Effects of electrical stimulation of autonomic nerves to the ovary on the ovarian testosterone secretion rate in rats

Effects of chronic exposure to cold stress on ovarian functions in prepubertal rats

Ovarian functions are modulated by the hypothalamus-pituitary-ovary axis and neural signals. Stress modifies the activity of the sympathetic nervous system. In adult female rats, cold stress results in higher noradrenergic and steroidogenic activity of the ovary, anovulation and the presence of ovarian cysts; however, it is unknown whether this response occurs in prepubertal rats. The purpose of this study was to analyse the effects of cold stress initiated in the prepubertal stage of female rats on ovarian function. Female rats 24 days old were exposed to three, five or eight weeks of cold stress. Autopsies were performed at the end of each stress period. The parameters analysed were the number of ova shed by ovulating animals; the number of ovulating animals; the serum concentrations of progesterone, testosterone, and oestradiol; and the ovarian concentrations of norepinephrine and 3-methoxy-4-hydroxyphenyl-glycol. Our results show that chronic cold stress applied to prepubertal rats did not modify the number of ovulating animals, the total number of ova shed, or progesterone and testosterone concentrations in any of the periods analysed. Oestradiol concentration was lower in the animals exposed to five or eight weeks of stress. The ovarian norepinephrine concentration was higher in the animals exposed to three weeks of stress and was lower at eight weeks of stress. No changes in ovarian morphology were observed. Our data suggest that the changes in noradrenergic activity resulting from chronic cold stress experienced in the prepubertal stage do not modify ovarian architecture or affect the ovulatory response in adulthood.

Association of age at diabetes complication diagnosis with age at natural menopause in women with type 1 diabetes: The Pittsburgh Epidemiology of Diabetes Complications (EDC) Study

OBJECTIVE

Vascular damage is thought to have a role in premature ovarian aging. We thus assessed the association between the presence, and age at onset of, vascular diabetes complications and age at natural menopause in women with type 1 diabetes.

METHODS

Female participants of the Epidemiology of Diabetes Complications study with type 1 diabetes who experienced natural menopause and who never received hormone therapy during their menopausal transition were included in the analysis (n=105). Microalbuminuria (MA), overt nephropathy, proliferative retinopathy, confirmed distal symmetric polyneuropathy, and coronary artery disease, were assessed during biennial clinical exanimations for the first 10 years of follow-up and at year 18, 25 and 30. Menopausal status was determined via self-report and sex hormone data. For each complication, separate linear regression models were used to assess whether, compared with women without the complication of interest, an earlier age at complication development (i.e., <30 years of age) was associated with an earlier age at natural menopause.

RESULTS

Although results from multivariable linear regression models suggested a similar age at menopause between women with normo-albuminuria and those diagnosed with MA after 30 years of age, menopause occurred 2.06 years earlier (β±SE=-2.06±1.08) among women diagnosed with MA before age 30 (p=0.06). No significant association was observed for other complications.

CONCLUSION

Among women with type 1 diabetes, menopause appears to occur earlier in those diagnosed with MA before age 30 compared to those with normo-albuminuria, suggesting that vascular dysfunction associated with early microvascular disease may affect ovarian aging.

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.

Electro-Acupuncture Affects the Activity of the Hypothalamic-Pituitary-Ovary Axis in Female Rats

Hypothalamic-pituitary-ovary (HPO) axis is a dominant system controlling ovulation during puberty. Electro-acupuncture (EA) has been widely used to cure the reproductive diseases associated with endocrinological disorders. However, whether EA treatment affects HPO axis activity of physiological animals and induces alterations on the hormones in the HPO axis was also unclear. Here, we performed the EA stimuli on bilateral acupoints of Sanyinjiao (SP6) and Zusanli (ST36) on female virgin rats every 3 days and for a total of 5 times. The results showed that GnRH levels in hypothalamus were greatly upregulated in EA-treated rats than untreated animals at day 7 and 13. The serum levels for FSH and LH were severely reduced after EA treatment compared with EA-untreated animals at day 1, while they were greatly increased at day 7 and 13. The serum concentrations of 17β-estradiol were lower in EA-treated rats versus untreated animals at day 7, while they were higher in EA-treated rats than other groups at day 13. However, the progesterone concentrations were lower in EA-treated rats than Control and Sham-EA rats both at day 7 and 13. More importantly, we found that the prostaglandin E₂ level in serum was reduced in EA-treated rats versus untreated rats at day 1, while they were upregulated at day 7 and 13. Conversely, the norepinephrine level in serum was increased at day 1, while they were decreased greatly in EA-treated rats versus untreated rats at day 7 and 13. The current results demonstrated that EA could modulate homeostasis of HPO axis in physiologic rats, which would be useful to clarify the mechanisms of EA application on pathological and physiological animals or human.

The Neural Signals of the Superior Ovarian Nerve Modulate in an Asymmetric Way the Ovarian Steroidogenic Response to the Vasoactive Intestinal Peptide

The superior ovarian nerve (SON) provides neuropeptide-Y, norepinephrine and vasoactive intestinal peptide (VIP) to the ovaries. Ovarian steroidogenesis is modulated by the SON. In the cyclic rat, the acute steroidogenic response to ovarian microinjection of VIP is asymmetric and varies during the estrous cycle. In the present study, we analyze whether the differential effects of VIP in each ovary are modulated by the neural signals arriving through the SON. Cyclic female rats were submitted on diestrus-1, diestrus-2, proestrus, or estrus to a unilateral section of the SON, and immediately afterward, the denervated ovary was either microinjected or not with VIP. Animals were sacrificed 1 h after treatment. The injection of VIP into the left denervated ovary performed on diestrus-1 decreased progesterone levels in comparison with the left SON sectioning group; similar effects were observed on proestrus when VIP was injected into either of the denervated ovaries. Compared to the left SON sectioning group, VIP treatment into the left denervated ovary on diestrus-2 or proestrus decreased testosterone levels, whereas on diestrus-1, proestrus or estrus, the same treatment resulted in higher estradiol levels. Compared to the right SON sectioning group, VIP injected into the right denervated ovary yielded higher testosterone levels on diestrus-1 and estrus and lower testosterone levels on proestrus. VIP injection into the right denervated ovary increased estradiol levels on diestrus-2 or estrus while decreasing them on proestrus. Our results indicate that in the adult cyclic rat, the set neural signals arriving to the ovaries through the SON asymmetrically modulate the role of VIP on steroid hormone secretion, depending on the endocrine status of the animal. The results also support the hypothesis that the left and right ovary respond differently to the VIPergic stimulus.

Both the Suprachiasmatic Nucleus and the Superior Ovarian Nerve Contribute to the Processes of Ovulation and Steroid Hormone Secretion on Proestrus

The aims of the present study were to analyze if the superior ovarian nerve (SON) plays a role in the neural signals from suprachiasmatic nucleus (SCN) that lead to ovulation and ovarian steroids secretion on proestrus day. Rats on proestrus day were treated at 11.00 to 11.30 or 17.00 to 17.30 hours with 1 of the 3 experimental procedures (1) unilateral or bilateral SON sectioning, (2) unilateral or bilateral injury to the SCN, or (3) unilateral injury to the SCN followed by unilateral sectioning of the SON ipsilateral to the treated SCN. Treatments were evaluated 24 hours after surgical procedures. Compared to laparotomized animals, right or bilateral SON sectioning treatment at 17.00 hours resulted in lower ovulation rates and number of ova shed by the right ovary. The ovaries of nonovulating animals showed early follicular luteinization signs and trapped ova. Bilateral SCN injury treatment at 11.00 hours resulted in anovulation; whereas right SCN injury treatment, with or without right SON sectioning, resulted in a lower number of ova shed. Injecting luteinizing hormone-releasing hormone to animals with bilateral SCN injury restored ovulation. In rats with unilateral or bilateral SON sectioning, or with injury to the SCN with or without unilateral sectioning of the SON, the effects on hormone levels depended of the hormone studied and the time of day treatment was performed. The present results suggest that on proestrus day, the role of the right or both SON in ovulation and steroid hormone secretion regulation takes place through different neuroendocrine mechanisms from SCN.

Sympathetic regulation of estradiol secretion from the ovary

It is well known that hormone secretion from endocrine glands is regulated by hierarchical feedback mechanisms. However, although Cannon revealed in the 1920s that sympathoadrenal medullary function increased during emergency situations, no studies on the autonomic nervous regulation of hormone secretion have been undertaken for many years. In the past 40 years, the autonomic nervous regulation of insulin secretion from the pancreas, gastrin secretion from the stomach, glucocorticoid secretion from the adrenal cortex, etc., has been demonstrated. Estradiol secretion from the ovary is strongly controlled by the hypothalamic-pituitary-ovarian axis, and its possible regulation by autonomic nerves has been largely unnoticed. Some histological studies have revealed rich adrenergic sympathetic innervation in the ovary. Recently, it has been demonstrated that the activation of the sympathetic nerves to the ovary directly reduces estradiol secretion from the ovary. This article reviews physiological and morphological studies, primarily in rats, on the sympathetic regulation of estradiol secretion from the ovary.

Autonomic nervous regulation of ovarian function by noxious somatic afferent stimulation

It is well known that ovarian function is regulated by hypothalamic–pituitary–ovarian hormones. However, although several histological studies have described the autonomic innervation of the ovary, the involvement of these autonomic nerves in ovarian function is unclear. Recently, it has been shown that both the superior ovarian nerve (SON) and the ovarian nerve plexus (ONP) induce vasoconstrictor activity by activation of alpha 1-adrenoceptors, whereas the SON, but not the ONP, inhibits ovarian estradiol secretion by activation of alpha 2-adrenoceptors. Furthermore, reflex activation of these ovarian nerves by noxious cutaneous stimulation of the rat hindpaw results in ovarian vasoconstriction and inhibition of estradiol secretion. Thus, in addition to long-term regulation of ovarian function by hormones, ovarian autonomic innervation may be involved in rapid regulation of ovarian function by responding to either internal or external environmental changes.