Inhibitory effect of gonadotrophin-releasing hormone (GnRH) on rat granulosa cell deoxyribonucleic acid synthesis

Apoptosis of bovine granulosa cells: Intracellular pathways and differentiation

Follicular atresia in granulosa and theca cells occurs by apoptosis through weak hormonal stimulation. We have previously proposed an in vitro model to study this process by inducing apoptosis in BGC-1, a bovine granulosa cell line, and in primary cultures from ovaries with or without corpus luteum (CPGB+ and CPGB-, respectively), with different doses of gonadotropin releasing hormone (GnRH) analogs (leuprolide acetate (LA) as agonist and antide as antagonist). BGC-1 represent immature granulosa cells, whereas CPGB represent different degrees of luteinization. Our aim was to evaluate the intracellular pathways involved in the GnRH regulation of apoptosis in BGC-1. Treatment with LA 100nM but not with antide led to an increase in BAX over BCL-2 expression, showing antagonism of antide. All treatments inhibited phospholipase-D (PLD) activity compared to control, implying agonist behavior of antide. Progesterone in vitro production and 3β-hydroxysteroid dehydrogenase (3β-HSD) expression revealed different degrees of luteinization: BGC-1 were immature, whereas CPGB+ were less differentiated than CPGB-. We concluded that LA-induced apoptosis in BGC-1 occurs by activation of the mitochondrial pathway and by inhibition of PLD activity and that antide might work both as an antagonist of the intrinsic pathway and as an agonist of the extrinsic protection pathway by inhibiting PLD activity.

Changes in GnRH I, bradykinin and their receptors and GnIH in the ovary of Calotes versicolor during reproductive cycle

The aim of this study was to investigate changes in the abundance of gonadotrophin releasing hormone I (GnRH I) and GnRH I receptor in the ovary of Calotes versicolor during the reproductive cycle and correlate them with the changes in gonadotrophin inhibitory hormone (GnIH), bradykinin and bradykinin B(2) receptor in order to understand their interaction during ovarian cycle. GnRH I, bradykinin and their receptors and GnIH, were localized immunohistochemically in the ovary. Relative intensity of these peptides was estimated from the contralateral ovary using slot/Western blot followed by densitometry. The immunostaining of GnRH I, bradykinin and their receptors and GnIH were localized in the granulosa cells of previtellogenic follicles and stroma cells, whereas in the peripheral part of the cytoplasm in oocytes of vitellogenic and ovulatory follicles. The GnRH I immunostaining was relatively higher in inactive phase, but was low during active preovulatory phase suggesting inverse correlation with circulating estradiol level. The study showed a positive correlation between the expression pattern of GnRH I and GnIH, but showed a negative correlation between GnIH with GnRH I receptor in the ovary. This study further suggests a possibility for bradykinin regulating GnRH I synthesis in the ovary. An increase in the immunostaining of both GnRH I and GnIH in the oocyte prior to ovulation suggests their involvement in the oocyte maturation. It is thus concluded that the ovary of C. versicolor possesses GnRH I-GnIH-bradykinin system and interaction between these neuropeptides may be involved in the regulation of follicular development and oocyte maturation.

Activity and expression of different members of the caspase family in the rat corpus luteum during pregnancy and postpartum

Studies were designed to examine the expression and activity of four caspases that contribute to the initial (caspases-2, -8, and -9) and final (caspase-3) events in apoptosis in the rat corpus luteum (CL) during pregnancy (days 7, 17, 19, and 21 of gestation), postpartum (days 1 and 4), and after injection (0, 8, 16, 24, and 36 h) of the physiological luteolysin PGF2alpha. In addition, the temporal relationship of caspase expression/activity relative to steroid production and luteal regression was evaluated. During pregnancy, the activity of all four caspases was significantly greater on day 19, before a decline in CL progesterone (P) and CYP11A1 levels at day 21 of gestation. The levels of the caspase-3 active fragment (p17, measured by Western blot) also increased at days 19 and 21 of pregnancy. Immunohistochemical analyses detected specific staining for the caspases in luteal cells (large and small) as well as in endothelial cells. However, the percentage of apoptotic cells did not increase in the CL until postpartum. Following PGF2alpha injection, there was a significant decrease in CL P by 24 h, although the activity of all four caspases did not increase until 36 h posttreatment. The active p17 fragment of caspase-3 also significantly increased at 36 h post-PGF2alpha. These results suggest that an increase in the activity of caspases-2, -8, -9, and -3 is associated with the early events of natural luteolysis at the end of pregnancy. Also, the exogenous administration of the luteolysin PGF2alpha may regulate members of the caspase family.

GnRH in non-hypothalamic reproductive tissues

Gonadotropin releasing hormone (GnRH) is a hypothalamic neuronal secretory decapeptide that plays a pivotal role in mammalian reproduction. GnRH and its analogues are used extensively in the treatment of hormone dependent diseases and assisted reproductive technology. Fourteen structural variants and three different forms of GnRH, named as hypothalamic GnRH or GnRH-I, mid brain GnRH or GnRH-II and GnRH-III across various species of protochordates and vertebrates have been recognised. The hormone acts by binding to cell surface transmembrane G protein coupled receptors (GPCRs) and activates Gq/11 subfamily of G proteins. Although hypothalamus and pituitary are the principal source and target sites for GnRH, several reports have recently suggested extra-hypothalamic GnRH and GnRH receptors in various reproductive tissues such as ovaries, placenta, endometrium, oviducts, testes, prostrate, and mammary glands. GnRH-II appears to be predominantly expressed in extra pituitary reproductive tissues where it produces its effect by PLC, PKA2, PLD, and AC cell signalling pathways. In these tissues, GnRH is considered to act by autocrine or paracrine manner and regulate ovarian steroidogenesis by having stimulatory as well as inhibitory effect on the production of steroid hormones and apoptosis in ovarian follicle and corpus luteum. In male gonads, GnRH has been shown to cause a direct stimulatory effect on basal steroidogenesis and an inhibitory effect on gonadotropin-stimulated androgen biosynthesis. Recent studies have shown that GnRH is more abundantly present in ovarian, endometrial and prostrate carcinomas. The presence of type-II GnRH receptors in reproductive tissues (e.g. gonads, prostrate, endometrium, oviduct, placenta, and mammary glands) suggests existence of distinct role(s) for type-II GnRH molecule in these tissues. The existence of different GnRH forms indicates the presence of distinctive cognate receptors types in vertebrates and is a productive area of research and may contribute to the development of new generation of GnRH analogues with highly selective and controlled action on different reproductive tissues and the target-specific GnRH analogues could be developed.

Gonadotropin-releasing hormone agonist induces apoptosis and reduces cell proliferation in eutopic endometrial cultures from women with endometriosis

OBJECTIVE

There is growing evidence that suggests a direct action of gonadotropin-releasing hormone agonist (GnRH-a) on endometrial growth. Consequently, our purpose was to evaluate the effect of GnRH-a on in vitro eutopic endometrial cell growth and apoptosis.

DESIGN

Prospective study.

SETTING

Research institute and clinical fertility center.

PATIENT(S)

Sixteen women with untreated endometriosis and 14 controls.

INTERVENTION(S)

Biopsy specimens of eutopic endometrium were obtained from all subjects. Apoptosis and cell proliferation were examined in epithelial endometrial cell cultures after incubation with leuprolide acetate (LA), antide, and a combination of both.

MAIN OUTCOME MEASURE(S)

The percentage of apoptotic cells was evaluated by the acridine orange-ethidium bromide technique; cell proliferation was assessed by (3)H-thymidine incorporation.

RESULT(S)

Leuprolide acetate (LA) (100 ng/mL) enhanced apoptosis in endometrial cultures from patients with endometriosis and controls, and this effect was reversed by antide 10(-7)M. Cell proliferation was down-regulated by LA at 1, 10, and 100 ng/mL in cultures from women without and with endometriosis. The addition of antide 10(-7)M reversed this inhibition.

CONCLUSION(S)

GnRH-a appears to have a direct effect by enhancing the apoptotic index and decreasing the cell proliferation in endometrial cells.

Autocrine role of transforming growth factor beta1 on rat granulosa cell proliferation

We evaluated the effects of transforming growth factor beta1 (TGFbeta1), alone or in combination with FSH and estradiol, on DNA synthesis in primary cultures of immature rat granulosa cells. 3H-Thymidine incorporation was significantly stimulated by TGFbeta1 (5.6-fold). This effect was enhanced by FSH (20 ng/ml, 27.7-fold) or estradiol (100 ng/ml, 13.4-fold) or by a combination of both hormones (59.2-fold). Measurement of TGFbeta bioactivity showed the presence of significant amounts of TGFbeta in conditioned medium from granulosa cell cultures, and most of the activity was present in the latent form. FSH alone or in combination with estradiol produced a marked suppression of the production of latent and active TGFbeta. Activated conditioned medium from control cultures of granulosa cell elicited a 1.4-fold increase in thymidine incorporation. This effect was markedly amplified by FSH (3-fold) and estradiol (4.3-fold) and by a combination of both (8.7-fold). The peptide containing the cell-binding domain of fibronectin (RGDSPC) partially inhibited thymidine incorporation stimulated by TGFbeta1. Fibronectin did not synergize with FSH, and the interaction between TGFbeta1 and FSH was even observed in the presence of this protein. The conclusions reached were as follows: 1) TGFbeta1 is an autocrine stimulator of rat granulosa cell DNA synthesis, 2) FSH and estradiol produce a suppression of latent and active TGFbeta production but markedly amplify TGFbeta action, presumably at a postreceptor level, and 3) the stimulatory effects of TGFbeta1 may be only partly mediated by the increased fibronectin secretion.

Comparative analysis of different puberty inhibiting mechanisms of two GnRH agonists and the GnRH antagonist cetrorelix using a female rat model

GnRH agonists are the established treatment of precocious puberty caused by premature stimulation of gonadotropin secretion. It has been reported that after an initial stimulation ("flare-up") they reduce LH secretion by desensitization of pituitary GnRH receptors. Little has been published about the use of GnRH antagonists such as cetrorelix to control the onset of puberty and whether they are potentially advantageous compared with GnRH agonists. We conducted two multigroup experiments (12 and 10 d, respectively) treating prepubertal/peripubertal female rats with either the GnRH agonist triptorelin or buserelin and compared them with rats treated with the GnRH antagonist cetrorelix and controls to assess the effects on pubertal progress and serum hormones. In the second experiment, the effects of buserelin and cetrorelix on gene expression of the GnRH receptor, LH-beta, FSH-beta, and the alpha subunit genes in the pituitary were also investigated. Cetrorelix, triptorelin, and buserelin retarded the onset of puberty as determined by delayed vaginal opening, lower ovarian weights, and lower serum estradiol levels. However, although LH and FSH levels were stimulated by both agonists, they were inhibited by cetrorelix. In the cetrorelix versus buserelin experiment, pituitary gene expression of the GnRH receptor and LH-beta subunit were significantly lower in cetrorelix treated rats compared with controls whereas buserelin had little effect. Expression of FSH-beta and alpha subunit were stimulated by buserelin but not by cetrorelix. Even though all three of these GnRH analogues inhibited gonadal development and delayed the onset of puberty, the GnRH agonists had stimulating and inhibiting effects on the pituitary-gonadal axis whereas cetrorelix exerted only inhibiting effects. We conclude from this female rat model that cetrorelix may offer advantages for a more controlled medical treatment of precocious puberty compared with GnRH agonist treatment.

Growth promoting activity of oocytes on granulosa cells is decreased upon meiotic maturation

An increasing body of evidence indicates that the oocyte plays an active role in the control of ovarian follicle development in mammals. In the present study, we have examined the role of oocytes in regulating granulosa cell proliferation. Rat and bovine oocytes cocultured with rat granulosa cells stimulated granulosa cell DNA synthesis and DNA content in the cultures. FSH or cAMP further amplified this effect. Poor-quality oocytes showed a marked decrease in their stimulatory effect. Stimulation of DNA synthesis by bovine oocytes seems to be cell-type specific, since Swiss 3T3 fibroblasts and CCL-64 mink lung epithelial cells were not responsive, while primary cultures of rat and bovine granulosa cells and the bovine granulosa cell line BGC-1 showed significant responses. Oocyte-conditioned medium produced only a slight stimulation of rat granulosa cell DNA synthesis. However, the effect of oocyte coculture was dependent on the total incubation volume, suggesting that the growth promoting activity was mediated by a soluble factor. The stimulation elicited by bovine oocytes was evident even in the presence of maximally effective doses of transforming growth factor-beta or tumor necrosis factor-alpha, indicating that neither of these growth factors was responsible for this effect. In vitro maturation of bovine oocytes was associated with a marked decrease in the stimulatory activity. This decrease was partially prevented when maturation was blocked by addition of cycloheximide. Comparison of the developmental pattern of the secretion of the growth promoting activity with that of the cumulus expansion-enabling factor indicated that both activities can be dissociated. Our data suggest the existence of a very labile factor produced by the oocyte before completion of the first meiotic division that promotes granulosa cell proliferation.