scholarly journals Estrogen promotes luteolysis by redistributing prostaglandin F2α receptors within primate luteal cells

Reproduction ◽  
2015 ◽  
Vol 149 (5) ◽  
pp. 453-464 ◽  
Author(s):  
Soon Ok Kim ◽  
Nune Markosyan ◽  
Gerald J Pepe ◽  
Diane M Duffy
Keyword(s):  
Estrogen Receptor ◽  
Granulosa Cells ◽  
Prostaglandin F2α ◽  
Luteal Cell ◽  
Corpora Lutea ◽  
Dependent Manner ◽  
Perinuclear Region ◽  
Luteal Cells ◽  
Progesterone Production

Prostaglandin F2α (PGF2α) has been proposed as a functional luteolysin in primates. However, administration of PGF2α or prostaglandin synthesis inhibitors in vivo both initiate luteolysis. These contradictory findings may reflect changes in PGF2α receptors (PTGFRs) or responsiveness to PGF2α at a critical point during the life span of the corpus luteum. The current study addressed this question using ovarian cells and tissues from female cynomolgus monkeys and luteinizing granulosa cells from healthy women undergoing follicle aspiration. PTGFRs were present in the cytoplasm of monkey granulosa cells, while PTGFRs were localized in the perinuclear region of large, granulosa-derived monkey luteal cells by mid-late luteal phase. A PTGFR agonist decreased progesterone production in luteal cells obtained at mid-late and late luteal phases, but did not decrease progesterone production by granulosa cells or luteal cells from younger corpora lutea. These findings are consistent with a role for perinuclear PTGFRs in functional luteolysis. This concept was explored using human luteinizing granulosa cells maintained in vitro as a model for luteal cell differentiation. In these cells, PTGFRs relocated from the cytoplasm to the perinuclear area in an estrogen- and estrogen receptor-dependent manner. Similar to our findings with monkey luteal cells, human luteinizing granulosa cells with perinuclear PTGFRs responded to a PTGFR agonist with decreased progesterone production. These data support the concept that PTGFR stimulation promotes functional luteolysis only when PTGFRs are located in the perinuclear region. Estrogen receptor-mediated relocation of PTGFRs within luteal cells may be a necessary step in the initiation of luteolysis in primates.

Conversion of 5(10)-oestrene-3β,17β-diol to 19-nor-4-ene-3-ketosteroids by luteal cells in vitro: possible involvement of the 3β-hydroxysteroid dehydrogenase/isomerase

1991 ◽  
Vol 129 (2) ◽  
pp. 233-243 ◽  
Author(s):  
C. M. H. Lee ◽  
F. R. Tekpetey ◽  
D. T. Armstrong ◽  
M. W. Khalil
Keyword(s):  
Granulosa Cells ◽  
Ovarian Follicle ◽  
Cell Types ◽  
Hydroxysteroid Dehydrogenase ◽  
Corpora Lutea ◽  
Dependent Manner ◽  
Luteal Cells ◽  
Porcine Granulosa Cells ◽  
Porcine Luteal Cells

ABSTRACT We have previously suggested that in porcine granulosa cells, a putative intermediate, 5(10)-oestrene-3,17-dione is involved in 4-oestrene-3,17-dione (19-norandrostenedione; 19-norA) and 4-oestren-17β-ol-3-one (19-nortestosterone: 19-norT) formation from C19 aromatizable androgens. In this study, luteal cells prepared from porcine, bovine and rat corpora lutea by centrifugal elutriation were used as a source of 3β-hydroxysteroid dehydrogenase/isomerase in order to investigate the role of this enzyme in the biosynthesis of 19-norsteroids. Small porcine luteal cells made mainly 19-norT and large porcine luteal cells 19-norA from 5(10)-oestrene-3β,17β-diol, the reduced product of the putative intermediate 5(10)-oestrene-3,17-dione. However, neither small nor large cells metabolized androstenedione to 19-norsteroids. Serum and serum plus LH significantly stimulated formation of both 19-norA and 19-norT from 5(10)-oestrene-3β,17β-diol, compared with controls. Inhibitors of the 3β-hydroxysteroid dehydrogenase/isomerase (trilostane and cyanoketone) significantly reduced formation of 19-norT in small porcine luteal cells and 19-norA in large porcine luteal cells, although they were effective at different concentrations in each cell type. In parallel incubations, formation of [4-14C]androstenedione from added [4-14C]dehydroepiandrosterone was also inhibited by cyanoketone in both small and large porcine luteal cells in a dose-dependent manner; however, trilostane (up to 100 μmol/l) did not inhibit androstenedione formation in large porcine luteal cells. In addition, the decrease in progesterone synthesis induced by trilostane and cyanoketone (100 μmol/l each) was accompanied by a parallel accumulation of pregnenolone in both cell types. These results suggest that 3β-hydroxysteroid dehydrogenase/isomerase, or a closely related enzyme, present in small and large porcine luteal cells can convert added 5(10)-3β-hydroxysteroids into 19-nor-4(5)-3-kestosteroids in vitro. In the porcine ovarian follicle, therefore, formation of 19-norA from androstenedione can be envisaged as a two-step enzymatic process: 19-demethylation of androstenedione to produce the putative intermediate 5(10)-oestrene-3,17-dione, and subsequent isomerization to 19-norA. In contrast to granulosa cells, porcine luteal cells synthesized 19-norA or 19-norT only when provided with the appropriate substrate. Unfractionated rat luteal cells also metabolized 5(10)-oestrene-3β,17β-diol to a mixture of 19-norA and 19-norT; conversion was inhibited by trilostane. In addition, small bovine luteal cells synthesized mainly 19-norT and formation was also inhibited by trilostane and cyanoketone. In addition to 19-norA, an unknown metabolite, formed in low amounts by large porcine luteal cells, appears to be related to another steroid which accumulated at high inhibitor concentrations; it may represent 5(10)-oestrene-3,17-dione postulated as a putative intermediate formed during 19-norsteroid biosynthesis. Journal of Endocrinology (1991) 129, 233–243

A POSSIBLE INTERRELATIONSHIP BETWEEN GONADOTROPHIN STIMULATION AND PROSTAGLANDIN F2α INHIBITION OF STEROIDOGENESIS BY GRANULOSA-LUTEAL CELLS IN VITRO

1977 ◽  
Vol 73 (1) ◽  
pp. 71-78 ◽  
Author(s):  
K. M. HENDERSON ◽  
K. P. McNATTY
Keyword(s):  
Tissue Culture ◽  
Corpus Luteum ◽  
Prostaglandin F2α ◽  
Luteal Cell ◽  
Luteal Cells ◽  
Lytic Action ◽  
Progesterone Production ◽  
Prostaglandin F

SUMMARY The newly formed corpus luteum of many species is refractory to the lytic action of prostaglandin F2α (PGF2α). This phenomenon was studied utilizing porcine, bovine and human granulosa-luteal cells in tissue culture. The steroidogenic potential of the granulosa-luteal cells was critical in determining whether PGF2α could inhibit progesterone production. Since the steroidogenic potential of the granulosa-luteal cell is related to the amount of LH bound to the cell, the bound LH may protect the granulosa-luteal cells from the lytic action of PGF2α. Finally, a 'see-saw' type of interaction between LH and PGF2α is postulated to account for the resistance of the newly formed corpus luteum to PGF2α

Possible involvement of leukotrienes in human luteal function

1992 ◽  
Vol 127 (3) ◽  
pp. 246-251 ◽  
Author(s):  
Yasunori Yoshimura ◽  
Yukio Nakamura ◽  
Fumitaka Ichikawa ◽  
Takahisa Oda ◽  
Masao Jinno ◽  
...  
Keyword(s):  
Nordihydroguaiaretic Acid ◽  
Corpora Lutea ◽  
Dependent Manner ◽  
Lipoxygenase Pathway ◽  
Luteal Function ◽  
Luteal Cells ◽  
Progesterone Production ◽  
Important Regulator ◽  
Dose Dependent

The present study was undertaken to assess the ability of human corpora lutea to produce leukotriene B4 (LTB4). The maximum capacity of luteal cells to secrete progesterone was attained on day 4, and both the basal production and the responsiveness to hCG decreased thereafter. In contrast, the production of LTB4 by cultured luteal cells was significantly reduced on day 4, but increased thereafter. The basal concentration of LTB4 produced by luteal cells varied from 75 to 590 pg/105 cells/2 days. LTB4 production appeared to decrease concomitantly with increased-progesterone production in cultured luteal cells. Exposure to hCG decreased significantly LTB4 production by cultured luteal cells on day 4. An inhibitor of the lipoxygenase pathway, nordihydroguaiaretic acid (NDGA), inhibited LTB4 production in a dose-dependent manner. However, NDGA did not affect basal progesterone production by the cultured luteal cells. A significant inverse relationship existed between the accumulation rates of progesterone and LTB4 in the luteal cells. Furthermore, the addition of LTB4 inhibited progesterone production in a dose-dependent manner in both the presence and absence of hCG. In conclusion, LTB4 could be synthesized by human corpora lutea in vitro, and correlated inversely with the secretion rates of progesterone. These data suggest that LTB4 produced locally in the corpus luteum may be an important regulator in human luteal regression.

Contrasting effects of prolactin on luteal and follicular steroidogenesis

1985 ◽  
Vol 104 (2) ◽  
pp. 241-250 ◽  
Author(s):  
B. Kalison ◽  
M. L. Warshaw ◽  
G. Gibori
Keyword(s):  
Luteal Cell ◽  
Corpora Lutea ◽  
Aromatase Activity ◽  
Luteal Cells ◽  
Progesterone Production ◽  
Progesterone Secretion ◽  
Hypophysectomized Rats ◽  
Stimulation Of

ABSTRACT To determine whether prolactin affects both luteal and follicular production of testosterone and oestradiol, pseudopregnant rats, either intact or hypophysectomized on day 8, were injected daily between days 8 and 9 with 1·5 i.u. human chorionic gonadotrophin (hCG), 250 μg prolactin or a combination of both. Control rats were given vehicle. On day 9, blood was obtained from the ovarian vein and corpora lutea and follicles were isolated and incubated in vitro for 2 h. Administration of hCG to intact rats increased ovarian secretion of testosterone and oestradiol dramatically, but did not affect progesterone secretion. Hypophysectomy on day 8 of pseudopregnancy was followed by a drop in ovarian steroid secretion. Prolactin treatment of hypophysectomized rats markedly enhanced progesterone production but had no stimulatory effect on either testosterone or oestradiol. In contrast, hCG dramatically enhanced ovarian secretion of both testosterone and oestradiol without affecting progesterone secretion. Prolactin administered together with hCG antagonized the stimulation of both testosterone and oestradiol secretion by hCG, yet increased progesterone production. When the specific effects of hCG and prolactin administration on follicles and corpora lutea were studied separately, it was found that hCG treatment in vivo greatly stimulated testosterone and oestradiol production by both tissues in vitro. Since hCG only marginally affected aromatase activity in the follicle, had no effect on aromatase activity in luteal cells and did not increase progesterone synthesis, it appears that hCG acts to increase the formation of androgen substrate for oestradiol biosynthesis. Prolactin, administered with or without hCG, inhibited both basal and hCG-stimulated testosterone and oestradiol synthesis by the follicle. In sharp contrast to its inhibitory effect on follicular production of steroids, prolactin appears to be essential for LH stimulation of testosterone and oestradiol by the corpus luteum. In the absence of prolactin, luteal cells gradually ceased to respond to LH and decreased their output of testosterone and oestradiol. Prolactin administration to hypophysectomized rats did not affect luteal cell production of either steroid. However, corpora lutea of rats treated with prolactin responded to the hCG challenge with an increase in testosterone and oestradiol synthesis. In summary, results of this investigation demonstrate that prolactin affects follicular and luteal production of testosterone and oestradiol in opposite ways. It acts on the follicle to inhibit both basal and LH-stimulated production of testosterone and oestradiol, yet it markedly enhances LH stimulation of testosterone and oestradiol synthesis by luteal cells. J. Endocr. (1985) 104, 241–250

scholarly journals Pentachloronitrobenzene alters progesterone production and primordial follicle recruitment in cultured granulosa cells and rat ovary†

2019 ◽  
Vol 102 (2) ◽  
pp. 511-520
Author(s):  
Yanrong Kuai ◽  
Xiaobo Gao ◽  
Huixia Yang ◽  
Haiyan Luo ◽  
Yang Xu ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Granulosa Cells ◽  
Crop Production ◽  
Follicular Development ◽  
Mitogen Activated Protein Kinase ◽  
Dependent Manner ◽  
Serum Progesterone ◽  
Primordial Follicles ◽  
Progesterone Production

Abstract Pentachloronitrobenzene (PCNB) is an organochlorine fungicide widely used for crop production and has become an environmental concern. Little is known about the effect of PCNB on ovarian steroidogenesis and follicular development. We found that PCNB stimulated Star expression and progesterone production in cultured rat granulosa cells in a dose-dependent manner. PCNB activated mitogen-activated protein kinase (MAPK3/1) extracellulat regulated kinase (ERK1/2), thus inhibition of either protein kinase A (PKA) or MAPK3/1 signaling pathway significantly attenuated progesterone biosynthesis caused by PCNB, suggesting that PCNB induced progesterone production by activating the cyclic adenosine monophosphate (cAMP/PKA) and MAPK3/1 signaling pathways. Further investigation demonstrated that PCNB induced Star expression and altered MAPK3/1 signaling in ovary tissues of immature SD rats treated with PCNB at the dose of 100, 200, or 300 mg/kg by daily gavage for 7 days, while serum progesterone level was dose-dependently decreased. We demonstrated that PCNB exposure accelerated the recruitment of primordial follicles into the growing follicle pool in ovary tissues, accompanied by increased levels of anti-Mullerian hormone (AMH) in both ovary tissues and serum. Taken together, our data demonstrate for the first time that PCNB stimulated Star expression, altered MAPK3/1 signaling and progesterone production in vivo and in vitro, and accelerated follicular development with a concomitant increase in AMH in ovary tissues and serum. Our findings provide novel insight into the toxicity of PCNB to animal ovary function.

scholarly journals Follicle-Stimulating Hormone and Luteinizing Hormone/Chorionic Gonadotropin Stimulation of Vascular Endothelial Growth Factor Production by Macaque Granulosa Cells from Pre- and Periovulatory Follicles1

1997 ◽  
Vol 82 (7) ◽  
pp. 2135-2142
Author(s):  
Lane K. Christenson ◽  
Richard L. Stouffer
Keyword(s):  
Vascular Endothelial Growth Factor ◽  
Growth Factor ◽  
Granulosa Cells ◽  
Dependent Manner ◽  
Vascular Endothelial ◽  
Progesterone Production ◽  
Endothelial Growth Factor ◽  
In Vitro Treatment

Granulosa cells in the ovulatory follicle express messenger ribonucleic acid encoding vascular endothelial growth factor (VEGF), an agent that may mediate the neovascularization of the developing corpus luteum, but it is not known whether luteinizing granulosa cells synthesize and secrete VEGF during the periovulatory interval. Studies were designed to evaluate the effects of an in vivo gonadotropin surge on VEGF production by macaque granulosa cells (study 1) and to test the hypothesis that gonadotropins act directly on granulosa cells to regulate VEGF production (study 2). Monkeys received a regimen of exogenous gonadotropins to promote the development of multiple preovulatory follicles. Nonluteinized granulosa cells (i.e. preovulatory; NLGC) and luteinized granulosa cells (i.e. periovulatory; LGC) were aspirated from follicles before and 27 h after an ovulatory gonadotropin bolus, respectively. Cells were either incubated for 24 h in medium with or without 100 ng/mL hCG (study 1) or cultured for 6 days in medium with or without 100 ng/mL hCG or 0.1, 1, 10, and 100 ng/mL of recombinant human LH (r-hLH) or r-hFSH (study 2). Culture medium was assayed for VEGF and progesterone. In study 1, LGC produced 8-fold greater levels of VEGF than NLGC (899 ± 471 vs. 111 ± 26 pg/mL, mean ± sem; P < 0.05). In vitro treatment with hCG increased (P < 0.05) VEGF production by NLGC to levels that were not different from the LGC incubated under control conditions. In vivo bolus doses of r-hCG (100 and 1000 IU) and r-hFSH (2500 IU) were equally effective in elevating granulosa cell VEGF production. In study 2, in vitro treatment with r-hFSH, r-hLH, and hCG markedly increased (P< 0.05) VEGF and progesterone production by the NLGC in a dose- and time-dependent manner. By comparison, the three gonadotropins (100 ng/mL dose) only modestly increased VEGF and progesterone production by LGC. These experiments demonstrate a novel role for the midcycle surge of gonadotropin (LH/CG or FSH) in primates to promote VEGF production by granulosa cells in the periovulatory follicle. Further, the data demonstrate that FSH-like as well as LH-like gonadotropins directly stimulate VEGF synthesis by granulosa cells.

Effects of prolactin on steroid production by human luteal cells in vitro

1983 ◽  
Vol 96 (3) ◽  
pp. 499-503 ◽  
Author(s):  
G. J. S. Tan ◽  
J. S. G. Biggs
Keyword(s):  
Menstrual Cycle ◽  
Ovarian Function ◽  
Chorionic Gonadotrophin ◽  
Human Chorionic Gonadotrophin ◽  
Corpora Lutea ◽  
Short Term ◽  
Steroid Production ◽  
Luteal Cells ◽  
Progesterone Production

The effects of prolactin on steroidogenesis were studied in dispersed luteal cells prepared from human corpora lutea of the menstrual cycle. Prolactin, at concentrations of 0·1–1000 ng/ml, had no effect on progesterone production by luteal cells during short-term incubation (3 h). However, in two out of five corpora lutea, higher concentrations of prolactin (100 and 1000 ng/ml) significantly reduced the oestradiol-17β production induced by human chorionic gonadotrophin (hCG; 10 i.u./ml); lower doses of prolactin had little effect. In the remaining corpora lutea, prolactin failed to affect either basal or hCG-induced production of oestradiol-17β. These results are discussed in relation to the mechanism by which prolactin influences human ovarian function.

60 EFFECTS OF CONCANAVALIN A ON THE PROGESTERONE PRODUCTION BY BOVINE STEROIDOGENIC LUTEAL CELLS IN VITRO

2017 ◽  
Vol 29 (1) ◽  
pp. 137
Author(s):  
F. C. Destro ◽  
I. Martin ◽  
F. D. C. Landim-Alvarenga ◽  
R. Sartori Filho ◽  
J. L. Pate ◽  
...  
Keyword(s):  
Concanavalin A ◽  
Culture Media ◽  
Prostaglandin F2α ◽  
Inhibitory Effect ◽  
Humid Atmosphere ◽  
Luteal Cells ◽  
Progesterone Production ◽  
Fetal Bovine ◽  
Culture Differences

The corpus luteum is a temporary organ that is responsible for progesterone (P4) secretion and is essential for the establishment and maintenance of pregnancy in cattle. Concanavalin A (CONA) is a lectin that was originally extracted from the Jack bean (Canavalia ensiformis) and that interacts with several kinds of cells, including immune cells and luteal cells. The aim of the present study was to evaluate the effects of CONA on the P4 production by bovine steroidogenic luteal cells (LC) in vitro. Luteal cells were collected during the mid-luteal stage (at 10–12 days following ovulation) and processed in the laboratory. Luteal cells were grown for 7 days in a humid atmosphere with 5% CO2, with or without 10% fetal bovine serum (FBS), and were subjected to the following treatments: control: no treatment; CONA (10 μg mL−1); LH (100 μg mL−1); CONA+LH; LH (100 μg mL−1) + prostaglandin F2α (PGF2α; 10 ng mL−1); CONA+LH+PGF2α. Samples of the culture media were collected on Day 1 and Day 7 for P4 quantification. The cells were counted on Day 7 of culture. Differences between treatments were considered statistically significant at P < 0.05. The P4 concentration in the culture media was numerically greater on Day 1 (558.0 ng mL−1) than on Day 7 (25.4 ng mL−1). The P4 concentration in the culture media was numerically greater for treatments with 10% FBS than for the FBS-free treatments, and the presence of CONA decreased LC P4-secreting capacity. This effect required more than 24 h of exposure to CONA to be fully manifested. On Day 1 of culture, CONA had no effect on P4 production of LC cultured in serum-free medium (P > 0.05).The suppressive action of CONA was more pronounced for cultures without FBS. By Day 7 of culture, the effects of CONA on P4 production were readily apparent. In the absence of serum, CONA had a highly significant (P < 0.01) inhibitory effect on basal progesterone production, as well as in the presence of LH or LH + PGF. In the presence of FBS, there was a tendency for decreased P4 in response to CONA in the LH- and the LH + PGF-treated cells (P = 0.090 and 0.085, respectively). The number of the cells present on Day 7 was not affected by the treatments tested (P > 0.05). More studies are required to better understand the effect of CONA on the P4 production of bovine LC. Financial support from FAPESP is acknowledged: grant no. 2013/00992–3, grant no. 2013/07439–8, and grant no. 2015/01940–2.

Effects of growth hormone and triiodothyronine on insulin-induced progesterone production by granulosa cells from prepubertal gilts

1992 ◽  
Vol 72 (3) ◽  
pp. 589-593 ◽  
Author(s):  
R. N. Kirkwood ◽  
P. A. Thacker ◽  
K. Rajkumar
Keyword(s):  
Growth Hormone ◽  
Granulosa Cells ◽  
Culture Medium ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Bovine Insulin ◽  
Dependent Manner ◽  
Progesterone Production ◽  
Porcine Granulosa Cells

Two experiments were performed using granulosa cells from medium-sized follicles (2–4 mm) derived from prepubertal gilts. Cells were cultured in a serum-free medium at a density of either 1 or 2 × 106 viable cells per well (experiments 1 and 2, respectively). For exp. 1, porcine growth hormone (pGH) (0 or 100 ng mL−1) was included in the culture medium from the time of plating, and low-density lipoprotein (LDL) (100 μg mL−1) was added at 72 h. For exp. 2, granulosa cells were plated in a culture medium containing either pGH (0 or 100 ng mL−1) or triiodothyronine (T3) (0 or 5 ng mL−1) or both pGH T3; LDL was not included. For both experiments, after 24 h of culture, bovine insulin at 0, 10, 100 or 1000 ng mL−1 was included in the medium. Hormones were replaced at 48 and 72 h, and the cultures were terminated at 96 h. Results from exp. 1 indicated that insulin increased (P < 0.01) progesterone production in a dose-dependent manner, both in the presence and absence of LDL. This response was augmented (P < 0.01) by co-culture with pGH. Results from exp. 2 confirmed the augmenting effect of pGH (P < 0.01). It was further observed that T3 increased (P < 0.01) progesterone production when cultured with insulin at 1000 ng mL−1, but at lower insulin-inclusion levels, results were equivocal. The progesterone production response was greatest (P < 0.01) when cells were cultured with both pGH and T3 at insulin levels of 100 or 1000 ng mL−1. There appeared to be little relationship between the media concentrations of insulin-like growth factor 1 and progesterone. The present results suggest that relatively high levels of pGH and T3 will enhance the in vitro steroidogenic capabilities of porcine granulosa cells. Key words: Granulosa cells, GH, T3, insulin

scholarly journals Assessment of the mechanism by which prolactin stimulates progesterone production by early corpora lutea of pigs

1998 ◽  
Vol 159 (2) ◽  
pp. 201-209 ◽  
Author(s):  
RE Ciereszko ◽  
BK Petroff ◽  
AC Ottobre ◽  
Z Guan ◽  
BT Stokes ◽  
...  
Keyword(s):  
Inositol Phosphate ◽  
Specific Binding ◽  
Positive Control ◽  
Free Calcium ◽  
Corpora Lutea ◽  
Pkc Inhibitor ◽  
Luteal Cells ◽  
Progesterone Production ◽  
Progesterone Secretion

Previously, we reported that administration of prolactin (PRL) during the early luteal phase in sows increases plasma progesterone concentrations. In the current study, we searched for the mechanisms by which PRL exerts this luteotrophic effect. The objectives of the study were (1) to examine the effect of PRL and/or low-density lipoproteins (LDL) on progesterone production by porcine luteal cells derived from early corpora lutea, and (2) to assess the ability of PRL to activate phosphoinositide-specific phospholipase C (PI-PLC) and protein kinase C (PKC) in these luteal cells. Ovaries with early corpora lutea (day 1-2 of the oestrous cycle) were obtained from the slaughterhouse. Progesterone production by dispersed luteal cells was measured after treatment with PRL, phorbol 12-myristate 13-acetate or inhibitors of PKC in the presence or absence of LDL. LDL increased progesterone concentration in the incubation medium (304.5 vs 178.6 ng/ml in control, P<0.05). PRL augmented LDL-stimulated progesterone secretion by luteal cells (to 416 ng/ml, P<0.05), but PRL alone did not affect progesterone production (209.6 ng/ml, P>0.05). Staurosporine, a PKC inhibitor, inhibited progesterone secretion stimulated by the combined action of LDL and PRL; however, such inhibition was not demonstrated when cells were treated with the PKC inhibitor, H-7. PKC activation was assessed by measuring the specific association of [H]phorbol dibutyrate (H-PDBu) with luteal cells after treatment with PRL or ionomycin (a positive control). PRL and ionomycin increased H-PDBu-specific binding in early luteal cells by 28+/-5.5% (within 5 min) and 70.2+/-19.3% (within 2 min) over control binding respectively (P<0.05). In addition, PRL did not augment the LDL-stimulated progesterone production in PKC-deficient cells. In contrast with PKC, total inositol phosphate accumulation, as well as intracellular free calcium concentrations, were not affected by PRL in the current study. We conclude that PRL, in the presence of LDL, stimulates progesterone production by early corpora lutea in vitro. Moreover, PRL appears to activate PKC, but not PI-PLC, in these cells. Thus intracellular transduction of the PRL signal may involve activation of PKC that is not dependent on PI-PLC.

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