Effects of prostaglandin F2 alpha on agonist-induced progesterone production in cultured bovine luteal cells

The present study examines the effects of prostaglandin F2 alpha (PGF2 alpha) on basal and agonist-stimulated progesterone (P4) production utilizing long-term, serum-free cultures of bovine luteal cells. During the first 24 h of culture, PGF2 alpha had no significant effect on P4 production, and was unable to inhibit either luteinizing hormone (LH)- or dibutyryl cAMP (dbcAMP)-stimulated increases in P4. Treatment with PGF2 alpha on Day 1 produced a moderate, nonsignificant (P greater than 0.05) inhibition of cholera toxin (CT)- and forskolin (FKN)-stimulated P4 synthesis. Beyond Day 1 of culture (Days 3-11), PGF2 alpha continued to have no significant effect on basal P4 production, but suppressed all stimulatory effects of LH, dbcAMP, CT and FKN. Treatment with indomethacin inhibited prostaglandin synthesis by the cultured cells and also elevated levels of P4 from Days 3 to 11 of culture. Concurrent treatment with PGF2 alpha suppressed the steroidogenic effect of indomethacin. From these studies it was concluded that in cultured bovine luteal cells, PGF2 alpha does not affect basal P4 production, but is able to inhibit agonist-stimulated P4 production at a site beyond the accumulation of cAMP. This inhibitory effect is not apparent during the first 24 h of culture, but appears after Day 1 and persists throughout the remaining 10 days of the culture period.     

Prostacyclin, prostaglandin F2 alpha and progesterone production by bovine luteal cells during the estrous cycle

Corpora lutea (CL) were collected from Holstein heifers on Days 5, 10, 15 and 18 (5/day) of the estrous cycle. Dispersed luteal cell preparations were made and 10(6) viable luteal cells were incubated with bovine luteinizing hormone (LH) and different amounts of arachidonic acid in the presence and absence of the prostaglandin (PG) synthetase inhibitor indomethacin. The concentrations of progesterone, PGF2 alpha and 6-keto-PGF1 alpha, the stable inactive metabolite of prostacyclin (PGI2), were measured. Day 5 CL had the greatest initial content of 6-keto-PGF1 alpha (1.01 +/- 0.16 ng/10(6) cells), and synthesized more 6-keto-PGF1 alpha (2.55 +/- 0.43) than CL collected on Days 10 (0.57 +/- 0.11), 15 (0.08 +/- 0.05) and 18 (0.19 +/- 0.03) during a 2-h incubation period. Arachidonic acid stimulated the production of 6-keto-PGF1 alpha by Days 10, 15 and 18 luteal tissue. PGF2 alpha was produced at a greater rate on Day 5 (0.69 +/- 0.17 ng/10(6) cells) than on Days 10 (0.06 +/- 0.01), 15 (0.04 +/- 0.02) and 18 (0.08 +/- 0.01). Arachidonic acid stimulated and indomethacin inhibited the production of PGF2 alpha, in most cases. The initial content of 6-keto-PGF1 alpha was higher than that of PGF2 alpha on all days of the cycle and more 6-keto-PGF1 alpha was synthesized in response to arachidonic acid addition. The ratio of 6-keto-PGF1 alpha content to PGF2 alpha content was 4.39, 2.30, 1.25 and 1.13 on Days 5, 10, 15 and 18, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Multiple classes of prostaglandin F2 alpha binding sites in subpopulations of ovine luteal cells

A cryostorage procedure was developed to provide ovine luteal cells throughout the period of seasonal anestrus. Corpora lutea obtained from midluteal phase, superovulated ewes were dispersed enzymatically. Some dispersed cells were fractionated into subpopulations by elutriation. Dimethylsulfoxide (7.5% final concentration) in Hanks' buffered saline was added to cells at 4 degrees C, and dispersed cell preparations were frozen in a programmable cell freezer and stored at -196 degrees C. After recovery from cryopreservation, cell viability and prostaglandin F2 alpha (PGF2 alpha) binding characteristics of thawed cells were not different from those of corresponding fresh cells. Additionally, thawed cells retained the capacity to attach to culture dishes and retained responsiveness of progesterone secretion to prostaglandin E2 (PGE2) and ovine luteinizing hormone (LH), although rates of progesterone secretion were attenuated in thawed compared with fresh cells. The cryopreservation procedure will prove useful to relieve constraints in utilization of ovine luteal cells arising from reproductive seasonality in sheep. Cells retrieved from cryostorage were evaluated by studying PGF2 alpha binding characteristics. From saturation analyses (increasing amounts of radiolabeled PGF2 alpha) of PGF2 alpha binding to unfractionated cells, we detected a single class of high affinity binding sites (Kd = 17.4 +/- 2.3 nM) in addition to the nonspecific binding component. Using displacement analyses (constant radiolabeled PGF2 alpha and increasing amounts of unlabeled PGF2 alpha) and unfractionated cells, we detected additional binding sites of lower affinity (Kd = 409 +/- 166 nM) as well as the nonspecific binding component. Small luteal cells obtained by elutriation, which were essentially devoid of large cell contamination, had only low affinity binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of prostaglandin F2alpha and progesterone on the ability of bovine luteal cells to stimulate T lymphocyte proliferation

Bovine luteal cells express class I and II major histocompatibility complex molecules and stimulate T lymphocyte proliferation in vitro. Proliferation of T lymphocytes is greater in cocultures of luteal cells and T lymphocytes collected following administration of a luteolytic dose of prostaglandin (PG) F2alpha to the cow. Whether this results from changes in luteal cells that increase their ability to stimulate T lymphocyte proliferation or from changes in T lymphocytes that enhance their ability to respond to luteal cells is unclear. To determine which is the case, luteal cell-T lymphocyte cocultures were performed using luteal cells and T lymphocytes isolated from the same animals before and 8 h after administration of PGF2alpha. In the presence of T lymphocytes collected before PGF2alpha administration, luteal cells isolated after PGF2alpha were more potent stimulators of T lymphocyte proliferation than were luteal cells collected before PGF2alpha (P<0.05). The effect of progesterone on luteal cell-stimulated T lymphocyte proliferation was also evaluated. Proliferation of T lymphocytes was greater (P<0.05) in cultures containing the cytochrome P450 side-chain cleavage enzyme-inhibitor aminoglutethimide. Exogenous progesterone caused a dose-dependent inhibition of luteal cell-stimulated T lymphocyte proliferation (P<0.05). Progesterone-receptor mRNA was undetectable in peripheral blood mononuclear cells collected before and after PGF2alpha administration, indicating that the effect of progesterone was not mediated via progesterone receptors in lymphocytes. These results imply that specific changes in luteal cells in response to PGF2alpha enhance the ability of these cells to stimulate T lymphocyte proliferation. These results also demonstrate that progesterone can suppress luteal cell-stimulated T lymphocyte proliferation.     

synthesis of progesterone and prostaglandin F by luteal tissue and prostaglandin F by endometrial tissue from the pig

The relationship between progesterone (P₄) synthesis by luteal tissue and prostaglandin F (PGF) synthesis by endometrium and luteal tissue from two stages of the cycle, Days 7 to 8 and 15 to 16, was determined. Luteal and endometrial tissues were collected from pigs in three experimental groups at two stages of the cycle: (A) 6 pigs on Days 7 to 8 with spontaneous, 5 to 6 day old corpora lutea (CL); (B) 5 pigs on Days 15 to 16 with spontaneous, 13 to 14 day old CL; and (C) 6 pigs on Days 15 to 16 with spontaneous, 13 to 14 day old CL and 5 to 6 day old CL induced by pregnant mares serum gonadotropin (PMSG) and human chorionic gonadotropin (HCG) injections. Pigs with spontaneous, 13 to 14 day old CL of the cycle and PMSG-HCG induced accessory, 5 to 6 day old CL were used so that P₄ and PGF synthesis in tissue from old and new CL could be compared in the same pig on Day 15 to 16 of the cycle. Tissues (100 mg minces) were incubated in 5 ml of Krebs Ringer solution in an atmosphere of 95% 0₂:5% CO₂ for 2 hours at 0° C, 37° C, or 37° C with 1.3 x 10⁻⁴M indomethacin (IND). An aliquot of the incubation medium and an aliquot of the supernatant after homogenization of the tissue in the remaining medium of each flask was quantified for P₄ and PGF by radioimmunoassay. P₄ and PGF release into the medium and total accumulation of P₄ and PGF in the flasks indicated that synthesis had occured at 37° C. Compared to tissue from 13 to 14 day old CL, tissue from 5 to 6 day old CL synthesized more P₄ per flask (53.9 25.0 ng/mg tissue, P<.001) and released more P₄ into the medium (20.8 8.8 ng/mg, P<.001). P₄ synthesis by luteal tissue from 5 to 6 day old and 13 to 14 day old CL from pigs in group C was similar to P₄ synthesis by luteal tissue from pigs in group A and group B, respectively. Luteul PGF synthesis was not affected significantly by either the age of the CL or by PMSG-HCG treatment. For endometrial samples, the synthesis of PGF was not significantly different among pigs in groups A, B and C. If uterine PGF is involved in luteal regression in the pig, the sensitivity of the CL to PGF may be more important than an increase in PGF secretion during the late luteal phase of the estrous cycle.     

Prostaglandin F2 alpha, oxytocin and progesterone secretion by bovine luteal cells at several stages of luteal development: effects of oxytocin, luteinizing hormone, prostaglandin F2 alpha and estradiol-17 beta

Bovine luteal cells from Days 4, 8, 14 and 18 of the estrous cycle were incubated for 2 h (1 x 10(5) cells/ml) in serum-free media with one or a combination of treatments [control (no hormone), prostaglandin F2 alpha (PGF), oxytocin (OT), estradiol-17 beta (E) or luteinizing hormone (LH)]. Luteal cell conditioned media were then assayed by RIA for progesterone (P), PGF, and OT. Basal secretion of PGF on Days 4, 8, 14 and 18 was 173.8 +/- 66.2, 111.1 +/- 37.8, 57.7 +/- 15.4 and 124.3 +/- 29.9 pg/ml, respectively. Basal release of OT and P was greater on Day 4 (P less than 0.01) than on Day 8, 14 and 18 (OT: 17.5 +/- 2.6 versus 5.6 +/- 0.7, 6.0 +/- 1.4 and 3.1 +/- 0.4 pg/ml; P: 138.9 +/- 19.5 versus 23.2 +/- 7.5, 35.4 +/- 6.5 and 43.6 +/- 8.1 ng/ml, respectively). Oxytocin increased (P less than 0.01) PGF release by luteal cells compared with control cultures irrespective of day of estrous cycle. Estradiol-17 beta stimulated (P less than 0.05) PGF secretion on Days 8, 14 and 18, and LH increased (P less than 0.01) PGF production only on Day 14. Prostaglandin F2 alpha, E and LH had no effect on OT release by luteal cells from any day. Luteinizing hormone alone or in combination with PGF, OT or E increased (P less than 0.01) P secretion by cells from Days 8, 14 and 18. However on Day 8, a combination of PGF + OT and PGF + E decreased (P less than 0.05) LH-stimulated P secretion. These data demonstrate that OT stimulates PGF secretion by bovine luteal cells in vitro. In addition, LH and E also stimulate PGF release but effects may vary with stage of estrous cycle.     

The effect of prostaglandin F2 alpha and its analogues on progesterone, estradiol and androgen production by the cultured bovine luteal cells

The effect of PGF2 alpha and its analogues on progesterone, estradiol and androgen production in cow corpus luteum in vitro was investigated. The cells derived from cow corpora lutea (CL) and collected in the early and middle luteal phases of the oestrus cycle were cultured as monolayers. The inhibitory effect was not apparent during the first 48 hr of culture, but appeared after this time and persisted through the remainder of the culture period. The direct luteolytic influence of PGF2 alpha was observed in the cultured cells and showed that this compound can act independently of the blood supply.     

Effect of human chorionic gonadotropin and prostaglandin F2a on progesterone production by human luteal cells

To determine and compare the direct effects of prostaglandin F2a (PGF2a) and human chorionic gonadotropin (hCG) on luteal cell progesterone production in vitro, 9 human corpora lutea obtained at tubal ligation were minced and treated with collagenase to disaggregate luteal cells. Dispersed luteal cells (80% viable) were incubated in air at 37 degrees C in a shaking water bath for 3 h and total progesterone in the media and cells was determined by radioimmunoassay. Optimum progesterone production was obtained using 25,000 or more cells per incubate and an incubation time of 2-4 h. hCG-stimulated progesterone production increased significantly with 0.01 IU to as high as 100 IU. In the early luteal phase (days 1-5 post ovulation or days 15-20 of the luteal phase), PGF2a (10-1000 ng) significantly inhibited progesterone production but significantly stimulated progesterone production in the mid-luteal phase (days 21-25). PGF2a had no effect on luteal cell progesterone production in the late luteal phase (days 26-30). This age-dependent direct effect of PGF2a on human luteal cell progesterone production in vitro indicates a role for PGF2a in the total intragonadal regulation of progesterone output, possibly through a paracrine or autocrine manner directed towards synchronizing luteal progesterone secretion and endometrial preparation for nidation.     

In vitro action of PG F2 alpha on progesterone and cAMP synthesis in small bovine luteal cells

The action of prostaglandin F2 alpha (PG F2 alpha) on incubated small bovine luteal cells in the presence or in the absence of bovine luteinizing hormone (LH) or dibutyryl cyclic adenosine monophosphate (db cAMP) was investigated. In the absence of LH and db cAMP, PG F2 alpha stimulated progesterone synthesis at concentrations of 10 ng/ml and 100 ng/ml but had no effects at concentrations below 1 ng/ml. PG F2 alpha partially inhibited the LH or db cAMP stimulated progesterone synthesis. This inhibition was maximal for PG F2 alpha concentrations around 100 pg/ml whereas distinctly higher or lower concentrations were without effect. At the concentration of 100 pg/ml, PG F2 alpha partially inhibited the LH induced cAMP accumulation. These results demonstrate an "in vitro" action of PG F2 alpha on bovine luteal cells. They indicate that the luteolytic action of PG F2 alpha in the bovine species could involve, as already suggested for the rat, both an inhibition of the LH induced synthesis of cAMP and an inhibition of the action of cAMP.     

Stimulation by prostaglandin F2 alpha of phosphatidic acid-phosphatidylinositol turnover in rat luteal cells

Prostaglandin F2 alpha (PGF 2 alpha) causes a rapid and marked increase of [32P]-orthophosphate incorporation into phosphatidylinositol (PI) and phosphatidic acid (PA) in rat luteal cells in culture. The incorporation of radioactivity is increased as early as 2 and 5 min after PGF 2 alpha addition into PA and PI, respectively, and by 10 min has reached a 2-fold stimulation over control in both lipid moieties. The labeling of other phospholipids is not affected. PGF 2 alpha exerts its stimulatory effect at an ED50 value of approximately 200 and 60 nM on PI and PA labeling, respectively. By contrast, human chorionic gonadotropin has no effect alone and does not interfere with the PGF 2 alpha-induced stimulation of PA-PI labeling. The striking similarity between the effects of PGF 2 alpha and LHRH on PA-PI labeling suggests that the two agents may exert their direct action on the corpus luteum via a common intracellular mechanism involving acidic phospholipid metabolism.     

Proteins secreted from the early ovine conceptus block the action of prostaglandin F2 alpha on large luteal cells.

In this study we evaluated whether the early conceptus secretes a factor that blocks the action of prostaglandin (PG) F2 alpha on cultured ovine large luteal cells. PGF2 alpha inhibited progesterone production by lipoprotein-stimulated large luteal cells and this anti-steroidogenic action was blocked in a dose-dependent manner by conceptus proteins secreted from Day 15 embryos. Purified ovine trophoblast protein-1 (oTP-1) did not exhibit the anti-PGF2 alpha activity, but secreted conceptus proteins devoid of oTP-1 did prevent the anti-steroidogenic effects of PGF2 alpha. This activity does not appear to be a nonspecific effect of protein since neither serum albumin nor thyroglobulin, gamma globulin, insulin, LH, secreted ovine endometrial proteins, or heat-inactivated secreted conceptus proteins had this action. After molecular-sizing chromatography we found a high- and a low-molecular weight fraction with luteal protective activity. Neither of the secreted conceptus protein fractions blocked the binding of 3H-PGF2 alpha to large luteal cells. However, conceptus proteins did block the anti-steroidogenic action of phorbol ester and calcium ionophore on large luteal cells, suggesting that secreted conceptus proteins act after activation of the free calcium/protein kinase C intracellular effector pathways. Thus, the early ovine conceptus secretes a luteal protective protein(s) that may be important for maintaining the corpus luteum during early pregnancy; however, the physiologic significance of this luteal protective protein(s) cannot be stated without further investigation.     

Effects of estradiol-17 beta and progesterone on the synthesis of prostaglandin F2 alpha, prostaglandin E2 and prostaglandin I2 by fibroblasts from human endometrium in vitro

Estradiol-17 beta increases the production of prostaglandin F2 alpha (PGF2 alpha) in long term monolayer cell cultures of the human endometrium in a dose dependent manner. Progesterone in pharmacological dosage stimulates the syntheses of PGF2 alpha and of prostaglandin E2 (PGE2). The synthesis of prostaglandin I2 (PGI2) is not influenced by sex steroids in long term monolayer cell cultures of the human endometrium.     

Localization of prostaglandin F2 alpha inhibition of lipoprotein use by bovine luteal cells.

Prostaglandin F2 alpha (PGF2 alpha) inhibits lipoprotein-stimulated progesterone production by bovine luteal cells in vitro and the objective of this study was to localize the site of action of PGF2 alpha. Cultured bovine luteal cells were treated with PGF2 alpha for seven days, and then with either lipoproteins or 25-hydroxycholesterol in the presence of aminoglutethimide (which inhibits cholesterol side-chain cleavage) for the final 48 h. The effects of PGF2 alpha on progesterone production, cellular cholesterol content, mitochondrial cholesterol content and cholesterol side-chain cleavage activity were determined. As expected, PGF2 alpha inhibited (P less than 0.05) lipoprotein-stimulated progesterone production. However, PGF2 alpha did not inhibit low-density lipoprotein-stimulated, or high density lipoprotein-stimulated, increases in cellular cholesterol (P less than 0.05) or inhibit lipoprotein-induced increases in mitochondrial cholesterol content (P less than 0.05). Additionally, cholesterol content of mitochondria increased (P less than 0.05) in the presence of PGF2 alpha alone. To determine if the PGF2 alpha-induced inhibition of steroidogenesis occurred at, or after, the side-chain cleavage reaction, we treated cells with the readily diffusable sterol, 25-hydroxycholesterol. Prostaglandin F2 alpha did not inhibit 25-hydroxycholesterol-stimulated progesterone production (P less than 0.05). Prostaglandin F2 alpha may therefore exert its luteolytic effect at a site after cholesterol transport to the mitochondria but before cholesterol side-chain cleavage.     

Effect of dose of prostaglandin F(2alpha) on steroidogenic components and oligonucleosomes in ovine luteal tissue

To determine whether prostaglandin (PG) F(2alpha) had a dose-dependent effect upon secretion of progesterone, oligonucleosome formation, or loss of luteal weight, ewes on Day 9 or 10 of the estrous cycle were administered 0, 3, 10, or 30 mg PGF(2alpha) per 60 kg BW (i.v.), and luteal tissue was collected 9 and 24 h after injection. All doses of PGF(2alpha) decreased (P < 0. 05) concentrations of progesterone in sera by 9 h; however, in ewes treated with 3 mg PGF(2alpha), concentrations of progesterone were similar to control values at 24 h and higher (P < 0.05) than those in the 10- or 30-mg groups. Concentrations of progesterone in sera over all dose levels were highly correlated to luteal concentrations of mRNA encoding steroidogenic acute regulatory protein (P < 0.001), cytochrome P450 side-chain cleavage (P < 0.02), and 3beta-hydroxysteroid dehydrogenase (P < 0.01). Corpora lutea collected at 24 h from ewes treated with the 10- and 30-mg doses of PGF(2alpha) weighed less (P < 0.05) than those from controls. Oligonucleosomes were not present in luteal tissues from control ewes. Surprisingly, all doses of PGF(2alpha)-induced oligonucleosomes in a majority of animals at 9 h and in a majority of ewes treated with 10 and 30 mg of PGF(2alpha) at 24 h. In conclusion, 3 mg of PGF(2alpha) per 60 kg BW transiently decreased serum concentrations of progesterone and induced oligonucleosome formation, but did not result in reduced luteal weight. The 10- and 30-mg doses of PGF(2alpha) decreased secretion of progesterone and induced oligonucleosome formation and luteolysis.     

Inhibition of prostaglandin F2alpha synthesis and oxytocin receptor by progesterone antagonists in bovine endometrial cells in vitro

Oxytocin receptor (OTR) expression is suppressed by progesterone (P4) during the luteal phase of the estrous cycle and then it increases at the time of luteolysis, but its regulation is still not completely understood. In vitro studies to determine the mechanism of action are hindered because OTR spontaneously upregulates in vitro and it is impossible to alter expression with P4 or estradiol. During recent studies examining the effect of P4 and an antagonist (mifepristone) on PG secretion, we found that mifepristone attenuated OT-stimulated PG secretion from endometrial epithelial cells. The objective of the present study was to determine, whether this effect of mifepristone was due to changes in prostaglandin synthesis and/or OTR. A time-course showed that mifepristone (5 microM) had no significant effect after 24 h but by 72 h it decreased PGF(2alpha) secretion (P<0.01) and abolished the response of the cells to OT (P<0.01). The presence or absence of P4 did not affect the response to mifepristone. To determine the site of action of mifepristone, cells were cultured for 72 h with or without mifepristone and then COX-1 and COX-2 were measured by Western blotting and OTR was measured by saturation analysis. The results showed that mifepristone did not affect basal or PMA-stimulated expression of either COX-1 or COX-2 but did, however, decrease OTR number (P<0.05). These data demonstrate that OTR and the response to OT can be downregulated in endometrial epithelial cells in vitro via a mechanism involving the P4 receptor.     

Anti-apoptotic roles of prostaglandin E2 and F2alpha in bovine luteal steroidogenic cells

Production of prostaglandins (PGs) and expression of their receptors have been demonstrated in bovine corpus luteum (CL). The aim of the present study was to determine whether PGE2 and PGF2alpha have roles in bovine luteal steroidogenic cell (LSC) apoptosis. Cultured bovine LSCs obtained at the midluteal stage (Days 8-12 of the cycle) were treated for 24 h with PGE2 (0.001-1 microM) and PGF2alpha (0.001-1 microM). Prostaglandin E2 (1 microM) and PGF2alpha (1 microM) significantly stimulated progesterone (P4) production and reduced the levels of cell death in the cells cultured with or without tumor necrosis factor alpha (TNF)/interferon gamma (IFNG), in the presence and absence of FAS ligand (P < 0.05). Furthermore, DNA fragmentation induced by TNF/IFNG was observed to be suppressed by PGE2 and PGF2alpha. Prostaglandin E2 and PGF2alpha also attenuated mRNA expression of caspase 3 and caspase 8, as well as caspase 3 activity (P < 0.05) in TNF/IFNG-treated cells. FAS mRNA and protein expression were decreased only by PGF2alpha (P < 0.05). A specific P4 receptor antagonist (onapristone) attenuated the apoptosis-inhibitory effects of PGE2 and PGF2alpha in the absence of TNF/IFNG (P < 0.05). A PG synthesis inhibitor (indomethacin) reduced cell viability in PGE2- and PGF2alpha-treated cells (P < 0.05). A specific inhibitor of cyclooxygenase (PTGS), PTGS2 (NS-398), also reduced cell viability, whereas an inhibitor of PTGS1 (FR122047) did not affect it. The overall results suggest that PGE2 and PGF2alpha locally play luteoprotective roles in bovine CL by suppressing apoptosis of LSCs.     

Regulation of luteal prostaglandin F(2 alpha) production and its relevance to cell death: an in vitro study using rat dispersed luteal cells

We investigated the mechanism by which rat luteal cells produce prostaglandin F(2 alpha) (PGF(2 alpha)) and its relevance to cell death in vitro. Treatment with progesterone (P4) of dispersed luteal cells prepared from rats on day 9 of pseudopregnancy caused dose-dependent inhibition of PGF(2 alpha) secretion. Cytokines, tumor necrosis factor alpha (TNFalpha) or interferon gamma (IFN gamma) alone had no or modest regulatory effects. Arachidonyl trifluoromethyl ketone (AACOCF(3)), a specific group IVA phospholipase A(2) inhibitor, depressed both basal and cytokine-regulated PGF(2 alpha) production. A combination of TNFalpha and IFN gamma stimulated PGF(2 alpha) synthesis and cytotoxicity (both, P<0.05). Agonistic anti-Fas antibody challenge caused a significant cytotoxic effect but without affecting PGF(2 alpha) production. The present data suggest that P4 inhibits and TNFalpha and IFN gamma cooperatively stimulate PGF(2 alpha) release by rat luteal cells. They also suggest that luteal cell death induced by TNFalpha/IFN gamma and Fas stimulation seems to occur via distinct signaling pathways involving PGF(2 alpha) production.     

Regulation of steroidogenesis and cholesterol synthesis by prostaglandin F-2 alpha and lipoproteins in bovine luteal cells

Bovine luteal cells can utilize low density lipoprotein (LDL) or high density lipoprotein (HDL) as a source of cholesterol for steroidogenesis, and administration of PGF-2 alpha in vitro suppresses lipoprotein utilization. The objective of this study was to examine the mechanism by which PGF-2 alpha exerts this effect. Cultured bovine luteal cells received 0.25 microCi[14C]acetate/ml, to assess rates of de-novo sterol and steroid synthesis, with or without lipoproteins. Both LDL and HDL enhanced progesterone production (P less than 0.01), but caused a significant reduction in the amount of radioactivity in the cholesterol fraction. PGF-2 alpha treatment inhibited the increase in lipoprotein-induced progesterone synthesis (P less than 0.01), but did not prevent the reduction in de-novo cholesterol synthesis brought about by LDL or HDL. PGF-2 alpha alone reduced cholesterol synthesis (P less than 0.01), but it was not as effective as either LDL or HDL. Both lipoproteins and PGF-2 alpha also decreased the amount of radioactivity in the progesterone fraction (P less than 0.01), and the effect of PGF-2 alpha was similar to that of the lipoproteins. It is concluded that lipoproteins can enhance progesterone production and also suppress de-novo cholesterol synthesis in bovine luteal cells, but only the former effect of lipoproteins is inhibited by PGF-2 alpha. Therefore, it is suggested that PGF-2 alpha allows entry of lipoprotein cholesterol into the cell, but prevents utilization for steroidogenesis. In addition, PGF-2 alpha alone can suppress cholesterol synthesis, as well as decrease conversion of cholesterol to progesterone.