Prostaglandin F2alpha increases endothelial nitric oxide synthase in the periphery of the bovine corpus luteum: the possible regulation of blood flow at an early stage of luteolysis

Mechanisms of angioregression of the corpus luteum

The corpus luteum is a transient ovarian endocrine gland that produces the progesterone necessary for the establishment and maintenance of pregnancy. The formation and function of this gland involves angiogenesis, establishing the tissue with a robust blood flow and vast microvasculature required to support production of progesterone. Every steroidogenic cell within the corpus luteum is in direct contact with a capillary, and disruption of angiogenesis impairs luteal development and function. At the end of a reproductive cycle, the corpus luteum ceases progesterone production and undergoes rapid structural regression into a nonfunctional corpus albicans in a process initiated and exacerbated by the luteolysin prostaglandin F2α (PGF2α). Structural regression is accompanied by complete regression of the luteal microvasculature in which endothelial cells die and are sloughed off into capillaries and lymphatic vessels. During luteal regression, changes in nitric oxide transiently increase blood flow, followed by a reduction in blood flow and progesterone secretion. Early luteal regression is marked by an increased production of cytokines and chemokines and influx of immune cells. Microvascular endothelial cells are sensitive to released factors during luteolysis, including thrombospondin, endothelin, and cytokines like tumor necrosis factor alpha (TNF) and transforming growth factor β 1 (TGFB1). Although PGF2α is known to be a vasoconstrictor, endothelial cells do not express receptors for PGF2α, therefore it is believed that the angioregression occurring during luteolysis is mediated by factors downstream of PGF2α signaling. Yet, the exact mechanisms responsible for angioregression in the corpus luteum remain unknown. This review describes the current knowledge on angioregression of the corpus luteum and the roles of vasoactive factors released during luteolysis on luteal vasculature and endothelial cells of the microvasculature.

Nanodelivery System for Ovsynch Protocol Improves Ovarian Response, Ovarian Blood Flow Doppler Velocities, and Hormonal Profile of Goats

Fifteen cyclic, multiparous goats were equally stratified and received the common Ovsynch protocol (GPG: intramuscular, IM, injection of 50 mg gonadorelin, followed by an IM injection of 125 µg cloprostenol 7 days later, and a further IM injection of 50 mg gonadorelin 2 days later) or the Ovsynch protocol using nanofabricated hormones with the same dosages (NGPG) or half dosages (HNGPG) of each hormone. The ovarian structures and ovarian and luteal artery hemodynamic indices after each injection of the Ovsynch protocol using B-mode, color, and spectral Doppler scanning were monitored. Levels of blood serum progesterone (P4), estradiol (E2), and nitric oxide (NO) were determined. After the first gonadotrophin-releasing hormone (GnRH) injection, the number of large follicles decreased (p = 0.02) in NGPG and HNGPG, compared with GPG. HNGPG resulted in larger corpus luteum (CL) diameters (p = 0.001), and improved ovarian and luteal blood flow, compared with GPG and NGPG. Both NGPG and HNGPG significantly increased E2 and NO levels compared with GPG. HNGPG increased (p < 0.001) P4 levels compared with GPG, whereas NGPG resulted in an intermediate value. After prostaglandin F2α (PGF2α) injection, HNGPG had the largest diameter of CLs (p = 0.001) and significantly improved ovarian blood flow compared with GPG and NGPG. Both NGPG and HNGPG increased (p = 0.007) NO levels, compared with GPG. E2 level was increased (p = 0.028) in HNGPG, compared with GPG, whereas NGPG resulted in an intermediate value. During the follicular phase, HNGPG increased (p = 0.043) the number of medium follicles, shortened (p = 0.04) the interval to ovulation, and increased (p < 0.001) ovarian artery blood flow and levels (p < 0.001) of blood serum P4, E2, and NO, compared with GPG and NGPG. During the luteal phase, the numbers of CLs were similar among different experimental groups, whereas the diameter of CLs, luteal blood flow, and levels of blood serum P4 and NO increased (p < 0.001) in HNGPG, compared with GPG and NGPG. Conclusively, the nanodelivery system for the Ovsynch protocol could be recommended as a new strategy for improving estrous synchronization outcomes of goats while enabling lower hormone dose administration.

Effects of neonatal exposure to methoxychlor on corpus luteum in gilts: A transcriptomic analysis

This study investigated the effects of neonatal exposure to methoxychlor (MXC), a synthetic organochlorine used as an insecticide with estrogenic, antiestrogenic, and antiandrogenic activities, on luteal function in pigs. Piglets were injected subcutaneously with MXC (20 μg/kg body weight) or corn oil (control) between postnatal Days 1 and 10 (N = 5/group). Corpora lutea from sexually mature gilts were examined for luteal steroid and prostaglandin concentrations and processed for total RNA isolation and subsequent RNA sequencing. Intra-luteal concentrations of androstenedione and prostaglandin E₂ were greater, while that of estrone was lower when compared to control. Fifty-three differentially expressed (DE) microRNAS (miRNAs) (p-adjusted <.05 and log2(fold change) ≥.5) and 359 DE genes (p-adjusted <.05 and log2(fold change) ≥1) were identified in luteal tissue in response to neonatal MXC treatment. MXC was found to affect the expression of genes related to lipogenesis, steroidogenesis, membrane transport, immune response, cell signaling and adhesion. These results suggest an earlier onset of structural luteolysis in pigs caused by MXC actions in neonates. Since negative correlation analysis showed the potential interactions of miRNAs with specific messenger RNAs, we propose that these miRNAs are potential mediators of the long-term MXC effect on the CL function in pigs.

Programmed necrosis - a new mechanism of steroidogenic luteal cell death and elimination during luteolysis in cows

Programmed necrosis (necroptosis) is an alternative form of programmed cell death that is regulated by receptor-interacting protein kinase (RIPK) 1 and 3-dependent, but is a caspase (CASP)-independent pathway. In the present study, to determine if necroptosis participates in bovine structural luteolysis, we investigated RIPK1 and RIPK3 expression throughout the estrous cycle, during prostaglandin F2α (PGF)-induced luteolysis in the bovine corpus luteum (CL), and in cultured luteal steroidogenic cells (LSCs) after treatment with selected luteolytic factors. In addition, effects of a RIPK1 inhibitor (necrostatin-1, Nec-1; 50 μM) on cell viability, progesterone secretion, apoptosis related factors and RIPKs expression, were evaluated. Expression of RIPK1 and RIPK3 increased in the CL tissue during both spontaneous and PGF-induced luteolysis (P < 0.05). In cultured LSCs, tumor necrosis factor α (TNF; 2.3 nM) in combination with interferon γ (IFNG; 2.5 nM) up-regulated RIPK1 mRNA and protein expression (P < 0.05). TNF + IFNG also up-regulated RIPK3 mRNA expression (P < 0.05), but not RIPK3 protein. Although Nec-1 prevented TNF + IFNG-induced cell death (P < 0.05), it did not affect CASP3 and CASP8 expression. Nec-1 decreased both RIPK1 and RIPK3 protein expression (P < 0.05). These findings suggest that RIPKs-dependent necroptosis is a potent mechanism responsible for bovine structural luteolysis induced by pro-inflammatory cytokines.

Possible role of interferon tau on the bovine corpus luteum and neutrophils during the early pregnancy

When pregnancy is established, interferon tau (IFNT), a well-known pregnancy recognition signal in ruminants, is secreted by embryonic trophoblast cells and acts within the uterus to prepare for pregnancy. IFNT acts as an endocrine factor on the corpus luteum (CL) to induce refractory ability against the luteolytic action of PGF2α. Hypothesising that IFNT may influence not only the uterine environment but also the CL in cows via local or peripheral circulation, we investigated qualitative changes in the CL of pregnant cows during the maternal recognition period (day 16) and the CL of non-pregnant cows. The CL of pregnant animals had a higher number of neutrophils, and the expression of interleukin 8 (IL8) mRNA and its protein was higher as well as compared with the CL of non-pregnant animals. Although IFNT did not affect progesterone (P4) secretion and neutrophil migration directly, it stimulated IL8 mRNA expression on luteal cells (LCs), influencing the neutrophils, resulting in the increased migration of IFNT-activated neutrophils. Moreover, both IFNT-activated neutrophils and IL8 increased P4 secretion from LCs in vitro. Our novel finding was the increase in neutrophils and IL8 within the CL of pregnant cows, suggesting the involvement of IFNT function within the CL toward establishment of pregnancy in cows. The present results suggest that IFNT upregulates neutrophil numbers and function via IL8 on LCs in the CL of early pregnant cows and that both neutrophils and IL8, stimulated by IFNT, are associated with an increase in P4 concentrations during the maternal recognition period in cows.

Relationships among nitric oxide metabolites and pulses of a PGF2α metabolite during and after luteolysis in mares

Hourly circulating concentrations of a PGF2α metabolite (PGFM), progesterone (P4), and LH were obtained from a reported project, and concentrations of nitric oxide (NO) metabolites (NOMs; nitrates and nitrites) were determined in eight mares. Unlike the reported project, hormone concentrations were normalized to the peak of the first PGFM pulse of luteolysis (early luteolysis), second PGFM pulse (late luteolysis), and a pulse after luteolysis. The duration of luteolysis was 23.1 ± 1.0 hours, and the peak of the first and second PGFM pulses occurred 6.5 ± 0.9 and 14.8 ± 0.8 hours after the beginning of luteolysis. Concentration of P4 decreased progressively within and between the PGFM pulses Changes were not detected in LH concentration in association with the PGFM pulses. Concentration of NOMs was greater (P < 0.05) at the peak of the PGFM pulse during early luteolysis (88.8 ± 15.0 μg/mL) than during late luteolysis (58.8 ± 9.0 μg/mL). Concentration of NOMs began to decrease (P < 0.05) 4 hours before the peak of the PGFM pulse of early luteolysis. Concentration began to increase (P < 0.05) an hour after the peak of the PGFM pulse of late luteolysis. An NOM decrease and increase was not detected during the PGFM pulse after luteolysis. On a temporal basis, results indicated that NO either is not required for luteolysis in mares or has a role in or responds only during late luteolysis. A caveat is that the relative contribution of the CL versus other body tissues to circulating concentrations of NOMs in mares has not been determined.

Prostaglandin F2α induces expression of activating transcription factor 3 (ATF3) and activates MAPK signaling in the rat corpus luteum

The current study was conducted to evaluate the expression of ATF3, in association with the activation of mitogen-activated protein kinases (MAPK) during prostaglandin F2α analog (PGF)-induced luteal regression in rats. A sequential PMSG/hCG treatment paradigm was used to obtain a single, well-defined generation of corpora lutea (CL) in rats. Rats were treated with PGF for 0-4h on day 7 of pseudopregnancy. Results showed that serum progesterone (P4) concentrations declined in a time dependent manner. Western blot results revealed that ATF3 increased within 2h post-PGF injection. Phosphorylated ERK1/2 (p-ERK) and JNK (p-JNK) increased within 30min and then were gradually reduced in response to PGF. In contrast, the levels of phosphorylated p38 MAPK (p-p38) were not significantly altered. The immunostaining density for p-ERK decreased from the periphery to the center of the corpus luteum following treatment with PGF, while ATF3 was expressed uniformly in the nuclei of luteal steroidogenic cells. These results indicated that treatment with PGF in vivo could induce increases in MAPK phosphorylation, especially in p-ERK, which might be correlated with the increases in ATF3 expression and the decline in P4 concentrations. To our knowledge, this is the first study to provide evidence for temporal relationships between MAPK activation and ATF3 expression during PGF-induced luteal regression in the rat.

Circulating nitric oxide metabolites during luteolysis and the effect of luteinizing hormone on circulating nitric oxide metabolites in heifers

Temporal relationships among circulating concentrations of nitric oxide metabolites (NOM), progesterone (P4), and luteinizing hormone (LH) within the hours of a PGFM pulse were studied during luteolysis in heifers. The peak of a PGFM pulse was designated Hour 0. All of the following increases and decreases were significant. Within a spontaneous PGFM pulse (experiment 1; n = 7), concentrations of P4 and LH decreased between Hours -1 and 0 and increased between Hours 0 and 1; NOM increased between Hours -1 and 2. In experiment 2, PGFM pulses were simulated by intrauterine infusion of PGF2α (PGF group, n = 6), and another group was also treated with acyline to inhibit LH secretion (acyline-PGF group, n = 6). Averaged over the two groups, concentration of P4 decreased between Hours -2 and 0, increased (rebounded) between Hours 0 and 1, and decreased after Hour 2. In the PGF group, concentration of LH decreased between Hours -2 and -0.5 and increased between Hour 0 and Hour 1.5 to a maximum at Hour 1.5; NOM decreased between Hours -2 and -1.5 and increased between Hours 0 and 1.5. In the acyline-PGF group, the effect of hour was not significant for concentrations of LH and NOM. The absence of an increase in NOM concentration when LH was inhibited is a novel finding. The hypotheses were supported that concentrations of LH and NOM are temporally related, and LH has a role in the increase in NOM within the hours of a PGFM pulse.

Nitric oxide synthase activity is critical for the preovulatory epidermal growth factor-like cascade induced by luteinizing hormone in bovine granulosa cells

In rabbits and rodents, nitric oxide (NO) is generally considered to be critical for ovulation. In monovulatory species, however, the importance of NO has not been determined, nor is it clear where in the preovulatory cascade NO may act. The objectives of this study were (1) to determine if nitric oxide synthase (NOS) enzymes are regulated by luteinizing hormone (LH) and (2) to determine if and where endogenous NO is critical for expression of genes essential for the ovulatory cascade in bovine granulosa cells in serum-free culture. Time- and dose-response experiments demonstrated that LH had a significant stimulatory effect on endothelial NOS (NOS3) mRNA abundance, but in a prostaglandin-dependent manner. NO production was stimulated by LH before a detectable increase in NOS3 mRNA levels was observed. Pretreatment of cells with the NOS inhibitor L-NAME blocked the effect of LH on the epidermal growth factor (EGF)-like ligands epiregulin and amphiregulin, as well as prostaglandin-endoperoxide synthase-2 mRNA abundance and protein levels. Similarly, EGF treatment increased mRNA encoding epiregulin, amphiregulin, and the early response gene EGR1, and this was inhibited by pretreatment with L-NAME. Interestingly, pretreatment with L-NAME had no effect on either ERK1/2 or AKT activation. Taken together, these results suggest that endogenous NOS activity is critical for the LH-induced ovulatory cascade in granulosa cells of a monotocous species and acts downstream of EGF receptor activation but upstream of the EGF-like ligands.

Profiling of luteal transcriptome during prostaglandin F2-alpha treatment in buffalo cows: analysis of signaling pathways associated with luteolysis

In several species including the buffalo cow, prostaglandin (PG) F2α is the key molecule responsible for regression of corpus luteum (CL). Experiments were carried out to characterize gene expression changes in the CL tissue at various time points after administration of luteolytic dose of PGF2α in buffalo cows. Circulating progesterone levels decreased within 1 h of PGF2α treatment and evidence of apoptosis was demonstrable at 18 h post treatment. Microarray analysis indicated expression changes in several of immediate early genes and transcription factors within 3 h of treatment. Also, changes in expression of genes associated with cell to cell signaling, cytokine signaling, steroidogenesis, PG synthesis and apoptosis were observed. Analysis of various components of LH/CGR signaling in CL tissues indicated decreased LH/CGR protein expression, pCREB levels and PKA activity post PGF2α treatment. The novel finding of this study is the down regulation of CYP19A1 gene expression accompanied by decrease in expression of E2 receptors and circulating and intra luteal E2 post PGF2α treatment. Mining of microarray data revealed several differentially expressed E2 responsive genes. Since CYP19A1 gene expression is low in the bovine CL, mining of microarray data of PGF2α-treated macaques, the species with high luteal CYP19A1 expression, showed good correlation between differentially expressed E2 responsive genes between both the species. Taken together, the results of this study suggest that PGF2α interferes with luteotrophic signaling, impairs intra-luteal E2 levels and regulates various signaling pathways before the effects on structural luteolysis are manifest.

Evaluation of bovine luteal blood flow by using color Doppler ultrasonography

Since luteal vascularization plays a decisive role for the function of the corpus luteum (CL), the investigation of luteal blood flow (LBF) might give valuable information about the physiology and patho-physiology of the CL. To quantify LBF, usually Power mode color Doppler ultrasonography is used. This method detects the number of red blood cells moving through the vessels and shows them as color pixels on the B-mode image of the CL. The area of color pixels is measured with computer-assisted image analysis software and is used as a semiquantitative parameter for the assessment of LBF. Although Power mode is superior for the evaluation of LBF compared to conventional color Doppler ultrasonography, which detects the velocity of blood cells, it is still not sufficiently sensitive to detect the blood flow in the small vessels in the center of the bovine CL. Therefore, blood flow can only be measured in the bigger luteal vessels in the outer edge of the CL. Color Doppler ultrasonographic studies of the bovine estrous cycle have shown that plasma progesterone (P4) concentration can be more reliably predicted by LBF than by luteal size (LS), especially during the CL regression. During the midluteal phase, cows with low P4 level showed smaller CL, but LBF, related to LS, did not differ between cows with low and high P4 levels. In contrast to non-pregnant cows, a significant rise in LBF was observed three weeks after insemination in pregnant cows. However, LBF was not useful for an early pregnancy diagnosis due to high LBF variation among cows. When the effects of an acute systemic inflammation and exogenous hormones on the CL are examined, the LBF determination is more sensitive than LS assessment. In conclusion, color Doppler ultrasonography of the bovine CL provides additional information on luteal function compared to measurements of LS and plasma P4, but its value as a parameter concerning assessment of fertility in cows has to be clarified.

Diverse roles of prostaglandins in blastocyst implantation

Prostaglandins (PGs), derivatives of arachidonic acid, play an indispensable role in embryo implantation. PGs have been reported to participate in the increase in vascular permeability, stromal decidualization, blastocyst growth and development, leukocyte recruitment, embryo transport, trophoblast invasion, and extracellular matrix remodeling during implantation. Deranged PGs syntheses and actions will result in implantation failure. This review summarizes up-to-date literatures on the role of PGs in blastocyst implantation which could provide a broad perspective to guide further research in this field.

Downregulation of lymphatic vessel formation factors in PGF2α-induced luteolysis in the cow

Prostaglandin F2α (PGF2α) induces luteolysis in cows and causes infiltration of immune cells, which resembles inflammatory immune response. Since the general immune response is mediated by the lymphatic system, we hypothesized that luteolysis is associated with generation of an immune response that involves lymphatic vessels in the bovine corpus luteum (CL). The CL was obtained from Holstein cows at the mid-luteal phase (days 10-12, ovulation = day 0) by ovariectomy at various time points after PGF2α injection. Lymphatic endothelial cell (LyEC) marker, endothelial hyaluronan receptor 1 (LYVE1), levels decreased significantly 12 h after PGF2α injection. Podoplanin, another LyEC marker, decreased from 15 min after PGF2α injection. PGF2α also diminished mRNA expression of lymphangiogenic factors, such as vascular endothelial growth factor (VEGF) C, VEGFD and VEGF receptor 3 (VEGFR3). During PGF2α-induced luteolysis, the levels of mRNA expression of tumor necrosis factor α (TNFα; the major pro-inflammatory cytokine) and chemokine (C-X-C motif) ligand 1 (neutrophil chemokine) were increased. On the other hand, chemokine (C-C motif) ligand 21, which regulates outflow of immune cells from tissues via the lymphatic vessels during an immune response, was decreased. This study demonstrated that the lymphatic network in the CL is disrupted during luteolysis and suggests that during luteolysis, immune cells can induce a local immune response in the CL without using the lymphatic vessels.

Expression of prostaglandin F2α (PGF2α) receptor and its isoforms in the bovine corpus luteum during the estrous cycle and PGF2α-induced luteolysis

Prostaglandin F2α (PGF2α) induces luteolysis via a specific receptor, PTGFR. Although PTGFR mRNA expression in the bovine corpus luteum (CL) has been studied previously, changes in PTGFR protein and its localization are not fully understood during the life span of the CL. In addition to full-length PTGFR, several types of PTGFR isoforms, such as PTGFRα (type I) and PTGFRζ (type II), were reported in the bovine CL, suggesting isoform-specific luteal action. Full-length PTGFR mRNA in the bovine CL increased from the early to the mid-luteal phase and decreased during luteolysis, whereas PTGFR protein remained stable. PTGFR protein was localized to both luteal and endothelial cells and was expressed similarly during the life span of the CL. Like full-length PTGFR mRNA, PTGFRα and PTGFRζ mRNA also increased from the early to mid-luteal phases, and mRNA of PTGFRζ, but not PTGFRα, decreased in the regressing CL. During PGF2α-induced luteolysis, the mRNAs of full-length PTGFR, PTGFR,α and PTGFRζ decreased rapidly (from 5 or 15 min after PGF2α injection), but PTGFR protein decreased only 12 h later. Silencing full-length PTGFR using small interfering RNA prevented PGF2α-stimulated cyclooxygenase-2 (PTGS2) mRNA induction. By contrast, PGF2α could stimulate vascular endothelial growth factor A (VEGFA) mRNA even when full-length PTGFR was knocked down, thus suggesting that PGF2α may stimulate PTGS2 via full-length PTGFR, whereas VEGFA is stimulated via other PTGFR isoforms. Collectively, PTGFR protein was expressed continually in the bovine CL during the estrous cycle, implying that PGF2α could function throughout this period. Additionally, the bovine CL expresses different PTGFR isoforms, and thus PGF2α may have different effects when acting via full-length PTGFR or via PTGFR isoforms.

Placental expression and localization of endothelin-1 system and nitric oxide synthases during bovine pregnancy

This study aimed to investigate mRNA expression of the endothelin-1 (EDN1) system (preproEDN1; precursor, ECE-1; converting enzyme, EDNRA and EDNRB; receptor subtypes A and B) and endothelial and inducible nitric oxide synthases (eNOS and iNOS) in the bovine utero-placental unit during pregnancy. We also investigated the cellular localization of mRNA and protein of components of the EDN1 system in the placentome. The bovine utero-placental unit on Day 60, 100, 150, 200 and 250 of gestation was separated into carunclar areas (CAR), intercaruncular areas (ICAR), cotyledonary villi (COT) and intercotyledonary areas (ICOT). PreproEDN1, ECE1, EDNRA, EDNRB, eNOS and iNOS mRNA expression was determined by real-time quantitative RT-PCR. In situ hybridization and immunohistochemistry were performed using placentomes on Day 94 or Day 250 of gestation. PreproEDN1 and ECE1 mRNA expression was higher on Day 100 than on other gestation days. The mRNA expression for EDNRA in COT and ICOT and eNOS in COT, CAR and ICAR were higher on Day 150 than on other gestation days. EDNRB mRNA expression increased from Day 60 to Day 150 then decreased. iNOS mRNA expression in COT and CAR was higher on Day 250 than on other gestation days. PreproEDN1, ECE1 and EDNRA mRNA was localized in the caruncular epithelial cells (CEs) and the COT. EDNRB mRNA was found in the CEs and the trophoblast binucleate giant cells (BNCs). PreproEDN1, EDNRA and EDNRB proteins were detected in COT and CEs, whereas ECE-1 was found in the BNCs. Our results demonstrate that differential cell-specific and spatiotemporal expression of the EDN1 system and NOS in the bovine utero-placental unit may be associated with regulation of vascular and cellular functions during pregnancy.

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.

Dynamics of circulating progesterone concentrations before and during luteolysis: a comparison between cattle and horses

The profile of circulating progesterone concentration is more dynamic in cattle than in horses. Greater prominence of progesterone fluctuations in cattle than in horses reflect periodic interplay in cattle between pulses of a luteotropin (luteinizing hormone; LH) and pulses of a luteolysin (prostaglandin F2alpha; PGF2alpha). A dose of PGF2alpha that induces complete regression of a mature corpus luteum with a single treatment in cattle or horses is an overdose. The overdose effects on the progesterone profile in cattle are an immediate nonphysiological increase taking place over about 30 min, a decrease to below the original concentration, a dose-dependent rebound 2 h after treatment, and a progressive decrease until the end of luteolysis. An overdose of PGF2alpha in horses results in a similar nonphysiological increase in progesterone followed by complete luteolysis; a rebound does not occur. An overdose of PGF2alpha and apparent lack of awareness of the rebound phenomenon has led to faulty interpretations on the nature of spontaneous luteolysis. A transient progesterone suppression and a transient rebound occur within the hours of a natural PGF2alpha pulse in cattle but not in horses. Progesterone rebounds are from the combined effects of an LH pulse and the descending portion of a PGF2alpha pulse. A complete transitional progesterone rebound occurs at the end of preluteolysis and the beginning of luteolysis and returns progesterone to its original concentration. It is proposed that luteolysis does not begin in cattle until after the transitional rebound. During luteolysis, rebounds are incomplete and gradually wane. A partial rebound during luteolysis in cattle is associated with a concomitant increase in luteal blood flow. A similar increase in luteal blood flow does not occur in mares.

Cyclooxygenase-2 prostaglandins mediate anandamide-inhibitory action on nitric oxide synthase activity in the receptive rat uterus

Anandamide, an endocannabinoid, prostaglandins derived from cyclooxygenase-2 and nitric oxide synthesized by nitric oxide synthase (NOS), are relevant mediators of embryo implantation. We adopted a pharmacological approach to investigate if anandamide modulated NOS activity in the receptive rat uterus and if prostaglandins mediated this effect. As we were interested in studying the changes that occur at the maternal side of the fetal-maternal interface, we worked with uteri obtained from pseudopregnant rats. Females were sacrificed on day 5 of pseudopregnancy, the day in which implantation would occur, and the uterus was obtained. Anandamide (2 ng/kg, i.p.) inhibited NOS activity (P<0.001) and increased the levels of prostaglandin E(2) (P<0.001) and prostaglandin F(2α) (P<0.01). These effects were mediated via cannabinoid receptor type 2, as the pre-treatment with SR144528 (10 mg/kg, i.p.), a selective cannabinoid receptor type 2 antagonist, completely reverted anandamide effect on NOS activity and prostaglandin levels. The pre-treatment with a non-selective cyclooxygenase inhibitor (indomethacin 2.5mg/kg, i.p.) or with selective cyclooxygenase-2 inhibitors (meloxicam 4 mg/kg, celecoxib 3mg/kg, i.p.) reverted anandamide inhibition on NOS, suggesting that prostaglandins are derived from cyclooxygenase-2 mediated anandamide effect. Thus, anandamide levels seemed to modulate NOS activity, fundamental for implantation, via cannabinoid receptor type 2 receptors, in the receptive uterus. This modulation depends on the production of cyclooxygenase-2 derivatives. These data establish cannabinoid receptors and cyclooxygenase enzymes as an interesting target for the treatment of implantation deficiencies.

Rapid accumulation of polymorphonuclear neutrophils in the Corpus luteum during prostaglandin F(2α)-induced luteolysis in the cow

Prostaglandin F_2α (PGF_2α) induces luteolysis within a few days in cows, and immune cells increase in number in the regressing corpus luteum (CL), implying that luteolysis is an inflammatory-like immune response. We investigated the rapid change in polymorphonuclear neutrophil (PMN) numbers in response to PGF_2α administration as the first cells recruited to inflammatory sites, together with mRNA of interleukin-8 (IL-8: neutrophil chemoattractant) and P-selectin (leukocyte adhesion molecule) in the bovine CL. CLs were collected by ovariectomy at various times after PGF_2α injection. The number of PMNs was increased at 5 min after PGF_2α administration, whereas IL-8 and P-selectin mRNA increased at 30 min and 2 h, respectively. PGF_2α directly stimulated P-selectin protein expression at 5–30 min in luteal endothelial cells (LECs). Moreover, PGF_2α enhanced PMN adhesion to LECs, and this enhancement by PGF_2α was inhibited by anti-P-selectin antibody, suggesting that P-selectin expression by PGF_2α is crucial in PMN migration. In conclusion, PGF_2α rapidly induces the accumulation of PMNs into the bovine CL at 5 min and enhances PMN adhesion via P-selectin expression in LECs. It is suggested that luteolytic cascade by PGF_2α may involve an acute inflammatory-like response due to rapidly infiltrated PMNs.

Possible involvement of IFNT in lymphangiogenesis in the corpus luteum during the maternal recognition period in the cow

The corpus luteum (CL), which secretes large amounts of progesterone and is thus essential for establishing pregnancy, contains various types of immune cells that may play essential roles in CL function by generating immune responses. The lymphatic system is the second circulation system and is necessary for immune function, but the lymphatic system of the bovine CL has not been characterized in detail. We collected bovine CLs on days 12 and 16 of the estrous cycle (C12 and C16) and days 16 and 40 of early pregnancy (P16 and P40). Lymphatic endothelial hyaluronan receptor 1 (LYVE1) protein was detected in the CL by immunohistochemistry and western blotting and increased at P40 compared with C16. The mRNA expression levels of lymphangiogenic factors, such as vascular endothelial growth factor-C (VEGFC), VEGFD, and their common receptor VEGFR3, as well as the lymphatic endothelial cell (LyEC) marker podoplanin, increased in P16 and P40 CLs. Thus, it is suggested that the lymphatic system of the bovine CL reconstitutes during early pregnancy. Interferon tau (IFNT) from the conceptus in the uterus is a candidate for activating luteal lymphangiogenesis during the maternal recognition period (MRP). We found that treatment of LyECs isolated from internal iliac lymphatic vessels with IFNT stimulated LyEC proliferation and significantly increased mRNA expression of VEGFC and IFN-stimulated gene 15. Moreover, both IFNT and VEGFC induced LyECs to form capillary-like tubes in vitro. In conclusion, it is suggested that new lymphangiogenesis in the bovine CL begins during the MRP and that IFNT may mediate this novel phenomenon.

Effect of dose of estradiol-17β on prominence of an induced 13,14-dihydro-15-keto-PGF(2α) (PGFM) pulse and relationship of prominence to progesterone, LH, and luteal blood flow in heifers

Various doses of estradiol-17β (E(2)) were used in heifers to induce a pulse of 13,14-dihydro-15-keto-prostaglandin F(2α) (PGFM). The effect of E(2) concentration on the prominence of PGFM pulses and the relationship between prominence and intrapulse concentration of progesterone (P(4)), LH, and luteal blood flow were studied. A single dose of 0 (vehicle), 0.01, 0.05, or 0.1 mg of E(2) was given (n = six/group) 14 d after ovulation. Blood samples were collected, and luteal blood flow was evaluated hourly for 10 h after the treatment. The 0.05-mg dose increased and the 0.1-mg dose further increased the prominence of the induced PGFM pulse, compared with the 0.0-mg dose and the 0.01-mg dose. The PGFM pulses were subdivided into three different prominence categories (<50, 50 to 150, and >150 pg/mL at the peak). In the 50 to 150 category, P(4) concentration increased (P < 0.05) between -2 h and 0 h (0 h = peak of PGFM pulse). In the >150 category, P(4) decreased (P < 0.05) between -1 h and 0 h, LH increased (P < 0.05) at 1 h, and luteal blood flow apparently decreased (P < 0.05) at 2 h of the PGFM pulse. The novel results supported the following hypotheses: (1) an increase in E(2) concentration increases the prominence of a PGFM pulse, and (2) greater prominence of a PGFM pulse is associated with a greater transient intrapulse depression of P(4) at the peak of the PGFM pulse. In addition, the extent of the effect of prostaglandin F(2α) on the increase in LH and changes in blood flow within the hours of a PGFM pulse was related positively to the prominence of the PGFM pulse.

Nitric oxide stimulates progesterone and prostaglandin E2 secretion as well as angiogenic activity in the equine corpus luteum

Cytokines and nitric oxide (NO) are potential mediators of luteal development and maintenance, angiogenesis, and blood flow. The aim of this study was to evaluate (i) the localization and protein expression of endothelial and inducible nitric oxide synthases (eNOS and iNOS) in equine corpora lutea (CL) throughout the luteal phase and (ii) the effect of a nitric oxide donor (spermine NONOate, NONOate) on the production of progesterone (P4) and prostaglandin (PG) E(2) and factor(s) that stimulate endothelial cell proliferation using equine luteal explants. Luteal tissue was classified as corpora hemorrhagica (CH; n = 5), midluteal phase CL (mid-CL; n = 5) or late luteal phase CL (late CL; n = 5). Both eNOS and iNOS were localized in large luteal cells and endothelial cells throughout the luteal phase. The expression of eNOS was the lowest in mid-CL (P < 0.05) and the highest in late CL (P < 0.05). However, no change was found for iNOS expression. Luteal explants were cultured with no hormone added or with NONOate (10(-5) M), tumor necrosis factor-α (TNFα; 10 ng/mL; positive control), or equine LH (100 ng/mL; positive control). Conditioned media by luteal tissues were assayed for P4 and PGE(2) and for their ability to stimulate proliferation of bovine aortic endothelial cells (BAEC). All treatments stimulated release of P4 in CH, but not in mid-CL. TNFα and NONOate treatments also increased PGE(2) levels and BAEC proliferation in CH (P < 0.05). However, in mid-CL, no changes were observed, regardless of the treatments used. These data suggest that NO and TNFα stimulate equine CH secretory functions and the production of angiogenic factor(s). Furthermore, in mares, NO may play a role in CL growth during early luteal development, when vascular development is more intense.

Prostaglandin F2α (PGF2α) stimulates PTGS2 expression and PGF2α synthesis through NFKB activation via reactive oxygen species in the corpus luteum of pseudopregnant rats

This study was undertaken to investigate how prostaglandin F2α (PGF2α) increases PGF2α synthesis and PTGS2 expression in the corpus luteum of pseudopregnant rats. We further investigated the molecular mechanism by which PGF2α stimulates PTGS2 expression. PGF2α (3 mg/kg) or phosphate buffer as a control was injected s.c. on day 7 of pseudopregnancy. Ptgs2 mRNA expression and PGF2α concentrations in the corpus luteum were measured at 2, 6, and 24 h after PGF2α injection. PGF2α significantly increased Ptgs2 mRNA expression at 2 h and luteal PGF2α concentrations at 24 h. PGF2α significantly decreased serum progesterone levels at all of the times studied. Simultaneous administration of a selective PTGS2 inhibitor (NS-398, 10 mg/kg) completely abolished the increase in luteal PGF2α concentrations induced by PGF2α. PGF2α increased NFKB p65 protein expression in the nucleus of luteal cells 30 min after PGF2α injection, and electrophoretic mobility shift assay revealed that PGF2α increased binding activities of NFKB to the NFKB consensus sequence of the Ptgs2 gene promoter. Simultaneous administration of both superoxide dismutase and catalase to scavenge reactive oxygen species (ROS) inhibited the increases of nuclear NFKB p65 protein expression, lipid peroxide levels, and Ptgs2 mRNA expression induced by PGF2α. In conclusion, PGF2α stimulates Ptgs2 mRNA expression and PGF2α synthesis through NFKB activation via ROS in the corpus luteum of pseudopregnant rats.

Luteal blood flow and concentrations of circulating progesterone and other hormones associated with a simulated pulse of 13,14-dihydro-15-keto-prostaglandin F2α in heifers

Progesterone and luteal blood flow effects of an i.u. 2-h infusion of 0.25 mg/h of prostaglandin F2α (PGF) that simulated a natural pulse of 13,14-dihydro-15-keto-PGF (PGFM) were compared to the effects of a single bolus i.u. injection of PGF (4 mg) that induced complete luteolysis in heifers. Blood sampling and an estimate of the percentage of luteal area with colour-Doppler signals of blood flow were performed every 2 min for 20 min and less frequently thereafter for 6 h. After the beginning of PGF infusion or a bolus injection, progesterone increased to a peak at 14 and 10 min respectively, and was accompanied by an increase in blood flow in the bolus group but not in the infusion group. Progesterone then decreased for 1 or 2 h and was accompanied by a continued elevation in blood flow in the PGF bolus group and by a slight increase in the PGF infusion group. Progesterone then rebounded in both groups, but the rebound was greater in the infusion group. Blood flow decreased during the descending arm of the progesterone rebound. Cortisol and prolactin began to increase 6 min after the bolus PGF injection but did not increase during or after PGF infusion. The increases in cortisol, prolactin and blood flow after a PGF bolus treatment but not during a simulated PGFM pulse indicated that the bolus treatment was pharmacologic, and its use may lead to faulty conclusions on the nature of physiologic luteolysis. The comparisons between progesterone and blood flow are novel.

Effect of prostaglandin F2 alpha on local luteotropic and angiogenic factors during induced functional luteolysis in the bovine corpus luteum

The essential role of endometrial prostaglandin F2 alpha (PTGF) for induction of the corpus luteum (CL) regression is well documented in the cow. However, the acute effects of PTGF on known local luteotropic factors (oxytocin [OXT] and its receptor, insulin-like growth factor [IGF] 1, and progesterone and its receptor), the principal angiogenic factor vascular endothelial growth factor (VEGF) A and the capillary destabilization factor angiopoietin (ANGPT) 2 were not thoroughly studied in detail. The aim of this study was therefore to evaluate the tissue concentration of these factors during PTGF induced luteolysis. In addition the mRNA expression of progesterone receptor (PGR), OXT receptor (OXTR), IGF1, IGFBP1, ANGPT1, and ANGPT2 was determined at different times after PTGF treatment. Cows (n = 5 per group) in the mid-luteal phase (Days 8-12, control group) were injected with the PTGF analog (cloprostenol), and CL were collected by transvaginal ovariectomy at 0.5, 2, 4, 12, 24, 48, and 64 h after injection. The mRNA expression was analyzed by quantitative real-time PCR, and the protein concentration was evaluated by enzyme immunoassay or radioimmunoassay. Progesterone concentrations, as well as mRNA expression of PGR, in CL tissue were significantly down-regulated by 12 h after PTGF. Tissue OXT peptide and OXTR mRNA decreased significantly after 2 h, followed by a continuous decrease of OXT mRNA. IGF1 and VEGFA protein already decreased after 0.5 h. By contrast, the IGFBP1 mRNA was up-regulated significantly after 2 h to a high plateau. ANGPT2 protein and mRNA significantly increased during the first 2 h, followed by a steep decrease after 4 h. The acute decrease of local luteotropic activity and acute changes of ANGPT2 and VEGFA suggest that modulation of vascular stability may be a key component in the cascade of events leading to functional luteolysis.

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

The corpus luteum (CL) of the estrous cycle in the cow is a dynamic organ which has a life time of approximately 17-18 days. The main function of the CL is to secrete a large amount of progesterone (P) thereby supporting the achievement of pregnancy. As the CL matures, the steroidogenic cells establish contact with many capillaries and the matured CL is composed of many vascular endothelial cells that account for up to 50% of all CL cells. The bovine CL produces several major angiogenic and vasoactive foctors such as vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), angiopoietin-1 and -2 (ANPT-1 and -2), prostaglandin F(2alpha) (PGF(2alpha)), endothelin-1 (EDN1), angiotensin II (Ang II) and nitric oxide (NO). These factors regulate P secretion directly and/or indirectly within the CL. Moreover, different actions of PGF(2alpha) in the early cycle CL (non-luteolytic) and the mid cycle CL (luteolytic) may provide insight into the luteolysis cascade in the cow. The aim of the present review is to describe the current concepts of the local mechanisms for the cascade of development and regression of the bovine CL as regulated by luteal angiogenic and vasoactive factors.

Effects of human chorionic gonadotropin on luteal blood flow and progesterone secretion in cows and in vitro-microdialyzed corpora lutea

To check human chorionic gonadotropin (hCG) effects on luteal blood flow (LBF) and progesterone (P(4)) synthesis, six cows received either 3000 IU hCG or saline (NaCl) on Day 7 (Day 1=ovulation) during two estrous cycles. Plasma P(4) and LBF were measured before (0h) and up to 48h after treatment. Luteal blood flow increased by 51% (P<0.05) at 1h after hCG administration and returned to baseline levels thereafter. Plasma P(4) levels were increased from pretreatment levels by 30% at 1h (P=0.05) and 81% at 48h (P=0.02) after hCG treatment. In contrast, NaCl did not cause changes in LBF and P(4) (P>0.05). Additionally, central and peripheral parts of 14 abattoir-derived corpora lutea of the mid-luteal phase (Day 8 to 12) were perfused with Ringer solution in an in vitro microdialysis system, supplemented with 50 or 150 IU/mL hCG for 1h. Application of 50 IU/mL hCG showed no influence on P(4) response (P>0.05) in both central and peripheral parts, whereas 150 IU/mL hCG resulted in an increase of P(4) synthesis (P=0.002) in the central parts only. In vivo, hCG provoked an immediate and long-term rise in P(4) but only a temporary elevation of LBF. Luteal blood flow itself does not seem to be the exclusive cause for an increase in P(4), because the in vitro data clearly showed direct effects of hCG on P(4) secretion. Interestingly, different P(4) secretion patterns could be found between central and peripheral parts of the corpus luteum in both control and hCG perfused corpora lutea.

Prostaglandin F(2alpha) regulates the nitric oxide generating system in bovine luteal endothelial cells

The objective of the present study was to elucidate whether luteolytic prostaglandin F(2alpha) (PGF) plays roles in regulating the nitric oxide (NO) generating system in luteal endothelial cells (LECs). Reverse transcriptase PCR, immunoblotting and immunostaining revealed the presence of PGF receptor mRNA (521 bp) and protein (64 kDa) in cultured LECs obtained from the mid-stage corpus luteum. When cultured LECs were exposed to 0.1 microM-10 microM PGF, NO production was significantly stimulated by PGF at 24 h. When LECs were exposed to 1 microM PGF for 2, 6 and 24 h, PGF did not affect the expressions of endothelial NO synthase (eNOS) mRNA and protein. On the other hand, PGF stimulated the expression of inducible NOS (iNOS) mRNA (P<0.05) and protein (P<0.05) at 2 h, but not at 6 and 24 h. By observing the conversion of [(3)C](L)-arginine to [(3)C](L)-citrulline, we found that PGF stimulated NOS activity in cultured LECs at 2 h (P<0.05). The overall findings indicate that bovine LECs are a target for PGF and that PGF stimulates iNOS expression and NOS activity in bovine LECs. Stimulation of the NO generating system and NOS activity by PGF may result in increasing local NO production followed by luteolysis.