Response Of Corpus Luteum Research Articles

Effect of season and frequency of embryo collections on superovulatory response and embryo recovery in Santa Inês hair sheep

Small ruminant breeds have different reactions to climate change, which influences reproductive performance and the application of biotechnologies. The aim of the present work was to evaluate whether the reproductive characteristics superovulation response, number of Corpus luteum (CL), embryo recovery rate, following superovulation of Santa Inês breed ewes were influenced by two-years seasons and frequency of embryo collection under subtropical condition. Ewes were housed in pens with water and salt ad libitum. Reproductive characteristics were evaluated in two- years seasons: Fall and Winter (F/W) and Spring and Summer (S/S). Decreased superovulatory response and viable embryo rates were observed in S/S (33.3 % and 10 %) compared to F/W (76.5 % and 59.6 %, P < 0.05). The frequency of one to three superovulation protocols and embryo collections at two-month intervals did not affect the superovulatory response and number of CL per ewe. However, collections after the third superovulation and embryo collection decreased the rate of recovered embryos of all recovered structures compared to the second collection. The superovulatory response and number of CL per ewe were not affected after two superovulation treatments and embryo collections. In conclusion, two embryo collections at two-month intervals can be conducted without impairment of the reproductive performance of Santa Ines breed ewes. Fall and Winter seemed to be the most suitable seasons to embryo transfer program of the Santa Inês donor ewes under subtropical conditions.

Preselection of high and low ovulatory responders in sheep multiple ovulation and embryo transfer programs

The present study evaluated the feasibility of carrying out an easy-to-handle and cost-efficient test for the preselection of high– and low–ovulatory responder ewes under superovulatory protocols. The test was based on the assessment of the number of ovulations obtained in response to the administration of a single-shot eCG treatment. The predictive value of the test was determined by comparing the number of ovulations with yields obtained in response to a multiple-dose FSH treatment. In addition, the study determined possible effects of follicular status at first FSH dose and their relationship with subsequent ovarian response. A total of 31 Merino ewes received hormonal treatment comprising the administration of 800 IU of eCG at the end of progestative treatment. Twenty-three days later, multiple-dose FSH treatment (80-mg FSH, in six decreasing doses between Days 12 and 14 of a second progestative treatment) was applied to the same ewes. The study showed a significant relationship between the number of corpora lutea obtained in response to eCG treatment with respect to those obtained in response to FSH treatment (r = 0.791; P < 0.05), which resulted in 84% recurrence rate. The number of embryos was greater for high-responder in relation to low-responder ewes (7.2 ± 3.7 and 4.0 ± 3.9, respectively; P < 0.05), whereas rates of recovery and fertilization were similar between groups (P > 0.05). Hence, there was a tendency for a higher mean of grades 1 and 2 embryos in high-responder in relation to low-responder ewes (6.1 ± 3.8 and 3.7 ± 4.0, respectively; P < 0.1). No significant relationship was found between the number of corpora lutea in response to FSH treatment and the number of small and total follicles at first FSH dose (P > 0.05). However, a negative low relationship was found between the presence of large follicles and the ovulation rate in response to FSH treatment (r = −0.361; P < 0.05). In conclusion, the results show the feasibility of carrying out an easy-to-handle and cost-efficient procedure for the preselection of embryo donors. The procedure was based on high recurrence rate between hormonal treatments, which in turn accounts for a distinctive ewe ovulatory response.

The Effects of Unpredictable Stress on the LHR Expression and Reproductive Functions in Mouse Models

Sung-Young Choi, Jin-Heum Park, Yuxia Zhu, Young-Jong kim, Jae-Ok Park, Changjong Moon, Taekyun Shin, Meejung Ahn, Suk-Soo Kim, Young-Sik Park, Hyung-Bok Chae, Tae-Kyun Kim and Seung-Joon Kim. J Vet Clin 2014;31:394-402. https://doi.org/10.17555/ksvc.2014.10.31.5.394

Involvement of Src family of kinases and cAMP phosphodiesterase in the luteinizing hormone/chorionic gonadotropin receptor-mediated signaling in the corpus luteum of monkey

BackgroundIn higher primates, during non-pregnant cycles, it is indisputable that circulating LH is essential for maintenance of corpus luteum (CL) function. On the other hand, during pregnancy, CL function gets rescued by the LH analogue, chorionic gonadotropin (CG). The molecular mechanisms involved in the control of luteal function during spontaneous luteolysis and rescue processes are not completely understood. Emerging evidence suggests that LH/CGR activation triggers proliferation and transformation of target cells by various signaling molecules as evident from studies demonstrating participation of Src family of tyrosine kinases (SFKs) and MAP kinases in hCG-mediated actions in Leydig cells. Since circulating LH concentration does not vary during luteal regression, it was hypothesized that decreased responsiveness of luteal cells to LH might occur due to changes in LH/CGR expression dynamics, modulation of SFKs or interference with steroid biosynthesis.MethodsSince, maintenance of structure and function of CL is dependent on the presence of functional LH/CGR its expression dynamics as well as mRNA and protein expressions of SFKs were determined throughout the luteal phase. Employing well characterized luteolysis and CL rescue animal models, activities of SFKs, cAMP phosphodiesterase (cAMP-PDE) and expression of SR-B1 (a membrane receptor associated with trafficking of cholesterol ester) were examined. Also, studies were carried out to investigate the mechanisms responsible for decline in progesterone biosynthesis in CL during the latter part of the non-pregnant cycle.Results and discussionThe decreased responsiveness of CL to LH during late luteal phase could not be accounted for by changes in LH/CGR mRNA levels, its transcript variants or protein. Results obtained employing model systems depicting different functional states of CL revealed increased activity of SFKs [pSrc (Y-416)] and PDE as well as decreased expression of SR-B1correlating with initiation of spontaneous luteolysis. However, CG, by virtue of its heroic efforts, perhaps by inhibition of SFKs and PDE activation, prevents CL from undergoing regression during pregnancy.ConclusionsThe results indicated participation of activated Src and increased activity of cAMP-PDE in the control of luteal function in vivo. That the exogenous hCG treatment caused decreased activation of Src and cAMP-PDE activity with increased circulating progesterone might explain the transient CL rescue that occurs during early pregnancy.

ウシ妊娠認識時期でのインターフェロンτ（IFN）による黄体内好中球動員機構

ウシ妊娠認識時期でのインターフェロンτ（IFN）による黄体内好中球動員機構

Recruitment of Neutrophils Within the Pregnant Corpus Luteum in Response to Interferon Tau at the Maternal Recognition Period in the Cow.

Recruitment of Neutrophils Within the Pregnant Corpus Luteum in Response to Interferon Tau at the Maternal Recognition Period in the Cow.

Tumor necrosis factor-α inhibits the stimulatory effect of luteinizing hormone and prostaglandin E 2 on progesterone secretion by the bovine corpus luteum

Tumor necrosis factor-α (TNF-α) is involved in the tissue remodeling that occurs in the corpus luteum (CL) during its development and regression. This cytokine is also implicated in the regulation of reproduction by its actions on ovarian steroidogenic cells. The aim of this study was to examine the influence of TNF-α on (1) progesterone (P 4) output by the bovine CL and on (2) the responsiveness of the CL to LH or prostaglandin E 2 (PGE 2) in vitro. In experiment 1, CL (days 8 to 10 of the estrous cycle) were perfused by using an in vitro microdialysis system with TNF-α (0.1, 0.5, or 1 μg/mL) alone or with TNF-α (1 μg/mL) followed by LH (1000 ng/mL) or PGE 2 (2 × 10 −5 M). Basal P 4 release ( P < 0.05) was increased by TNF-α (0.5 or 1 μg/mL). Moreover, TNF-α (1 μg/mL) inhibited the stimulatory effect of LH or PGE 2 on P 4 output ( P < 0.05). In experiment 2, 4 h after intrauterine infusion of TNF-α (0.01 μg/mL or 1 μg/mL), CL (days 8 to 10 of the estrous cycle) were collected by colpotomy, cultured, and stimulated with LH (10 ng/mL) or PGE 2 (10 −6 M). Intrauterine infusion of TNF-α at a concentration of 1 μg/mL increased basal P 4 output by CL ( P < 0.05). Moreover, the intrauterine infusion of TNF-α at a concentration of 0.01 μg/mL inhibited the stimulatory effect of LH or PGE 2 on P 4 output ( P < 0.05). These results indicate that TNF-α (1) does not have an effect on the autonomous, pulsatile release of P 4; (2) increases P 4 secretion by bovine CL with increasing doses, and (3) reduces in a dose-dependent manner the responsiveness of CL to luteotropic factors both directly (after infusion to CL) and indirectly (after intrauterine infusion).

Distribution of Arteriolovenous Vessels, Capillaries and eNOS Expression in the Bovine Corpus Luteum During the Estrous Cycle: a Possible Implication of Different Sensitivity by Luteal Phase to PGF2.ALPHA. in the Increase of Luteal Blood Flow

We have shown that luteal blood flow increases in the peripheral vasculature of the mature corpus luteum (CL) prior to the onset of luteolysis in response to prostaglandin F(2alpha) (PGF(2alpha)) in the cow, but this phenomenon does not occur in the early CL. We therefore hypothesize that this acute increase of luteal blood flow occurs by vasodilation of large blood vessels due to local release of nitric oxide (NO). In the present study, we characterized the CL vasculature together with endothelial NO synthase (eNOS) expression during the estrous cycle in the cow. Immunohistochemistry was used to quantify the number of arteriolovenous vessels (surrounded with smooth muscle actin-positive smooth muscle cells), capillaries (with von Willebrand Factor-positive endothelial cells) and eNOS protein. The arteriolovenous vessels existed more in the periphery of the matured CL (mid, late and regressing CL) than in the center region. In the early CL, there were as many arteriolovenous vessels in the periphery as in the center, while more capillaries existed in the center than in the periphery of the mid and late CL. Also, eNOS protein existed in the periphery more than in the center of the matured CL. These results indicate that the early CL has a homogeneous vascular and eNOS distribution. In contrast, the matured CL is a heterogeneous organ having a higher vascular and eNOS distribution in the periphery than in the center. In conclusion, the distribution of arteriolovenous vessels and eNOS in the matured CL was higher in the periphery than in the center of the CL. Thus, this suggests that this structural change from the early (homogeneous) to the mid (heterogeneous) luteal phase is related to the difference in the CL response of blood flow increase due to PGF(2alpha), which is only observed in the mature CL.

Characterization of the ovarian and reproductive abnormalities in prepubertal and adult estrogen non-responsive estrogen receptor α knock-in (ENERKI) mice

Estrogen non-responsive estrogen receptor alpha (ERα) knock-in (ENERKI) mice have a mutation (glycine 525 to leucine, G525L) in the ligand-binding domain of ERα. The mutant ERα protein has a significantly lower affinity and response to endogenous estrogens, while not altering growth factor activated ligand-independent pathways. ENERKI females demonstrated signs of early follicle development as determined by a significant increase in antral follicle formation by 20 days of age. Adult ENERKI females were infertile, had hemorrhagic ovarian follicular cysts, and failed to develop corpora lutea in response to a superovulation regimen. These results illustrate the importance of ERα ligand-induced signaling for ovarian development and for estrogen feedback on the hypothalamus and pituitary. Although ERα ligand-induced signaling by endogenous estrogens is lost in ENERKI females, the ERα selective agonist propyl pyrazole triol (PPT), a synthetic nonsteroidal compound, is still able to activate G525L ERα in vivo to increase uterine weight. To test whether PPT could restore ligand-dependent receptor activation, ENERKI females were treated with PPT and evaluated for spontaneous ovulation, ovarian hemorrhagic cysts, and LH serum levels. Daily PPT treatments beginning on day 4 of life prevented formation of ovarian hemorrhagic cysts in adult ENERKI animals. In accordance with this result, preputial gland weight and LH levels were also lowered in these animals, indicating PPT treatments most likely led to restoration of ERα negative feedback of the hypothalamic–pituitary axis.

The human corpus luteum: life cycle and function in natural cycles

To summarize recent advances in the understanding of the endocrine signaling pathways between the hypothalamus, pituitary, and human corpus luteum (CL); to examine the major paracrine and autocrine mechanisms and the key genes and proteins involved in CL development, function, and regression in natural cycles; to review the endocrine and molecular response of the midluteal phase CL to in vivo administration of human chorionic gonadotropin (hCG); and to describe the ultrasonographic and Doppler evaluation of the ovary and endometrium throughout the luteal phase. Published data in the literature, including the basic and clinical research studies of the authors. University-affiliated hospital and research centers. None. None. Clinical and molecular analysis of human CL function. The endocrine function of the subpopulations of luteal cells is critical for the maintenance of CL function, including neovacularization and steroid hormones production. We consider the key genes and proteins that favor development of luteal structure and function throughout the menstrual cycle and in our model of hCG treatment resembling early pregnancy. These data indicate that the functional lifespan of the CL depends on paracrine and autocrine mechanisms. Therefore, the significance of the key genes and proteins that we analyze in lutein cells during CL development, function, demise, and rescue by hCG is likely to bring new therapeutic applications for the management of fertility defects and the control of fertility.

FSH and folliculogenesis: from physiology to ovarian stimulation

FSH is a glycoprotein hormone consisting of two peptide subunits. The role of FSH in folliculogenesis is well known: to stimulate the formation of a large pre-ovulatory follicle that, because of its FSH-dependent maturation, is capable of ovulation and forming a corpus luteum in response to the mid-cycle surge of LH. FSH is widely used in ovarian stimulation for assisted reproduction techniques. Ovarian stimulation protocols combine the use of human menopausal gonadotrophin, urinary FSH or recombinant FSH with gonadotrophin-releasing hormone (GnRH) agonists or antagonists in order to increase oocyte number and to avoid premature LH surge. Recently, the availability of recombinant LH has permitted new stimulation protocols, combining recombinant FSH, recombinant LH and GnRH antagonists. Due to the limitations of the new Italian law in terms of the number of oocytes that can be fertilized, protocols with a softer ovarian stimulation are now considered, reducing risk of ovarian hyperstimulation syndrome, multiple pregnancies and emotional and physical burdens on the patients. Long-acting FSH preparations are also under clinical study. Knowledge of the stereochemical three-dimensional structure of FSH and its receptor will allow the study of new non-peptide orally administered molecules that fit the FSH receptors.

217LUTEAL REGRESSION AND FOLLICLE DEVELOPMENT FOLLOWING PROSTAGLANDIN-F2± TREATMENT 3 DAYS AFTER OVULATION IN MARES

The corpus luteum (CL) is responsive to exogenous prostaglandin-F2α (PGF) 1 to 2 days after ovulation in the mare (Troedsson et al. 2001 Theriogenology 55, 1891–1899); however, complete and sustained demise of the CL beginning less than 5 days after ovulation in response to PGF treatment has not been documented. The present study was designed to compare the morphological and physiological response of the primary CL to PGF given at early diestrus with a more conventional treatment given at about mid-cycle. In addition, follicle status pre- and post-treatment were examined and compared between the treatment groups. On the day of pretreatment ovulation (Day 0), riding-type horse mares were randomly assigned to receive a single dose of PGF (Lutalyse, Upjohn, Kalamazoo, MI, USA;; 10mg/mare, i.m.) on Day 3 (n=17) or Day 10 (n=17). Beginning on either Days 3 or 10, transrectal ultrasonography was used to determine follicle and CL diameters, determine luteal tissue gray-scale scores (echogenicity), and to detect ovulation. Follicular and luteal measurements and jugular blood samples were collected daily until the post-treatment ovulation. Structural and functional regression of the CL was indicated by: 1) a progressive decrease (day effect;; P&amp;lt;0.0001) in mean diameter of the CL beginning 24h after PGF treatment in the Day 3 and Day 10 groups;; 2) a precipitous decrease (P&amp;lt;0.009) in mean plasma progesterone concentrations within 24h in both groups followed by a more gradual decline to basal concentrations by the second day in the Day 10 group or after the fourth day in the Day 3 group;; and 3) an increase (P&amp;lt;0.02) in mean luteal tissue echogenicity in both groups after the second day following PGF treatment. The mean intervals from PGF treatment to ovulation were not different (P&amp;gt;0.2) between groups (combined, 9.9 days) but the mean (±SEM) interovulatory interval was shorter (P&amp;lt;0.0001) in the Day 3 group (13.2±0.9 days;; range, 7 to 20 days) than in the Day 10 group (19.2±0.7 days;; range, 14 to 26 days). The greater the diameter of the largest follicle at the time of PGF treatment, the shorter the interval to post-treatment ovulation in the Day 3 (r=−0.57, P&amp;lt;0.02) and Day 10 (r=−0.74, P&amp;lt;0.001) groups. Growth rates of the preovulatory follicles were similar (P&amp;gt;0.59) between groups (combined, 3.6mm/day) but the maximum diameter was smaller (P&amp;lt;0.05) in the Day 3 group (40.5±1.2mm) compared to the Day 10 group (43.4±0.8mm). Unexpectedly, more (P&amp;lt;0.03) double ovulations occurred in the Day 3 group (6/17, 35%) than in the Day 10 group (1/17, 6%). In conclusion, an immature CL at early diestrus responded to PGF treatment in a manner comparable to a mature CL at mid-cycle. The Day 3 group ovulated an average of 6 days earlier than the Day 10 group as a result of the difference in timing of the PGF treatment between groups. Thus, these results warrant a reassessment of the prevailing concept that the equine CL is resistant to PGF-induced regression before 5 days after ovulation, especially when considering the potential benefits of a shortened interovulatory interval and an increased double ovulation rate.

Expression and Binding Activity of Luteinizing Hormone/Chorionic Gonadotropin Receptors in the Primary Corpus Luteum During Early Pregnancy in the Mare1

Luteal steroids are necessary to maintain the first 70-90 days of pregnancy in the mare. At 35 days postovulation, the resurgence of the primary corpus luteum (CL) coincides with the secretion of the fetal hormone eCG. In order to study the responsiveness of the primary CL to eCG, we have examined levels of luteal equine LH/CG receptors (eLH/CG-R) mRNAs by Northern blot analysis and measured concentrations of eLH/CG binding sites on luteal membranes using 125I-eLH saturation binding assays at three stages of gestation: before the onset of eCG secretion (Days 14-31), from onset to maximum eCG secretion (Days 38-62), and during decline of eCG secretion (Days 83-101). Multiple transcripts of eLH/CG-R (7, 5.7, 4.9, 3.9, 2.8, 1.8, 0.6 kilobase [kb]) were identified in the primary CL at all stages examined. Three of them (5.7, 2.8, 0.6 kb) coded for truncated eLH/CG-R lacking the transmembrane domain. The relative intensities of the four major transcripts tended to decrease (5.7 and 3.9 kb) or were steadily expressed (7 and 1.8 kb) during pregnancy. The affinity of eLH/CG binding sites did not change during pregnancy whereas the number of eLH/CG binding sites decreased significantly after the onset of eCG secretion. Nevertheless, levels of binding sites were still at 44.6% (Days 38-62) to 24.7% (Days 83-101) of those measured before the onset of eCG secretion. Taken together, the presence of eLH/CG-R mRNAs and of a substantial part of eLH/CG binding sites with high affinity suggest that the primary CL still expresses a high number of eLH/CG-R and remains responsive to eCG during early pregnancy.

Influence of Nitric Oxide on the Secretory Function of the Bovine Corpus Luteum: Dependence on Cell Composition and Cell-to-Cell Communication

The objective of the present study was to investigate the role of cell-to-cell contact in the influence of nitric oxide (NO) on the secretory function of the bovine corpus luteum (CL). In Experiment 1, separate small luteal cells (SLC) or large (LLC) luteal cells were perfused with 100 micro M spermineNONOate, a NO donor, or with 100 micro M Nomega-nitro-L-arginine methyl ester (L-NAME), a NO synthase (NOS) inhibitor; in Experiment 2, a mixture of LLC and SLC and endothelial cells was cultured and incubated with spermineNONOate or L-NAME; in Experiment 3, spermineNONOate was perfused into the CL (100 mg/4 hr) by a microdialysis system in vivo. Perfusion of isolated SLC and LLC with the NO donor or NOS inhibitor (Experiment 1) did not affect (P > 0.05) secretion of progesterone (P(4)) or oxytocin (OT). L-NAME perfusion increased (P < 0.05) leukotriene C(4) (LTC(4)) secretion by both SLC and LLC cells. Treatment of mixtures of luteal cells with an NO donor (Experiment 2) significantly decreased (P < 0.001) secretion of P(4) and OT and increased (P < 0.001) production of prostaglandin F(2alpha) (PGF(2alpha)) and LTC(4). L-NAME stimulated (P < 0.001) P(4) secretion, but did not influence (P > 0.05) OT, PGF(2alpha) or LTC(4) production. Intraluteal administration (Experiment 3) of spermineNONOate increased (P < 0.001) LTC(4) and PGF(2alpha), decreased OT, but did not change P(4) levels in perfusate samples. These data indicate that cell-to-cell contact and cell composition play important roles in the response of bovine CL to treatment with NO donors or NOS inhibitors, and that paracrine mechanisms are required for the full secretory response of the CL in NO action. Endothelial cells appear to be required for the full secretory response of the CL to NO.

Reproductive season affects inhibitory effects from large follicles on the response to superovulatory FSH treatments in ewes

The main objective of this study was to compare the effect of the presence of large follicles at the start of FSH treatment on the superovulatory response in ewes in the breeding and nonbreeding seasons. A second objective was to verify the effect on the superovulatory response of the presence of a corpus luteum at the start of the FSH treatment during the breeding season. Fifteen ewes in breeding season (October) and 14 in nonbreeding season (May–June) were treated with 40 mg FGA sponges (Chronogest ®) for 14 days, together with a single dose of 125 μg cloprostenol on Day 12, considering Day 0 as day of progestagen insertion. Superovulatory treatments consisted of eight decreasing doses (1.5 ml×3, 1.25ml×2 and 1ml×3) of Ovagen™ twice daily from 60 h before to 24 h after sponge removal. Ovarian structures were assessed by transrectal ultrasonography using a 7.5 MHz linear array probe. Luteal activity at progestagen insertion (Day 0) and presence of corpus luteum and of large follicles at first FSH dose (Day 12) were determined. There were no significant differences between the breeding season and nonbreeding season for ovulation rate (11.6±1.4 versus 11.6±1.3), number of recovered embryos (8.0±1.1 versus 9.6±1.3) or number of viable embryos (7.2±1.1 versus 5.8±1.2). During the breeding season, there were fewer recovered embryos in ewes with a large follicle (≥6 mm) at first FSH dose (6.9±1.1 versus 12.3±1.8, P<0.05) and fewer viable embryos (5.0±1.2 versus 10.5±0.5, P<0.05) than in ewes without such a follicle. During the nonbreeding season, however, there were no significant differences between ewes with or without a large follicle for either recovered (9.0±2.5 versus 11.3±1.2) or viable embryos (6.3±2.3 versus 8.1±1.2). Analysis of seasonal differences in ewes with a large follicle showed a lower number of recovered embryos in the breeding season ( P<0.05) due to a lower recovery rate (65.7% versus 92.3%, P<0.05), since mean number of corpora lutea in response to the FSH treatment was similar (10.9±1.3 versus 10.0±2.5). These results indicate that, in sheep, the inhibitory effects of large follicles during the nonbreeding season are not as obvious as during the breeding season.

Corpus luteum response to exogenous HCG during the mid-luteal phase of the menstrual cycle.

To assess a range of exogenous HCG regimes designed to simulate the endocrine environment occurring in biochemical, single and multiple pregnancies and to study the response of the corpus luteum to those regimes. Prospective clinical study. Twenty-five normally cycling women aged 24-35 years were given one of four regimes of HCG injections designed to mimic the HCG concentrations found following spontaneous implantation. Regimes A, B, C and D were designed with starting HCG doses of 60, 140, 250 and 1000 iu, respectively. The daily HCG injections were then increased to give a doubling concentration every 30 h for regime A, every 27 h for regime B, every 24 h for regimes C and D. HCG administration was started on either days 7 or 8 after the LH peak. Plasma HCG and progesterone concentrations. Subjects given regime A failed to demonstrate any rescue of the corpus luteum despite low-detectable amounts of HCG in the circulation equivalent to those seen in some biochemical pregnancies. In contrast, subjects given regimes B and C demonstrated prompt increases in progesterone secretion immediately after the first HCG injection achieving HCG and progesterone concentrations in plasma similar to those seen in normal singleton pregnancies. Subjects given regime D also showed rapid rescue of the corpus luteum but this time achieved plasma HCG concentrations in the range normally seen in multiple pregnancies. All subjects in regimes B, C and D secreted significantly higher amounts of progesterone than those in regime A (P<0.001). However, despite the greater amounts of HCG used in regime D, the amount of progesterone produced was not significantly different from regimes B or C. The exogenous HCG regimes used in this study successfully mimicked the hormonal environment found in biochemical, single and multiple pregnancies and elicited appropriate corpus luteum responses.

Nitric oxide synthase activity and progesterone release by isolated corpora lutea of rabbits in the early and mid-luteal phases of pseudopregnancy are modulated differently by prostaglandin E-2 and prostaglandin F-2alpha via adenylate cyclase and phospholipase C.

By examining in vitro the effects of prostaglandin E-2 (PGE-2) and prostaglandin F-2alpha (PGF-2alpha) induced in the corpora lutea (CL) of pseudopregnant rabbits, we have demonstrated that these prostaglandins modulate luteal nitric oxide synthase (NOS) activity and progesterone production differently, depending on the age of the CL. On CL obtained on day 4 of pseudopregnancy (day-4), PGE-2 was found to depress NOS total activity to 13% of control and to significantly increase basal progesterone secretion by 61%, while PGF-2alpha had no effect. On day-9 CL, PGE-2 was ineffective, but PGF-2alpha caused a 2.5-fold increase of NOS activity and a marked decrease in progesterone production. Using specific inhibitors, we found that the regulatory actions of PGE-2 in vitro are mediated via the adenyl cyclase/protein kinase A (PKA) second messenger system, while the PGF-2alpha-induced luteolytic effects on day-9 CL depend upon activation of the phospholipase C/protein kinase C (PKC) system. The different responsiveness of day-4 and day-9 CL to PGE-2 and PGF-2alpha could depend on receptor availability for these two prostaglandins, even if other cellular mechanisms cannot be excluded. The present study supports a functional role for NOS in regulating the steroidogenic capacity of rabbit CL, and reveals a novel interaction between a stimulatory G-protein-coupled receptor and PKC/PKA-mediated signal transduction modulating NOS activity.

Sensitivity of bovine corpora lutea to prostaglandin F2alpha is dependent on progesterone, oxytocin, and prostaglandins.

Prostaglandin (PG) F2alpha that is released from the uterus is essential for spontaneous luteolysis in cattle. Although PGF2alpha and its analogues are extensively used to synchronize the estrous cycle by inducing luteolysis, corpora lutea (CL) at the early stage of the estrous cycle are resistant to the luteolytic effect of PGF2alpha. We examined the sensitivity of bovine CL to PGF2alpha treatment in vitro and determined whether the changes in the response of CL to PGF2alpha are dependent on progesterone (P4), oxytocin (OT), and PGs produced locally. Bovine luteal cells from early (Days 4-5 of the estrous cycle) and mid-cycle CL (Days 8-12 of the estrous cycle) were preexposed for 12 h to a P4 antagonist (onapristone: OP; 10(-4) M), an OT antagonist (atosiban: AT; 10(-6) M), or indomethacin (INDO; 10(-4) M) before stimulation with PGF2alpha. Although OP reduced P4 secretion (p < 0.001) only in early CL, it reduced OT secretion in the cells of both phases examined (p < 0.001). OP also reduced PGF2alpha and PGE2 secretion (p < 0.01) from early CL. However, it stimulated PGF2alpha secretion in mid-cycle luteal cells (p < 0.001). AT reduced P4 secretion in early and mid-cycle CL (p < 0.05). Moreover, PGF2alpha secretion was inhibited (p < 0.05) by AT in early CL. The OT secretion and the intracellular level of free Ca2+ ([Ca2+]i) were measured as indicators of CL sensitivity to PGF2alpha. PGF2alpha had no influence on OT secretion, although [Ca2+]i increased (p < 0.05) in the early CL. However, the effect of PGF2alpha was augmented (p < 0.01) in cells after pretreatment with OP, AT, and INDO in comparison with the controls. In mid-cycle luteal cells, PGF2alpha induced 2-fold increases in OT secretion and [Ca2+]i. However, in contrast to results in early CL, these increases were magnified only by preexposure of the cells to AT (p < 0.05). These results indicate that luteal P4, OT, and PGs are components of an autocrine/paracrine positive feedback cascade in bovine early to mid-cycle CL and may be responsible for the resistance of the early bovine CL to the exogenous PGF2alpha action.

In vivo responses of the primate corpus luteum to luteinizing hormone and chorionic gonadotropin.

Although it is well established that the secretory activity of the corpus luteum absolutely depends on the presence of pituitary-derived luteinizing hormone (LH), it is unknown why the life span of the corpus luteum is extended during early pregnancy by the placental production of chorionic gonadotropin (CG) but regresses in the presence of LH despite the fact that CG and LH have similar actions on the corpus luteum. To compare the responses of the corpus luteum to LH and human CG (hCG), cynomolgus monkeys whose endogenous gonadotropin secretion was blocked during the luteal phase of the menstrual cycle with a gonadotropin-releasing hormone antagonist were i.v. infused with either LH or CG. Infusion of LH at a constant rate overcame the gonadotropin-releasing hormone antagonist-mediated premature luteal regression but failed to prolong the functional life span of the corpus luteum. Continuous infusions of hCG did not effect a pregnancy-like pattern of gonadotropin secretion, but the functional life span of the corpus luteun was extended in two of three animals. Infusion of either LH or hCG in an exponentially increasing manner prolonged the functional life span of the corpus luteum beyond its normal duration. These results indicate that luteal regression at the termination of nonfertile menstrual cycles is caused by a large reduction in the responsiveness of the aging corpus luteum to LH, which can be overcome by elevated concentrations of either LH or CG.

Suppression of ovarian oxytocin secretion after intra-luteal administration of the arachidonate 5-lipoxygenase inhibitor BWA4C in the ewe

The effect of an intra-luteal injection of the 5-lipoxygenase (5-LO) inhibitor BWA4C (2 mg in 50 μ1 dmso) on the secretion of oxytocin (OT) from the corpus luteum in response to a close-arterial infusion of prostaglandin (PG)-F 2α (5 ng mint) was examined in anaesthetised sheep. Within 30 minutes of administration both basal (pre-infusion) and PGF 2 α stimulated OT release into the posterior vena cava were significantly (P<0·01) reduced. These results are consistent with the proposition that 5-LO products of arachidonic acid may modulate OT secretion from the ovine corpus luteum.