Direct stimulation of ovarian progesterone-metabolizing enzyme by gonadotropin-releasing hormone in cultured granulosa cells

FSH Stimulation promotes progesterone synthesis and output from human granulosa cells without luteinization

STUDY QUESTION

Can granulosa cells produce progesterone (P) in response to FSH stimulation?

SUMMARY ANSWER

FSH actively promotes P synthesis and output from granulosa cells without luteinization by up-regulating the expression and increasing enzymatic activity of 3β-hydroxysteriod dehydrogenoase (3β-HSD), which converts pregnenolone to P.

WHAT IS KNOWN ALREADY

Serum P level may rise prematurely prior to ovulation trigger in stimulated IVF cycles and adversely affect implantation and clinical pregnancy rates by impairing endometrial receptivity.

STUDY DESIGN, SIZE, DURATION

A translational research study.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Human ovarian cortical samples (n = 15) and non-luteinizing FSH-responsive human mitotic granulosa cell line (HGrC1) were stimulated with rec-FSH at 12.5, 25 and 50 mIU/ml concentrations for 24 and 48 h. FSH receptor expression was knocked-down and up-regulated in the granulosa cells using short hairpin RNA (shRNA) technology and activin-A administration, respectively. The expressions of the steroidogenic enzymes were analyzed at mRNA level by real-time quantitative RT-PCR, and protein level by western blot and immunoprecipitation assay. The enzymatic activity of 3β-HSD was measured using a spectrophotometric method. In vitro estradiol (E2) and P productions of the cells before and after FSH stimulation were measured by electro-chemiluminescence immunoassay method.

MAIN RESULTS AND THE ROLE OF CHANCE

Stimulation of the HGrC1 cells with FSH resulted in a dose-dependent increase in the mRNA and protein level of 3β-HSD. Overall, when all time points and FSH doses were analyzed collectively, FSH significantly up-regulated the mRNA expression of its own receptor (3.73 ± 0.06-fold, P < 0.001), steroidogenic acute regulatory protein (stAR, 1.7 ± 0.03-fold, P < 0.01), side-chain cleavage enzyme (SCC, 1.75 ± 0.03-fold, P < 0.01), aromatase (4.49 ± 0.08-fold, P < 0.001), 3β-HSD (1.68 ± 0.02-fold, P < 0.01) and 17β-hydroxy steroid dehydrogenase (17β-HSD, 2.16 ± 0.02-fold, P < 0.01) in the granulosa cells. Expression of 17α-hydroxylase (17α-OH, 1.03 ± 0.01-fold P > 0.05) did not significantly change. Similar changes were observed in the protein expression analysis of these enzymes on western blotting after FSH stimulation. FSH significantly increased 3β-HSD, 17β-HSD and aromatase in a dose-dependent manner but did not affect 17α-OH. Protein expression of P was increased along with 3β-HSD after FSH stimulation, which was further evidenced by immunoprecipitation assay. Enzymatic activity of 3β-HSD was significantly enhanced by FSH administration in the HGrC1 cells in a dose-dependent manner. In line with these findings P output (1.05 ± 0.3 vs. 0.2 ± 0.1 ng/ml, respectively, P < 0.001) from the samples stimulated with FSH were significantly increased along with E2 (1918 ± 203 vs. 932 ± 102 pg/ml, respectively, P < 0.001) compared to unstimulated controls. FSH-induced increase in 3β-HSD expression was amplified and reversed in the HGrC1 cells when FSH receptor expression was up-regulated by activin-A and down-regulated with shRNA, respectively.

LIMITATIONS AND REASONS FOR CAUTION

As only the effect of FSH was studied we cannot extrapolate our findings to the potential effects of HMG and recombinant LH.

WIDER IMPLICATIONS OF THE FINDINGS

This data provides a molecular explanation for the largely unexplained phenomenon of P rise during the follicular phase of gonadotropin stimulated IVF cycles. Our findings may progress the research to uncover potential mechanisms for preventing premature P rise that appears to be associated with inferior outcomes in women undergoing IVF.

STUDY FUNDING/COMPETING INTEREST(S)

Funded by the School of Medicine and the Graduate School of Health Sciences of Koc University. All authors declare no conflict of interest.

TRIAL REGISTRATION NUMBER

None.

Ovarian and placental expression of 20α-hydroxysteroid dehydrogenase during pregnancy in deer

The enzyme 20α-hydroxysteroid dehydrogenase (20α-HSD) catalyzes the conversion of progesterone to its inactive form, 20α-hydroxyprogesterone. This enzyme has been shown to play a critical role in the regulation of luteal function in experimental animals. In this study, we cloned and expressed the gene encoding elk deer 20α-HSD from reproductive placental and ovarian tissues. PCR, 3'- and 5'-RACE, and northern blot analysis were performed for the cloning and characterization of deer 20α-HSD gene. We expressed recombinant deer 20α-HSD protein and used western blot analysis to determine protein expression levels in the placenta and ovary during pregnancy. The full cDNA sequence of 20α-HSD was used to clone an open reading frame encoding 323 amino acids and consisting of 1142 bp. The nucleotide sequence of deer 20α-HSD showed high homology with the sequences of the bovine (96%), goat (96%), and human (83%) 20α-HSD genes. 20α-HSD mRNA was strongly expressed in the placenta on days 30, 60, and 70 of pregnancy. A high level of the protein was also detected in the placenta but not in fetal skin tissue. The recombinant 20α-HSD protein produced in mammalian cells and bacterial systems had a molecular weight of approximately 37-kDa. The deer 20α-HSD protein signal was specifically localized in the basal part of the primary chorionic villi and chorionic stem villus of the placenta during early pregnancy. The 20α-HSD protein was also intensively localized in the larger luteal cells of the corpus luteum during pregnancy.

Distribution and metabolism of 20 alpha-hydroxylated progestins in the female rat

The C21 steroids, progesterone and 20 alpha-hydroxy-4-pregnen-3-one (20 alpha-DHP) play pivotal roles in the initiation, timing and maintenance of ovulatory function and pregnancy in female mammals. They also have growth factor and central nervous system (CNS) effects; some of these are non-genomic effects mediated through 5 alpha-reduced and 3 alpha-hydroxylated derivatives. These studies examined the in vivo uptake and conversion of 20 alpha-DHP in selected CNS sites and peripheral tissues after injection of [(3)H]-20 alpha-DHP. The effects of steroid mass, time after injection, and ovariectomy, adrenalectomy and estradiol treatment were assessed in the pineal gland, preoptic area of the hypothalamus (POA), medial basal hypothalamus (MBH), midbrain, cerebellum, cerebral cortex, anterior pituitary (AP), uterus and skeletal muscle. Tissue extracts were analyzed by scintillation counting and chromatography to quantify and localize 20 alpha-DHP and its 5 alpha-reduced derivatives. Injection of increasing mass of [(3)H]-20 alpha-DHP to ovariectomized/adrenalectomized (ovx/adx) rats results in a linear increase in (3)H-steroid 10 min post injection in all tissues. (3)H-steroid content increases with time over 1 h post injection in the pineal, AP and uterus. Tissue differences in (3)H-steroid level are observed with higher levels in pineal, MBH, POA, AP and midbrain than in cerebral cortex and cerebellum, and in uterus, ovary and adrenal than in muscle. Ovariectomy, adrenalectomy and estradiol treatment affect (3)H-steroid levels in a tissue dependent manner, and the metabolites of 20 alpha-DHP in MBH and AP differ between groups. The findings demonstrate that target tissues, including areas of the CNS, are able to selectively take up and retain 20 alpha-DHP, and also support a physiological role for this progestin and its metabolites in modulation of CNS and reproductive functions.

Epinephrine intracerebroventricular stimulation modifies the LH effect on ovarian progesterone and androstenedione release

This study investigates the interaction between the effect of epinephrine intracerebroventricular (icv) injection and LH on the progesterone concentration in ovarian vein blood (Po) in vivo, and also, on the release of ovarian progesterone and androstenedione in vitro, in rats on dioestrus day 2. When 2 mg ovine LH were injected in vein (i.v.), Po increased reaching 120+/-12.2 and 151+/-17.5 ng ml(-1) at 22 and 25 min, respectively. Another group of rats was injected intracerebroventricular with 5 microgram epinephrine at time zero, and with 2 mg ovine LH i.v. 3 min later. This time Po decreased during the first 3 min, then increased, reaching 64+/-7.1 ng ml(-1) at 25 min, lower than the Po obtained 22 min after LH i.v. injection only (P<0.01). Moreover, rats were injected i.v. with 2 mg ovine LH at time zero, and 7 min later with epinephrine intracerebroventricular. Po increased during the first 7 min, decreased until the 13th minute and reached 70+/-8.9 ng ml(-1) at 25 min, lower than the Po obtained 25 min after LH i.v. injection only (P<0.01). In other experience, rats with one (either right or left) superior ovarian nerve transected (SON-t), were injected intracerebroventricular with epinephrine. Five minutes later, the ovaries were removed and incubated in vitro with LH. Both ovaries (right or left) in which the SON was intact at time of epinephrine i. c.v. injection, showed a reduction of progesterone and androstenedione released in vitro (P<0.05). These results suggest that, on dioestrus day 2, the central adrenergic stimulus competes with LH in the release of ovarian progesterone. Also, the neural input that arrives at the ovary through the SON would antagonize the ovarian progesterone and androstenedione response to LH.

Molecular cloning and characterization of the rat ovarian 20 alpha-hydroxysteroid dehydrogenase gene

The rat 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSD) is an enzyme responsible for the catabolism of progesterone to the inactive 20 alpha-hydroxprogesterone. We have previously shown that the expression of this enzyme is not regulated by post-translational modification, but at the level of transcription. In this study we have established that the 20 alpha-HSD gene contains nine exons and have isolated a 2.5 kb promoter region. The transcription start site was identified and a TATA box was found. 5' deletions of this promoter significantly decreased basal promoter activity. Treatment with forskolin led to a dose dependent inhibition of the 2.5kg-20 alpha-HSD-luciferase construct. Computer analysis identified one CRE, two Nur77 response elements, two putative AP1 sites and one progesterone response element half-site. In summary, we have identified and partially characterized the promoter region of the rat ovarian 20 alpha-HSD and demonstrated that the regulatory elements for 20 alpha-HSD are present within a 2.5 kb 5' flanking region of the gene.

Possible direct effect of gonadotropin releasing hormone on human endometrium and decidua

Decidualization of endometrial tissues, which is essential for implantation and the continuation of pregnancy, is induced by pituitary hormones that are regulated by gonadotropin releasing hormone (GnRH). Our objective was to determine the role of a direct action of GnRH on endometrial tissues by comparing the characteristics of receptors for GnRH in human endometrial and decidual tissues. Competitive binding studies were performed with the protease-resistant GnRH analogues, buserelin and [125I] buserelin. The effects of buserelin on phosphoinositol turnover were determined by the measurement of inositol 1,4,5-triphosphate(IP3). The values for the dissociation constant (Kd) and number of binding sites (Bmax) per unit protein versus buserelin for endometrial tissues did not differ from the values for decidual tissues. However, the Bmax per unit DNA was significantly higher in endometrial tissues. Also, buserelin induced a significant increase in IP3 in decidual tissue. These results indicate that GnRH may be a potential modulator of the function in human endometrium and decidua. The signal transduction mechanism for GnRH action appeared to involve the accelerated turnover of phosphoinositol.

GnRH receptors and GnRH endocrine effects on luteoma cells

An ovary implanted into the spleen of an ovariectomized rat develops into a luteinized tumor, growing in response to gonadotrophins. Previously, it was shown that in vivo Buserelin, a gonadotrophin-releasing hormone (GnRH) analog, inhibited tumor growth. To determine if GnRH had a direct effect on tumor cells, the presence of GnRH receptors as well as the endocrine effects of buserelin were studied on tumoral tissue. GnRH receptors were present in luteoma in similar concentrations and dissociation constant (Kd) to control estrous ovaries. In vivo treatment with buserelin did not modify luteoma GnRH receptors. In organ incubations, luteoma secreted significantly higher estradiol and lower progesterone than estrous ovaries; addition of buserelin did not modify steroid secretion. The same difference in basal steroid secretion between luteoma cells and luteal cells superovulated prepubertal ovaries was observed in cell cultures. Although luteinizing-hormone (LH)-stimulated progesterone in both kinds of cells, buserelin significantly inhibited LH-stimulated progesterone only in luteoma cells. These results describe clear differences in basal steroid secretion between tumoral and normal tissue. Furthermore, they show that luteoma possess GnRH receptors similar to those in normal ovarian tissue, and that GnRH analogs have endocrine effects on these cells. Therefore, a direct effect of buserelin on luteoma cells can be postulated.

Induction of rat granulosa cell steroidogenic enzyme activities and their messenger ribonucleic acids by a splenocyte-derived factor

We have previously identified and purified a splenocyte-derived factor (PSF) that stimulates the accumulation of progesterone and 20 alpha-dihydroprogesterone (20 alpha-OH-P) in rat ovarian granulosa cells independently of FSH. In the present study, time course experiments comparing the response to PSF with that to FSH revealed that PSF-stimulated progesterone accumulation was slower than that of FSH, but PSF-stimulated 20 alpha-OH-P accumulation had a time course similar to that of FSH. To determine the basis for the slower progesterone response to PSF, the effect of these two agents on each step of the steroidogenic pathway was assessed. First, to examine whether PSF-stimulated cholesterol mobilization was limiting, cultured granulosa cells were treated with 22(R)-hydroxycholesterol. While both FSH- and PSF-stimulated progesterone and 20 alpha-OH-P accumulation approximately doubled, the overall time courses did not change indicating that cholesterol availability was not the factor limiting the response to PSF. Next, PSF and FSH induction of steroidogenic enzyme activities and messenger RNAs were compared. While FSH-stimulated cytochrome P450 side chain cleavage enzyme (SCC) activity rapidly increased (peaking at 2 days) and then slowly declined, PSF-stimulated SCC activity gradually increased over 5 days to approximately 35% of the maximal activity stimulated by FSH. PSF also induced slower increases in P450scc mRNA levels than did FSH. In addition, PSF stimulated 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity more slowly than did FSH, but after 3 days of culture, PSF-stimulated activity was significantly higher than that induced by FSH.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of luteal steroidogenesis by two LHRH antagonists (Nal-Glu and Nal-Arg antagonists) in the pregnant rat

We have examined the effect of two LHRH antagonists (Nal-Glu and Nal-Arg antagonists) on the basal progesterone (P4), pregnenolone (P5) and 20 alpha-dihydroprogesterone (20 alpha-DHP) production by luteal cells obtained from day 8 pregnant rats. A dose of 0.1 mmol/l of Nal-Glu or Nal-Arg attenuated basal P4 production by luteal cells after 12, 24 or 48 h of incubation. P5, a precursor for P4 synthesis was also reduced by both doses of Nal-Glu or Nal-Arg (0.1 mmol or 0.1 mumol/l) after 24 h of incubation. A period of 12 h was not sufficient to inhibit P5 production by luteal cells incubated with both doses of Nal-Glu or with the lower dose of Nal-Arg. The higher dose of Nal-Glu and Nal-Arg remained effective in attenuating P5 production by luteal cells after 48 h of incubation. We measured the production of a metabolite of P4, i.e., 20 alpha-DHP to assess whether this suppression in P4 production is due to an enhancement in the P4 metabolism by increasing the activity of 20 alpha-hydroxydehydrogenase. However, instead, we observed (i) a decrease in the production of 20 alpha-DHP by the higher dose of Nal-Glu and Nal-Arg after 12, 24 or 48 h of incubation and (ii) a decrease or no change in the production of 20 alpha-DHP by the lower dose of Nal-Glu or Nal-Arg at all time periods of incubation. Based on these observations we conclude that LHRH antagonists exert a direct effect on the corpus luteum and suppress luteal steroidogenesis. This suppression in luteal steroidogenesis could be due to a decrease in the activity of any one of these enzymes of the steroidogenic pathway, viz., cholesterol side chain cleavage (P450scc), a rate limiting enzyme involved in the synthesis of P5 from cholesterol, or 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), which catalyzes the oxidation of P5 to P4 or due to a decrease in activity of both enzymes.

Follicular fluid contents of hyaluronic acid, follicle-stimulating hormone and steroids relative to the success of in vitro fertilization of human oocytes

OBJECTIVES

To determine the concentrations of hyaluronic acid, FSH, P, and E2 in the follicular fluid (FF) obtained from IVF-ET patients and to assess the value of these measurements in predicting the outcome of fertilization.

DESIGN

One hundred eleven samples were retrospectively analyzed for the hyaluronic acid and hormone contents.

SETTING

University-based tertiary care center.

PATIENTS

Preovulatory FF samples were collected from 67 women undergoing IVF-ET treatment because of tubal absence or obstruction.

MAIN OUTCOME MEASURES

The FF hyaluronic acid and hormone concentrations were compared according to the type of ovulation induction, follicular development, and IVF outcome.

RESULTS

According to the type of ovulation induction, a significantly lower hyaluronic acid concentration was found in FF harvested from the patients treated with GnRH agonist-hMG. No significant correlation was found between FF hyaluronic acid and either morphological maturity of the oocyte-cumulus complex or fertilizability of oocytes. The level of FSH was significantly higher in FF, yielding a mature oocyte-cumulus complex and from which the oocyte obtained successfully fertilized and cleaved. A significant increase in the E2 concentration was found in FF in which mature cumuli oophori were present. The levels of hyaluronic acid significantly correlated with FSH in FF.

CONCLUSIONS

Expansion of the human oocyte-cumulus cell complex is an FSH-dependent phenomenon. The data are in agreement with the hypothesis that intrafollicular FSH plays an important role in the secretion of hyaluronic acid by granulosa cells and may act synergistically with E2 to enhance cytoplasmic maturation, resulting in successful fertilization.

20-alpha-Hydroxysteroid dehydrogenase from pseudopregnant rat ovary: obtention and characterization of a monoclonal antibody against the enzyme activity

The enzyme 20-alpha-hydroxysteroid dehydrogenase (20-alpha-HSD) was purified from pseudopregnant rat ovaries and used as antigen for the development of a monoclonal antibody by the hybridoma technique. Spleen cells of BALB/c mice immunized with purified 20-alpha-HSD were fused with SP2/0 mouse myeloma cells. Among the colonies of hybrid cells, one (designated mAb-HSD 11) was found to be secreting antibodies (IgM) able to inhibit 20-alpha-HSD activity. The antibody-secreting hybridome was amplified by ascitic fluid production and the monoclonal antibody purified by Bakerbond ABx procedure. Purified mAb-HSD 11 was able to inhibit 20-alpha-HSD activity in a dose-dependent manner. Studies of Michaelis constants of 20-alpha-HSD indicate that this monoclonal antibody increases the Km for 20-alpha-dihydroprogesterone and decreases the Vmax.

Diacylglycerol rather than Ca2+ mediates GnRH inhibition of FSH induced steroidogenesis in ovarian granulosa cells

Treatment of cultured granulosa cells with PLC or GnRH stimulated the rapid generation of DAG and phosphoinositide turnover. The PKC activators PLC (3 mU/ml) and TPA (10(-7)M) or the decapeptide GnRH (10(-6)M) elicited similar inhibitory responses on FSH or cAMP stimulated granulosa cell steroidogenesis. Mobilization of intracellular Ca2+ with A23187 (10(-8)M) was followed by a slight increase in the steroidogenic activity of cultured granulosa cells, whereas elevation of extracellular K+ (50 mM) largely augmented the steroid biosynthetic activity of the granulosa cells. These results suggest that the inhibitory effect of GnRH on granulosa cell steroidogenesis is mediated by generation of DAG, rather than by increases in intracellular Ca2+ concentrations.

Porcine lymphocytes secrete a bioactive and immunoreactive LH-like factor in response to LHRH and concanavalin A

Lymphocyte conditioned medium (CM) was prepared by incubating 0 (cell-free control) or 4 x 10(6) lymphocytes/ml in serum-supplemented RPMI containing 0, 10(-9), 10(-7), and 10(-5) M luteinizing hormone releasing hormone (LHRH), 10(-5) M LHRH antagonist (LHRHA), or 10(-7) M LHRH + 10(-5) M LHRHA. Treatments were applied with and without 10 micrograms/ml concanavalin A (con A), and media were analyzed for LH. Aliquots of the CM from cultures incubated for 48 h were later applied to porcine granulosa cell cultures (suspended to 1.25 x 10(5) cells in 450 mul). Thereafter, 50 mul of CM were added to granulosa cell cultures. Media were collected after 12, 24, and 48 h and progesterone determined. Immunoreactive LH increased with time of incubation in lymphocyte CM but not cell-free CM. LH content of lymphocyte CM increased as LHRH concentration increased. LHRHA significantly reduced the amount of LH measured. The presence of con A in the medium resulted in maximal concentrations of LH, irrespective of dose of LHRH or LHRHA. Cell-free CM containing LHRH, LHRHA, and/or con A did not affect progesterone production by granulosa cells at any of the time periods. Lymphocyte CM containing LHRH caused a dose-dependent increase in progesterone production at 48 h. This stimulation was blocked by lymphocyte CM containing LHRHA. Lymphocyte CM containing con A also stimulated progesterone production at all of the LHRH concentrations studied. This response was not inhibited by lymphocyte CM containing the LHRHA.(ABSTRACT TRUNCATED AT 250 WORDS)

Steroidogenesis in vitro of human granulosa-luteal cells pretreated in vivo with gonadotropin-releasing hormone analogs

A modulatory role for gonadotropin-releasing hormone (GnRH) on granulosa cell functions has been demonstrated in animals. Because human granulosa cells have specific receptors for GnRH, we have compared steroidogenesis in vitro of cells pretreated in vivo with GnRH analogs (GnRH-a) with other ovarian stimulation regimens used in in vitro fertilization (IVF) cycles. Cells from 13 patients treated with a GnRH-a for 26.8 +/- 1.1 days during pituitary desensitization and ovarian stimulation with gonadotropins were cultured. Their steroidogenesis was evaluated in basal conditions as well as after stimulation with follicle-stimulating hormone (FSH) and human chorionic gonadotropin (hCG). Granulosa-luteal cells from 9 women treated with a combination of clomiphene citrate (CC) and gonadotropins were also cultured. Estradiol production in response to FSH was stimulated only in the GnRH-a-treated cells. Basal, FSH-, and hCG-induced progesterone (P) accumulation was higher in the CC-treated cells. The peak of P production was delayed 2 days in the GnRH-a-treated group. Only cells pretreated in vivo with GnRH-a accumulated 20 alpha-hydroxyprogesterone in culture. The results of the present study suggest that the use of GnRH-a during a long period of time for IVF affects the steroidogenic pathway of human granulosa-luteal cells. It seems that, at least in part, this change is due to the stimulation of the metabolizing enzyme 20 alpha-hydroxysteroid dehydrogenase by GnRH-a.

Gonadotropin-releasing hormone inhibition of LH stimulated progesterone secretion by porcine granulosa cells in vitro

GnRH has several direct actions on rat granulosa cells. Specific receptors for GnRH have been demonstrated on rat and human ovaries. Whether the porcine ovary has specific receptors for GnRH is still debated and the physiological actions of GnRH on porcine granulosa cells have not yet been clarified. Consequently, we have examined the actions of a GnRH agonist (GnRHa) on basal and LH stimulated progesterone secretion by porcine granulosa cells. GnRHa inhibited both basal and LH stimulated progesterone secretion by granulosa cells from medium (3-5 mm) and large (6-10 mm) antral follicles during 3 day incubations. LH stimulated progesterone secretion was more sensitive to inhibition than basal progesterone secretion. Studies on the time course for GnRHa inhibition of progesterone secretion indicated that the decrease in progesterone secretion occurred 48 to 72 hr after first exposure to GnRHa. Earlier inhibition occurred in only a fraction of the experiments. GnRHa did not have to be present during the time when inhibition occurred. Incubations of 2 days with GnRHa were just as effective as 3 day incubations at inhibiting progesterone secretion on day 3. Furthermore, a 30 min exposure to GnRHa on day 1 was just as inhibitory as a full 2 day incubation with GnRHa in inhibiting LH stimulated progesterone secretion on day 3. Incubation of the cells for 3 days prior to exposure of the cells to GnRHa did not alter the time course for GnRHa action. GnRHa did not alter the DNA content of the cultures in up to 6 day incubations or the number of viable cells attached to the wells in up to 3 day incubations.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of a teleost GnRH analog on steroidogenesis by the follicle-enclosed goldfish oocytes, in vitro

The influence of an agonist analog of teleost GnRH [(D-Arg6, Trp7, Leu8, Pro9-NEt)-GnRH; tGnRH-A] on steroidogenesis was studied in prophase-I arrested, follicle-enclosed, goldfish oocytes in vitro. Incubation of the follicles with carp gonadotropin (GtH) significantly increased production of 17 alpha-hydroxyprogesterone (HP) and testosterone following 24 hr of incubation in vitro. Concomitant incubation with tGnRH-A (10(-7) M) significantly attenuated the dose-related increase in GtH-induced testosterone production, but was without effect on the GtH-induced HP level. Time course studies indicated that tGnRH-A exerted its maximum inhibitory action on the GtH-induced testosterone production during the initial 8 hr of incubation in vitro. The inhibition of GtH-induced testosterone production by tGnRH-A was dose dependent with an ED50 of 1.39 +/- 2.88 nM. A significantly higher testosterone level was obtained in the incubation media containing HP as substrate; concomitant treatment with tGnRH-A reduced the conversion of HP to testosterone. The incubation media also contained low, but measurable levels of 17 alpha-hydroxy-20 beta-dihydroprogesterone (DHP), which increased in the presence of 3-isobutyl-methyl-xanthine; lower levels of DHP were obtained in the groups incubated with tGnRH-A. In view of our present findings and previous observations concerning inhibitory effects of tGnRH-A on the progestogen and GtH-induced reinitiation of meiosis in the follicle-enclosed goldfish oocytes (H. R. Habibi, G. Van Der Kraak, E. Bulanski, and R. E. Peter, Amer. J. Physiol. 255, R268-R273 (1988] the influence of testosterone on the GtH- and DHP-induced meiosis in vitro was also studied. Testosterone (1 micrograms/ml) enhanced both GtH- and DHP-induced oocyte meiosis in the goldfish oocytes. Testosterone alone was also found to significantly increase oocyte meiosis in the goldfish oocytes in a dose-related fashion. The present findings demonstrate an inhibitory effect of a GnRH agonist on GtH-induced testosterone production in goldfish oocytes and suggest that tGnRH-A might influence oocyte meiosis in part by influencing steroidogenesis.

Time-dependent effects of follicle-stimulating hormone on progesterone metabolism by cultured rat granulosa cells

The effects of FSH on the accumulation of endogenous progesterone and 20 alpha-hydroxy-4-pregnen-3-one as well as on the metabolism of [4-14C]progesterone were studied in 24, 48 and 72 h cultures of rat granulosa cells. FSH stimulated the accumulation of both progesterone and 20 alpha-hydroxy-4-pregnen-3-one by 6-18 fold and 2.5-44 fold, respectively. Short term exposure (24 h) to FSH resulted in the ratio of progesterone to 20 alpha-hydroxy-4-pregnen-3-one accumulations significantly increased (by 2.6 fold), while the reverse was observed for the longer (48 and 72 h) cultures whereby control levels of the ratio of progesterone to 20-alpha-hydroxy-4-pregnen-3-one were significantly greater (by 50% and 270%, respectively) than those of FSH-treated cultures. Effects of FSH on [4-14C]progesterone were also time-dependent. Twenty-four hour cultures were associated with FSH induced inhibition of 20 alpha-reduced metabolites of progesterone (by 55%) while the 48 and 72 h exposures to FSH resulted in a significant increase of the 20 alpha-reduced metabolites above control levels (by 73% and 230%, respectively). Consequently, it is postulated that FSH may exert biphasic time-dependent actions on 20 alpha-hydroxysteroid dehydrogenase activity with short term inhibitory and longer term stimulatory effects.

Actions of LH/hCG on accumulation and catabolism of progestins in cultured rat granulosa cells

Immature hypophysectomized rats were treated with estradiol-17 beta and follicle-stimulating hormone. Granulosa cells were isolated and incubated for 24 h with or without varying doses of ovine luteinizing hormone (NIMADD-oLH-24) or human chorionic gonadotropin (NIADDK CR 125) and accumulations of progesterone and 20 alpha-hydroxy-4-pregnen-3-one were determined. The cells were reincubated for 3 h with [4-14C]progesterone (0.5 nmol/mL) and the radiolabelled metabolites were separated and quantified. Both LH (0.04-1.0 ug/mL) and hCG (0.04-1.0 ug/mL) enhanced the accumulation of endogenous progesterone (by up to 300 and 150%, respectively) and 20 alpha-hydroxy-4-pregnen-3-one (by up to 90 and 85%, respectively) producing dose-dependent increases of the ratio of progesterone to 20 alpha-hydroxy-4-pregnen-3-one (by up to 125 and 70%, respectively). Studies of the metabolism of [1-14C] progesterone have demonstrated that both LH and hCG led to a dose-dependent decrease of the utilization of radiolabelled progesterone (down to 64 and 70%, respectively, of the control value). This effect was associated with an LH- and hCG-dependent inhibition of 20 alpha-hydroxysteroid dehydrogenase activity (down to 60 and 70%, respectively, of the control value) but had no significant effect on 5 alpha-reductase. The present results indicate that LH and hCG stimulate accumulation of progesterone at least in part by decreasing the 20 alpha-hydroxysteroid dehydrogenase activity.

Paracrine regulation of luteal function

The mechanisms controlling luteal function may involve factors that are produced both within the corpus luteum and outside the ovary. The process of luteal control appears to involve a series of molecular species, proteins, peptides, steroids and prostaglandins. Each of these factors may act independently or in concert modifying the actions of one another. The effect of GnRH on luteal function has not been completely examined and thus its significance is unclear. The neurohypophyseal peptides, oxytocin and arginine vasopressin, in combination with LH, prolactin, oestrogens and prostaglandins may play an important regulatory role on the corpus luteum.

The mechanisms by which phorbol ester inhibits LH stimulation of progesterone production in rat granulosa cells

Tumor-promoting phorbol esters are believed to affect cell functions by activating a Ca+2-and lipid-dependent protein kinase (protein kinase C). 12-0-Tetradecanoyl phorbol-13-acetate (TPA) inhibits LH stimulation of progesterone (P) accumulation in rat granulosa cells. To determine the mechanisms by which TPA inhibits LH stimulation of P accumulation, TPA regulation of various ovarian steroidogenic enzymes was investigated. Cells were obtained from immature (28-29 days old) rats 48 h after injection of 20 IU PMSG and incubated for up to 5 h. TPA decreased the P responses to LH, cholera toxin, and (Bu)2cAMP by 20%, 24%, and 28%, respectively. One locus of inhibition of LH action, therefore, was after cAMP. TPA decreased LH-stimulated 3-beta-hydroxysteroid dehydrogenase activity. Furthermore, TPA stimulated 20-alpha-hydroxysteroid dehydrogenase activity. The combination of TPA and A23187 inhibited LH-stimulated P accumulation to the same extent as TPA alone. These data suggest that TPA-induced decreases in LH-stimulated P production result from both the inhibition of P biosynthesis and the stimulation of P breakdown.

Progestin regulation of progesterone biosynthetic enzymes in cultured rat granulosa cells

Progestins have recently been shown to augment gonadotropin-stimulated progesterone and 20 alpha-hydroxypregn-4-en-3-one (20 alpha-OH-P) biosynthesis in cultured rat granulosa cells. The mechanism by which progestins autoregulate ovarian progestin biosynthesis was investigated by studying the modulation of pregnenolone biosynthesis as well as the activities of the enzymes 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSD). Granulosa cells obtained from immature hypophysectomized, estrogen-treated rats were cultured with FSH and/or progestins. Pregnenolone production was measured in the presence of cyanoketone (10(-6) M) to inhibit 3 beta-HSD activity. Enzymatic activities of 3 beta-HSD and 20 alpha-HSD were determined in cell homogenates by direct enzyme assays. FSH stimulated pregnenolone production, while treatment with progesterone or R5020 alone was ineffective. Concomitant treatment with the progestins further enhanced FSH-stimulated pregnenolone production in a dose-dependent manner with minimal effective doses of 10(-8) and 10(-7) M for R5020 and progesterone, respectively. In FSH-primed cells, LH increased pregnenolone accumulation, and concomitant treatment with R5020 also enhanced the LH action. Furthermore, the gonadotropins stimulated the activity of 3 beta-HSD, and this effect was further enhanced by concomitant treatment with either R5020 or progesterone in a dose-dependent manner. In addition, the 20 alpha-HSD activities were enhanced by progestins in cells treated with FSH but not with LH. Thus, both natural and synthetic progestins stimulate the gonadotropin-induced progesterone production in cultured granulosa cells via enhancing the 3 beta-HSD enzyme as well as pregnenolone biosynthesis.

Gonadotropin-releasing hormone as a modulator of ovarian function

GnRH and its agonist analogs exert direct inhibitory and stimulatory effects on the ovaries of animals from several species. In the immature follicle, GnRH inhibits the actions of FSH on an integrated array of biochemical responses that lead to follicular development and corpus luteum formation. GnRH also suppresses gonadotropin action in mature follicles, and stimulates certain ovarian processes such as steroidogenesis and oocyte maturation. The inhibitory and stimulatory effects of GnRH are mediated through the binding of the peptide to high-affinity receptors in granulosa and thecal cells. Recent studies have shown that GnRH action in the ovary is dependent upon calcium mobilization and probably operates through stimulation of phospholipid turnover and activation of protein kinase C.

Fetal Leydig cell culture--an in vitro system for the study of trophic hormone and GnRH receptors and actions

In fetal and neonatal rat Leydig cells cultured in the presence of LH, gonadotropin and GnRH receptors and acute testosterone responses to hCG, were maintained for up to 78 days. Addition of GnRH agonists markedly inhibited steroid production in LH-treated cultures, and abolished the acute testosterone response to hCG. GnRH receptors were not detectable in fetal testes but were present post-natally and increased markedly with age. In cultured fetal testis, GnRH receptors were detected on the third day, and were increased by exposure to GnRH agonists. In LH-treated cultures, GnRH sites were reduced by about 50% and did not increase during incubation with GnRH agonists. LH supported 17 alpha-hydroxylase/17-20 desmolase activities and pregnenolone formation were observed in short (1-4 days) and long-term cultures. Also, LH stimulation of 3 beta-hydroxysteroid dehydrogenase was observed by histochemical studies at 7 days of culture. GnRH agonists inhibited LH dependent steroid production in a dose-dependent fashion and abolished the acute testosterone response to human chorionic gonadotropin. The major component of the steroid inhibitory effect of GnRH agonist occurs beyond cAMP production. A distal lesion of the microsomal enzymes of the androgen pathway is largely responsible for the GnRH-induced decreases in LH-supported androgen production. The expression of functional GnRH receptors during culture and their suppression by LH suggest that pituitary gonadotropins exert a tonic inhibitory effect upon testicular GnRH receptors. The presence of functional GnRH receptors and inhibitory actions in cultured fetal and neonatal Leydig cells indicates that GnRH-related peptides can influence the actions of gonadotropins on the fetal Leydig cell population.

Gonadotropin-releasing hormone as a paracrine hormone and neurotransmitter in extra-pituitary sites

Gonadotropin-releasing hormone (GnRH), in addition to its classical releasing action at the pituitary level, acts on multiple extrapituitary sites to regulate various reproductive functions. In the rat ovary, specific high affinity GnRH receptors have been identified in granulosa and theca cells. These binding sites mediate the inhibitory effects of GnRH and its agonists on gonadotropin-stimulated estrogen, progestin and androgen biosynthesis. At the granulose cell level, GnRH treatment decreases aromatase activity as well as the biosynthesis of pregnenolone and progesterone via inhibition of cholesterol side-chain cleavage and 3 beta-hydroxysteroid dehydrogenase enzymes. High concentrations of GnRH also stimulate low but significant levels of various steroids. In addition, treatment with high concentrations of GnRH induces ovulation and oocyte maturation in hypophysectomized rats. This is associated with the ability of GnRH to stimulate plasminogen activator activity in cultured granulosa cells. In the rat testis, GnRH receptors have been identified in Leydig but not Sertoli cells. Treatment with GnRH inhibits gonadotropin-stimulated androgen biosynthesis by the cultured Leydig cells. The inhibitory effect of GnRH on testicular androgen production occurs at sites distal to the formation of cyclic AMP and pregnenolone and may be due to decreases in the activity of the enzyme 17 alpha-hydroxylase and 17-20 desmolase. Since hypothalamic GnRH is unlikely to act at the gonadal level, several laboratories have attempted to isolate gonadal GnRH-like peptide which may serve as the ligand for specific gonadal GnRH receptors. Although the presence of ovarian GnRH-like substance still remains elusive, testicular GnRH-like substance has been identified. This gonadal peptide(s) may be an important local paracrine hormone. In addition to its action at the gonadal level, GnRH or GnRH-like peptides may play an important role as a neurotransmitter in the central nervous system. Exogenous administration of GnRH in selected brain areas has been shown to modulate sexual behavior in experimental animals, while neural pathways containing GnRH-like immunoreactive substances have been identified in several brain areas. We have recently synthesized a bioluminescent GnRH analog capable of serving as a specific GnRH ligand for a bioluminescent ligand receptor assay which is more sensitive than classical 125I-ligand assays. We have identified GnRH receptors in small, discrete brain regions. Thus, GnRH and GnRH-like peptides may play important paracrine and neurotransmitter roles in the regulation of various reproductive functions in extra-pituitary sites.

Comparison between the steroidogenic responses after pulsatile and continuous administration of gonadotrophin releasing hormone to superfused rat follicles

Gonadotrophin releasing hormone (GnRH) exhibits both stimulatory and inhibitory effects on the ovarian tissue in the rat. For the action of GnRH on the pituitary, the mode of administration is of utmost importance. The binding characteristics and regulation of the GnRH receptors found in the ovary are very similar to those of the pituitary. The aim of the present study was to compare the steroidogenic response of superfused, preovulatory rat follicles to continuous and pulsatile administration of a GnRH analogue (GnRHa). The results obtained with a single pulse of luteinizing hormone (LH) served as a control. Repeated pulses (1 pulse X h-1) or continuous administration of GnRHa was found to be more effective than a single pulse of GnRHa. The effect of GnRHA, irrespective of the mode of administration, was most pronounced on the secretion of 20 alpha-OH-progesterone (20 alpha-OHP). Also the release of testosterone (T) and oestradiol (E2) was stimulated but to a lesser extent. In comparison to LH, the GnRHa response was delayed and without detectable release of cyclic AMP (cAMP). These results illustrate that pulses of GnRH stimulate the steroidogenesis in preovulatory follicles. In contrast to the effects of GnRHa on the pituitary, the modes of administration seem to be of less importance for the stimulation of the rat ovary.

Insulin enhances FSH-stimulated steroidogenesis by cultured rat granulosa cells

Experimentally induced diabetes in female rats is associated with decreased ovarian functions. We have investigated the ovarian action of insulin using granulosa cells obtained from immature hypophysectomized, estrogen-treated rats. The cells were cultured for 2 days in a serum-free medium in the presence of follicle-stimulating hormone (FSH), with or without insulin. Medium steroids were determined by specific radioimmunoassay. Treatment with FSH caused a dose-dependent increase in the production of estrogen, progesterone, 20 alpha-hydroxypregn-4-en-3-one (20 alpha-OH-progesterone) and pregnenolone. Concomitant treatment with 100 ng/ml insulin increased the responsiveness of granulosa cells to FSH, decreasing the ED50 values for FSH-stimulated estrogen and progestin production 2-2.75-fold. A lower dose of insulin, 10 ng/ml, also augmented FSH action. In contrast, treatment with insulin alone had no effect on steroid production. The insulin effect on progestin and estrogen biosynthesis was detected by 24 and 44 h after treatment, respectively. Also, the insulin action appeared to be specific since an insulin fragment, desoctapeptide insulin, exhibited no effect. Insulin also increased the FSH-stimulated increase in activity of 3 beta-hydroxysteroid dehydrogenase, the rate-limiting enzyme in the formation of progesterone, but was without effect on the activity of 20 alpha-hydroxysteroid dehydrogenase, which converts progesterone to the inactive 20 alpha-OH-progesterone. The effects of insulin on increasing FSH responsiveness could not be accounted for by changes in cell viability or total cell number. These results indicate that insulin exerts a specific action on granulosa cells to increase the FSH stimulation of estrogen and progestin production.(ABSTRACT TRUNCATED AT 250 WORDS)

Androgen and progestogen production by prepubertal rat interstitial cells: study of the effects of LHRH and its analogues and their interactions with LH

The effects of luteinizing hormone-releasing hormone (LHRH) and an agonistic analogue (LHRHa) have been examined in freshly isolated prepubertal rat interstitial cells and in cells precultured for 6 days in the presence or absence of luteinizing hormone (LH). C19-steroid output (testosterone and androstenedione), C21-steroid output (mainly progesterone and 20 alpha-hydroxypregn-4-en-3-one) and cyclic AMP secretion were used as parameters of interstitial cell activity. A potent 5 alpha-reductase inhibitor was added to the incubation media to simplify the pattern of steroid secretion. It could be demonstrated that LHRHa uniformly stimulates C21-steroid production whereas C19-steroid output is increased only in freshly isolated cells and in cells precultured with LH. At suboptimal concentrations of LH, LHRH and its agonist again uniformly potentiate C21-precursor production whereas LH-induced androgen production is slightly inhibited in freshly isolated cells, strongly inhibited in cells precultured in the absence of LH and markedly enhanced in cells precultured in the presence of LH. The concentrations (ED50 values) of the oligopeptides required to elicit these synergistic or antagonistic effects with LH are lower than those required for their direct effects. An antagonistic LHRH analogue blocks all the stimulatory and inhibitory activities of LHRHa. None of these activities is accompanied by noticeable changes in cyclic AMP secretion. Evidence is presented that LHRH and its agonistic analogue have a stimulatory effect early in the steroidogenic pathway and an inhibitory effect at the level of the conversion of C21-precursors into androgens. Our data suggest that the existing level of 17 alpha-hydroxylase and/or 17,20-desmolase activity is the major factor that determines the ultimate effect of LHRHa on androgen secretion.

Androgen regulation of progestin biosynthetic enzymes in FSH-treated rat granulosa cells in vitro

The influence of androgens on the FSH modulation of progestin biosynthetic enzymes was studied in vitro. Granulosa cells obtained from immature, hypophysectomized, estrogen-treated rats were cultured for 3 days in a serum-free medium containing FSH (20 ng/ml) with or without increasing concentrations (10(-9)-10(-6)M) or 17 beta-hydroxy-5 alpha-androstan-3-one (dihydrotestosterone; DHT), 5 alpha-androstane-3 alpha,17 beta-diol (3 alpha-diol), or the synthetic androgen 17 beta-hydroxy-17-methyl-4,9,11-estratrien-3-one (methyltrienolone; R1881). FSH treatment increased progesterone and 20 alpha-hydroxy-4-pregnen-3-one (20 alpha-OH-P) production by 10.2- and 11-fold, respectively. Concurrent androgen treatment augmented FSH-stimulated progesterone and 20 alpha-OH-P production in a dose-related manner (R1881 greater than 3 alpha-diol greater than DHT). In the presence of an inhibitor of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), the FSH-stimulated pregnenolone (3 beta-hydroxy-5-pregnen-20-one) production (a 20-fold increase) was further enhanced by co-treatment with R1881, 3 alpha-diol or DHT. Furthermore, FSH treatment increased 4.4-fold the activity of 3 beta-HSD, which converts pregnenolone to progesterone. This stimulatory action of FSH was further augmented by concurrent androgen treatment. In contrast, androgen treatment did not affect FSH-stimulated activity of a progesterone breakdown enzyme, 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSD). These results demonstrate that the augmenting effect of androgens upon FSH-stimulated progesterone biosynthesis is not due to changes in the conversion of progesterone to 20 alpha-OH-P, but involves an enhancing action upon 3 beta-HSD/delta 5,delta 4-isomerase complexes and additional enzymes prior to pregnenolone biosynthesis.

20 alpha-Hydroxysteroid dehydrogenase activity in the rat corpus luteum; a quantitative cytochemical study

A quantitative cytochemical method for the demonstration of 20 alpha-hydroxysteroid dehydrogenase activity (20 alpha-HSD) in the regressing corpora lutea of the adult rat ovary is described. The method employs unfixed tissue sections and relies upon the oxidation of 20 alpha-hydroxy-4-pregnen-3-one (20 alpha-OH-P) with nitro blue tetrazolium as the hydrogen acceptor. The enzyme was dependent upon NADP+ for its activity and was inactive when 20 beta-hydroxy-4-pregnen-3-one (20 beta-OH-P) was used as a substrate. The apparent Km values for 20 alpha-OH-P and NADP+ were 3 x 10(-4) M and 2.5 x 10(-5) M respectively. Inhibition of 20 alpha-HSD activity by steroids was demonstrable at pH 8. Androstenedione was by far the most potent inhibitor, followed by progesterone (the product of the enzyme activity) 17 alpha-hydroxyprogesterone, Compound S and 20 beta-OH-P. At pH 6.8, a pH more favourable to the progesterone leads to 20 alpha-OH-P reaction, only progesterone and 17 alpha-hydroxyprogesterone were inhibitory. Testosterone was without demonstrable effect at either pH.

Modulation of prolactin receptors in cultured rat granulosa cells by FSH, LH and GnRH

The hormonal modulation of prolactin (PRL)-binding capacity of rat granulosa cells was studied. Granulosa cells obtained from immature, hypophysectomized, estrogen-treated rats were cultured for 2 days in a serum-free medium in the presence of various hormones. FSH treatment in vitro stimulated granulosa cell PRL-binding capacity by approximately 4-6-fold in a dose-dependent manner. Concomitant treatment with 10-8 M GnRH inhibited the FSH-induced increase in PRL-binding capacity by 64%. In contrast, the inhibitory effect of GnRH was blocked by concomitant treatment with 10-6 M of a GNRH antagonists, [D-pGlu1, D-Phe2, D-Trp3,6]GnRH. PRL-binding capacity was also increased (approximately 2-fold) by in vitro treatment with cholera toxin (10 microgram/ml). In granulosa cells pre-treated with FSH in vitro for 2 days, hCG treatment for 2 additional days stimulated PRL-binding capacity in a dose-dependent manner (approximately 2-fold). Likewise, treatment with LH (100 ng/ml) also stimulated PRL-binding capacity by approximately 2-fold. These in vitro studies demonstrated that gonadotropins (FSH, LH and hCG) directly enhanced PRL binding by granulosa cells, whereas GnRH inhibited FSH action.

Gonadotropin-releasing hormone: regulation of adenosine 3',5'-monophosphate in ovarian granulosa cells

The antigonadal effects of gonadotropin-releasing hormone in ovarian granulosa cells are due to attenuation of the adenosine 3',5'-monophosphate (cyclic AMP) response to follicle-stimulating hormone. Agonists of gonadotropin-releasing hormone progressively inhibit adenylate cyclase and stimulate phosphodiesterase activities in cultured granulosa cells, indicating that blockade of gonadotropin action is attributable to the combined effects of decreased production and increased degradation of cyclic AMP.