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Luteotrophic and luteolytic interactions between bovine small and large luteal-like cells and endothelial cells

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Endothelial cells, the most abundant cell type in the bovine CL, were shown to establish intercellular contact with steroidogenic cells of the CL. Two experimental models were used to study the involvement of endothelial cells in luteal cell function: 1) luteal slices in which the integrity and communication between the different cells were maintained and 2) pure large and small luteal-like cells, cultured separately or co-cultured with endothelial cells. The luteolytic effect of prostaglandin (PG) F2 alpha was examined in these two models. Treatment with PGF2 alpha did not alter P4 secretion stimulated by LH in young (2-4-day-old) CL slices, whereas, in slices from mature (6-12 days old) CL, PGF2 alpha significantly reduced (by 40%) the stimulatory effect of LH on P4 secretion. In pure large luteal-like cells, the effect of forskolin plus PGF2 alpha on P4 secretion did not differ from forskolin given alone after 3 or 24 h of incubation. However, when co-cultured with endothelial cells, PGF2 alpha significantly inhibited forskolin stimulation. Endothelial cells significantly stimulated P4 production from large luteal-like cells only. This effect may be attributed to the action of PGI2 secreted by endothelial cells. In summary, endothelial cells may play an essential role in luteal functions by being involved in both luteotrophic and luteolytic processes.
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... One area of investigation has been interactions of the prostaglandin (PG) and endothelin systems. The inhibitory effect of PGF 2 α on luteal progesterone production in vitro was observed in luteal slices and large steroidogenic luteal cells only when co-cultured with endothelial cells (Girsh et al., 1995) indicating that PGF 2 α might influence steroidogenic cells indirectly through endothelial cells. The endothelin system includes a group of at least 6 genes that encode a family of signaling peptides, receptors, and converting enzymes (Meidan and Levy, 2002). ...
... In bovine CL, synthesis of ET-1 has been demonstrated by the presence of ET-1 protein and mRNA (Girsh et al., 1996a). Addition of ET-1 reduced in vitro production of progesterone by dispersed luteal cells from midcycle CL (Girsh et al., 1995;Hinckley and Milvae, 2001). Furthermore, in the midluteal phase of the bovine estrous cycle, PGF 2 α stimulated expression of preproendothelin-1 (Girsh et al., 1996b). ...
... However, despite the massive research effort (see previous reviews [19,36,37]), no agreed mechanisms by which PGF2α exerts a direct anti-steroidogenic effect could be determined. At the same time, there were reports demonstrating that PGF2α paradoxically increases progesterone production [38][39][40][41]. It was then proposed that these inconsistent results [24,36,[38][39][40][41][42] were caused by the variable degrees of homogeneity in the luteal cell preparations used, which typically contain other nonsteroidogenic cell types. ...
... At the same time, there were reports demonstrating that PGF2α paradoxically increases progesterone production [38][39][40][41]. It was then proposed that these inconsistent results [24,36,[38][39][40][41][42] were caused by the variable degrees of homogeneity in the luteal cell preparations used, which typically contain other nonsteroidogenic cell types. For instance, contradictory results were obtained with large ovine luteal cells enriched by elutriation or luteinized bovine granulosa cells, a pure cell population that provides a valid model for large luteal cells [43,44]. ...
Chapter
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It is well established that in ruminants, and in other species with estrous cycles, luteal regression is stimulated by the episodic release of prostaglandin F2α (PGF2α) from the uterus, which reaches the corpus luteum (CL) through a countercurrent system between the uterine vein and the ovarian artery. Because of their luteolytic properties, PGF2α and its analogues are routinely administered to induce CL regression and synchronization of estrus, and as such, it is the basis of protocols for synchronizing ovulation. Luteal regression is defined as the loss of steroidogenic function (functional luteolysis) and the subsequent involution of the CL (structural luteolysis). During luteolysis, the CL undergoes dramatic changes in its steroidogenic capacity, vascularization, immune cell activation, ECM composition, and cell viability. Functional genomics and many other studies during the past 20 years elucidated the mechanism underlying PGF2α actions, substantially revising old concepts. PGF2α acts directly on luteal steroidogenic and endothelial cells, which express PGF2α receptors (PTGFR), or indirectly on immune cells lacking PTGFR, which can be activated by other cells within the CL. Accumulating evidence now indicates that the diverse processes initiated by uterine or exogenous PGF2α, ranging from reduction of steroid production to apoptotic cell death, are mediated by locally produced factors. Data summarized here show that PGF2α stimulates luteal steroidogenic and endothelial cells to produce factors such as endothelin-1, angiopoietins, nitric oxide, fibroblast growth factor 2, thrombospondins, transforming growth factor-B1, and plasminogen activator inhibitor-B1, which act sequentially to inhibit progesterone production, angiogenic support, cell survival, and ECM remodeling to accomplish CL regression.
... These cells express neural cell adhesion molecule (NCAM), which could mediate interaction between EC and LLC, which express NCAM. This functional adhesion between EC and LLC has been suggested to stimulate progesterone production by large luteal cells (Girsh et al. 1995). Endothelial cells are much smaller than large and small luteal cell with a diameter of 10-11 µm. ...
Thesis
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ABSTRACT Reproductive tract inflammatory diseases (RTID) of dairy cows are common worldwide and have been associated with a decrease in reproductive performance. The aims of this thesis were: (1) to quantify the effect of RTID on reproductive performance using data from 80 dairy herds across England and Wales, and from the University of Nottingham Dairy Centre; (2) to determine the effect of endometritis on the normality of post-partum milk progesterone profiles; (3) to investigate the association between endometritis and luteal vasculature and protein expression of steroidogenesis enzymes ex vivo; (4) to determine the expression of LPS-associated receptors including TLR4, CD14 and MD-2 in bovine CL using multiplex PCR; (5) to investigate the dose dependent effects of LPS on luteal endothelial cell vasculature in vitro and protein expression of steroidogenesis enzymes. Data analysis of 59118 cows from 80 dairy herds across England and Wales showed 12% prevalence of RTID from 2000-2007 (P<0.001). Cows with RTID had significantly longer intervals from calving to both first service and to conception by about 5 days (P<0.001) and 22 days (P<0.001), respectively. Moreover, cows with RTID had a lower conception rate to 1st service by 14% (P<0.001) and required more services per conception about 1 service more (P<0.001). In addition, they were 1.2 times more likely to be exited from the herd (P<0.001), and had higher 305d milk yield (P<0.01). Furthermore, this study analysed data from 708 cows at Nottingham dairy centre showed about 15% of prevalence of RTID form 2008-2014 (P<0.001). Similar effects were observed in the Nottingham dairy centre. However, only the day to 1st service was significant (P<0.001). The association between endometritis and milk progesterone profiles was investigated to establish the importance of endometritis on postpartum ovarian activity. Endometritis increased the incidence of atypical progesterone profile with prolonged luteal phase being the most affected. In the ex vivo study, there was a negative association between presence of endometritis with luteal vasculature, CL size, luteal progesterone content and quantification of steroidogenic enzyme expression. Endometritis caused significant inhibition in the degree of luteal vasculature, progesterone content and protein expression of steroidogenic enzymes by corpora lutea.LPS has been implicated in influencing ovarian function. Multiplex PCR showed that LPS receptors (TLR4, CD14, and MD-2) are expressed in bovine CL at all stages of CL development, indicating that CL could be a target for LPS action. A physiological cell culture system was consequently utilised to examine the effect of LPS on luteal endothelial cell network formation, progesterone (P4) production by luteal cells and steroidogenic enzyme expression in vitro. Treatment with VEGFA/FGF2 increased progesterone production by luteal cells (P<0.001). Moreover, progesterone production increased significantly from day 3-9 of culture. Under both basal condition and/or angiogenic stimulus (VEGFA/FGF-2), LPS (0.01, 0.1, 1 and 10 µg/ml) had no effect on P4 production by luteal cells on day 3, 5, and 9 of culture. LPS significantly inhibited luteal endothelial cells network formation. This was due to inhibition of endothelial cell proliferation and increasing endothelial cell apoptosis (P<0.001). In summary, the adverse impact that endometritis has on dairy cow fertility was identified by this work. This work offers a greater understanding of the effect of endometritis on dairy cow’s reproductive performance, early luteal development and function. In particular, this work provides evidence of a novel effect of endometritis on bovine luteal development and adequacy. It also offers further awareness into the role of LPS in terms of its negative effect on luteal endothelial cell angiogenesis and steroidogenesis.
... One of the primary steps to achieve this goal is driven by the early conceptus, which must signal its presence to the dam in a well-orchestrated biological process referred to as maternal recognition of pregnancy (Thatcher et al., 1986;Niswender et al., 2000;Mamo et al., 2012). In cycling cattle, prostaglandin-induced lysis of the corpus luteum (CL; i.e., luteolysis) occurs at approximately d 16 to 20 of the estrous cycle in nonpregnant females (Niswender et al., 1994;Fields and Fields, 1996) and involves a transient increase followed by a dramatic decrease in CL blood flow (Girsh et al., 1995;Plendl, 2000;Fraser and Wulff, 2003) to PGF 2α (Wiltbank et al., 1995;Acosta et al., 2002. ...
Article
Our objective was to retrospectively compare pregnant versus nonpregnant cattle in terms of vascular and morphometric changes in corpora lutea between d 12 and 20 following timed artificial insemination (TAI). Crossbred (Gir × Holstein) lactating dairy cows (n = 136) and heifers (n = 111) were bred after synchronizing ovulations using an estradiol plus progesterone (P4)-based protocol. Corpus luteum (CL) characteristics (area, echotexture, blood flow) were recorded at 48-h intervals from d 12 to 20 following TAI using an ultrasound equipped with color Doppler. Blood samples were collected to determine CL function (plasma P4). Pregnancy diagnosis was performed at d 30. Quantitative assessment of colored pixels within the CL was performed using ImageJ software (National Institutes of Health, Bethesda, MD) and echotexture was quantified using custom software. Continuous variables such as luteal tissue area (LTA), CL blood flow (CLBF), adjusted CLBF (ratio LTA:CLBF), mean pixel value (MPV), pixel heterogeneity (HETER), and plasma P4 were analyzed retrospectively as repeated measures (d 12 to 20) in pregnant versus nonpregnant females using PROC MIXED (SAS Institute Inc., Cary, NC). Main effects were pregnancy status, day of cycle, and their interaction. Further analyses used only data from d 16, because this was the earliest time point of deviation between CLBF of pregnant and nonpregnant animals. We created quartiles for each variable and calculated the risk of pregnancy within quartile. Differences were determined using the chi-squared test. Plasma P4 was significantly higher in prospective pregnant versus nonpregnant cattle on d 18 and 20, whereas LTA differed only on d 20. On d 16, CLBF and adjusted CLBF diverged between pregnant and nonpregnant, followed by a progressive reduction in the latter until d 20. Mean pixel value was not affected by pregnancy status, but HETER was lower on d 20 in pregnant than in nonpregnant cattle. Likelihood of pregnancy increased from quartile (Q)1 (lowest values) to Q4 (highest) of CLBF (Q4 vs. Q1, odds ratio = 32.8, 95% confidence interval: 9.6 to 112.1) and adjusted CLBF [Q4 vs. Q1, odds ratio = 25.4, 95% confidence interval: 8.1 to 80.4), whereas a lower risk of pregnancy was observed only for animals within Q1 of plasma P4 [Q4 vs. Q1, odds ratio = 3.1, 95% confidence interval: 1.3 to 7.2). Day 16 quartiles of LTA, MPV, and HETER did not affect odds of pregnancy. In conclusion, we identified distinct CLBF patterns as early as 16 d after TAI and confirmed that CL function is lost by a reduction in blood flow, which precedes physical regression.
... These cells express neural cell adhesion molecule (NCAM), which could mediate interaction between EC and LLC, which express NCAM. This functional adhesion between EC and LLC has been suggested to stimulate progesterone production by large luteal cells (Girsh et al. 1995). Endothelial cells are much smaller than large and small luteal cell with a diameter of 10-11 µm. ...
Article
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Introduction: In dairy cows, post-partum endometritis caused by Gram negative bacteria (e.g. E. coli) adversely affects follicular function and is associated with subfertility. However, there is limited information of the effects of endometritis on the corpus luteum (CL). Recently, we showed that LPS dose-dependently decreased luteal endothelial cell (EC) network formation in vitro. The hypothesis tested was that CL from cows with endometritis would have reduced vascularisation and steroidogenic capacity. Methods: Mid-luteal phase bovine ovaries were collected from cows with either no signs of endometritis (control, n=3) or presence of purulent endometrial discharge (n=3) confirmed macroscopically and histologically. Luteal sections were either snap frozen or fixed in Bouin’s. Ether-extracted progesterone content was determined by ELISA. Immunohistochemical analysis determined the degree of vascularisation (von Willebrand Factor) and pericyte coverage (smooth muscle actin SMA). Western blots assessed STAR, HSD3B, P450SCC and SMA protein expression (normalised to Histone H3). Groups were compared by t-tests. Results and discussion: CL from cows with endometritis were slightly smaller (P<0.05) with reduced luteal progesterone content (1.2-fold, P<0.05). Control CL contained extensive vascularisation with steroidogenic cells largely adjacent to endothelial cells. This vascularisation (3-fold, P<0.01) and pericyte coverage (4-fold, P<0.001) was much lower in endometritic cows. Western blot confirmed that SMA protein expression was lower (6-fold, P<0.001). Quantification of Western blots clearly showed lower STAR (2-fold), HSD3B (8-fold) and P450SCC (3-fold) protein levels in cows with endometritis (all P<0.01). In summary, cows with endometritis had smaller CL with reduced progesterone content. This was associated with decreased expression of progesterone synthesis proteins. Dramatically attenuated luteal endothelial cell area and pericyte coverage suggest that the luteal vasculature might be particularly sensitive to uterine-derived bacterial endotoxins.
... 450 Morphometric and biochemical studies of cellular constituents also suggest that cell-cell interactions are important in luteal regression. 451 When steroidogenic cells (i.e., large and small luteal cells) isolated from the bovine corpus luteum are incubated without other luteal cell types (i.e., immune and endothelial cells), PGF 2α failed to inhibit progesterone production. 452 When endothelial and immune cells are included, PGF 2α reduced progesterone production and induced the synthesis of nitric oxide (NO) and other arachidonic acid-derived mediators (e.g., leukotrienes). ...
Chapter
The corpus luteum is a transient endocrine gland in the adult ovary that differentiates from the follicle wall after ovulation. It is vital to mammalian reproduction as it produces the steroid hormone, progesterone, which acts on the reproductive tract to permit embryo implantation and to support a maternal environment that sustains intrauterine pregnancy. This chapter will review the remarkable species differences in endocrine and local control of the development (luteinization), functional lifespan, and regression (luteolysis) of the corpus luteum. The review will focus on luteotropic and luteolytic factors that regulate the structure and function of the corpus luteum during the ovarian cycle, and in some species extend the luteal lifespan if pregnancy occurs.
... All these findings strongly suggest a physiological impact of PGF 2 a and ET-1 in the rapid cascade of functional luteolysis in vivo, and a possible interaction between endothelial cells and luteal cells during luteolysis. Such local mechanisms have been postulated as the essential functions of growth, maintenance, and regression of the CL [12][13][14][15] and the follicle [16]. ...
Article
Recent observations suggest that the endothelial cell-derived vasoconstrictive peptide endothelin-1 (ET-1) interacts with prostaglandin F2alpha (PGF2alpha) and that luteal ET-1 participates in the rapid cascade of functional luteolysis in vivo. Thus, the present study aimed to determine in detail the real-time changes in ET-1, oxytocin (OT), and progesterone (P4) concentrations within the regressing corpus luteum (CL), along with the changes in ovarian venous plasma (OVP) ipsilateral to the CL as well as in jugular venous plasma (JVP) in the cow. In the first study, peripheral plasma from daily sampling during the estrous cycle (n = 6) showed clear changes in ET-1 concentration with the stage of the cycle (p < 0.05). ET-1 remained at basal concentrations (23.2+/-1.3 pg/ml) on Days 2-12, increased (p < 0.05) on Days 13-19 (33.5+/-2.6 pg/ml), and reached the highest (p < 0.001) concentrations (45.6+/-4.4 pg/ml) on Days 20-22 after estrus. These data indicate that plasma ET-1 concentration increases around luteolysis and estrus. In the second study, a microdialysis system (MDS) was surgically implanted into the CL of 11 cows in the midluteal phase. In 4 of the 11 cows, the catheter was also fitted to the ovarian vein ipsilateral to the CL at surgery. A PGF2alpha analogue (cloprostenol; 500 microg) was then injected (designated as 0 h) i.m. to induce luteolysis. In the cows fitted with an MDS, the PGF2alpha injection clearly induced a rapid decrease in intraluteal P4 release within 4 h (p < 0.05), and the levels decreased to 20% of the baseline after 24 h. Intraluteal release of ET-1 increased (p < 0.05) to 160% within 4 h after PGF2alpha injection, when an enormous OT release (to 950%) occurred, which reached a plateau of 250% after 20 h that persisted until 72 h. ET-1 release into the ovarian vein began to increase at 2 h after PGF2alpha injection, when the acute OT release almost dropped to the baseline. The ET-1 concentration was temporarily (between 0 and 24 h after PGF2alpha) 2-3 times higher in OVP than in JVP (p < 0.05), and increased again to higher levels than in JVP from 32 to 64 h (p < 0.05). ET-1 concentrations in JVP gradually increased from 10 pg/ml to 30 pg/ml during PGF2alpha-induced luteolysis (p < 0.05). In conclusion, PGF2alpha injection rapidly increased ET-1 release within the regressing CL as well as into the ovarian venous blood in the cow. The overall results strongly support the hypothesis that luteal ET-1 is a local luteolytic mediator/promotor in the regressing bovine CL.
Article
The corpus luteum (CL) forms following ovulation from the remnant of the Graafian follicle. This transient tissue produces critical hormones to maintain pregnancy, including the steroid progesterone. In cattle and other ruminants, the presence of an embryo determines if the lifespan of the CL will be prolonged to ensure successful implantation and gestation, or if the tissue will undergo destruction in the process known as luteolysis. Infertility and subfertility in dairy and beef cattle results in substantial economic loss to producers each year. In addition, this has the potential to exacerbate climate change because more animals are needed to produce high-quality protein to feed the growing world population. Successful pregnancies require coordinated regulation of uterine and ovarian function by the developing embryo. These processes are often collectively termed "maternal recognition of pregnancy." Research into the formation, function, and destruction of the bovine CL by the Northeast Multistate Project, one of the oldest continuously funded Hatch projects by the USDA, has produced a large body of evidence increasing our knowledge of the contribution of ovarian processes to fertility in ruminants. This review presents some of the seminal research into the regulation of the ruminant CL, as well as identifying mechanisms that remain to be completely validated in the bovine CL. This review also contains a broad discussion of the roles of prostaglandins, immune cells, as well as mechanisms contributing to steroidogenesis in the ruminant CL. A triadic model of luteolysis is discussed wherein the interactions among immune cells, endothelial cells, and luteal cells dictate the ability of the ruminant CL to respond to a luteolytic stimulus, along with other novel hypotheses for future research.
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The corpus luteum (CL) is an ovarian structure that produces progesterone to maintain pregnancy, begins its growth from the third day of the beginning of estrus growing until the eighteenth day. If the CL is fertilized, the formation of the embryo will produce the interferon τ (IFN-τ) substance responsible for maternal recognition of pregnancy (RMG) in cattle during their entire pregnancy. When CL is not fertilized, the uterine endometrium secretes prostaglandins F2α (PGF2α) causing lysis of the corpus luteum. The serum levels of progesterone decrease generating hypothalamus unlocking and gonadotropin-releasing hormone (GnRH) secretion to activate the hypothalamic-pituitary-gonadal axis that develops new follicles 48 to 72 h later and initiates a new estrus. This bibliographic review details the physiological mechanisms involved in the formation of the corpus luteum during the estrous cycle of cattle in the function and regression of the corpus luteum during the estrous cycle of cows.
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The present studies were conducted to determine whether luteinizing hormone (LH), a hormone which increases intracellular cAMP, also increases "second messengers" derived from inositol phospholipid hydrolysis in isolated bovine luteal cells. In luteal cells prelabeled with 32PO4, LH provoked increases in labeling of phosphatidic acid, phosphatidylinositol, and polyphosphatidylinositol (PIP). No reductions in 32P-prelabeled PIP and PIP2 were observed in LH-treated cells. In luteal cells prelabeled with myo-[2-3H]inositol, LH provoked rapid (10-30 s) and sustained (up to 60 min) increases in the levels of inositol mono-, bis-, and trisphosphates (IP, IP2, and IP3, respectively. IP3 was formed more rapidly than IP2 or IP following LH treatment. In addition, LH increased (50%) levels of [3H]inositol phospholipids in 30-min incubations. LiCl (10 mM) enhanced inositol phosphate accumulation in response to LH. Maximal increases in IP3 occurred at 1-10 micrograms/ml of LH. Similar temporal and dose-response relationships were observed for LH-stimulated IP3 and cAMP accumulation. However, exogenous cAMP (8-bromo-cAMP, 5 mM) and forskolin (10 microM) had no effect on inositol phosphate synthesis. The initial (1 min) effects of LH on IP3 and cAMP were independent of extracellular calcium concentrations, whereas the sustained (5 min) effect of LH on IP3, but not cAMP, was dependent on a source of extracellular calcium. LH-stimulated progesterone synthesis was also dependent on the presence of extracellular calcium. LH induced rapid and concentration-dependent increases in [Ca2+]i as measured by Quin 2 fluorescence. The LH-induced increases in [Ca2+]i were maximal within 30 s (approximately 2-fold) and remained elevated for at least 10 min. In Ca2+-free media containing 2 mM [ethylenebis(oxyethylenenitrilo)]tetraacetic acid, LH was still able to increase [Ca2+]i, but the increase was slightly less in magnitude and of shorter duration (2-4 min). These findings demonstrate that LH can rapidly raise levels of IP3 and [Ca2+]i, as well as, cAMP in bovine luteal cells. These findings suggest that at least two second messenger systems exist to mediate the action of LH in the corpus luteum.
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In the adult mammalian ovary morphogenesis and differentiation processes are under hormonal control and, thus, occur in a highly regulated way during the sexual cycle. Cell-cell interactions, such as cell adhesion and cell separation, are crucial during these events. Here we show that the ovarian endocrine cells, which are prototypes of steroid-producing cells, express neural cell adhesion molecules (NCAMs). The combined use of in situ hybridization histochemistry, immunocytochemistry at the light and electron microscope levels, S1 nuclease protection assays, and Western blotting revealed that in the ovary of the adult rat during the estrus cycle and pregnancy, NCAM mRNA and the 140-kDa isoform of this protein are expressed mainly in granulosa cells of growing preantral and antral follicles and in corpora lutea. Since the granulosa cells lining the forming antrum and the antral fluid were strongly immunoreactive, a role for NCAM in the formation of the follicular antrum is proposed. The expression of NCAM was also associated with luteal cells of the active corpus luteum, indicating a role for NCAM in the morphogenesis of this endocrine compartment. Moreover, thecal cells of large follicles and hypertrophic thecal cells of atretic follicles expressed NCAM, as did interstitial cells, which are derived from thecal cells of atretic follicles. We propose that the adhesion molecule, NCAM, is an important factor involved in the recognition and intercellular interaction of ovarian endocrine cells and, thus, participates in the regulation of the cyclic remodeling processes of the ovarian endocrine compartments
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The bovine corpus luteum contains two steroidogenic cell types, small and large luteal cells. The present study aimed to examine molecular mechanisms regulating progesterone (P4) production in long term cultures. The content of the side-chain cleavage (SCC) enzymes cytochrome P450scc and adrenodoxin (ADX) and the steady state availability of their mRNAs were determined and compared to P4 production in each of the luteal cell types. Small-like (SLC) and large-like (LLC) luteal cells were obtained by incubating theca interna and granulosa cells with forskolin and insulin. Upon luteinization, LLC expressed 2- to 3-fold higher amounts of both SCC enzyme mRNAs than did SLC. Moreover, 8 days after stimulant removal, LLC retained their P4 production capacity, expressed P450scc and ADX mRNAs, and contained these proteins. Nevertheless, the presence of the luteinizing agents in LLC culture medium was required for maximal expression of SCC enzymes. In the SLC, P4 production, P450scc and ADX content, and their mRNAs showed a much stronger dependence on chronic cAMP (and insulin) stimulation. In SLC, stimulant removal was accompanied by a sharp decrease (95% reduction) in P4 production, P450scc and ADX enzyme content (57% and 90% reduction, respectively), and their mRNAs (90% and 95% reduction, respectively). However, their steroidogenic capacity could be restored by forskolin and insulin replenishment. Interestingly, P4 production by both luteal cells types was reflected better in ADX than in P450scc content. These observations emphasize the contribution of the large luteal cell to P4 output, which may become crucial when hormonal support of the corpus luteum is deficient.
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Effects of season and incubation temperature on progesterone and prostaglandin F2alpha (PGF2alpha) production by bovine luteal cells were examined. Estrous cycles of Israeli-Holstein cows were Synchronized and ovaries collected following slaughter on Day 11 of the estrous cycle in winter and summer, and on Day 16 in winter. After enzymatic dispersion, cell count and viability determination. 300 000 luteal cells were incubated at 38 or 40-degrees-C for 2 h followed by 16 h at 38-degrees-C. Effects of bovine luteinizing hormone (LH) and forskolin, with or without PGF2alpha were examined. Cell number and viability were lower in summer than in winter. Incubation temperature did not affect cell viability. Winter Day 11 cells incubated at 40-degrees-C produced about 30% less progesterone than when incubated at 38-degrees-C. In summer Day 11 cells incubated at 38-degrees-C, LH or forskolin stimulated progesterone production was lower than in winter, and was not further reduced by incubation at 40-degrees-C. In winter Day 16 cells, less progesterone was produced compared with winter Day 11 cells (except for basal production after 2 h), and incubation temperature did not modify this result. Addition of PGF2alpha to the medium did not affect progesterone production. PGF2alpha production by luteal cells on Day 11 after 2 h incubation was higher in summer than in winter, being five and two times higher at 38-degrees-C and 40-degrees-C, respectively. These data indicate that the capacity of luteal cells to produce progesterone is impaired by both long-term seasonal heat stress and short-term incubation temperature effects.
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PROSTACYCLIN (PGI2) was reported by Vane and co-workers as a novel short-lived metabolite of prostaglandin endoperoxides (PGG2 and PGH2) which inhibited platelet aggregation1. Subsequent studies have demonstrated that PGI2 is the most potent inhibitor of platelet aggregation so far described, acting by stimulating platelet adenylate cyclase2-4. PGI2 is produced by isolated blood vessel segments5 and is therefore likely to be of great importance in the maintenance of vascular homeostasis. The cellular localisation and regulation of PGI2 synthesis have not previously been established, although it has been proposed that the main source of PGI2 is through pro-aggregatory prostaglandin endoperoxides released from platelets being enzymatically converted to PGI2 by vascular endothelial cells5,6. We show here that pig aortic endothelial cells, but not aortic smooth muscle cells or fibroblasts, synthesise PGI2. This production of PGI2 is stimulated by incubating endothelial cells with PGG2 or with its precursor, arachidonic acid. Furthermore, PGI2 synthesis is powerfully stimulated by cell-free plasma.
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As observed by SEM, the repair of an ovulated mammalian follicle is accompanied by a sequence of morphogenetic processes. In the initial phase, a mass of cells and coagulated fluids forms at the site of rupture. Shortly thereafter, connective cells, recruited from the adjacent and subjacent connective tissue stroma begin to proliferate and to migrate over this mass such that in the rabbit, the entire site of disruption is covered by a layer of connective cells by approximately 2 days following ovulation. Coincident with the migration of the connective tissue, superficial cells from undisturbed lateral and basal areas of an ovulated follicle also proliferate and begin to migrate over the newly established connective tissue matrix. By approximately 4 days following ovulation in the rabbit, the surface of an ovulated follicle is repopulated by elements of the superficial epithelium. The formation of the underlying corpus luteum (corpora lutea) involves characteristic morphological changes as granulosa cells transform into steroid secreting luteal cells. The luteal cells become organized into cords of cells which usually surround capillary vessels. When examined by SEM, the smooth-surfaced endoplasmic reticulum of the luteal cell is quite apparent and is observed to form a three-dimension network of anastomosing tubules which are continuous with the nuclear membrane. Variations in the appearance of the surface of the ovary which directly overlies corpora lutea were observed when the mouse, rat and rabbit were compared. The regression of corpora lutea involves the infiltration of the luteal mass by connective tissue and both degeneration and vacuolization of the luteal cells. The regressing corpus luteum is a honey-comb-like structure in which each space is occupied by a degenerating luteal cell.
An inhibitory effect of PGF2alpha at a dose of 7 X 10(-7) M on LH stimulated synthesis of progesterone was observed in vitro after incubation of pseudopregnant rat ovaries for a period of 2 hours. A similar effect was seen with cyclic and gestant ewe corpora lutea at the same dose of PGF2alpha. This effect was observed both in the secretion of progesterone and on the amount of progesterone present in the tissue. This inhibitory effect of PGF2alpha on LH stimulated progesterone synthesis may explain the modification in the time course for gonadotropin action in luteal tissue at high and low doses.