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PubMed1996

Endocrine regulation of ascorbic acid transport and secretion in luteal cells.

Luteal ascorbic acid depletion by LH and prostaglandin (PG) F2 alpha is well known, but how such depletion occurs is not. We therefore investigated the nature and regulation of ascorbic acid uptake and depletion in the rat CL and luteal cells. In vivo studies showed that blockade of steroidogenesis by aminoglutethimide prevented ascorbate depletion by LH, but not PGF2 alpha. Also, the time course for half-maximal depletion of ascorbic acid in vivo in response to PGF2 alpha was extremely rapid (2-3 min) compared to that known for LH (60 min). Thus, ascorbate depletion by LH and PGF2 alpha appears to occur by different mechanisms. In luteal cells, ascorbate uptake was energy-, sodium-, and microfilament-dependent with a Michaelis constant (Km) of 33 microM, similar to that reported for other cells. In contrast to findings for other cells, PGF2 alpha was found to be a potent and rapid inhibitor of ascorbate uptake with a half-maximal inhibition (IC50) of about 5 nM in luteal cells. Ascorbate uptake was unaffected by LH, PGE2, glucose, bromo-cAMP, progesterone, phorbol ester, ionomycin, hydrogen peroxide (H2O2), or aminoglutethimide. Also novel was the finding that luteal cell secretion of ascorbic acid was rapidly and potently stimulated by PGF2 alpha (IC50 about 5 nM), an effect mimicked by LH, H2O2, generators of reactive oxygen, calcium ionophore, and cytochalasin B. Basal release of ascorbic acid was energy-dependent, as secretion was blocked by a mitochondrial uncoupler and lowered temperature. Phorbol ester, bromo-cAMP, progesterone, aminoglutethimide, and ouabain had no effect on ascorbic acid secretion in luteal cells. These findings indicate that the secretion of ascorbic acid induced by PGF2 alpha, and possibly LH, may be mediated by calcium, reactive oxygen, and cytoskeletal changes. The ability of PGF2 alpha to inhibit ascorbate transport and to stimulate secretion implicates these processes as the basis for the rapid depletion of ascorbic acid in the CL. Ascorbate depletion by LH is associated with stimulation of steroidogenesis and an increase in ascorbic acid secretion.

Aminoglutethimide↗
PubMed2000

Effects of high density lipoprotein containing high or low beta-carotene concentrations on progesterone production and beta-carotene uptake and depletion by bovine luteal cells.

Luteal cells were isolated from mid-luteal heifer ovaries by collagenase digestion. Cells were cultured with DMEM/Ham's F12 medium in serum pre-treated plastic culture dishes for periods of up to 11 days. As beta-carotene is almost completely insoluble in all polar solvents, it was added to cultures in either dimethyl sulphoxide (DMSO), tetrahydrofuran (THF) or as high-density lipoprotein (HDL) containing high or low beta-carotene concentrations. Medium was replaced after 24 h, thereafter medium was changed every 48 h. Treatment of cells with DMSO alone or with beta-carotene (5 micromol/l) in DMSO both resulted in significant (P<0.01) stimulation of progesterone production. beta-Carotene (5 micromol/l) in THF did not alter progesterone production but 50 micromol/l beta-carotene in THF resulted in significant inhibition (P<0.02) of progesterone production on days 3 and 7. Cultures were also supplemented with bovine HDL preparations containing equal concentrations of cholesterol (25 microg/ml) but high or low beta-carotene (12.4 or 0.44 microg/mg of cholesterol). Both HDL preparations significantly stimulated progesterone production (P<0. 001) but the high beta-carotene HDL was significantly (P<0.02) more effective than the low beta-carotene HDL. However, when given together with bovine luteinizing hormone (bLH) or dibutyryl cAMP (dbcAMP), the high beta-carotene HDL stimulated progesterone production less than did the low HDL (P<0.01). Uptake and depletion of beta-carotene by luteal cells were also examined in culture. beta-Carotene supplementation increased luteal cell beta-carotene from an initial level of 373 ng per 10(6) cells to 2030 ng per 10(6) cells by day 6. In contrast, the levels in control cells decreased to 14% of starting values during the same period. Cells treated with HDL containing high beta-carotene on day 1 or days 1 and 3 were then incubated with or without bLH or dbcAMP for a further 2 days to investigate the effect of bLH and dbcAMP on depletion of beta-carotene by luteal cells. beta-Carotene depletion in the luteal cells was significantly higher (P<0.05) in LH- and dbcAMP-treated cells than in the control cells in both groups. These results indicate that the use of solvents such as DMSO or THF may have undesirable effects due to alteration of cell membrane permeability. Supplementation with bLH or dbcAMP may increase the metabolism of beta-carotene in luteal cells. bLH or dbcAMP together with high beta-carotene HDL may, when combined with the effect of increased beta-carotene metabolism, give less stimulation than with low beta-carotene HDL.

Animals↗
PubMed1989

Studies on the prostaglandin E-2-9-ketoreductase mediated production of prostaglandin F-2 alpha and its metabolism in cultured rabbit luteal cells.

Luteal cells were isolated from pseudopregnant rabbits on days 3, 6, 9, 12 and 15 post ovulation. Prostaglandin concentration and the activities of the enzymes prostaglandin E-2-9-ketoreductase and prostaglandin-15-hydroxydehydrogenase were determined. Luteal cells from day 7 and 12 of pseudopregnancy were maintained in culture for 24 h and then exposed to a mixture of [1-14C]PGE2 (70 mumol/l) in the presence or absence of estradiol-17 beta. After a 24 h incubation period, the culture medium was adjusted to pH 3.5, immediately extracted and analysed for PG. Cultured luteal cells were able to convert exogenously applied PGE2 to PGF2 alpha and to metabolize both PGs. Primary PGs as well as their metabolites 15-keto PGE2, 15-keto PGF2 alpha, 13,14-dihydro-15-keto PGE2, and 13,14 dihydro-15-keto PGF2 alpha were detected in the culture medium and in the cells. The addition of estradiol-17 beta together with PGE2 caused a significant reduction in the PGE2-9-ketoreductase mediated PGF2 alpha synthesis, whereas the metabolism of PGE2 remained unchanged. This inhibitory effect of estradiol-17 beta was dose-dependent on day 12 of pseudopregnancy. The results demonstrate that isolated rabbit luteal cells are able to synthesize and metabolize the luteolytic factor PGF2 alpha. Whether the inhibitory effect of estradiol-17 beta may have any physiological relevance has to be examined in further studies.

Animals↗
PubMed1999

Functional and subcellular changes in the A-kinase-signaling pathway: relation to aromatase and Sgk expression during the transition of granulosa cells to luteal cells.

The responsiveness of granulosa cells to FSH (cAMP) changes as these cells switch from the proliferative stage in growing follicles to the terminally differentiated, nonproliferating stage after LH-induced luteinization. To analyze this transition, two well characterized culture systems were used. 1) Granulosa cells isolated from immature rats were cultured in serum-free medium, a system that permits analysis of dynamic, short-term responses to hormones/cAMP. 2) Granulosa cells from preovulatory (PO) follicles that have been exposed in vivo to surge concentrations of hCG (PO/ hCG) were cultured in medium containing 1% FBS, a system that permits analyses of cells that have undergo irreversible, long-term changes associated with luteinization. To analyze the biochemical basis for the switch in cAMP responsiveness, the localization of A-kinase pathway components was related to the expression of two cAMP target genes, aromatase (CYP19) and serum-and glucocorticoid-induced kinase (Sgk). Components of the A-kinase pathway were analyzed by Western blotting and indirect immunofluorescence using specific antibodies to the C subunit, RIIalpha/beta subunits, CREB (cAMP-regulatory element binding protein), phospho-CREB, CBP (CREB binding protein), and Sgk. Cellular levels of C subunit and CREB were similar in all cell types and hormone treatments. CREB and CBP were nuclear; RIIalpha/beta was restricted to a cytoplasmic basket-like structure. Addition of FSH to immature granulosa cells caused rapid nuclear import of C subunit within 1 h. Nuclear C subunit decreased by 6 h after FSH but could be rapidly reimported to the nucleus by the addition of forskolin at 6, 24, or 48 h. Nuclear C subunit was associated with the rapid but transient increases in phospho-CREB. FSH induced Sgk in a biphasic manner in which the protein was nuclear at 1 h and cytoplasmic at 48 h. Aromatase mRNA was only expressed at 24-48 h after FSH, a pattern that was not altered by phosphodiesterases or phosphatases. In the luteinized (PO/hCG) granulosa cells, immunoreactive C subunit was localized in a punctate pattern in the nucleus as well as to a cytoplasmic basket-like structure, a distribution pattern not altered by forskolin. Aromatase, Sgk, and phospho-CREB were expressed at elevated levels in a non-forskolin-responsive manner. Most notable, both phospho-CREB and Sgk were preferentially localized in a punctate pattern within the cytoplasm and not altered by forskolin. Collectively, these data indicate that when granulosa cells differentiate to luteal cells the subcellular localization (nuclear vs. cytoplasmic) of A-kinase pathway components changes markedly. Thus, either the mechanisms of nuclear import and export or the presence of distinct docking sites (and functions ?) dictate where A-kinase, phospho-CREB and Sgk are localized in granulosa cells compared with the terminally differentiated luteal cells.

Animals↗
PubMed1975

Comparison of the binding of human chorionic gonadotropin to isolated bovine luteal cells and bovine luteal plasma membranes.

The specific binding of [125-I]iodohCG to intact luteal cells obtained from bovine corpus luteum by enzymatic treatment, or to purified plasma membranes obtained from bovine corpus luteum has been compared. It was a saturable process with respect to the [125-]iodohCG concentration. Specific binding could be detected at concentrations as low as 1.8 ng of HCG per ml and saturation achieved at 92 ng/ml. The [125-I]iodohCG specifically bound to the luteal cells or to the plasma membranes was displaced by increasing concentrations of native hCG. Subunits hCGalpha and beta had respectively 200- and 800-fold less activity than hCG. Four to 10 times more ovine LH than hCG was required to displace an identical amount of bound [125-I]iodohCG. The binding of hCG to its receptor site was a function of time and temperature. The affinity of hCG for its receptor sites in luteal cells or plasma membranes of luteal cells was similar (dissociation constants of 5.3 and 3.8 times 10- minus 10 M, respectively). The number of sites per luteal cell was 5 times 10-4 and the capacity of plasma membranes to bind hCG was 140 fmol per mg of protein at saturation. The data does not, however, allow a comparison between the number of binding sites in the two preparations. It is concluded that the enzymatic treatment necessary to obtain a suspension of viable luteal cells does not affect the kinetic characteristics of the binding of hCG to receptor sites since they are similar to those of plasma membranes not treated with proteolytic enzymes.

Animals↗
PubMed1992

Increased cellular cholesterol upregulates high density lipoprotein binding to rat luteal cells.

Rat luteal cells preferentially utilize cholesterol derived from high density lipoproteins (HDL) as a substrate for steroid hormone synthesis. The uptake of cholesterol from HDL by these cells is in contrast to nonsteroidogenic cells, which export cholesterol to HDL. A previous study demonstrated that HDL binding to luteal cell membranes was increased in conjunction with in vivo cholesterol depletion or cholesterol loading of the ovary induced by pharmacological agents. These results suggest a biphasic regulation of the HDL receptor in luteinized rat ovaries. In the present studies, the in vitro regulation of HDL binding in rat luteal cells by increased intracellular cholesterol was examined. Cultured luteal cells were incubated with increasing doses of low density lipoproteins (LDL) for 2 days after which the cellular sterol content and the effects on progesterone production and HDL binding were measured. As expected, the LDL treatment increased total cellular sterol content in a dose-dependent manner, resulting in a 2.1-fold increase over control at a dose of 1 mg LDL/ml. Increased cellular cholesterol was accompanied by a comparable increase in progesterone secretion. These results suggest that exogenous cholesterol was utilized by these cells. The LDL treatment also increased the binding of HDL to the cells in a dose-dependent manner to a maximum of 2.2-fold over control. The effect of increased cellular sterol on HDL binding was also examined using a more polar cholesterol derivative, 25-hydroxycholesterol. Cells were cultured for 2 days in media containing 0.3-40 micrograms/ml 25-hydroxycholesterol in the presence of 100 micrograms/ml aminoglutethimide, an inhibitor of cholesterol metabolism. The HDL binding to luteal cells exhibited dose-dependent up-regulation by 25-hydroxycholesterol with a 5.8-fold increase in binding at the maximum dose tested. Equilibrium binding studies using cells treated with 10 micrograms/ml 25-hydroxycholesterol revealed a 2.1-fold increase in the number of HDL binding sites on the luteal cells without affecting the binding affinity. From the results of this study, it is concluded that HDL binding in rat luteal cells is up-regulated by an increase in the intracellular cholesterol level.

Aminoglutethimide↗
PubMed1993

Basic fibroblast growth factor (bFGF) receptors decrease with luteal age in rat ovarian luteal cells: colocalization of bFGF receptors and bFGF in luteal cells.

Ovarian growth factors have been implicated in the development and differentiation of corpus luteum. We have characterized both high and low affinity receptors for basic fibroblast growth factor (bFGF) in luteal cells and tissue throughout the life span of corpus luteum using gonadotropin-treated rat luteinized ovaries. Additionally, we determined bFGF location in luteal tissue. High affinity (Kd, approximately 0.2 nM) and low capacity (approximately 500-6000 sites/cell, depending on luteal ages) [125I] bFGF-binding sites (mol wt, 140 kilodaltons, determined by affinity labeling) were found on luteal cells. [125I]bFGF binding to luteal cells and corpus luteum membranes progressively decreased in binding capacity without affecting binding affinity as the age of corpus luteum advanced. bFGF receptor (flg) mRNA in luteinized ovaries decreased with the luteal age similar to the [125I]bFGF binding. In contrast, low affinity binding sites, identified as heparan sulfate proteoglycans, which were immunohistochemically visualized around luteal cells, did not appear to change with luteal age. The signals for heparan sulfate proteoglycans that were found only in granulosa, but not theca-interstitial, cells of follicles became intense during folliculogenesis. The functionality of the bFGF receptors was shown by tyrosine phosphorylation of 16.5- and 18-kilodalton proteins in luteal cells with the antiphosphotyrosine antibody. Immunohistochemistry localized bFGF to steroidogenic luteal cells, and immunoblotting displayed larger molecular forms of bFGF in luteal cells. These results suggest that the bFGF receptors may be associated with the development and differentiation of corpus luteum in an autocrine manner.

Animals↗
PubMed1983

Progesterone production in vitro by small and large ovine luteal cells.

Corpora lutea from cyclic ewes were dissociated by collagenase digestion and trypsin/EGTA treatment. Enriched fractions of endothelial cells, small luteal cells and large luteal cells were prepared on a stepped gradient of Ficoll 400. Progesterone was measured by radioimmunoassay and the results corrected so that progesterone production by each cell type could be determined. Endothelial cells did not produce significant amounts of progesterone, with or without LH stimulation, and endothelial cell contamination of small and large luteal cell fractions did not influence progesterone production by these fractions. Mean +/- s.e.m. basal progesterone production (n = 10) by large luteal cells was greater (P less than 0.001) on a per cell basis than that by small luteal cells (1.16 +/- 0.16 compared with 0.25 +/- 0.06 pg/h/cell). However LH, which stimulated a maximal 3-4-fold increase in progesterone production by small luteal cells (LH ED50 = 0.14 ng/ml), had no significant effect on production by large luteal cells, when contamination by small luteal cells was taken into account. The response of small luteal cells was specific to LH, other hormones having had no significant effect. Basal progesterone production by small luteal cells (0.12 +/- 0.03 fg/h/micron3) calculated per unit volume of cell was not significantly different from that of large luteal cells (0.17 +/- 0.02 fg/h/micron3). After LH stimulation, small luteal cells produced more progesterone than did large luteal cells (0.40 +/- 0.09 compared with 0.18 +/- 0.03 fg/h/micron3) (P less than 0.05). When the amounts of progesterone produced per cell were multiplied by the absolute numbers of large luteal (1 X 10(7] and small luteal (5 X 10(7] cells in the intact corpus luteum, basal progesterone production by large luteal cells (11.6 +/- 1.6 micrograms/h) was similar to that by small luteal cells (12.3 +/- 3.0 micrograms/h). However, under LH stimulation, progesterone production by the small luteal cell type (39.9 +/- 9.5 micrograms/h) was approximately 3 times greater than that by the large luteal cell type (12.3 +/- 1.6 micrograms/h) (P less than 0.05). We therefore conclude that small luteal cells may be the principal source of luteal progesterone production in the sheep.

Animals↗
PubMed2005

Effect of progesterone on the expression of bax and bcl-2 and on caspase activity in bovine luteal cells.

Bovine luteal cells from days 6-10 and 11-15 of the estrous cycle were exposed (6 h) to factors that support or disrupt steroidogenesis. The expression of bcl-2 and bax and level of active caspase-3 in cells was measured. Progesterone (P4) increased (P<0.01) while staurosporine decreased (P<0.01-P<0.001) bcl-2 expression at both stages of the estrous cycle studied. In cells from 11-15 days of the estrous cycle expression of bcl-2 was stimulated (P<0.05) by prostaglandin (PG)E2 and inhibited (P<0.01) by 3,3',4,4'-tertrachlorobiphenyl (PCB)-77. Treatment with aminoglutethimide (blocker of cytochrome P450scc; 1.5 x 10(-4)M), nitric oxide donor (spermine NONOate), and staurosporine increased bax expression in cells collected from both experimental periods. The influence of these factors was greater in cells from days 11-15 (P<0.001) than by cells on days 6-10 (P<0.05) of the estrous cycle. PCB-77 stimulated expression of bax in cells from 11-15 days of cycle (P<0.01) only. Treatment of luteal cells with P4 and PGE2 for 24 h decreased (P<0.05) level of active caspase-3 while aminoglutethimide (P<0.05), spermine NONOate (P<0.05), and staurosporine (P<0.001) increased caspase-3 activity in the cells. Moreover, P4 decreased (P<0.05) while staurosporine increased (P<0.01) the ratio of bax/bcl-2 at both stages of the cycle. Aminoglutethimide, spermine NONOate and PCB increased (0<0.05) this ratio in cells on days 11-15 of the cycle. These results suggest that P4 concentrations in luteal cells protects against apoptosis, while disruption of steroidogenesis and reduced ability of luteal cells to produce P4 can induce cell death.

Aminoglutethimide↗
PubMed1989

Evidence for a switch in the site of relaxin production from small theca-derived cells to large luteal cells during early pregnancy in the pig.

The presence of immunoreactive relaxin was studied in corpora lutea of sows during the oestrous cycle and early pregnancy by immunohistochemistry and radioimmunoassay using three different anti-relaxin sera. Sections were immunostained using the peroxidase-anti-peroxidase or the immunogold-silver technique. Before Day 14, staining in corpora lutea from non-pregnant and pregnant animals was indistinguishable. With all antisera, no immunostaining was seen on Day 3, but was detected on Days 5-7 in cells from the theca interna. In non-pregnant animals, this immunostaining decreased and by Day 15 only an occasional large cell in the centre of the corpus luteum was stained. No staining was seen by Day 22. The relaxin content of corpora lutea measured by radioimmunoassay remained low throughout the luteal phase. In contrast, the amount of immunoreactive relaxin in corpora lutea rose dramatically (140-fold) between Days 11 and 14 of pregnancy and by Day 14 of pregnancy immunostaining was seen in the majority of large luteal cells. By Day 20 of pregnancy the concentrations of immunoreactive relaxin had further increased. Histochemical staining for alkaline phosphatase suggested that, while the relaxin-immunoreactive cells seen in the early luteal phase may be theca-derived, those during early pregnancy may be derived from the granulosa. The results are compatible with the suggestion that relaxin is produced by theca-derived cells during the early luteal phase and that between Days 11 and 14 there is a switch in the site of relaxin synthesis from theca-derived cells to granulosa-derived large luteal cells. In the absence of luteolysis, as during pregnancy, this switch is accompanied by a dramatic increase in relaxin synthesis.

Animals↗
PubMed1983

Large luteal cells the source of luteal oxytocin in the sheep.

To determine the cellular origin of oxytocin produced by the cyclical corpus luteum (CL) of the sheep, enriched fractions of enzymatically dispersed small and large luteal cells from 12 CL were prepared on a Ficoll 400 gradient. Oxytocin was measured by RIA. Large luteal cells contained 1.08 +/- (SD) 0.70 fg/cell oxytocin, which was congruent to 30 X the content of small luteal cells. Endothelial cells contained little if any oxytocin. During a 12-h incubation, large luteal cells produced 0.28 fg/cell.h oxytocin: small luteal cells did not produce measurable amounts of oxytocin. It is concluded that the large luteal cells are the source of the oxytocin produced by the CL of the sheep.

Animals↗
PubMed1993

Human growth hormone enhances progesterone production by human luteal cells in vitro. II. Evidence of a distinct effect on two luteal cell types.

OBJECTIVE: To examine the differential effect of human GH (hGH) on basal and hCG-stimulated production by cultured small and large human luteal cells. DESIGN: Distinct cultures of small and large luteal cells from early and midluteal phase. SETTING: All corpora lutea were obtained from the Obstetrics and Gynecology Department of the Catholic University, a public care center in Rome, Italy. PATIENTS, PARTICIPANTS: Ten nonpregnant women between 31 and 43 years of age underwent surgery for various nonendocrine disorders such as leiomyomatosis. INTERVENTIONS: Corpora lutea were obtained at the time of hysterectomy. MAIN OUTCOME MEASURES: Small and large luteal cells were incubated with or without hCG and/or hGH at different concentrations. RESULTS: Human GH neither at 250 nor at 500 micrograms/L increased basal P production by small luteal cells, whereas from 1,000 micrograms/L, P concentration in media was significantly increased. The concomitant treatment with ineffective doses of hCG (30 and 60 IU/L) and hGH (250 and 500 micrograms/L) enhanced P production to that obtained with the highest doses of hGH (1,000 micrograms/L or more) or hCG (125 to 250 IU/L) alone. Human GH addition did not change the amount of P release by large luteal cells at any concentration. CONCLUSIONS: These results indicate a distinct and differential effect of hGH on in vitro luteal steroidogenesis by the two luteal cell types.

Adult↗
PubMed2000

Decreased progesterone levels and progesterone receptor antagonists promote apoptotic cell death in bovine luteal cells.

We tested the hypothesis that progesterone (P(4)) acts at a local level to inhibit luteal apoptosis. Initial experiments employed aminoglutethimide, a P450 cholesterol side-chain cleavage inhibitor, to inhibit steroid synthesis. Cultured bovine luteal cells were treated with aminoglutethimide (0.15 mM) +/- P(4) (500 ng/ml) for 48 h. Luteal cells were recovered and snap frozen for isolation and analysis of oligonucleosomal DNA fragmentation or fixed for morphological analysis. Medium was collected for analysis of P(4) levels by RIA. Aminoglutethimide inhibited P(4) synthesis by > 95% and increased the level of apoptosis as evidenced by (32)P-labeled oligonucleosomal DNA fragmentation (> 40%). P(4) supplementation inhibited the onset of apoptosis that was induced by aminoglutethimide. These data were further supported by morphological assessment of apoptotic cells utilizing a Hoechst staining technique and together strongly suggest that P(4) has anti-apoptotic capacity. Using reverse transcription-polymerase chain reaction, we were able to isolate a 380-base pair cDNA from the bovine corpus luteum (CL) that was 100% homologous to the progesterone receptor (PR) previously found in bovine oviductal tissue. Furthermore, PR transcripts were present in large and small luteal cells. Immunohistochemistry also revealed that PR protein was present in both large and small luteal cells. To determine whether the anti-apoptotic effect of P(4) was regulated at the receptor level, luteal cells were cultured in the presence of PR antagonists, RU-486 and onapristone, for 48 h. Both antagonists caused approximately a 40% increase in (32)P-labeled oligonucleosomal DNA fragmentation. Interestingly, there was no difference (P >/= 0.05) in P(4) levels after treatment with PR antagonists. These observations support the concept that P(4) represses the onset of apoptosis in the CL by a PR-dependent mechanism.

Aminoglutethimide↗
PubMed1989

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.

Animals↗
PubMed1998

Peripheral blood mononuclear cells stimulate progesterone production by luteal cells derived from pregnant and non-pregnant women: possible involvement of interleukin-4 and interleukin-10 in corpus luteum function and differentiation.

Human luteal cells have been reported to express human leukocyte antigen-DR and lymphocyte functional antigen-3 on the cell surface, suggesting physiological interaction between luteal cells and T-lymphocytes through the menstrual cycle into early pregnancy. To elucidate the role of peripheral lymphocytes on corpus luteum differentiation, the effect of peripheral blood mononuclear cells (PBMC) on steroidogenesis by luteal cells was investigated. The production of Th-2 cytokines such as interleukin (IL)-4 and IL-10 by the co-cultured cells was also examined, and the effects of these cytokines on progesterone production by luteal cells were investigated. Corpora lutea were obtained from eight non-pregnant women in the luteal phase and five women in early pregnancy for luteal cell culture. PBMC were isolated from unrelated women in the follicular phase, secretory phase, and early pregnancy. After coculture with allogenic PBMC for 48 h, progesterone production was significantly enhanced by PBMC from the secretory phase and early pregnancy in the non-pregnant luteal cell culture. In the pregnant luteal cell culture, a significant increase in progesterone production was also observed by the co-culture with PBMC from women in early pregnancy, showing that PBMC have a luteotrophic effect. The stimulatory effects of PBMC were also observed in co-culture conditions which prevented direct cell-to-cell interaction with luteal cells, showing the minor influence of mixed lymphocyte reaction. By co-culture with PBMC, the production of IL-10, but not IL-4, was significantly augmented in luteal cell culture derived from non-pregnant women, whereas the production of both IL-4 and IL-10 was significantly enhanced in the luteal cell culture derived from pregnant women. Moreover, IL-4 and IL-10 promoted progesterone production by cultured luteal cells, especially in the luteal cell culture derived from corpora lutea of early pregnancy. These findings indicate that PBMC stimulate progesterone production by luteal cells and suggest the involvement of PBMC in corpus luteum function and differentiation probably via the Th-2-type lymphocytes.

Adult↗
PubMed1981

Negatively stained punctated cell contacts between luteal cells in rabbit and rat.

Cell contacts from rat and rabbit luteal cells have been spread on phosphotungstic acid solution after tissue fractionation or spreading was accomplished by a direct technique avoiding homogenization. Sectioned material was also examined. It was shown by negative staining that the cell contacts were composed of a multitude of bridges. These bridges were either filamentous (condensed form) or clearly showed a larger (expanded form) central particle. The corresponding image in top view showed respectively small and larger granules without any particular arrangement. Large granular structures were also seen on single plasma membranes. Evidence is presented that the condensed and the expanded form are two aspects of the same junctional structure. It is also suggested that both aspects are related to the tightness of the contact. Up to now this type of cell contract has been called "septate-like". However because of the dotted appearance of these contacts after colloidal lanthanum and after negative staining the denomination "punctated cell contact" may be better adapted.

Animals↗
PubMed1992

Prostaglandin F2 alpha- and phorbol 12-myristate-13-acetate-stimulated progesterone production by cultured human luteal cells in the mid-luteal phase: prostaglandin F2 alpha increases cytosolic Ca2+ and inositol phosphates.

While prostaglandin F2 alpha (PGF2 alpha) has been thought to be a natural luteolysin in non-primates, a luteolytic effect in the human corpus luteum is less evident. We therefore investigated the action of PGF2 alpha on monolayer cultures of human luteal cells obtained from mid-luteal phase corpora lutea. PGF2 alpha increased basal and human chorionic gonadotrophin (hCG)-stimulated progesterone production by human cultured luteal cells. A potent tumour-promoting phorbol ester, phorbol 12-myristate-13-acetate (PMA), also stimulated progesterone production by cultured human luteal cells. Although human luteal cells were incubated for 24 h with PMA, hCG was still able to stimulate the production of progesterone by PMA-pretreated cells. However, PMA pretreatment blocked the ability of PGF2 alpha to stimulate progesterone production. It is possible that the luteotrophic effect of PGF2 alpha may be mediated, in part, by the activation of protein kinase C. Addition of PGF2 alpha to suspensions of human luteal cells preincubated with myo-[2-3H]inositol promoted an increase in labelled inositol phosphates. PGF2 alpha also rapidly increased intracellular free Ca2+ in human luteal cells loaded with the fluorescent Ca2+ probe, fura-2. We conclude that PGF2 alpha and PMA stimulate progesterone production and that PGF2 alpha increases the intracellular free calcium and inositol phosphates of human cultured luteal cells in the mid-luteal phase.

Calcium↗