymphatic vasculature has now been reported in a number of species and the data also implicate the ovarian lymphatic vasculature in ovarian pathologies, including cancer and those linked with use of artificial reproduction technologies.

Hormonal manipulations in the 5-day timed artificial insemination protocol to optimize estrous cycle synchrony and fertility in dairy heifers

Objectives were to determine the effects of GnRH at the initiation of the 5-d timed artificial insemination (AI) program combined with 2 injections of PGF2α on ovarian responses and pregnancy per AI (P/AI) in dairy heifers, and the role of progesterone concentrations on LH release and ovulation in response to GnRH. In study 1, heifers received a controlled internal drug release (CIDR) insert containing 1.38 g of progesterone on d 0, an injection of 25 mg of PGF2α and CIDR removal on d 5, and an injection of 100 μg GnRH concurrently with AI on d 8. Heifers were assigned to receive no additional treatment (control; n=559) or an injection of GnRH on d 0 and a second injection of PGF2α on d 6 (G2P; n=547). In study 2, all heifers were treated as described for the control in study 1, and were allocated to receive no additional treatment (control; n=723), an injection of PGF2α on d 6 (NG2P; n=703), or an injection of GnRH on d 0 and an injection of PGF2α on d 6 (G2P; n=718). In study 3, heifers received a CIDR on d 7 after ovulation and were assigned randomly to a low-progesterone (LP; n=6) treatment in which 2 injections of 25 mg of PGF2α each were administered 12h apart, on d 7 and 7.5 after ovulation, or to a high-progesterone (HP; n=12) treatment in which no PGF2α was administered. On d 8, heifers received 100 μg of GnRH and blood was sampled at every 15 min from -30 to 180 min relative to the GnRH for assessment of LH concentrations. Additionally, 94 heifers were assigned to LP or HP and ovulation in response to GnRH was evaluated. In study 1, P/AI was greater for G2P than for the control on d 32 (59.4 vs. 53.5%) and 60 after AI (56.6 vs. 51.3%). In study 2, administration of GnRH on d 0 increased the proportion of heifers with a new corpus luteum on d 5 (control=21.9 vs. NG2P=20.1 vs. G2P=34.4%). Administration of a second PGF2α increased the proportion of heifers with progesterone <0.5 ng/mL at AI (control=83.1 vs. NG2P=93.0 and G2P=87.2%). Pregnancy per AI was greater for G2P than for control and NG2P on d 32 (control=52.9 vs. NG2P=55.0 vs. G2P=61.7%) and 60 (control=49.0 vs. NG2P=51.6 vs. G2P=59.1%). In study 3, HP attenuated LH release and reduced ovulation (19.0 vs. 48.4%) in response to GnRH compared with LP. Combining GnRH and 2 doses of PGF2α in the 5-d timed AI protocol improved follicle turnover, luteolysis, and P/AI in heifers. Elevated concentrations of progesterone suppressed LH release and are linked with the low ovulatory response to the initial GnRH treatment of the protocol.

Emerging roles of immune cells in luteal angiogenesis

In the mammalian ovary, the corpus luteum (CL) is a unique transient endocrine organ displaying rapid angiogenesis and time-dependent accumulation of immune cells. The CL closely resembles 'transitory tumours', and the rate of luteal growth equals that of the fastest growing tumours. Recently, attention has focused on multiple roles of immune cells in luteal function, not only in luteolysis (CL disruption by immune responses involving T lymphocytes and macrophages), but also in CL development (CL remodelling by different immune responses involving neutrophils and macrophages). Neutrophils and macrophages regulate angiogenesis, lymphangiogenesis, and steroidogenesis by releasing cytokines in the CL. In addition, functional polarisation of neutrophils (proinflammatory N1 vs anti-inflammatory N2) and macrophages (proinflammatory M1 vs anti-inflammatory M2) has been demonstrated. This new concept concurs with the phenomenon of immune function within the luteal microenvironment: active development of the CL infiltrating anti-inflammatory N2 and M2 versus luteal regression together with proinflammatory N1 and M1. Conversely, excessive angiogenic factors and leucocyte infiltration result in indefinite disordered tumour development. However, the negative feedback regulator vasohibin-1 in the CL prevents excessive tumour-like vasculogenesis, suggesting that CL development has well coordinated time-dependent mechanisms. In this review, we discuss the physiological roles of immune cells involved in innate immunity (e.g. neutrophils and macrophages) in the local regulation of CL development with a primary focus on the cow.

Fertility in a high-altitude environment is compromised by luteal dysfunction: the relative roles of hypoxia and oxidative stress

BACKGROUND

At high altitudes, hypoxia, oxidative stress or both compromise sheep fertility. In the present work, we tested the relative effect of short- or long-term exposure to high altitude hypobaric hypoxia and oxidative stress on corpora luteal structure and function.

METHODS

The growth dynamics of the corpora lutea during the estrous cycle were studied daily by ultrasonography in cycling sheep that were either native or naïve to high-altitude conditions and that were supplemented or not supplemented with antioxidant vitamins. Arterial and venous blood samples were simultaneously drawn for determination of gases and oxidative stress biomarkers and progesterone measurement. On day five after ovulation in the next cycle, the ovaries were removed for immunodetection of luteal HIF-1alpha and VEGF and IGF-I and to detect IGF-II gene expression.

RESULTS

The results showed that both short- and long-term exposure to high-altitude conditions decreased luteal growth and IGF-I and IGF-II gene expression but increased HIF-1 alpha and VEGF immunoexpression. The level of plasma progesterone was also increased at a high altitude, although an association with increased corpus luteum vascularization was only found in sheep native to a high-altitude location. Administration of antioxidant vitamins resulted in a limited effect, which was restricted to decreased expression of oxidative stress biomarkers and luteal HIF-1alpha and VEGF immunoexpression.

CONCLUSIONS

Exposure of the sheep to high-altitude hypobaric hypoxia for short or long time periods affects the development and function of the corpus luteum. Moreover, the observed association of oxidative stress with hypoxia and the absence of any significant effect of antioxidant vitamins on most anatomical and functional corpus luteum traits suggests that the effects of high altitude on this ovarian structure are mainly mediated by hypoxia. Thus, these findings may help explain the decrease in sheep fertility at a high altitude.

Effects of hypo- and hyperthyroidism on proliferation, angiogenesis, apoptosis and expression of COX-2 in the corpus luteum of female rats

Although thyroid dysfunction occurs frequently in humans and some animal species, the mechanisms by which hypo- and hyperthyroidism affect the corpus luteum have not been thoroughly elucidated. This study evaluated the levels of proliferative activity, angiogenesis, apoptosis and expression of cyclooxygenase-2 in the corpus luteum of female rats with thyroid dysfunction. These processes may be important in understanding the reproductive changes caused by thyroid dysfunction. A total of 18 adult female rats were divided into three groups (control, hypothyroid and hyperthyroid) with six animals per group. Three months after treatment to induce thyroid dysfunction, the rats were euthanized in the dioestrus phase. The ovaries were collected and immunohistochemically analysed for expression of the cell proliferation marker CDC-47, vascular endothelial growth factor (VEGF), VEGF receptor Flk-1 and cyclooxygenase-2 (COX-2). Apoptosis was evaluated using the TUNEL assay. Hypothyroidism reduced the intensity and area of COX-2 expression in the corpus luteum (p < 0.05), while hyperthyroidism did not alter COX-2 expression in the dioestrus phase. Hypothyroidism significantly reduced the expression of CDC-47 in endothelial cells and pericytes in the corpus luteum, whereas hyperthyroidism did not induce a detectable change in CDC-47 expression (p > 0.05). Hypothyroidism reduced the level of apoptosis in luteal cells (p < 0.05) and increased VEGF expression in the corpus luteum. In contrast, hyperthyroidism increased the level of apoptosis in the corpus luteum (p < 0.05). In conclusion, thyroid dysfunction differentially affects the levels of proliferative activity, angiogenesis and apoptosis and COX-2 expression in the corpus luteum of female rats.

The phenotype of hormone-related allergic and autoimmune diseases in the skin: annular lesions that lateralize

Introduction. Sexual dimorphism with an increased prevalence in women has long been observed in various autoimmune, allergic, and skin diseases. Recent research has attempted to correlate this female predilection to physiologic changes seen in the menstrual cycle in order to more effectively diagnose and treat these diseases. Cases. We present five cases of cutaneous diseases in women with annular morphology and distributive features that favor one side over the other. In all cases, skin disease improved with ovarian suppression. Conclusion. Sexual dimorphism in the innate and adaptive immune systems has long been observed, with females demonstrating a more vigorous immune response compared to males. Female sex hormones promote T and B lymphocyte autoreactivity and favor the humoral arm of adaptive immunity. In addition to ovarian steroidogenesis and immunity, intricate pathways coexist in order to engage a single oocyte in each cycle, while simultaneously sustaining the ovarian reserve. Vigorous proinflammatory, vasoactive, and pigment-related cytokines emerge during the demise of the corpus luteum, influencing peripherical sex hormone metabolism of the level of the macrophage and fibroblast. We propose that annular and lateralizing lesions are important manifestations of hormone-related inflammation and recognition of this linkage can lead to improved immune and reproductive health.

Life or death decisions in the corpus luteum

The corpus luteum (CL) is an ephemeral endocrine organ. During its lifespan, it undergoes a period of extremely rapid growth that involves hypertrophy, proliferation and differentiation of the steroidogenic cells, as well as extensive angiogenesis. The growth phase is followed by a period in which remodelling of the tissue ceases, but it engages in unparalleled production of steroids, resulting in extraordinarily high metabolic activity within the tissue. It is during this stage that a critical juncture occurs. In the non-fertile cycle, uterine release of prostaglandin (PG)F(2α) initiates a cascade of events that result in rapid loss of steroidogenesis and destruction of the luteal tissue. Alternatively, if a viable embryo is present, signals are produced that result in rescue of the CL. This review article summarizes the major concepts related to the fate of the CL, with particular focus on recent insights into the mechanisms associated with the ability of PGF(2α) to bring about complete luteolysis. It has become clear that the achievement of luteolysis depends on repeated exposure to PGF(2α) and involves coordinated actions of heterogeneous cell types within the CL. Together, these components of the process bring about not only the loss in progesterone production, but also the rapid demise of the structure itself.

Bovine luteal blood flow: basic mechanism and clinical relevance

The introduction of transrectal colour Doppler sonography (CDS) has allowed the evaluation of luteal blood flow (LBF) in cows. Because appropriate angiogenesis plays a decisive role in the functioning of the corpus luteum (CL), studies on LBF may provide valuable information about the physiology and pathophysiology of the CL. Studies on cyclic cows have shown that progesterone concentrations in blood plasma can be more reliably predicted by LBF than by luteal size (LS), especially during the regression phase of the CL. In contrast with non-pregnant cows, a significant increase in LBF is seen in pregnant cows during the third week after insemination. However, because there are high interindividual variations in LBF between animals, LBF is not useful for the early diagnosis of pregnancy. Determination of LBF is more sensitive than LS for detecting the effects of acute systemic inflammation and exogenous hormones on the CL. Cows with low progesterone levels have smaller CL during the mid-luteal phase, but LBF related to LS did not differ between cows with low and high progesterone levels. In conclusion, LBF determined by CDS provides additional information about luteal function compared with LS and plasma progesterone concentrations, but its role concerning fertility in the cow is yet to be clarified.

A mathematical model of the bovine oestrous cycle: simulating outcomes of dietary and pharmacological interventions

A mathematical model was constructed to simulate the bovine oestrous cycle by using nonlinear differential equations to describe the biological mechanisms which regulate the cycle. The model predicts circulating concentrations of gonadotrophin-releasing hormone, follicle-stimulating hormone, luteinizing hormone, oestradiol, inhibin and progesterone. These hormones collectively provide control and feedback mechanisms between the hypothalamus, pituitary gland and ovaries, which regulate ovarian follicular dynamics, corpus luteum function and ovulation. When follicular growth parameters are altered, the model predicts that cows will exhibit either two or three follicular waves per cycle, as seen in practice. Changes in other parameters allow the model to simulate: effects of nutrition on follicle recruitment and size of the ovulatory follicle; effects of negative energy balance on postpartum anoestrus; and effects of pharmacological intervention on hormone profiles and timing of ovulation. It is concluded that this model provides a sound basis for exploring factors that influence the bovine oestrous cycle in order to test hypotheses about nutritional and hormonal influences which, with further validation, should help to design dietary or pharmacological strategies for improving reproductive performance in cattle.

Vascular and immune regulation of corpus luteum development, maintenance, and regression in the cow

The bovine corpus luteum (CL) is a unique, transient organ with well-coordinated mechanisms by which its development, maintenance, and regression are effectively controlled. Angiogenic factors, such as vascular endothelial growth factor A and basic fibroblast growth factor, play an essential role in promoting progesterone secretion, cell proliferation, and angiogenesis. These processes are critically regulated, through both angiogenic and immune systems, by the specific immune cells, including macrophages, eosinophils, and neutrophils, that are recruited into the developing CL. The bovine luteolytic cascade appears to be similar to that of general acute inflammation in terms of time-dependent infiltration by immune cells (neutrophils, macrophages, and T lymphocytes) and drastic changes in vascular tonus and blood flow, which are regulated by luteal nitric oxide and the vasoconstrictive factors endothelin-1 and angiotensin II. Over the period of maternal recognition of pregnancy, the maternal immune system should be well controlled to accept the semiallograft fetus. The information on the presence of the developing embryo in the genital tract is suggested to be transmitted to the ovary by both the endocrine system and the circulating immune cells. In the bovine CL, the lymphatic system, but not the blood vascular system, is reconstituted during early pregnancy, and interferon tau from the embryo could trigger this novel phenomenon. Collectively, the angiogenic and vasoactive factors produced by luteal cells and the time-dependently recruited immune cells within the CL and their interactions appear to play critical roles in regulating luteal functions throughout the life span of the CL.