The regulation of steroidogenesis is different in the two types of ovine luteal cells

Effect of estradiol preceding and progesterone subsequent to ovulation on proportion of postpartum beef cows pregnant

Two experiments were conducted to examine the effect of plasma concentrations of 17β-estradiol (E₂) preceding and progesterone (P₄) subsequent to ovulation on proportions of beef cows pregnant following embryo transfer. Timing of ovulation (d 0) among postpartum cows was synchronized and cows that expressed estrus were removed from each study. In Experiment 1, plasma E₂ concentration on d 0 was used to classify cows (n = 353) into Low, Medium, and High E₂ groups. Pregnancy rate for cows with Low, Medium, or High E₂ concentrations were different (P < 0.05). In Experiment 2, there were multiple administrations of PGF_2α to evaluate the independent effects of Low or High E₂ before ovulation and Low or Normal (no treatment) P₄ after ovulation on proportions of cows pregnant. Treatment groups in Experiment 2, therefore, were: Low E₂-Low P₄ (LL; n = 71), Low E₂-Normal P₄ (LN; n = 69), High E₂-Low P₄ (HL; n = 74), and High E₂-Normal P₄ (HN; n = 73). Concentrations of P₄ on d 7 subsequent to ovulation were less (P < 0.05) in cows of the HL compared to HN, and in LL compared to LN groups. Concentrations of E₂ on d -2, 0, and change in E₂ (d -2 to d 0) had a positive effect (P < 0.008) on pregnancy rates. In summary, relatively greater E₂ concentrations preceding ovulation; and relatively greater P₄ concentrations subsequent to ovulation combined with lesser E₂ concentrations preceding ovulation had a positive effect on proportions of postpartum cows pregnant.

Administration of gonadotropin-releasing hormone agonist on Day 5 increases luteal blood flow and improves pregnancy prediction accuracy on Day 14 in recipient Holstein cows

This study assessed the effects of gonadotropin-releasing hormone (GnRH) treatment on Day 5 (Day 0 = estrus) on luteal blood flow and accuracy of pregnancy prediction in recipient cows. On Day 5, 120 lactating Holstein cows were randomly assigned to a control group (n = 63) or GnRH group treated with 100 μg of GnRH agonist (n = 57). On Days 3, 5, 7, and 14, each cow underwent ultrasound examination to measure the blood flow area (BFA) and time-averaged maximum velocity (TAMV) at the spiral arteries at the base of the corpus luteum using color Doppler ultrasonography. Cows with a corpus luteum diameter ≥ 20 mm (n = 120) received embryo transfers on Day 7. The BFA values in the GnRH group were significantly higher than those in the control group on Days 7 and 14. TAMV did not differ between these groups. According to receiver operating characteristic analyses to predict pregnancy, a BFA cutoff of 0.52 cm² yielded the highest sensitivity (83.3%) and specificity (90.5%) on Day 7, and BFA and TAMV values of 0.94 cm² and 44.93 cm/s, respectively, yielded the highest sensitivity (97.1%) and specificity (100%) on Day 14 in the GnRH group. The areas under the curve for the paired BFA and TAMV in the GnRH group were 0.058 higher than those in the control group (0.996 and 0.938, respectively; P < 0.05). In conclusion, GnRH treatment on Day 5 increased the luteal BFA in recipient cows on Days 7 and 14, and improved the accuracy of pregnancy prediction on Day 14.

Size distribution of steroidogenic and non-steroidogenic ovine luteal cells throughout pregnancy

The present study examines the size distribution of ovine steroidogenic and non-steroidogenic luteal cells throughout pregnancy. Cells were isolated from corpora lutea collected from early (< 8 weeks), mid (9 to 14 weeks) or late (15 to 18 weeks) stages of pregnancy. Cells were stained for 3β-hydroxysteroid dehydrogenase (3β-HSD) activity, a marker for steroidogenic cells. Both 3β-HSD positive and β-HSD negative cells covered a wide spectrum of size ranging from 7 to 37 μm in diameter. There was a significant increase (P > 0·01) in mean diameter of non-steroidogenic luteal cells as pregnancy progressed. Mean diameter of 3β-HSD negative cells increased from 17·8 (s.e. 0·4) μm in the corpus luteum of early stage of pregnancy to 22·4 (s.e. 0·3) μm in the corpus luteum of advanced pregnancy. However, there was no significant increase in the mean diameter of 3β-HSD positive cells. Corpora lutea obtained from early stages of the pregnancy contained more steroidogenic cells than the cells obtained from mid and late pregnancy (P < 0·01). Percentage of 3β-HSD negative cells had increased 2·07-fold by 18 weeks of pregnancy when compared with the early stage of pregnancy. In contrast, percentage of 3β-HSD positive cells had decreased to 50% of starting values during the same period (P < 0·05). These results indicate that the ovine corpus luteum of pregnancy is morphologically dynamic over the course of pregnancy. Steroidogenic activity of luteal cells may decrease as pregnancy progresses, especially activity of the large luteal cells.

Equine chorionic gonadotropin alters luteal cell morphologic features related to progesterone synthesis

Exogenous eCG for stimulation of a single dominant follicle or for superovulation are common strategies to improve reproductive efficiency by increasing pregnancy rates and embryo production, respectively. Morphofunctional changes in the CL of eCG-treated cattle include increases in CL volume and plasma progesterone concentrations. Therefore, we tested the hypothesis that eCG alters the content of luteal cells and mitochondria related to hormone production. Twelve crossbred beef cows were synchronized and then allocated into three groups (four cows per group) and received no further treatment (control) or were given eCG either before or after follicular deviation (superovulation and stimulation of the dominant follicle, respectively). Six days after ovulation, cows were slaughtered and CL collected for morphohistologic and ultrastructural analysis. Mitochondrial volume per CL was highest in superovulated followed by stimulated and then control cows (18,500 ± 2630, 12,300 ± 2640, and 7670 ± 3400 μm(3); P < 0.001), and the density of spherical mitochondria and the total number of large luteal cells were increased (P < 0.05) in stimulated cows compared with the other two groups (110.32 ± 14.22, 72.26 ± 8.77, and 70.46 ± 9.58 mitochondria per μm(3) and 678 ± 147, 245 ± 199, and 346 ± 38 × 10(6) cells, respectively. However, the largest diameters of the large luteal cells were increased in superovulated and control cows versus stimulated ones (32.32 ± 0.06, 31.59 ± 0.81, and 29.44 ± 0.77 μm; P < 0.0001). In contrast, the total number of small luteal cells was increased in superovulated cows (1456 ± 268, 492 ± 181, and 822 ± 461 × 10(6), P < 0.05). In conclusion, there were indications of cellular changes related to increased hormonal production (stimulatory treatment) and increased CL volume (superovulatory treatment).

Effects of prostaglandin E and F receptor agonists in vivo on luteal function in ewes

Loss of progesterone secretion at the end of the estrous cycle is via uterine PGF(2alpha) secretion; however, uterine PGF(2alpha) is not decreased during early pregnancy in ewes to prevent luteolysis. Instead the embryo imparts resistance to PGF(2alpha)-induced luteolysis, which is via the 2-fold increase in prostaglandins E(1) and E(2) (PGE(1), PGE(2); PGE) in the endometrium during early pregnancy. Chronic intrauterine infusion of PGE(1) or PGE(2) prevents spontaneous or an estradiol-17beta, IUD, or PGF(2alpha)-induced luteolysis. Four PGE receptor subtypes (EP(1), EP(2), EP(3), and EP(4)) and an FP receptor specific for PGF(2alpha) have been identified. The objective of this experiment was to determine the effects of EP(1), EP(2), EP(3), or FP receptor agonists in vivo on luteal mRNA for LH receptors, occupied and unoccupied LH receptors, and circulating progesterone in ewes. Ewes received a single treatment of 17-phenyl-tri-Nor-PGE(2) (EP(1), EP(3)), butaprost (EP(2)), 19-(R)-OH-PGE(2) (EP(2)), sulprostone (EP(1), EP(3)), or PGF(2alpha) (FP) receptor agonists into the interstitial tissue of the ovarian vascular pedicle adjacent to the luteal-containing ovary. 17-Phenlyl-tri-Nor-PGE(2) had no effect (P> or =0.05) on any parameter analyzed. Butaprost and 19-(R)-OH-PGE(2) increased (P< or =0.05) mRNA for LH receptors, occupied and unoccupied LH receptors, and circulating progesterone. Both sulprostone and PGF(2alpha) decreased (P< or =0.05) mRNA for LH receptors, occupied and unoccupied LH receptors, and circulating progesterone. It is concluded that both EP(3) and FP receptors may be involved in luteolysis. In addition, EP(2) receptors may mediate prevention of luteolysis via regulation of luteal mRNA for LH receptors to prevent loss of occupied and unoccupied LH receptors and therefore to sustaining luteal function.

Effects of human chorionic gonadotropin on luteal blood flow and progesterone secretion in cows and in vitro-microdialyzed corpora lutea

To check human chorionic gonadotropin (hCG) effects on luteal blood flow (LBF) and progesterone (P(4)) synthesis, six cows received either 3000 IU hCG or saline (NaCl) on Day 7 (Day 1=ovulation) during two estrous cycles. Plasma P(4) and LBF were measured before (0h) and up to 48h after treatment. Luteal blood flow increased by 51% (P<0.05) at 1h after hCG administration and returned to baseline levels thereafter. Plasma P(4) levels were increased from pretreatment levels by 30% at 1h (P=0.05) and 81% at 48h (P=0.02) after hCG treatment. In contrast, NaCl did not cause changes in LBF and P(4) (P>0.05). Additionally, central and peripheral parts of 14 abattoir-derived corpora lutea of the mid-luteal phase (Day 8 to 12) were perfused with Ringer solution in an in vitro microdialysis system, supplemented with 50 or 150 IU/mL hCG for 1h. Application of 50 IU/mL hCG showed no influence on P(4) response (P>0.05) in both central and peripheral parts, whereas 150 IU/mL hCG resulted in an increase of P(4) synthesis (P=0.002) in the central parts only. In vivo, hCG provoked an immediate and long-term rise in P(4) but only a temporary elevation of LBF. Luteal blood flow itself does not seem to be the exclusive cause for an increase in P(4), because the in vitro data clearly showed direct effects of hCG on P(4) secretion. Interestingly, different P(4) secretion patterns could be found between central and peripheral parts of the corpus luteum in both control and hCG perfused corpora lutea.

Distribution of cyclooxygenase-1, cyclooxygenase-2, and cytosolic phospholipase A2 in the luteal phase human endometrium and ovary

OBJECTIVE

To identify the distribution of the enzymes cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), and cytosolic phospholipase A(2) (cPLA(2)) in the human ovary and endometrium.

DESIGN

Prospective clinical study.

SETTING

Hospital-based unit for reproductive health and research laboratories.

PATIENT(S)

Twenty-nine healthy fertile women with normal menstrual cycles.

INTERVENTION(S)

Endometrial and ovarian biopsy samples were obtained from healthy, fertile women in the luteal phase of the menstrual cycle or during caesarean section.

MAIN OUTCOME MEASURE(S)

Pinopode formation and immunohistochemical staining of cPLA(2), COX-1, and COX-2.

RESULT(S)

In the endometrium, the immunostaining of cPLA(2) was most intense in the luminal epithelium when pinopodes were present. The staining of both COX-1 and COX-2 was most intense in the epithelial cells, with the stroma staining positive only for COX-2. The endometrial vessels expressed COX-2 but not COX-1. The staining of COX-1 and COX-2 was intense on the surface epithelial cells on the outer lining of the ovary.

CONCLUSION(S)

This study details the distribution of these prostaglandin synthase enzymes and emphasizes their importance for the functions of both the endometrium and the ovary.

Regulation of progesterone and prostaglandin F2alpha production in the CL

After the luteinizing hormone (LH) surge, the cells that remain from the ovulated follicle undergo a process of differentiation termed luteinization. Two key features of the cells after luteinization are the capacity for tremendous production of progesterone [10(16) molecules of progesterone per (min/(g of CL))] and the capacity to undergo regression or death of the cells at the appropriate time. There are two steroidogenic cell types, the small and large luteal cells that are regulated by different mechanisms. In small luteal cells, production of progesterone is stimulated by LH through the protein kinase A (PKA) pathway. The large luteal cells of ruminants produce large quantities of progesterone that is independent of LH stimulation. Although luteotrophins clearly regulate luteal function, much of luteal progesterone production in some species appears to be constitutive, consistent with the autonomous aspects of the large luteal cell. The key regulated step in luteal progesterone production appears to be regulation of transport of cholesterol to the inner mitochondrial membrane apparently mediated by the steroidogenic acute regulatory protein (StAR). In addition, our recent research indicates that PKA is tonically active in large luteal cells and this may be responsible for the high, relatively autonomous nature of luteal progesterone production. Regression of the corpus luteum (CL) in many species is initiated by prostaglandin (PG) F2alpha secreted from the uterus. Luteal cells also have the capacity for production of PGF2alpha. Luteal PGF2alpha production can be regulated by a variety of substances including inhibition by progesterone and stimulation by cytokines. We have also characterized a positive feedback pathway in ruminant and porcine CL in which small amounts of uterine PGF(2alpha) stimulate intraluteal production of PGF2alpha due to induction of the cycloxygenase-2 (Cox-2) enzyme in large luteal cells. This positive feedback pathway is only present in CL that has acquired the capacity for luteal regression ( approximately day 7 in cow, approximately day 13 in pig). Regulation by protein kinase C (PKC) of transcriptional factors interacting with an E-box in the 5' flanking region of the Cox-2 gene is the critical regulatory element involved in this positive feedback pathway. Thus, luteinization in some species appears to change specific gene transcription such that progesterone production becomes relatively independent of acute luteotrophic regulation and intraluteal PGF2alpha synthesis is induced by the second messenger pathways that are activated by PGF2alpha.

Effects of second messengers on gap junctional intercellular communication of ovine luteal cells throughout the estrous cycle

Corpora lutea (CL) from Days 5, 10, and 15 after superovulation were enzymatically dispersed, and a portion of the cells were elutriated to obtain fractions enriched with small or large luteal cells. Mixed, small, and large luteal cell fractions were incubated with no treatment or with agonists or antagonists of cAMP (dbcAMP or Rp-cAMPS), protein kinase C (PKC; TPA or H-7), or calcium (A23187, EGTA, or A23187 + EGTA). The rate of contact-dependent gap junctional intercellular communication (GJIC) was evaluated by laser cytometry. Media were collected for progesterone (P(4)) radioimmunoassay, and luteal cells cultured with no treatment were fixed for immunocytochemistry or frozen for Western blot analysis. Luteal cells from each stage of the estrous cycle exhibited GJIC. The dbcAMP increased (P < 0.05) GJIC for all cell types across the estrous cycle. The Rp-cAMPS decreased (P < 0.05) GJIC for small luteal cells on Day 5 and for all cell types on Days 10 and 15. The TPA inhibited (P < 0.01), but H-7 did not affect, GJIC for all cell types across the estrous cycle. The A23187 decreased (P < 0.05) GJIC for large luteal cells touching only small or only large luteal cells, whereas A23187 + EGTA decreased (P < 0.05) GJIC for all cell types across the estrous cycle. For the mixed and large luteal cell fractions, dbcAMP increased (P < 0.05), but TPA and A23187 + EGTA decreased (P < 0.05), P(4) secretion. The A23187 alone decreased (P < 0.05) P(4) secretion by large, but not by mixed, luteal cells. For all days and cell types, the rate of GJIC and P(4) secretion were correlated (r = 0.113-0.249; P < 0.01). Connexin 43 was detected in cultured luteal cells by immunofluorescence and Western immunoblotting. Thus, intracellular regulators like cAMP, PKC, or calcium appear to regulate GJIC, which probably is an important mechanism for coordinating function of the ovine CL.

Secretion and gene expression of metalloproteinases and gene expression of their inhibitors in porcine corpora lutea at different stages of the luteal phase

We hypothesize that spontaneous regression of corpora lutea (CL) involves short-lasting restructure of luteal tissue with an activation of matrix metalloproteinases (MMPs) and their respective inhibitors (tissue inhibitors of metalloproteinase, TIMPs). This was tested by determining the gene expression of MMP-1, MMP-2, and MMP-9 and respective TIMP-1 and TIMP-2 in luteal tissue from sows at the early, midluteal, and late luteal phase (Days 6-8, Days 9-11, and Days 13-15 of estrous cycle). Gene expression of the three MMPs was low in early, slightly higher in midluteal, and significantly elevated (P < 0.05) in regressing CL. An inverse pattern was found for gene expression of TIMP-1 and TIMP-2. Under culture conditions, the release of MMPs was determined from steroidogenic large luteal cells (LLC). LLC harvested from regressing CL released significantly (P < 0.05) more active MMPs than cells obtained from CL at the early luteal phase. As luteolysis can be induced by prostaglandin F(2alpha) (PGF(2alpha)) and tumor necrosis factor alpha (TNF), we studied their effects on LLC under culture conditions. Treatment of cells with PGF(2alpha) or TNF (10(-7) M or 3 x 10(-9) M, respectively) induced a significantly higher release of MMPs, and gene expression was also significantly stimulated in comparison to that in untreated LLC. The gene expression of TIMPs remained unaffected by either treatment. It is concluded that at the beginning of luteolysis, MMPs are expressed and released in high amounts and that this is essential for the structural regression of the CL.

Relationship between maternal plasma progesterone concentration and interferon-tau synthesis by the conceptus in cattle

The objective of this study was to determine the relationship between maternal progesterone concentration and conceptus synthesis of interferon-tau as an index of conceptus viability at the time of maternal recognition of pregnancy. Heifers of mixed beef breeds were randomly assigned to receive 1 of 2 treatments: 1) intramuscular injection of 1500 IU hCG on Day 5 after artificial insemination (AI; n = 12) or 2) intramuscular injection of saline on Day 5 after AI (n = 17). Ovaries were scanned daily by transrectal real-time ultrasonography. Progesterone concentrations were determined from daily blood samples collected from the jugular vein. Heifers were slaughtered on Day 18 after AI and conceptus tissues were collected. These were incubated individually at 37 degrees C in RPMI medium, and supernatant collected after 24 h. Conceptus secretory products in the supernatant were analyzed for interferon concentration by antiviral assay using vesicular stomatitis virus. Transrectal ultrasonography showed all heifers that received hCG had at least 1 extra corpus luteum (CL) in addition to the spontaneous CL formed from the previous ovulation (10 with 2 CL, 2 with 3 CL). A significant increase in plasma progesterone concentration was detected in pregnant heifers treated with hCG (n = 9) vs pregnant control heifers (n = 11; P < 0.001). There was a tendency for an increase (P = 0.059) in synthesis of interferon-tau by conceptuses from hCG-treated heifers compared to control heifers. Maternal plasma progesterone concentrations were correlated with interferon-tau production by the conceptuses (r = 0.593, P < 0.006), suggesting that higher maternal progesterone may provide a more suitable environment for the developing conceptus.

Effects of luteinizing hormone and prostaglandin F(2α) on gap junctional intercellular communication of ovine luteal cells throughout the estrous cycle

Cellular interactions mediated by contact-dependent pathways may be important to maintain luteal function. The objective of the present experiment was to evaluate the role of LH and prostaglandin F(2α) (PGF) in regulation of contact-dependent, gap junctional intercellular communication (GJIC) of ovine luteal cells from several stages of luteal development. Corpora lutea (CL) obtained from superovulated ewes on days 5 (n=7), 10 (n=8), and 15 (n=9) after estrus were dispersed with collagenase and cell types were separated by elutriation. Cells were plated as a mixed population (nonelutriated), or as small or large luteal cell fractions, and incubated in serum-free media containing no hormone, LH (100 ng/mL), PGF (100 ng/mL), LH+PGF, or dibutyryl cAMP (dbcAMP; 2 mM) for 18-24 h. Media were collected for evaluation of progesterone (P4) concentrations and replaced with media containing fluorescent dye. Then the rate of GJIC was evaluated by using the fluorescence recovery after photobleaching technique and laser cytometry. The rate of GJIC was determined for selected cells: small luteal cells in contact only with small luteal (S-S) cells; large luteal cells in contact only with small luteal (L-S) cells; and large luteal cells in contact only with large luteal (L-L) cells. LH increased (p<0.01) GJIC for S-S on d 5 and 10 and for L-S cells across the estrous cycle, but did not affect GJIC for L-L cells. PGF increased (p<0.05) GJIC for L-L cells on d 10 and 15, and decreased (p<0.05) GJIC for S-S cells from d 5 and 10 of the estrous cycle. LH+PGF increased (p<0.05) GJIC for S-S cells on d 5 and 10, and for L-S and L-L cells on d 10 and 15 of the estrous cycle. In addition, PGF diminished (p<0.05) LH-stimulatory effects on GJIC for S-S cells from d 5 and 10, and for L-S cells from d 5 of the estrous cycle. Dibutyryl cAMP stimulated (p<0.05) GJIC between all evaluated cell types across the estrous cycle. LH and dbcAMP stimulated (p<0.05) P4 secretion by mixed and small luteal cell fractions, PGF alone did not affect basal P4 secretion, but LH+PGF stimulated (p<0.05) P4 production by small luteal cells across the estrous cycle. PGF diminished (p<0.05) LH-stimulatory effects on P4 production in mixed populations of luteal cells across the estrous cycle.These data demonstrate that both luteal cell types communicate with each other, and the rate of communication was affected by LH, PGF, and dbcAMP. Modulation of gap junctional contact-dependent intercellular communication may be an important mechanism by which regulatory signals are transduced during luteal growth, differentiation, and regression in sheep.

Comparison of mRNA levels for the PGF(2α) receptor (FP) during luteolysis and early pregnancy in the ovine corpus luteum

Prostaglandin F(2α) (PGF(2α)) is the physiological signal that triggers luteolysis in the non-pregnant ewe. This is associated with a decline in circulating levels of progesterone, beginning around day 14 of a 16-17 day estrous cycle. Recently, the receptor for PGF(2α) (FP) was cloned from an ovine day 10 large luteal cell cDNA library. The purpose of this study was to measure relative abundance of FP mRNA as it may change with luteolysis during the luteal phase. Corpora lutea (CL) were collected from ewes on day 10, 12, 14 or 16 (n≥4/day; day 0=synchronized estrus); 12 h after PGE(2α)-treatment on day 10, 12 or 14 (n≥3/day) of the estrous cycle; or on day 16 of pregnancy (n=6). Pregnancy was confirmed by visualization of the conceptus. Blood samples were collected 12 h prior to and at the time of tissue collection to determine levels of progesterone. Serum concentrations of progesterone declined with the onset of luteolysis in control animals (day 14, day 16;P<0.05) as well as 12 h following PGF(2α)-treatment (day 10, day 12;P<0.05). Genomic DNA from these tissues was prepared and visualized by agarose gel electrophoresis. Internucleosomal fragmentation (indicative of apoptosis) was seen in CL from animals in which luteolysis had been initiated (all PGE(2α)-treated and day 16 control ewes), but not in ewes with functional CL. Total RNA isolated from each CL was separated through a denaturing 1% agarose gel, transferred to nylon membranes and hybridized to a radioactive ovine FP cDNA probe. Hybridization to a radiolabeled 18S ribosomal cRNA probe was used to confirm equal loading of RNA in each lane. By northern analysis, a major transcript was seen at ∼6.1 kb. A relatively high level of FP mRNA was measured in CL collected from control non-pregnant ewes during the mid luteal phase (day 10, 2.73±0.17; day 12, 2.47±0.91; FP/18S ratio), but varied among animals (3.09±1.59) on day 14. Administration of PGF(2α) resulted in the lowest amounts of FP mRNA on days 10, 12, and 14 (P<0.05). Amounts of FP mRNA were higher (P<0.05) on day 16 of pregnancy as compared to day 10 (by 1.9-fold) or to day 16 (by 5.9-fold) of the estrous cycle. From these observations we conclude that PGF(2α) or some event associated with luteolysis appears to down regulate amounts of the FP mRNA. Furthermore, pregnancy, and/or the antiluteolytic signals associated with maternal recognition of pregnancy may prevent the decline in the amount of FP mRNA.

The ability of steroid hormones to control cAMP and cGMP production by human granulosa cells in culture

The aim of our in vitro experiments was to discover the effects of steroid hormones (progesterone, androstenedione and estradiol-17 beta, 10, 100, 1000 or 10,000 pg/ml medium) on the output of cyclic nucleotides adenosine 2',3'-cyclic monophosphate (cAMP) and guanosine 2',3'-cyclic monophosphate (cGMP) by granulosa cells isolated from human ovaries. The dramatic increase of cAMP release after progesterone treatment was observed. Low doses of androstenedione (10 or 100 pg/ml) significantly decreased while higher doses (1000 or 10,000 pg/ml) tended to increase cAMP output. All doses of estradiol significantly inhibited cAMP release. Low doses (10 or 100 pg/ml) of all investigated steroid inhibited while higher doses (1000 or 10,000 pg/ml) stimulated cGMP output. cGMP-stimulating effects of progesterone and androstenedione were expressed significantly more than that of estradiol. The influence of progestagen, androgen and estrogen on cyclic nucleotide release by granulosa cells may suggest the involvement of cAMP- and cGMP-dependent intracellular mechanisms in the realization of steroid hormone effects within human ovaries.

A morphometric analysis of the corpus luteum of the cow during the estrous cycle and early pregnancy

Corpora lutea were collected from cows on Days 6, 8, 10, 12, 14, 16, 18 and 19 of the estrous cycle and early pregnancy (n=2/d) and were examined by light microscopy. Mean lutein cell diameter was significantly (P<0.05) greater in pregnant than in cyclic cows on Days 6, 8, 10, 12, 16, 18 and 19 (cyclic versus pregnant: Day 6: 13.9 +/- 0.22 vs 14.9 +/- 0.24; Day 8: 13.8 +/- 0.20 vs 15.4 +/- 0.2; Day 10: 14.8 +/- 0.24 vs 17.4 +/- 0.24; Day 12: 13.2 +/-0.25 vs 17.9 +/- 0.31; Day 16: 13.9 +/- 0.28 vs 16.5 +/- 0.31; Day 18: 13.0 +/- 0.22 vs 16.5 +/- 09.36, and Day 19: 15.0 +/- 0.23 vs 17.6 +/- 0.33 mum, respectively). The distribution of cell sizes was leptokurtotic throughout the estrous cycle and the first 10 d of pregnancy, but tended towards bimodality after Day 14 of pregnancy. The proportion of lutein cell cytoplasm occupied by vacuoles was lower in pregnant than in cyclic cows from the 12th day post estrus, but there was a marked (P<0.05) increase in vacuolation of cells from cows undergoing luteolysis. Stainable intercellular collagen was also less abundant in pregnant than cyclic cows from the 12th day post estrus. The higher rate of progesterone secretion of pregnant, compared with cyclic cows may be attributed to the greater numbers and greater contribution to luteal mass of large lutein cells in the corpus luteum of pregnancy.

Steroid hormones regulate cAMP and cGMP production by porcine granulosa cells in vitro

The influence of steroid hormones on the output of the cyclic nucleotides adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) by porcine granulosa cells was investigated. Both progesterone (100, 1000, 10,000 and 100,000 pg/ml medium) and estradiol (100, 1000, 10,000 and 100,000 pg/ml medium) activated cAMP and cGMP production. Testosterone (100 or 1000 pg/ml medium) also stimulated cAMP output. The stimulating effect of steroid hormones on cyclic nucleotide production may suggest the involvement of cAMP- and cGMP-dependent intracellular mechanisms in the action of steroid hormones on porcine ovarian cells.

Steroidogenic enzyme activity after acute activation of protein kinase (PK) A and PKC in ovine small and large luteal cells

Intracellular effector systems which utilize PKA and PKC can be pharmacologically activated by forskolin and phorbol 12-myristate 13-acetate (PMA) and appear to be important for regulation of steroidogenesis by cells of the corpus luteum. In this study the effect of pharmacologic activation of PKA (forskolin) or PKC (PMA) on the activity of adenylate cyclase, cholesterol esterase, P450 cholesterol side chain cleavage (P450scc) and 3 beta-hydroxysteroid dehydrogenase/delta 5, delta 4 isomerase (3 beta HSD) was determined. Basal adenylate cyclase activity (as measured by intracellular and secreted cAMP) was extremely low in both large and small luteal cells. Forskolin stimulated adenylate cyclase activity in both large and small luteal cells but progesterone production was increased only in small cells. PMA inhibited progesterone production by large and forskolin-stimulated small cells without altering adenylate cyclase activity. Basal cholesterol esterase activity was greater in small than in large cells and was stimulated by forskolin only in small cells. PMA did not significantly alter cholesterol esterase activity in either cell type. Activity of P450scc or 3 beta HSD was measured by conversion of hydroxylated cholesterol derivatives (P450scc) or pregnenolone (3 beta HSD) to progesterone. Although basal progesterone production was 47 times greater in large than small cells, there was only 5.1 (P450scc) and 6.4 (3 beta HSD) times greater enzyme activity in large than in small luteal cells. Activation of PKA and/or PKC did not alter the activity of P450scc or 3 beta HSD in either cell type.(ABSTRACT TRUNCATED AT 250 WORDS)

Gossypolone suppresses progesterone synthesis in bovine luteal cells

Gossypolone, a proposed major metabolite of gossypol, was synthesized and investigated for its effect on progesterone synthesis in cultured bovine luteal cells. Gossypolone inhibited human chorionic gonadotropin(hCG)-stimulated progesterone secretion, reduced substrate-enhanced conversions of 25-hydroxycholesterol to pregnenolone and of pregnenolone to progesterone in a dose-dependent fashion. These findings indicate that gossypolone inhibits not only 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity, as gossypol does, but also side-chain cleavage enzyme complex (cytochrome P450scc) activity. However, the two compounds appear to have a similar potency in inhibiting progesterone secretion. Both gossypolone and gossypol (8.5 microM) induced morphological changes in cellular organelles.

Inhibitory effect of gossypol on steroidogenic pathways in cultured bovine luteal cells

Gossypol inhibits the reproductive system and steroidogenesis in both sexes. The present study investigated some possible sites subsequent to cAMP formation at which gossypol may inhibit progesterone biosynthesis. Bovine luteal cells were cultured with dibutyryl cAMP (dbcAMP), 25-OH cholesterol, or pregnenolone in the presence or absence of gossypol. Gossypol, at 17-34 microM, inhibited dbcAMP-induced progesterone secretion. Gossypol significantly inhibited the conversions of exogenous 25-OH cholesterol and pregnenolone to progesterone. However, the conversion of 25-OH cholesterol to pregnenolone was not significantly inhibited by gossypol at low doses (less than or equal to 34 microM). These results suggest that gossypol inhibits progesterone synthesis in bovine luteal cells by suppressing steroidogenic enzyme activity.

Protein kinase A and C activities and endogenous substrates in ovine small and large luteal cells

Protein kinase A (cAMP-dependent) and C (calcium, phospholipid-dependent) activities were measured and in vitro phosphorylation of endogenous proteins by these kinases were observed by SDS-PAGE in 100,000 x g supernatant (soluble) fractions of ovine small (12-22 microns) and large (greater than 22 microns) luteal cells. No differences in stimulation (P less than 0.05) of A kinase activity between small and large cells were detected. Protein kinase C activity was stimulated (P less than 0.05) 2.9-fold in small cells but not significantly enhanced above basal (P greater than 0.05) in large cells. By direct comparison, greater stimulation (P less than 0.05) over basal of A versus C kinase (6.1- versus 2.9-fold) was measured in small cells. These stimulations were greater than those observed in large cells (A kinase, 4.8-fold; C kinase, 1.8-fold). Maximal specific activities of both kinases (per mg protein) were greater (P less than 0.05) in small than in large cells. Endogenous proteins that could serve as substrates for phosphorylation by A and C kinases differed between small and large cells. Phosphorylation of six proteins by A kinase was consistently greater in small than in large cells. One endogenous protein (37 kDa) appeared to serve as a preferred substrate for phosphorylation by A kinase in small cells and C kinase in large cells. One protein (81 kDa) was predominantly phosphorylated in large rather than small cells by a calcium-dependent, C kinase-independent mechanism. These results support the accepted role of cAMP via A kinase and a possible role for C kinase in regulating steroidogenesis in ovine small luteal cells. The inability of large cells to respond to cAMP with enhanced secretion of progesterone may be due to an unavailability of phosphoprotein substrates for A kinase. Furthermore, protein kinase C activity and available protein substrates display quantitative and qualitative differences between small and large cells. Differences in regulation of steroidogenesis between the cell types may be due to these observed differences.

Human corpus luteum: immunocytochemical evidence for presence of prolactin

Six human corpora lutea (day 17-25) of the menstrual cycle and 4 ovarian stromal tissues from 7 cycling women were examined for the presence of the hormone, prolactin, by immunohistochemistry using the indirect peroxidase-antiperoxidase method. After mounting tissue sections of 4 micron, endogenous peroxidases were removed with hydrogen peroxide and the sections were incubated for 1 h at room temperature followed by 16 h at 4 degrees C with a highly specific antisera for human prolactin, nonimmunized normal rabbit serum for a control reaction, or antiserum preadsorbed with excess human prolactin for specificity determination. Following the reaction with the second antibody (goat antirabbit IgG) for 1 h at room temperature, prolactin was localized using peroxidase anti-peroxidase and 3.3'-diaminobenzidine as the chromogen. Prolactin was present and could be localized in the luteal cells of all 6 corpora lutea, but not in any of the ovarian stroma studied. Human adenohypophysis served as a positive tissue control for prolactin immunopositive staining. The localization of immunoreactive prolactin in the corpus luteum demonstrates directly the presence of this hormone in the human ovary, adding further evidence for its role in luteal function.