Release of ovarian progesterone during the rat oestrous cycle by ganglionic cholinergic influence: the role of norepinephrine

Administration of a VIP-antagonist in vivo modifies ovarian hormone secretion in a rat model with polycystic ovary syndrome

AIMS

In the cyclic rat in estrus, the vasoactive intestinal peptide (VIP) has an impact on ovarian function, which depends on the endocrine status of the animal. In this work, we aimed to clarify the participation of VIP in the pathophysiological condition of polycystic ovary syndrome (PCOS) using a model of PCOS induced by estradiol valerate (EV-PCOS) in rats.

MAIN METHODS

In the cyclic rat in estrus and in the EV-PCOS model, we analyzed the acute effects of blocking VIP receptors with the use of an antagonist (Ant-VIP) injected into the left or right ovarian bursa on the steroidogenic response and ovarian catecholamine levels.

KEY FINDINGS

In the cyclic animal in estrus, the treatment with Ant-VIP in the left ovarian bursa resulted in a reduction in testosterone serum levels and in ovarian levels of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC), without changes in 4-hydroxy-3-methoxyphenyl (MHPG) and norepinephrine (NE). When the treatment was applied on the right side, only MHPG levels increased. In the EV-PCOS model, the treatment with Ant-VIP in the left ovarian bursa increased testosterone, estradiol, MHPG, and NE levels. When the treatment was performed on the right side, progesterone levels decreased and estradiol increased, without changes in ovarian catecholamines.

SIGNIFICANCE

The binding of VIP to its receptors differentially regulates steroidogenesis in the cyclic animal in estrus and in the EV-PCOS model. The blocking of VIP signaling produces changes in ovarian catecholamines.

Role of the superior ovarian nerve in the regulation of follicular development and steroidogenesis in the morning of diestrus 1

PURPOSE

Little is known about the role of the superior ovarian nerve (SON) in follicular development during the estrus cycle. The aim of the present study was to analyze the role of neural signals arriving through the SON at the ovaries in the regulation of follicular development and ovarian steroid secretion in diestrus 1 of cyclic rats.

METHODS

Cyclic rats were subjected to left, right, or bilateral SON sectioning or to unilateral or bilateral laparotomy at diestrus 1 at 11:00 h. Animals were sacrificed 24 h after surgery.

RESULTS

Compared to laparotomized animals, unilateral SON sectioning decreased the number of preovulatory follicles, while bilateral SON sectioning resulted in a decreased number of atretic preantral follicles. An important observation was the presence of invaginations in the follicular wall of large antral and preovulatory follicles in animals with denervation. Furthermore, left SON sectioning increased progesterone levels but decreased testosterone levels, which are effects that were not observed in animals that were subjected to right denervation.

CONCLUSIONS

At 11:00 h of diestrus 1, the SON was found to stimulate follicle development, possibly via neural signals, such as noradrenaline and/or vasoactive intestinal peptide, and this stimulation induced the formation of follicle-stimulating hormone receptors. The role of the SON in the regulation of ovarian steroid secretion is asymmetric: the left SON inhibits the regulation of progesterone and stimulates testosterone secretion, and the right nerve does not participate in these processes.

"Rapid actions of the neurosteroid allopregnanolone on ovarian and hypothalamic steroidogenesis: Central and peripheral modulation"

The present study aimed to determine whether an i.c.v. administration of allopregnanolone (ALLO) rapidly modifies the hypothalamic and ovarian 3β-hydroxysteroid dehydrogenase (3β-HSD) enzymatic activity and gene expression in in vivo and ex vivo systems in pro-oestrus (PE) and dioestrus I (DI) rats. Animals were injected with vehicle, ALLO, bicuculline or bicuculline plus ALLO and were then killed. In the in vivo experiment, the hypothalamus, ovaries and serum were extracted and analysed. In the ex vivo experiment, the superior mesenteric ganglion - ovarian nerve plexus - ovary system was extracted and incubated during 120 minutes at 37 ºC. The serum and ovarian compartment fluids were used to determine progesterone by radioimmunoanalysis. In the in vivo experiments, ALLO caused a decrease in hypothalamic and ovarian 3β-HSD enzymatic activity during PE. During DI, ALLO increased hypothalamic and ovarian 3β-HSD activity and gene expression. The ovarian 3β-HSD activity increased in both stages in the ex vivo system; gene expression increased only during DI. ALLO induced an increase in serum progesterone only in D1 and in the ovarian incubation liquids in both stages. All findings were reversed by an injection of bicuculline before ALLO. Ovarian steroidogenic changes could be attributed to signals coming from ganglion neurones, which are affected by the acute central neurosteroid stimulation. The i.c.v. administration of ALLO via the GABAergic system altered 3β-HSD activity and gene expression, modulating the neuroendocrine axis. The present study reveals the action that ALLO exerts on the GABAA receptor in both the central and peripheral nervous system and its relationship with hormonal variations. ALLO is involved in the "fine tuning" of neurosecretory functions as a potent modulator of reproductive processes in female rats.

In Adult Rats With Polycystic Ovarian Syndrome, Unilateral or Bilateral Vagotomy Modifies the Noradrenergic Concentration in the Ovaries and the Celiac Superior Mesenteric Ganglia in Different Ways

In rats with polycystic ovarian syndrome (PCOS) induced by estradiol valerate (EV) injection, sectioning of the vagus nerve in the juvenile stage restores ovulatory function, suggesting that the vagus nerve stimulates the onset and development of PCOS. We analyzed whether in adult rats, the role played by the vagus nerve in PCOS development is associated with the nerve’s regulation of noradrenergic activity in the celiac superior mesenteric ganglion (CSMG). Ten-day-old rats were injected with corn oil [vehicle (Vh)] or EV (2 mg). At 76 days of age, rats injected with Vh or EV were subjected to sham surgery or the sectioning of one or both vagus nerves (vagotomy). The animals were sacrificed at 80–82 days of age at vaginal estrus smear. Compared to Vh-treated animals, EV-induced PCOS rats showed a lack of ovulation, the presence of follicular cysts, and a high concentration of testosterone, without changes in noradrenaline concentrations in the CSMG or ovaries. In PCOS rats, sham surgery lowered serum testosterone and noradrenaline concentrations in the CSMG but did not restore ovulation. In animals with PCOS, vagotomy lowered testosterone concentrations to a larger degree than in sham-surgery animals. The ovaries of rats with PCOS and vagotomy showed fresh corpora lutea, indicating ovulation. In EV-treated rats with unilateral vagotomy, the concentration of noradrenaline in the CSMG was similar to that in rats with PCOS and sham surgery, which did not ovulate, while in the ovaries of PCOS rats with left or bilateral vagotomy, the noradrenaline concentration was lower than that in sham-surgery-treated animals. Our results suggest that the vagus nerve regulates PCOS development through a different mechanism than the increase in the noradrenergic activity in the CSMG; however, in ovaries, the restoration of ovulation is associated with a decrease in ovarian noradrenaline.

Ganglionic and ovarian action of acetylcholine during diestrous II in rats. Neuroendocrine control of the luteal regression

Our aim was to investigate if acetylcholine (Ach), added to the celiac ganglion-superior ovarian nerve-ovary system (CG-SON-ovary) or in ovary incubations, modifies the release of progesterone (P₄), androstenedione (A₂), dopamine (DA), norepinephrine (NE), gonadotropin-releasing hormone (GnRH), and alters the expression of 3β-hydroxysteroid dehydrogenase (3β-HSD), 20α-hydroxysteroid dehydrogenase (20α-HSD), and apoptotic genes in ovarian tissue during the diestrous II (DII) in rats. The CG-SON-ovary system or the ovary alone were removed and placed into separate cuvettes both containing Krebs-Ringer solution (control groups). In experimental groups, 10^-6 M Ach was added into the ganglion compartment or into the ovary compartment. P₄, A₂ and GnRH were measured by RIA, mRNA expression by RT-PCR, and catecholamines by HPLC. In addition, a routine histological technique was applied. In ex-vivo system, 10^-6 M Ach into the ganglion compartment decreased P₄ and NE release, altered 3β-HSD and 20α-HSD expression, and decreased bax/bcl-2 ratio, while increasing the release of A₂ and DA, and bcl-2 expression. In ovary incubations, 10^-6 M Ach decreased P₄ and GnRH release, decreased 3β-HSD and bcl-2 expression, increased A₂ release, increased 20α-HSD and bax expression, and the bax/bcl-2 ratio, and induced disorganization of the corpus luteum structure. The peripheral nervous system protected the ovary from the apoptotic mechanisms while in the ovary incubation the effect was reversed. Our results indicate that Ach in DII regulates steroidogenesis and apoptosis in the ovary, by modulating the concentration of neurotransmitters. In vivo, an alteration in the extrinsic cholinergic innervation of the ovary could disrupt the endocrine control of the reproductive function.

The production of nitric oxide in the coeliac ganglion modulates the effect of cholinergic neurotransmission on the rat ovary during the preovulatory period

The aim of the present work was to investigate whether the nitric oxide produced by the nitric oxide/nitric oxide synthase (NO/NOS) system present in the coeliac ganglion modulates the effects of cholinergic innervation on oxidative status, steroidogenesis and apoptotic mechanisms that take place in the rat ovary during the first proestrous. An ex vivo Coeliac Ganglion- Superior Ovarian Nerve- Ovary (CG-SON-O) system was used. Cholinergic stimulation of the CG was achieved by 10^-6 M Acetylcholine (Ach). Furthermore, 400 μM Aminoguanidine (AG) - an inhibitor of inducible-NOS was added in the CG compartment in absence and presence of Ach. It was found that Ach in the CG compartment promotes apoptosis in ovarian tissue, probably due to the oxidative stress generated. AG in the CG compartment decreases the release of NO and progesterone, and increases the release of estradiol from the ovary. The CG co-treatment with Ach and AG counteracts the effects of the ganglionic cholinergic agonist on ovarian oxidative stress, increases hormone production and decreases Fas mRNA expression. These results suggest that NO is an endogenous modulator of cholinergic neurotransmission in CG, with implication in ovarian steroidogenesis and the apoptotic mechanisms that take place in the ovary during the preovulatory period in rats.

Participation of the extrinsic cholinergic innervation in the action of nitric oxide on the ovarian steroidogenesis in the first proestrous in rats

An ex-vivo Coeliac Ganglion-Superior Ovarian Nerve-Ovary (CG-SON-O) system and an ovary without peripheral neural influence from virgin rats in the first proestrous were used to test whether ovarian extrinsic innervation and nitric oxide (NO) affects steroidogenesis in the ovary. The CG and the ovary were placed in separate buffered-compartments, connected by the SON. Stimulation of the CG was achieved by 10(-6)M acetylcholine (Ach). The ovary without peripheral neural influence was placed alone in a buffered-compartment. To test a possible role of NO in the ovarian response to peripheral neural influence, 100μM sodium nitroprusside (SNP, an NO donor) and 100μM N(G)-nitro-l-arginine methyl ester (l-NAME, an inhibitor of NO synthase) were added to the ovarian compartment separately. In the CG-SON-O system, SNP into the ovarian compartment increased the concentration of NO, reduced the release of progesterone and increased the release of estradiol (E2), increasing the mRNAs related to their synthesis enzyme. The addition of l-NAME to the ovarian compartment caused an opposite effect. In the ovary alone, NO manifested an antisteroidogenic effect on both hormones. These results show that the ovarian extrinsic innervation maintains a direct relationship between NO and E2, both needed at high levels during the follicular phase, allowing the continuity of the estrous cycle.

Oxidative stress and altered steroidogenesis in the ovary by cholinergic stimulation of coeliac ganglion in the first proestrous in rats. Implication of nitric oxide

An ex-vivo Coeliac Ganglion-Superior Ovarian Nerve-Ovary (CG-SON-O) system from virgin rats in the first proestrous was used to test whether cholinergic stimulation of CG affects oxidative status and steroidogenesis in the ovary. The CG and the O were placed in separate buffered-compartments, connected by the SON, and the CG was stimulated by acetylcholine (Ach). To test a possible role of nitric oxide (NO) in the ovarian response to cholinergic stimulation of CG, aminoguanidine (AG) - an inhibitor of inducible-NO synthase was added to the O compartment. After 180 min incubation, the oxidative status was assessed in O whereas nitrite and steroidogenesis were assessed at 30, 120 and 180 min. Ach in CG decreased the total antioxidant capacity, but increased NO production and protein carbonization in O. Ach stimulation of CG increased estradiol, but decreased progesterone release in O by reducing the mRNAs related to their synthesis and degradation. The addition of AG to the O compartment caused an opposite effect, which was more pronounced in the presence of Ach in the CG compartment than in its absence. These results show that the stimulation of the extrinsic-cholinergic innervation of the O increases the concentration of NO, causes oxidative stress and modulates steroidogenesis in the first rat proestrous.

Noradrenaline modulates the presence of gonadotropin-releasing hormone in ovary. The importance of its interrelation on the ovarian steroidogenesis and apoptosis on dioestrus II in rat

The aim of this work was to investigate if noradrenaline (NA), added in the coeliac ganglion -superior ovarian nerve- ovary system (CG-SON-O) and in ovary incubation, modifies the release of ovarian progesterone (P4), gonadotropin-releasing hormone (GnRH) and oestradiol (E2), and the expression of 3β-HSD and 20α-HSD and proapoptotic bax and antiapoptotic bcl-2 on dioestrus II in the rat. The CG-SON-O system and the ovary were removed and placed in one cuvette containing Krebs-Ringer solution (control groups), and NA was added to the ganglion compartment in the ex vivo system and in the ovary compartment in the ovary incubation (experimental groups). P4, GnRH and E2 were measured by RIA, and gene expression was measured by RT-PCR. In the ex-vivo system, the release of ovarian P4 and GnRH and the expression of 3β-HSD and bax decreased; E2 and bcl-2 increased, and the bax/bcl-2 ratio decreased. However, in the ovary incubation, P4, GnRH, the expression of 3β-HSD and bax increased; E2, the expression of 20α-HSD and bcl-2 decreased while the bax/bcl-2 ratio increased, thus favoring apoptosis. The peripheral nervous system protected the ovary from the apoptotic mechanisms while in the ovary incubation the effect was reverted. Our results indicate that NA regulates ovarian steroidogenesis and apoptosis by modulating GnRH release from the coeliac ganglion and ovary, being NA a possible generator of a GnRH-gonadotropins axis in the ovary. This work is expected to contribute with new evidence of the clinical importance of catecholamines and GnRH in therapy and prevention of ovarian pathologies.

Protective effect of oestradiol in the coeliac ganglion against ovarian apoptotic mechanism on dioestrus

The aims of this work were to investigate if oestradiol 10(-8)M in the incubation media of either the ovary alone (OV) or the ganglion compartment of an ex vivo coeliac ganglion-superior ovarian nerve-ovary system (a) modifies the release of ovarian progesterone (P4) and oestradiol (E2) on dioestrus II, and (b) modifies the ovarian gene expression of 3β-HSD and 20α-HSD enzymes and markers of apoptosis. The concentration of ovarian P4 release was measured in both experimental schemes, and ovarian P4 and E2 in the ex vivo system by RIA at different times. The expression of 3β-hydroxysteroid dehydrogenase, 20α-hydroxysteroid dehydrogenase and antiapoptotic bcl-2 and proapoptotic bax by RT-PCR were determined. E2 added in the coeliac ganglion caused an increase in the ovarian release of the P4, E2 and 3β-HSD, while in the ovary incubation alone it decreased P4 and 3β-HSD but increased and 20α-HSD and bax/bcl-2 ratio. It is concluded that through a direct effect on the ovary, E2 promotes luteal regression in DII rats, but the addition of E2 in the coeliac ganglion does not have the same effect. The peripheral nervous system, through the superior ovarian nerve, has a protective effect against the apoptotic mechanism on DII.

Involvement of the mesenteric ganglia on androstenedione, noradrenaline and nitrite release using a testis ex vivo system

The autonomic nerve fibres converge to the testis along two major pathways, the superior spermatic nerve (SSN) and the inferior spermatic nerve (ISN). The object of this work was to evaluate whether the addition of noradrenaline (NA) in the ganglionic compartment of two ex vivo systems: superior mesenteric ganglion (SMG)-SSN-testis, inferior mesenteric ganglion (IMG)-ISN-testis modulate androstenedione (A₂), NA and nitrite release and to determine whether there are secretory differences between the right and the left testis. Each gonad with its respective ganglion was transferred into a cuvette with two compartments and incubated in a Dubnoff metabolic shaker. The testis incubation liquids were collected and analysed for NA by HPLC, A₂ by RIA and nitrites by the Griess method. When NA is added to the IMG, A₂ and NA release diminishes and nitrite increases in the left testis, while in the right gonad, A₂ and NA increase and nitrite decreases. When NA was administered to the SMG, A₂ and NA increase and nitrite diminishes in the left gonad, but they show opposite fluctuations in the right testis. These ex vivo systems appear to be excellent models for studying the sympathetic ganglionic control of the testis though A₂, NA and nitrite release from the male gonad. It is evident that a better knowledge about the role of catecholamines and nitric oxide in the testis physiology may facilitate the understanding of some reproductive diseases.

Involvement of the oestrogenic receptors in superior mesenteric ganglion on the ovarian steroidogenesis in rat

Oestradiol (E(2)) is a key hormone in the regulation of reproductive processes. The aims of this work were a) to examine the distributions of oestrogen receptor α (ERα) and ERβ in the neurons of the superior mesenteric ganglion (SMG) in the oestrus stage by immunohistochemistry, b) to demonstrate whether E(2) in the SMG modifies progesterone (P(4)), androstenedione (A(2)) and nitrite release in the ovarian compartment on oestrus day and c) to demonstrate whether E(2) in the ganglion modifies the activity and gene expression in the ovary of the steroidogenic enzymes 3β-hydroxysteroid dehydrogenase (3β-HSD) and 20α-hydroxysteroid dehydrogenase (20α-HSD). The ex vivo SMG-ovarian nervous plexus-ovary system was used. E(2), tamoxifen (Txf) and E(2) plus Txf were added in the ganglion to measure ovarian P(4) release, while E(2) alone was added to measure ovarian A(2) and nitrites release. Immunohistochemistry revealed cytoplasmic ERα immunoreactivity only in the neural somas in the SMG. E(2) increased ovarian P(4) and A(2) release at 15, 30 and 60 min but decreased nitrites. The activity and gene expression of 3β-HSD increased, while the activity and gene expression of 20α-HSD did not show changes with respect to the control. Txf in the ganglion diminished P(4) release only at 60 min. E(2) plus Txf in the ganglion reverted the effect of E(2) alone and the inhibitory effect of Txf. The results of this study demonstrate that ERα activation in the SMG has an impact on ovarian steroidogenesis in rats, thus providing evidence for the critical role of peripheral system neurons in the control of ovarian functions under normal and pathological conditions.

Pregnancy in rats is modulated by ganglionic cholinergic action

The control of ovarian steroidogenesis during pregnancy is mainly of endocrine origin. At present, there is little information about the influence of neural factors on the gestation physiology. The purpose of this work was to study the action of cholinergic agents in celiac ganglion upon the liberation of progesterone and ovarian androstenedione in the second half of pregnancy in rats. We used the ex vivo celiac ganglion-superior ovarian nerve-ovary integrated system (celiac ganglion-SON-ovary) that was incubated in buffer solution for 180 min, with the celiac ganglion and the ovary located in different compartments and linked by the SON. The results obtained indicate that the control values of ovarian androstenedione vary according to the pregnancy day analyzed. The addition of acetylcholine in ganglion decreased the liberation of both steroids on Day 15 whereas at the end of pregnancy it decreased the liberation of androstenedione without modifying progesterone. Due to the effect observed with atropine and hexametonium, acetylcholine action might occur through unspecific ganglionic pathways (Days 15 and 21) or through muscarinic ganglionic receptors (Days 19 and 20). Thus, we conclude that the cholinergic sympathetic system from the celiac ganglion might be a fine modulator of the pregnancy physiology.

Ganglionic adrenergic action modulates ovarian steroids and nitric oxide in prepubertal rat

Both peripheral innervation and nitric oxide (NO) participate in ovarian steroidogenesis. The purpose of this work was to analyse the ganglionic adrenergic influence on the ovarian release of steroids and NO and the possible steroids/NO relationship. The experiments were carried out in the ex vivo coeliac ganglion-superior ovarian nerve (SON)-ovary system of prepubertal rats. The coeliac ganglion-SON-ovary system was incubated in Krebs Ringer-bicarbonate buffer in presence of adrenergic agents in the ganglionic compartment. The accumulation of progesterone, androstenedione, oestradiol and NO in the ovarian incubation liquid was measured. Norepinephrine in coeliac ganglion inhibited the liberation of progesterone and increased androstenedione, oestradiol and NO in ovary. The addition of alpha and beta adrenergic antagonists also showed different responses in the liberation of the substances mentioned before, which, from a physiological point of view, reveals the presence of adrenergic receptors in coeliac ganglion. In relation to propranolol, it does not revert the effect of noradrenaline on the liberation of progesterone, which leads us to think that it might also have a "per se" effect on the ganglion, responsible for the ovarian response observed for progesterone. Finally, we can conclude that the ganglionic adrenergic action via SON participates on the regulation of the prepubertal ovary in one of two ways: either increasing the NO, a gaseous neurotransmitter with cytostatic characteristics, to favour the immature follicles to remain dormant or increasing the liberation of androstenedione and oestradiol, the steroids necessary for the beginning of the near first estral cycle.

Involvement of the coeliac ganglion in the luteotrophic effect of androstenedione in late pregnant rats

Using the ex vivo coeliac ganglion-superior ovarian nerve-ovary system at the end of pregnancy when luteal regression starts, we investigated whether, when administered systemically or when added directly to the ganglion compartment, androstenedione (A2) can reverse such regression, and whether the neural (noradrenaline (NA)) and endocrine (A2) joint action modifies the release of ovarian progesterone. The experimental groups were as follows: group 1 – A2 injected systemically 48 h before incubation of the system (A2)s; group 2 – A2 directly added to the ganglion compartment (A2)g; group 3 – A2 injected 48 h before incubation of the system with NA in the ganglion compartment (A2 + NA); group 4 – A2 plus NA added to the ganglion compartment (NA + A2)g. The controls were ex vivo systems without treatment (control), and with the addition of NA alone in the ganglion compartment (NA). The results were as follows. For (A2)s versus control, progesterone increased on days 19 and 21 of pregnancy at all the studied times and only at 180 min on day 20. For (A2 + NA) versus (A2)s, progesterone increased on days 19 and 21. For (A2 + NA) versus NA, progesterone increased at all the studied times on days 19 and 21 and at 180 min on day 20. For (A2)g versus control, progesterone significantly increased every pregnancy day. For (NA + A2)g versus (A2)g, progesterone decreased at 120 and 180 min on day 19. For (NA + A2)g versus NA, progesterone increased on days 20 and 21. We can conclude that A2 can reverse the functional regression of the corpus luteum either systemically or, what is more surprising, when directly added to the coeliac ganglion, whose action on the ovary is exerted via superior ovarian nerve.