Intraluteal regulation of prostaglandin F2α-induced prostaglandin biosynthesis in pseudopregnant rabbits

The Effects of Prostaglandin E2 Treatment on the Secretory Function of Mare Corpus Luteum Depends on the Site of Application: An in vivo Study

We examined the effect of prostaglandin (PG) E₂ on the secretory function of equine corpus luteum (CL), according to the application site: intra-CL injection vs. an intrauterine (intra-U) administration. Moreover, the effect of intra-CL injection vs. intra-U administration of both luteotropic factors: PGE₂ and human chorionic gonadotropin (hCG) as a positive control, on CL function was additionally compared. Mares were assigned to the groups (n = 6 per group): (1) an intra-CL saline injection (control); (2) an intra-CL injection of PGE₂ (5 mg/ml); (3) an intra-CL injection of hCG (1,500 IU/ml); (4) an intra-U saline administration (control); (5) an intra-U administration of PGE₂ (5 mg/5 ml); (6) an intra-U administration of hCG (1,500 IU/5 ml). Progesterone (P₄) and PGE₂ concentrations were measured in blood plasma samples collected at −2, −1, and 0 (pre-treatment), and at 1, 2, 3, 4, 6, 8, 10, 12, and 24 h after treatments. Moreover, effects of different doses of PGE₂ application on the concentration of total PGF_2α (PGF_2α and its main metabolite 13,14-dihydro-15-keto-prostaglandin F_2α– PGFM) was determined. The time point of PGE₂, hCG, or saline administration was defined as hour “0” of the experiment. An intra-CL injection of PGE₂ increased P₄ and PGE₂ concentrations between 3 and 4 h or at 3 and 12 h, respectively (p < 0.05). While intra-U administration of PGE₂ elevated P₄ concentrations between 8 and 24 h, PGE₂ was upregulated at 1 h and between 3 and 4 h (p < 0.05). An intra-CL injection of hCG increased P₄ concentrations at 1, 6, and 12 h (p < 0.05), while its intra-U administration enhanced P₄ and PGE₂ concentrations between 1 and 12 h or at 3 h and between 6 and 10 h, respectively (p < 0.05). An application of PGE₂, dependently on the dose, supports equine CL function, regardless of the application site, consequently leading to differences in both P₄ and PGE₂ concentrations in blood plasma.

Effects of Dietary Polyphenols from Olive Mill Waste Waters on Inflammatory and Apoptotic Effectors in Rabbit Ovary

The aim of this study was to evaluate the effect of dietary polyphenols on the expression of the effectors involved in inflammation and apoptosis in rabbit ovary. New Zealand White female rabbits were fed a basal control diet (CTR), or the same diet supplemented with a polyphenolic concentrate (POL, 282.4 mg/kg) obtained from olive mill waste waters. The follicle counts and the relative mRNA (RT-qPCR) and protein (immunohistochemistry) expression of the effectors involved in inflammation (cyclooxygenase-2; interleukin-1beta; tumor necrosis factor-alpha, TNFA) and apoptosis (BCL2-associated X protein, BAX), detected in the ovaries of both groups, were examined. The POL diet increased the primary and total follicles number. Cyclooxygenase-2 gene expression was higher (p < 0.05) in the POL group than in the CTR group, whereas BAX was lower (p < 0.05) in POL than CTR. Immunohistochemistry revealed the presence of all the proteins examined, with weaker (p < 0.05) COX2 and BAX signals in POL. No differences between the CTR and POL groups were observed for IL1B and TNFA gene and protein expression. These preliminary findings show that dietary polyphenols modulate inflammatory and apoptotic activities in rabbit ovary, regulating cyclooxygenase-2 and BAX expression, thus suggesting a functional involvement of these dietary compounds in mammalian reproduction.

Cloprostenol, a synthetic analog of prostaglandin F2α induces functional regression in cultured luteal cells of felids†

In the present study, we investigated the effect of the synthetic analog of prostaglandin F2α (PGF2α)-cloprostenol-on cultured steroidogenic luteal cells of selected felid species over a 2-day culture period. The changes induced by cloprostenol were measured based on progesterone concentration and mRNA expression analysis of selected genes. Cloprostenol significantly reduced concentration of progesterone in cell culture medium of small luteal cells isolated from domestic cat corpora lutea (CL) at the development/maintenance stage (P < 0.05), but did not influence progesterone production in cultured cells from the regression stage. A decrease or complete silencing of progesterone production was also measured in cultured luteal cells of African lion (formation stage) and Javan leopard (development/maintenance stage). Gene-expression analysis by real-time PCR revealed that treatment with cloprostenol did not have an influence on expression of selected genes coding for enzymes of steroidogenesis (StAR, HSD3B, CYP11A1) or prostaglandin synthesis (PTGS2, PGES), nor did it effect hormone receptors (AR, ESR1, PGR, PTGER2), an anti-oxidative enzyme (SOD1) or factors of cell apoptosis (FAS, CASP3, TNFRSF1B, BCL2) over the studied period. Significant changes were measured only for expressions of luteinizing hormone (P < 0.05), prolactin (P < 0.05) and PGF2α receptors (P < 0.005) (LHCGR, PRLR, and PTGFR). The obtained results confirm that PGF2α/cloprostenol is a luteolytic agent in CL of felids and its impact on progesterone production depends on the developmental stage of the CL. Cloprostenol short-term treatment on luteal cells was associated only with functional but not structural changes related to luteal regression.

Current Knowledge on the Multifactorial Regulation of Corpora Lutea Lifespan: The Rabbit Model

Simple Summary

Corpora lutea (CL) are temporary endocrine structures that secrete progesterone, which is essential for maintaining a healthy pregnancy. A variety of regulatory factors come into play in modulating the functional lifespan of CL, with luteotropic and luteolytic effects. Many aspects of luteal phase physiology have been clarified, yet many others have not yet been determined, including the molecular and/or cellular mechanisms that maintain the CL from the beginning of luteolysis during early CL development. This paper summarizes our current knowledge of the endocrine and cellular mechanisms involved in multifactorial CL lifespan regulation, using the pseudopregnant rabbit model.

Abstract

Our research group studied the biological regulatory mechanisms of the corpora lutea (CL), paying particular attention to the pseudopregnant rabbit model, which has the advantage that the relative luteal age following ovulation is induced by the gonadotrophin-releasing hormone (GnRH). CL are temporary endocrine structures that secrete progesterone, which is essential for maintaining a healthy pregnancy. It is now clear that, besides the classical regulatory mechanism exerted by prostaglandin E2 (luteotropic) and prostaglandin F2α (luteolytic), a considerable number of other effectors assist in the regulation of CL. The aim of this paper is to summarize our current knowledge of the multifactorial mechanisms regulating CL lifespan in rabbits. Given the essential role of CL in reproductive success, a deeper understanding of the regulatory mechanisms will provide us with valuable insights on various reproductive issues that hinder fertility in this and other mammalian species, allowing to overcome the challenges for new and more efficient breeding strategies.

Immunohistochemical localization of progesterone receptors alpha (PRA) in ovary of the pseudopregnant rabbit

Progesterone plays an important role in the reproductive function and follicular development in mammals. The aim of the present study was to examine the localization of progesterone receptor alpha (PRA) in ovary of pseudopregnant rabbit by immunohistochemical methods. Samples were collected from 14 h. to 18 days of pseudopregnancy. At the first stage of pseudopregnancy (14 h.), the rabbit ovary showed moderate immunostaining of PRA in the granulosa cells and theca interna cells of preovulatory follicle and in the stroma cells. At the middle stage of pseudopregnancy (3-7 days), the rabbit ovary showed strong immunostaining of PRA in ovarian surface epithelial cells, follicular cells of the primary follicle, granulosa cells and theca interna cells of the growing and antral follicles. Moderate immunoexpression of PRA were observed in the large lutein cells and endothelial cells of the corpus haemorrhagicum and corpus luteum and in the stroma cells. At the end of pseudopregnancy (18 days) strong PRA reactions were detected in the small lutein cells of the regressed corpus luteum. Moderate to strong PRA immuno-expression were observed in the proliferated theca interna cells of the atretic antral follicles. The atretic large lutein cells of the regressed corpus luteum showed negative immunostaining for PRA. This study showed that the PRA positive small lutein cells of the regressed corpus luteum and the PRA positive proliferated theca interna cells of the atretic antral follicles were transformed into PRA positive interstitial gland cells. In conclusion, the present study had described the distribution of PRA in the ovary of pseudopregnant rabbit, which is not discussed before in the available literature. It also gives more information about follicular dynamic, formation and origin of interstitial glands, mechanism of ovulation, formation and regression of the corpus luteum.

Kisspeptin/kisspeptin receptor system in pseudopregnant rabbit corpora lutea: presence and function

Kisspeptin (KiSS) and its related receptors (KiSS1R) have a critical role in the reproduction of mammals. The KiSS/KiSS1R system is expressed in numerous reproductive organs including the ovary. Here, we studied the expression of the KiSS/KiSS1R system and its functional role in rabbit corpora lutea (CL) at days 4 (early-), 9 (mid-), and 13 (late-stage) of pseudopregnancy. In vitro progesterone, prostaglandin (PG) F2α (PGF2α) and E2 (PGE2) productions and prostaglandin-endoperoxide synthase 1 (PTGS1) and 2 (PTGS2) activities were evaluated. Immune reactivity (IR) for KiSS and KiSS1R were detected in luteal cells at nuclear and cytoplasmic level at all luteal stage for KiSS and only at early- and mid-stage for KiSS1R; IR decreased from early- to later stages of pseudopregnancy. The KiSS-10 augmented progesterone and PGE2 and diminished PGF2α secretions by early- and mid-CL; KiSS-10 reduced PTGS2 activity at early- and mid-stages, but did not affect PTGS1 at any luteal stages. The antagonist KiSS-234 counteracted all KiSS-10 effects. This study shows that the KiSS/KiSS1R system is expressed in CL of pseudopregnant rabbits and exerts a luteotropic action by down-regulating PTGS2, which decreases PGF2α and increases PGE2 and progesterone.

Intra-ovarian dynamic blood flow in pseudopregnant rabbits during prostaglandin F2α-induced luteolysis

In the present study, we evaluated the dynamic changes of intra-ovarian blood flow, by real-time colour-coded and pulsed Doppler ultrasonography, as well as the immunopresence of prostaglandin F2α (PGF2α) receptor (FP) and peripheral plasma progesterone concentrations in pseudopregnant rabbit after PGF2α treatments at either early- (4 days) and mid-luteal (9 days) stages. During the pre-treatment observation interval of one hour, the ovarian blood flows showed a fluctuating pattern. Independently of luteal stage, PGF2α administration caused a fourfold decline in the blood flow within 40 min that was followed 50 min later by a reactive hyperaemia that lasted several hours, while the resistive index showed an opposite trend. Twenty-four hour later, the blood flow was one half that measured before PGF2α injection. At day 4 of pseudopregnancy, PGF2α did not affect peripheral plasma progesterone concentrations, but at day 9, it caused functional luteolysis as progesterone levels declined 6 hr later to reach basal values after 24 hr. The changes in the ovarian blood flows of pseudopregnant rabbits receiving PGF2α were accompanied by simultaneous changes in the resistance index. This biphasic response in the blood flow and vascular resistances likely reflects reactive hyperaemia following vasoconstriction. By immunohistochemistry, strong positive immune reaction for FP was detected in the cytoplasm of endothelial cells of ovarian arteries, veins and capillaries. In conclusion, these results suggest that PGF2α could acutely regulate the ovarian blood flow of pseudopregnant rabbits, even if there is no evidence of a blood flow reduction anticipating luteolysis.

Prostaglandin synthesis by the porcine corpus luteum: effect of tumor necrosis factor-α

The porcine corpus luteum (CL) displays delayed sensitivity to PGF-2α (luteolytic sensitivity, [LS]) until days 12 to 13 of cycle. The control of LS is unknown, but it is temporally associated with macrophage (which secrete tumor necrosis factor-α; TNF-α) infiltration into the CL. Other studies showed that TNF-α induces LS in vitro and that prostaglandins (PGs) may be involved in this mechanism. In experiment 1, PGF-2α and PGE secretion by luteal cells (LCs) was measured on days 4 to 14 of the estrous cycle, and the expression of PTGFS/AKR1B1 and PTGES/mPGES-1, determined by Western blot, before (day 7) vs after (day 13) the onset of LS. Results showed that the PGF-2α:PGE ratio increased significantly (P < 0.05) from day 4 to 13-14, and PTGFS/AKR1B1 and PTGES/mPGES-1 were significantly increased (P < 0.05) on day 13 (vs day 7). In experiment 2, LCs were collected from porcine CL at early (∼days 4-6) or mid (∼days 7-12) stages of the estrous cycle and cultured with 0, 0.1, 1, or 10 ng/mL TNF-α. Results showed that TNF-α significantly increased (P < 0.05) messenger RNA (mRNA) expression of cyclooxygenase (COX)-2 and mPGES-1 but not AKR1B1. TNF-α had no significant effects on AKR1B1 or mPGES protein abundance. TNF-α significantly increased (P < 0.05) PGE-2 but had no effect on PGF-2α secretion or on the PGF-2α:PGE2 ratio. In conclusion, although TNF-α increased COX2 and mPGES-1 mRNA, and PGE-2 secretion in vitro, it did not increase the PGF-2α:PGE2 ratio. Studies are currently directed toward exploring other pathways (eg, FP receptor signaling) by which TNF-α induces LS in the porcine CL.

Expression of nerve growth factor and its receptors in the uterus of rabbits: functional involvement in prostaglandin synthesis

The aim of the present study was to evaluate: (1) the presence of nerve growth factor (NGF), neurotrophic tyrosine kinase receptor 1 (NTRK1), and nerve growth factor receptor (NGFR) in the rabbit uterus; and (2) the in vitro effects of NGF on PGF2α and PGE2 synthesis and on the PGE2-9-ketoreductase (PGE2-9-K) activity by the rabbit uterus. Nerve growth factor, NTRK1, and NGFR were immunolocalized in the luminal and glandular epithelium and stroma cells of the endometrium. reverse transcriptase polymerase chain reaction indicated the presence of messenger RNA for NGF, NTRK1, and NGFR in the uterus. Nerve growth factor increased (P < 0.01) in vitro secretions of PGF2α and PGE2 but coincubation with either NTRK1 or oxide nitric synthase (NOS) inhibitors reduced (P < 0.01) PGF2α production and blocked (P < 0.01) PGE2 secretion. Prostaglandins releases were lower (P < 0.01) than control when uterine samples were treated with NGF plus cyclooxygenase inhibitor. However, addition of NGFR inhibitor reduced (P < 0.01) PGF2α secretion less efficiently than NTRK1 or NOS inhibitors but had no effect on PGE2 yield. Nerve growth factor increased (P < 0.01) the activity of PGE2-9-K, whereas coincubation with NTRK1 or NOS inhibitors abolished (P < 0.01) this increase in PGE2-9-K activity. However, cotreatment with either cyclooxygenase or NGFR inhibitors had no effect on PGE2-9-K activity. This is the first study to document the distribution of NGF/NTRK1 and NGFR systems and their effects on prostaglandin synthesis in the rabbit uterus. NGF/NTRK1 increases PGF2α and PGE2 productions by upregulating NOS and PGE2-9-K activities, whereas NGF/NGFR augments only PGF2α secretion, through an intracellular mechanism that is still unknown.

Evidence for a dopamine intrinsic direct role in the regulation of the ovary reproductive function: in vitro study on rabbit corpora lutea

Dopamine (DA) receptor (DR) type 1 (D1R) has been found to be expressed in luteal cells of various species, but the intrinsic role of the DA/DRs system on corpora lutea (CL) function is still unclear. Experiments were devised to characterize the expression of DR types and the presence of DA, as well as the in vitro effects of DA on hormone productions by CL in pseudopregnant rabbits. Immunoreactivity and gene expression for D1R decreased while that for D3R increased in luteal and blood vessel cells from early to late pseudopregnant stages. DA immunopositivity was evidenced only in luteal cells. The DA and D1R agonist increased in vitro release of progesterone and prostaglandin E2 (PGE2) by early CL, whereas the DA and D3R agonist decreased progesterone and increased PGF2α in vitro release by mid- and late CL. These results provide evidence that the DA/DR system exerts a dual modulatory function in the lifespan of CL: the DA/D1R is luteotropic while the DA/D3R is luteolytic. The present data shed new light on the physiological mechanisms regulating luteal activity that might improve our ability to optimize reproductive efficiency in mammal species, including humans.

Auto-amplification system for prostaglandin F2α in bovine corpus luteum

The bovine corpus luteum (CL) is hypothesized to utilize a local auto-amplification system for prostaglandin (PG) F2α production. The objective of the present study was to determine if such a PGF2α auto-amplification system exists in the bovine CL, and if so, which factors regulate it. PGF2α significantly stimulated intra-luteal PGF2α production in all luteal phases, but did not affect PGE2 production. The stimulatory effect of exogenous PGF2α on CL PGF2α production was lower at the early luteal phase. Indomethacin, an inhibitor of prostaglandin-endoperoxide synthase (PTGS), significantly suppressed the PGF2α-stimulated PGF2α production by luteal tissue, indicating that the PGF2α in the medium was of luteal origin. Consistent with these secreted-PGF2α profiles, PGF2α receptor (PTGFR) protein expression was higher during the mid and late luteal phases than at early and developing luteal phases. Treatment of cultured bovine luteal cells obtained from the mid-luteal phase with PGF2α (1 µM) significantly increased the expressions of PTGS2, PGF synthase (PGFS), and carbonyl reductase1 (CBR1) at 24 hr post-treatment. Together, these results suggest the presence of a local auto-amplification system for PGF2α mediated by PTGS2, PGFS, and CBR1 in the bovine CL, which may play an important role in luteolysis.

In vivo chronic and in vitro acute effects of di(2-ethylhexyl) phthalate on pseudopregnant rabbit corpora lutea: possible involvement of peroxisome proliferator-activated receptor gamma

The in vivo chronic and in vitro acute effects of di(2-ethylhexyl) phthalate (DEHP) on the reproductive function of peroxisome proliferator-activated receptor gamma (PPARG) were studied in rabbit corpora lutea (CL) at early stage (Day 4), midstage (Day 9), and late stage (Day 13) of pseudopregnancy. The rabbits were in vivo treated with DEHP for 15 days before induction of pseudopregnancy. Immunohistochemistry provided evidence for the presence of PPARG, prostaglandin endoperoxide synthase 1 (PTGS1), PTGS2, prostaglandin E2-9-ketoreductase (PGE2-9-K), and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) in all the luteal cells during pseudopregnancy. DEHP decreased progesterone plasma levels and CL production in all the luteal stages and PPARG protein and gene expressions in early and mid-CL. DEHP in vivo treatment reduced PTGS2 protein expression at the late stage and that of PGE2-9-K at all the stages, whereas PTGS1 and 3beta-HSD were not affected. In in vitro cultured CL, DEHP alone, the PPARG antagonist T0070907 alone, or DEHP plus T0070907 diminished progesterone production and 3beta-HSD activity and increased PGF2alpha and PTGS2 in early and mid-CL, whereas DEHP plus the PPARG agonist 15d-PGJ2 did not affect these hormones and enzymes. All the in vitro treatments did not affect PGE2 secretion as well as PTGS1 and PGE2-9-K enzymatic activities in all the luteal stages. These results provided evidence that DEHP favors functional luteolysis of pseudopregnant rabbit CL, with a mechanism that seems to involve PPARG expression down-regulation, an increase of PTGS2 activity and prostaglandin F2alpha secretion, 3beta-HSD down-regulation, and decrease in progesterone.

A comprehensive immunohistochemistry of prostaglandins F2α and E2 synthetic enzymes in rat ovary and uterus around parturition

A comprehensive immunohistochemistry with the isoform-distinguishable antibodies against prostaglandin (PG) F2α and PGE2 biosynthetic enzymes was undertaken to identify the cellular types and enzyme isoforms in rat ovary and uterus around parturition. In general ovarian and uterine cells showed positive immunoreactions for phospholipase A2 groups 4A and 6A, but not group 2A, and cyclooxygenase (COX)-1 rather than COX-2. Their immunoreactions for PGF2α synthase and PGE2 synthase were cell type-dependently variable. The putative PGF2α and PGE2 producing cell types included, as expected, ovarian luteal cells, uterine endometrial epithelium and myometrium, and cervical connective tissue and, unexpectedly, ovarian stromal cells and basal lamina of cervical endometrium. Obtained data indicate the generation of PGF2α and PGE2 by multiple sites, which are entirely the same as established sites of actions, in parturition processes and tissue-dependent differential usage of PG biosynthetic pathway.

Evidence for a luteotropic role of peroxisome proliferator-activated receptor gamma: expression and in vitro effects on enzymatic and hormonal activities in corpora lutea of pseudopregnant rabbits

The expression of peroxisome proliferator-activated receptor gamma (PPARgamma) and its role in corpora lutea (CL) function were studied in pseudopregnant rabbits. Corpora lutea were collected at an early stage (Day 4), midstage (Day 9), and late stage (Day 13) of pseudopregnancy. Immunohistochemistry found evidence for the presence of PPARgamma in the perinuclear cytoplasm and nucleus of all the luteal cells; immunoreactivity decreased from the early to the late stage, with immunonegativity of the nuclei of late stage CL. PPARgamma mRNA transcript was expressed in all the luteal stages with the lowest level in the late stage. In CL cultured in vitro, the PPARgamma agonist (15-deoxy delta12,14 prostaglandin J2 [15d-PGJ2], 200 nM) increased and the antagonist (T0070907, 50 nM) decreased progesterone secretion at early and midluteal stages, whereas 15d-PGJ2 reduced and T0070907 increased PGF2alpha at the same stages. Prostaglandin-endoperoxide synthase 2 (PTGS2) activity was reduced by 15d-PGJ2 and increased by T0070907 in CL of early and midluteal stages. Conversely, 15d-PGJ2 increased and T0070907 reduced 3beta-hydroxysteroid dehydrogenase (3beta-HSD) activity in early and midluteal stage CL. PGE2 in vitro secretion as well as PTGS1 and 20alpha-HSD enzymatic activities were not affected by 15d-PGJ2 and T0070907 in any CL types. These results indicate that PPARgamma plays a luteotropic role in pseudopregnant rabbits, through PTGS2 down-regulation and 3beta-HSD up-regulation, with a consequent PGF2alpha decrease and progesterone increase.

Opposite effects of methanandamide on lipopolysaccharide-induced prostaglandin E2 and F2α synthesis in uterine explants from pregnant mice

Prostaglandins (PG) are effective abortifacients and are important mediators of lipopolisaccharide (LPS)-induced embryonic resorption (ER). Besides, anandamide (AEA) has been described as one of the major endocannabinoids present in the uterus suggesting that it might play a role in reproduction. It has been reported that high levels of AEA are associated with pregnancy failure and that LPS increases AEA production. Also, it has been observed that AEA modulates PG production in different tissues. In this sense, we studied whether LPS-induced PG production is modulated by AEA and we also assessed the effect of this endocannabinoid on PG metabolism in an in vitro model. Uterine explants from BALB/c implantation sites were cultured in the presence of LPS plus cannabinoid receptor (CB) specific antagonists and PG production was assessed. Then, we studied the effect of exogenous AEA on different steps of PG metabolic pathway. We showed that AEA is involved in LPS-induced PG biosynthesis. Also, we observed that AEA exerts opposite effects on PGE(2) and PGF(2α) biosynthesis, by inhibiting PGE(2) production and increasing PGF(2α) levels. We suggest that AEA could be involved in the mechanisms implicated in LPS-induced ER. A better understanding of how AEA could be affecting ER could help developing specific interventions to prevent this pathology.

Patterns of gene expression in the bovine corpus luteum following repeated intrauterine infusions of low doses of prostaglandin F2alpha

Natural luteolysis involves multiple pulses of prostaglandin F2alpha (PGF) released by the nonpregnant uterus. This study investigated expression of 18 genes from five distinct pathways, following multiple low-dose pulses of PGF. Cows on Day 9 of the estrous cycle received four intrauterine infusions of 0.25 ml of phosphate-buffered saline (PBS) or PGF (0.5 mg of PGF in 0.25 ml of PBS) at 6-h intervals. A luteal biopsy sample was collected 30 min after each PBS or PGF infusion. There were four treatment groups: Control (n = 5; 4 PBS infusions), 4XPGF (4 PGF infusions; n = 5), 2XPGF-non-regressed (2 PGF infusions; n = 5; PGF-PBS-PGF-PBS; no regression after treatments), and 2XPGF-regressed (PGF-PBS-PGF-PBS; regression after treatments; n = 5). As expected, the first PGF pulse increased mRNA for the immediate early genes JUN, FOS, NR4A1, and EGR1 but unexpectedly also increased mRNA for steroidogenic (STAR) and angiogenic (VEGFA) pathways. The second PGF pulse induced immediate early genes and genes related to immune system activation (IL1B, FAS, FASLG, IL8). However, mRNA for VEGFA and STAR were decreased by the second PGF infusion. After the third and fourth PGF pulses, a distinctly luteolytic pattern of gene expression was evident, with inhibition of steroidogenic and angiogenic pathways, whereas, there was induction of pathways for immune system activation and production of PGF. The pattern of PGF-induced gene expression was similar in corpus luteum not destined for luteolysis (2X-non-regressed) after the first PGF pulse but was very distinct after the second PGF pulse. Thus, although the initial PGF pulse induced mRNA for many pathways, the second and later pulses of PGF appear to have set the distinct pattern of gene expression that result in luteolysis.

Direct actions of ACTH on ovarian function of pseudopregnant rabbits

The present study sought to assess whether the receptors for adrenocorticotropic hormone (ACTH), MC2R, and for glucocorticoid (GR) are expressed in corpora lutea (CL) of pseudopregnant rabbits and whether ACTH and cortisol exert any direct action on luteal function. By immunohistochemistry, positive reaction for MC2R and GR was detectable within luteal cells of CL. The MC2R mRNA levels were five-fold less abundant in day 9 than in day 4 CL (P<0.01). At both stages, ACTH agonist (ACTH 1-24) increased progesterone and prostaglandin (PG) E(2) (PGE(2)) (P<0.01), but reduced PGF(2α) releases (P<0.01) in vitro. ACTH 1-24 injection increased plasma cortisol levels within 4h (P<0.01), but decreased (P<0.01) progesterone 24h later and for the following two days. ACTH administration to estrous rabbits caused a transitory increase in blood progesterone concentrations (P<0.01). Daily injections of ACTH did not modify progesterone profile following ovulation. In conclusion, ACTH directly up-regulates CL progesterone production in vitro via MC2R, but indirectly hampers luteal function via cortisol-GR associated mechanism.

Immunopresence and enzymatic activity of nitric oxide synthases, cyclooxygenases and PGE2-9-ketoreductase and in vitro production of PGF2α, PGE2 and testosterone in the testis of adult and prepubertal alpaca (Lama pacos)

This study presents the first evidence for differences in COXs, PGE2-9-ketoreductase and NOSs immunopresence and enzyme activity, and prostaglandin and testosterone production between the testes of adult and prepubertal alpacas. The prepubertal testis immunohistochemical data revealed that COX1 was expressed in spermatogonia and endothelial cells whereas COX2 was present only in the stromal cells. In adult animals, COX2 immunosignals were evidenced in germ cells, as well as both COX1 and -2 in Leydig and Sertoli cells. In adult testes, the spermatogonia, spermatocytes and round spermatids had expression of e- and n-NOS only, whereas elongated spermatids exhibited immunopositivity for i- and e-NOS and Sertoli cells expressed only n-NOS. In prepubertal alpacas, i-NOS was localized in spermatogonia, e-NOS in Sertoli cells and all three NOS isoforms in Leydig cells. PGE2-9-ketoreductase immunopresence was observed in spermatogonia nuclei and cytoplasm of prepubertal testis whereas they were localized in spermatid acrosomal vesicle of adult. The enzymatic data indicated that COX1 activity was higher than COX2 in adult alpaca testis whereas the activity of COX2 was greater than that of COX1 in prepubertal animals. Total NOS and PGE2-9-ketoreductase activities were more extensive in adult alpacas. In vitro hormone production results showed that prepubertal testes released lower amounts of testosterone and PGF2α while PGE2 synthesis was six times more elevated than in in vitro incubated adult testes. Taken together, the data on COX2, i-NOS and PGE2 led us to hypothesize that development in prepubertal male reproductive tissues utilizes a mechanism similar to that of inflammation.

In vitro effects of gonadotropin-releasing hormone (GnRH) on Leydig cells of adult alpaca (Lama pacos) testis: GnRH receptor immunolocalization, testosterone and prostaglandin synthesis, and cyclooxygenase activities

The main objective of this study was to examine the modulatory in vitro effects of gonadotropin-releasing hormone (GnRH) on isolated Leydig cells of adult alpaca (Lama pacos) testis. We first evaluated the presence of GnRH receptor (GnRHR) and cyclooxygenase (COX) 1 and COX2 in alpaca testis. We then studied the in vitro effects of buserelin (GnRH analogue), antide (GnRH antagonist), and buserelin plus antide or inhibitor of phospholipase C (compound 48/80) and COXs (acetylsalicylic acid) on the production of testosterone, PGE(2), and PGF(2α) and on the enzymatic activities of COX1 and COX2. Immunoreactivity for GnRHR was detected in the cytoplasm of Leydig cells and in the acrosomal region of spermatids. COX1 and COX2 immunosignals were noted in the cytoplasm of spermatogonia, spermatocytes, spermatids, Leydig cells, and Sertoli cells. Western blot analysis confirmed the GnRHR and COX1 presence in alpaca testis. The in vitro experiments showed that buserelin alone increased (P < 0.01) and antide and buserelin plus acetylsalicylic acid decreased (P < 0.01) testosterone and PGF(2α) production and COX1 activity, whereas antide and compound 48/80 counteracted buserelin effects. Prostaglandin E(2) production and COX2 activity were not affected by buserelin or antide. These data suggest that GnRH directly up-regulates testosterone production in Leydig cells of adult alpaca testis with a postreceptorial mechanism that involves PLC, COX1, and PGF(2α).

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.

Expression of luteal estrogen receptor, interleukin-1, and apoptosis-associated genes after PGF2alpha administration in rabbits at different stages of pseudopregnancy

The dynamic expression for estrogen receptor subtype-1 (ESR1), interleukin-1beta (IL1B), and apoptosis-associated genes, as well as nitric oxide synthase activity, were examined in corpora lutea (CL) of rabbits after prostaglandin F(2alpha) (PGF(2alpha)) administration on either day 4 or day 9 of pseudopregnancy. By reverse transcriptase polymerase chain reaction, the steady-state level of ESR1 transcript was lower (P < 0.01) and that of anti-apoptotic B-cell CLL/lymphoma 2 (BCL2) -like 1 (BCL2L1) was greater in day 4 (P < 0.01) than in day 9 CL. Western blot analysis revealed that BCL2-associated X protein (BAX) abundance was greater in day 4 (P < 0.01) than in day 9 CL, whereas BCL2L1 protein was undetectable at both luteal stages. After PGF(2alpha), ESR1 transcript decreased (P < 0.01) in day 9 CL, whereas IL1B mRNA showed a transitory increase (P < 0.01) at both stages. The pro-apoptotic tumor protein p53 (TP53) gene had diminished (P < 0.01) on day 4 and on day 9 after a transitory increase (P < 0.01), whereas the BAX/BCL2L1 expression ratio increased (P < 0.01) in day 9 CL 24 h after treatment. Following PGF(2alpha), TP53 protein increased (P < 0.01) at both luteal stages, and BAX decreased (P < 0.01) in day 4 CL but increased (P < 0.01) 24 h later in day 9 CL; BCL2L1 became detectable 6 h later in day 4 CL. Nitric oxide synthase activity temporarily increased (P < 0.01) following PGF(2alpha). These findings suggest that PGF(2alpha) regulates luteolysis by ESR1 mRNA down-regulation and modulation of pro- and anti-apoptotic pathways in CL that have acquired a luteolytic capacity.

Evidence suggesting multiple promoting roles of luteal group IVA phospholipase A(2) in prostaglandin F(2alpha)-induced regression in pseudopregnant rats

We evaluated effects of local administration of selective inhibitors of group IVA phospholipase A(2) (GIVA PLA(2)) and cyclooxygenase (COX) on exogenous prostaglandin (PG) F(2alpha)-induced luteal regression in pseudopregnant rats. Intra-bursal treatment with a GIVA PLA(2) inhibitor AACOCF(3) just prior to PGF(2alpha) (30microg, subcutaneously) on day 6 of pseudopregnancy (PSP6) prevented a decline in circulating progesterone and inhibited TUNEL-positive reactions of steroidogenic cell. Its treatment on PSP9 failed to inhibit functional regression, but reduced significantly apoptosis of steroidogenic cells and vascular endothelial cells, and suppressed the infiltration of macrophages. A COX-2-selective inhibitor NS398 inhibited the decline of progesterone and apoptosis of steroidogenic cells on PSP6 but not on PSP9. A COX-1 inhibitor SC560 exerted insignificant anti-luteolytic effects. Overall data suggest that luteal GIVA PLA(2) plays multiple promoting roles in PGF(2alpha)-induced luteal regression at least partly by a COX-2 activity-related mechanism in pseudopregnant rats.