Ovarian androstenedione production is enhanced by insulin during the period of delayed ovulation in a vespertilionid bat, Scotophilus heathi

A model combining testosterone, Androstenedione and free testosterone index improved the diagnostic efficiency of polycystic ovary syndrome

OBJECTIVE

Hyperandrogenism is frequently observed in patients with polycystic ovary (PCOS). The purpose of this study was to develop an easy-to-use tool for predicting polycystic ovary syndrome (PCOS) and to evaluate and compare the value of androstenedione (Andro) and other hormone indicators in the diagnosis of patients with hyperandrogenic PCOS.

METHODS

This study included 139 women diagnosed with hyperandrogenic PCOS according to the Rotterdam criteria and 74 healthy control women from Shanghai Tenth People's Hospital. The serum hormone levels of the patients and controls were measured using a chemiluminescence immunoassay (CLIA) and incorporated for further analysis.

RESULTS

Total testosterone (TT), Andro, Dehydroepiandrosterone sulfate (DHEAS), and Free androgen index (FAI) were significantly higher in the PCOS group than the control group. Further, Andro, FSH, LH, TT, FAI and LH/FSH in the hyper-androstenedione (HA) group were higher than the normal Andro (NA) group. The Youden index was the highest for Andro (0.65), with 81.82% sensitivity and 83.16% specificity. Correlation analysis showed that FSH, LH, TT, FAI, Insulin Sensitivity Index (ISI), and LH/FSH were positively correlated with Andro, while Fasting blood glucose (FPG) and two-hour postprandial blood glucose (2h PG) were negatively correlated with Andro.

CONCLUSIONS

The model using Andro, TT, FAI may help to identifying women with undiagnosed PCOS. Serum Andro is a meaningful biomarker for hyperandrogenism in PCOS patients and may further aid disease diagnosis.

Role of 14-3-3β protein on ovarian folliculogenesis, steroidogenesis and its correlation in the pathogenesis of PCOS in mice

This study was designed to assess for the first time the circulating and ovarian level of 14-3-3β protein in the PCOS mice and the possible correlation between 14-3-3β protein with PCOS related increase in testosterone (HA), insulin levels (HI) and reduced insulin sensitivity in the ovary. PCOS was induced in mice using treatment of letrozole (by oral gavage) for 21 days. Immunohistochemical study showed increased expression of 14-3-3β protein in PCOS ovary compared to the control ovary. The circulating testosterone and insulin levels, together with circulating and ovarian levels of 14-3-3β protein also showed significant increase in PCOS mice compared to the control mice. An increase in 14-3-3β protein was observed positively correlated with circulating testosterone and insulin levels but showed a negative correlation with ovarian expression of insulin receptor protein in PCOS mice. The treatment of 14-3-3β protein in vitro to the normal ovary showed a significant increase in testosterone synthesis but a significant decline in insulin receptor protein expression compared to the vehicle-treated ovary of adult mice. The present study showed the direct role of 14-3-3β protein in increasing testosterone synthesis along with decreasing insulin sensitivity. Thus, 14-3-3β protein may be playing possible role in PCOS pathogenesis.

Sperm Storage in the Female Reproductive Tract

The capacity for sperm storage within the female reproductive tract occurs widely across all groups of vertebrate species and is exceptionally well developed in some reptiles (maximum duration seven years) and fishes (maximum duration >1 year). Although there are many reports on both the occurrence of female sperm storage in diverse species and its adaptive benefits, few studies have been directed toward explaining the mechanisms involved. In this article we review recent findings in birds and mammals in an effort to develop hypotheses that could be translated into research applications in animal breeding technologies. There are pockets of evidence to suggest that the local epithelial cells, sometimes arranged as sperm storage tubules, can respond to spermatozoa by producing heat shock proteins as well as providing an environment rich in antioxidants. Moreover, the local immune system seems to tolerate the arrival of spermatozoa, while retaining the ability to combat the arrival of infectious microorganisms.

Localization of resistin and its possible roles in the ovary of a vespertilionid bat, Scotophilus heathi

The aim of the present study was to evaluate the expression and effect of resistin on ovarian activities of Scotophilus heathi. Immunohistochemical study showed marked variation in resistin immunostaining during different reproductive phases. Most intense immunostaining of resistin was noticed in thecal-interstitial cells in ovary during the period of delayed ovulation, the period of increased androgen synthesis and suppressed ovulation. The changes in ovarian resistin level also correlated positively with circulating leptin level and body white adipose tissue accumulation. The in vitro study showed that resistin alone preferentially stimulated progesterone synthesis, but with luteinizing hormone (LH) stimulated androgen secretion. Resistin alone dose-dependently increased expression of LH-receptor, steroidogenic acute regulatory protein and insulin receptor proteins in the ovary, whereas together with LH showed dose-dependent stimulatory effect on expression of androgen receptor and insulin receptor proteins in the ovary. In conclusion, during the period of fat accumulation increased ovarian resistin level may be responsible for increased androgen synthesis through insulin receptor mediated pathways in the ovary of S. heathi.

Effects of seasonal adiposity on ovarian activity of Vespertilionid bat, Scotophilus heathi: proteomics analysis

In present study comparative proteomics was utilized to identify ovarian protein profiles and correlate the expression of these proteins with adiposity induced changes in ovarian activity leading to suppression of ovulation (delayed ovulation) in the bat, S. heathi. To achieve this, two-dimension gel electrophoresis combined with protein identification by tandem mass spectrometry (LC-MS/MS) was applied. Protein profiles were obtained from intact ovaries of bats collected during recrudescence (basal body weight) and delayed ovulation (increased body weight) phases of reproductive cycle. Out of 42 differentially expressed protein spots, 15 protein spots were identified by LC-MS/MS. A majority of the 15 protein spots identified belonged to a group of enzymes within the glycolytic and citrate cycles. Greater concentrations of these enzymes were found during the period of delayed ovulation, which may be responsible for an increase in the production of ATP within the ovary. The increased metabolic activity and energy production observed within the ovary during winter dormancy may be required for increased steroidogenic activity during this period. The protein 14-3-3 identified by LC-MS/MS was verified by immunoblotting, which confirmed its increased expression during the period of delayed ovulation and may be associated with development of insulin resistance. Treatment with adipokines (adiponectin, resistin) is responsible for increased expression of 14-3-3 protein in the ovary of S. heathi. Adiposity-associated rise in adipokines are thus responsible for increased expression of 14-3-3 protein in the ovary of S. heathi, which may be responsible for prolonged survival of antral follicles and suppression of ovulation. The 14-3-3 protein may represent a new marker for adiposity associated ovarian anovulation (disorders).

Effects of resistin on ovarian folliculogenesis and steroidogenesis in the vespertilionid bat, Scotophilus heathi

The bat Scotophilus heathi exhibit prolonged anovulatory condition known as delayed ovulation coinciding with the period of extensive fat accumulation. The present study was undertaken to find out whether extensive accumulation of fat in S. heathi is responsible for suppression of ovarian activity by increasing production of adipokine resistin in the bat. This was achieved by (a) investigating variation in serum resistin level in relation to the changes in the body fat mass and (b) evaluating the effect of resistin treatment on ovarian activity with reference to steroid synthesis. An attempt was also made to determine whether resistin mediate its effects on ovary through signal transducer and activator of transcription 3 (STAT3) signaling mechanism. The results showed significant seasonal variation in serum resistin level with the peak level coinciding with the period of maximum fat accumulation, high circulating androgen level and period of anovulation. The treatment with resistin to the bat caused increase in androstenedione due to stimulatory effects on 3β-hydroxysteroid dehydrogenase, but decrease in estradiol level due to inhibitory effect on aromatase. Resistin treatment increased androgen receptor protein together with increased insulin receptor but not through conventional luteinizing hormone receptor and steroidogenic acute regulatory protein mediated pathways. This study further showed that resistin treatment increases androstenedione synthesis and up-regulates insulin receptor in the ovary through STAT3 mediated pathways. These findings suggest that obese women through increased resistin synthesis may causes development of non-ovulatory antral follicles through insulin receptor signaling cascade.

Effects of adiponectin on ovarian folliculogenesis and steroidogenesis in the vespertilionid bat, Scotophilus heathi

The bat Scotophilus heathi undergo anovulation, known as delayed ovulation, coinciding with the period of seasonal adiposity due to fat accumulation. Because adiponectin is a well known fat cell product, it might be responsible for adiposity related anovulation in S. heathi. The aim of this study was thus to evaluate the effects of adiponectin treatment on ovarian activity in S. heathi. The bat during the period of delayed ovulation was treated with adiponectin (25 μg/day) for 12 days. Changes taken place in the ovarian activity of the treated bat was compared with the control bat and results obtained are presented here. Adiponectin treatment significantly decreased body mass by depleting adipose tissue. It acts directly upon the ovary and promotes antral follicular development by stimulating cell proliferation and modulating ovarian steroidogenesis. The bat treated with adiponectin showed significant decrease in circulating androstenedione (A4) and estradiol (E2) levels, but increase in circulating progesterone (P4) level. The inhibitory effect of adiponectin on androgen synthesis may be due to decreased thecal-interstitial cells differentiation in stroma by suppressing adiponectin receptor type 1 (AdipoR1), luteinizing hormone (LH) and insulin receptors in the ovary of S. heathi. The study provides evidences suggesting that the adiponectin treatment suppresses adiposity and restores normal ovarian activity.

Localization of adiponectin and its receptor and its possible roles in the ovary of a vespertilionid bat, Scotophilus heathi

The aim of this study was to evaluate the seasonal variation in serum adiponectin levels and ovarian expression of adiponectin and its receptor in the Scotophilus heathi bat and their relationship to the changes in the body fat mass, serum insulin and luteinizing hormone (LH) levels, and ovarian activity. A very high level of circulating adiponectin was found during recrudescence, whereas a very low level of circulating adiponectin was observed during pre-ovulatory period. The increased circulating adiponectin level coincided with fat deposition, insulin resistance and hyperinsulinemia (HI) in S. heathi. Immunocytochemical study in the ovary of bat showed localization of adiponectin mainly in thecal-interstitial cells (TICs), and adiponectin receptor 1 (AdipoR1) in the granulosa cells of growing follicles, but showed no staining in atretic follicle. Seasonal changes in ovarian adiponectin and AdipoR1 levels showed two peaks (during recrudescence and ovulatory phases) coinciding with two periods of follicular development. Adiponectin in the absence of LH, as occur during recrudescence, stimulates androstenedione (A4) synthesis in vitro by up-regulating the insulin receptor (IR). Adiponectin in presence of LH, as occur during pre-ovulatory phase, inhibits A4 synthesis in vitro by down-regulating androgen receptor (AR). Further, the in vitro study showed that adiponectin, in presence of LH, also promotes luteinizing hormone receptor (LH-R) and steroidogenic acute regulatory protein (StAR) level in the ovary, which might help in development of ovulatory follicles. In brief, adiponectin in the absence of LH induces increased A4 synthesis and consequently the condition of delayed ovulation, whereas in the presence LH suppresses both synthesis and action of A4 and thus induces preovulatory condition in the ovary of S. heathi.

Mechanisms of sperm storage in the female reproductive tract: an interspecies comparison

Once semen has been collected for artificial insemination, it is diluted into extenders designed to prevent its deterioration over the period prior to insemination. If the semen is not frozen, the extenders provide protection for a period of a few hours to a few days, depending on species. Despite the efforts of biotechnologists to increase the duration of storage without compromising fertility, there has been relatively little progress for many years. However, comparative studies in diverse species have revealed that long-term sperm storage (up to months and years) within the female reproductive tract is relatively commonplace in reptiles, fishes, birds and amphibians. Even among mammals, some species of bat have evolved mechanisms for storing spermatozoa for several months in the uterus or oviduct so that they can mate in the autumn but postpone fertilization until the spring. We currently know little about the mechanisms that support such long-term sperm storage, mainly because evidence from such species is either absent or fragmentary. Nevertheless, parallels between mammalian and other systems, where spermatozoa are sequestered in sperm storage tubules, suggest that the enclosure of spermatozoa within pockets of epithelial cells may be sufficient to achieve long-term sperm storage. In addition, recent evidence from sperm-storing bats has suggested an alternative, or additional, hypothesis that the modulation of apoptosis within epithelial cells is important in controlling sperm survival. Despite a lack of direct experimental evidence from a wide variety of species, I propose that there is now enough evidence to warrant investigation of these hypotheses.

Regulation of leptin synthesis during adipogenesis in males of a vespertilionid bat, Scotophilus heathi

The aim of this study was to elucidate the hormonal regulation of leptin synthesis by the white adipose tissue (WAT) during the period of fat accumulation in male Scotophilus heathi. An in vivo study showed a significant correlation between the seasonal changes in serum insulin level with the circulating leptin level and with the changes in body fat mass in S. heathi. An in vitro study showed insulin induced a significant increase in expression of leptin protein in WAT. The insulin-stimulated increase in leptin expression was associated with increased uptake of glucose in the WAT. Two glucose transporters (GLUT4 and GLUT8) are utilized for transport of glucose in the WAT during adipogenesis in the bat. The bats showed high insulin and glucose levels, but a reduction in insulin receptor protein during the period of fat deposition, suggesting insulin resistance, which improved in late winter (January) when most of the fat has been utilized as a metabolic fuel. The in vitro study confirmed that insulin enhanced leptin and GLUT4 expression in WAT. The in vitro study further showed that the expression of leptin is directly proportional to the amount of glucose uptake by the WAT. The expression of GLUT4 and GLUT8 were also shown to be differentially regulated by insulin during adipogenesis. The insulin-stimulated increase in leptin synthesis by WAT is mediated through phosphorylation of MAPK in S. heathi. The specific role of GLUT4 and GLUT8 in the regulation of leptin synthesis during adipogenesis needs further investigation.

Increased circulating leptin level inhibits folliculogenesis in vespertilionid bat, Scotophilus heathii

The present study investigates the mechanism by which obesity associated rise in leptin and insulin levels cause anovulation in vespertilionid bat, Scotophilus heathii. In the ovary of S. heathii, leptin and insulin receptors were mainly localized in interstitial and thecal cells and in the granulosa cells of primary follicles suggesting its possible role in androgen synthesis and follicular development. Adiposity associated increase in circulating leptin level down regulate ovarian LH-receptor expression and produce characteristic morphological changes in the antral follicles, such as hypertrophy of granulosa cells and a sharp decline in the rate of proliferation as well as apoptosis in the antral follicles. These follicles are referred as unique antral follicle. The in vitro study confirmed the in vivo findings that the high dose of leptin suppresses apoptosis and LH receptors. The present study thus showed that the adiposity associated increase in leptin during the first phase of follicular development inhibits folliculogenesis and simultaneously suppresses both follicular proliferation and apoptosis by reducing sensitivity to gonadotropin stimulation and decreasing circulating LH levels.

Pattern of ovarian protein synthesis and secretion during the reproductive cycle ofScotophilus heathi: synthesis of an albumin-like protein

Ovarian proteins synthesized de novo and secreted in vitro were investigated during different stages of the reproductive cycle of Scotophilus heathi. We found increased ovarian protein synthesis and secretion during the recrudescence and the preovulatory periods, coinciding with two peaks of follicular development and steroidogenesis. The ovaries synthesized protein at a low rate during quiescence and the late phase of delayed ovulation. In vitro analysis using 35 S-methionine incorporation showed increased synthesis of 66 kDa protein during delayed ovulation, but secretion of this protein declined markedly during the preovulatory period. N-terminal sequencing of the 66 kDa protein showed that it shares 70% homology with human serum albumin. Immunocytochemistry indicated that this protein is found primarily in the granulosa cells of the follicles. Whether the increase in albumin production by the ovaries during delayed ovulation is associated with a hyperinsulinemic and hyperandrogenic condition requires further investigation.

Adiposity associated rise in leptin impairs ovarian activity during winter dormancy in Vespertilionid bat, Scotophilus heathi

The aim of the study was to evaluate the seasonal variation in serum leptin levels in a natural population of the female bat,Scotophilus heathiand their relationship to the changes in the body mass, serum insulin level, and ovarian activity. Circulating leptin level varied significantly over the season and correlated positively with the changes in body mass, and circulating insulin and androstenedione (A4) levels. Circulating leptin concentrations showed two peaks; one coincides with the maximum fat accumulation prior to winter dormancy, whereas the second shorter peak coincides with late pregnancy. Thein vivostudy inS. heathishowed that the increased circulating leptin level during winter dormancy coincides with the decreased expression of ovarian steroidogenic acute regulatory (StAR) protein, and low circulating estradiol (E2) level. At the same time, increased circulating leptin level coincides with increased expression of ovarian insulin receptor and high circulating A4 level. The low circulating leptin level during preovulatory period coincides with the increase in StAR protein but decrease in insulin receptor protein. Thein vitrostudy confirmed thein vivoobservations of inhibitory effect of leptin on LH induced StAR expression and E2production, whereas the stimulatory effect of leptin (high dose) on LH induced expression of insulin receptor protein and A4 production. However, pharmacological dose of leptin produced inhibitory effect on the expression of insulin receptor protein. The results of the present study thus suggest that high circulating leptin level during winter dormancy promotes adiposity and impairs ovarian activity by suppressing StAR-mediated E2production as well as by enhancing insulin receptor-mediated A4 synthesis thereby contributing anovulatory condition of delayed ovulation inS. heathi.

Hormonal induction of ovulation stimulates atresia of antral follicles in a vespertilionid bat, Scotophilus heathi

Scotophilus heathi is a seasonally monoestrous subtropical vespertilionid bat found at Varanasi, India. Although the antral follicles remain present in the ovaries of S. heathi from November till March, ovulation is delayed in this species until early March. In order to understand the mechanism of ovulation suppression during this period of delayed ovulation, the effects of human chorionic gonadotropin (hCG), pregnant mare's serum gonadotropin (PMSG), follicle stimulating hormone (FSH) and gonadotropin releasing hormone agonist (GnRH agonist) on ovarian morphology and steroid concentration were investigated. Hormonal treatments were given as a single i.p. dose 24 h after capture. The bats were sacrificed 48 h after the injection. Treatment with hCG, PMSG, FSH and GnRH agonist failed to induce ovulation in S. heathi, although these hormones produced a high degree of ovarian stimulation. The administration of hCG and PMSG induced ovarian enlargement, intense hyperemia, marked changes in the interstitial cells (ICs), development of several antral follicles and a varying degree of abnormalities in the oocytes of most of the antral follicles. In the bats treated with hCG, PMSG and GnRH agonist, androstenedione concentration increased significantly to extraordinarily high levels, whereas estradiol concentration decreased. Administration of FSH caused regression of ICs and pyknosis of granulosa cells in the majority of antral follicles. FSH did not enhance androstenedione concentration. The results of the present study suggest that the failure of hormonal treatments to induce ovulation during the period of delayed ovulation might be due to a seasonal desensitization of ovarian follicles in S. heathi. The hormonal treatment instead stimulated the ICs to produce a high level of androstenedione resulting in atretic changes of the antral follicles.

Histochemical localization of enzymes and lipids in the ovary of a vespertilionid bat, Scotophilus heathi, during the reproductive cycle

The present study describes seasonal changes in delta5 3beta hydroxysteroid dehydrogenase (3beta-HSD), glusose-6 phosphates dehydrogenase (G-6-PD), and lipids in the ovary of a vespertilionid bat, Scotophilus heathi. Total lipids and 3beta-HSD activity are restricted to thecal and interstitial cells of the ovary. The total lipids, 3beta-HSD, and G-6-PD significantly increase during recrudescence, and remain high during winter dormancy and breeding as compared to the other reproductive phases. High incidence of lipids and enzyme activity in interstitial cells during the breeding period and at the time of ovulation clearly suggests that these cells are actively involved in steroidogenesis. A decline in enzymes and lipid activity during winter dormancy, which correlates with the declining levels of steroidogenesis, might be the factors responsible for prolonged survival of the Graafian follicle in the ovary of S. heathi.

Relationship between corticosterone and body weight, androstenedione and insulin during the period of delayed ovulation in a vespertilionid bat, Scotophilus heathi

The aim of the present study was to evaluate the relationship between corticosterone, body weight, insulin and androstenedione in order to understand the role of adrenal in contributing hyperandrogenism during delayed ovulation in S. heathi. The circulating corticosterone concentration in female S. heathi showed significant seasonal variation. The peak corticosterone concentration observed during August-September coincides with increased feeding activities in S. heathi. The present study noted a seasonal variation in relationship of corticosterone with insulin and androstenedione in S. heathi. An inverse relationship of corticosterone with insulin and androstenedione was found during August to December, but not during January to May. A seasonal variation in the effect of adrenocorticotropic hormone (ACTH) on adrenal corticosterone production in vitro was observed during reproductive cycle. Corticosterone production in vitro by adrenal declined significantly as compared to the control during quiescence in September. The finding suggests that adrenal attained the peak responsiveness to ACTH during September. ACTH significantly enhanced the androstenedione production by the adrenal in vitro during December, when the circulating androstenedione was also high in S. heathi. This suggests that the adrenal may also contribute to hyperandrogenism during the period of delayed ovulation in S. heathi. Further studies are required to reveal the unique pattern of seasonal relationship between corticosterone, insulin and androstenedione in S. heathi.

Seasonal adiposity and delayed ovulation in a vespertilionid bat, Scotophilus heathi: role of tumor necrosis factor-alpha

The aim of this article was to evaluate the physiological significance of tumor necrosis factor-alpha (TNF-alpha) in seasonal accumulation of adipose tissue, hyperinsulinemia, and anovulation in Scotophilus heathi. The result showed seasonal variations in the circulating TNF-alpha level. A higher level of circulating TNF-alpha was observed during quiescence and recrudescence, whereas a lower level of TNF-alpha was observed during winter dormancy and the preovulatory period. An increased circulating TNF-alpha level coincided closely with accumulation of adipose tissue and hyperinsulinemia. Immunocytochemical localization of TNF-alpha in the ovary showed immunoreactivity mainly in the oocytes and theca-interstitial cells. The oocytes of small and medium-sized follicles showed strong TNF-alpha immunostaining, whereas weak immunoreactivity was observed in the large antral follicles. The atretic follicles showed mild TNF-alpha immunostaining. TNF-alpha immunoreactivity in the ovary was slightly higher during the quiescence and preovulatory periods compared with the periods of recrudescence and winter dormancy. TNF-alpha alone significantly increased androstenedione and estradiol production by the ovary in vitro but did not augment the luteinizing hormone (LH)-induced androstenedione production. However, TNF-alpha did augment LH-induced estradiol production. The results of this study suggest the involvement of TNF-alpha in the interaction among adipose tissue accumulation, insulin resistance, and ovarian activity in S. heathi.

Seasonal changes in circulating steroid concentration and their correlation with the ovarian activity in the female Indian sheath-tailed bat, Taphozous longimanus

The relationship between ovarian activity and circulating steroid concentration was studied in the female sheath-tailed bat, Taphozous longimanus. T. longimanus breeds twice in rapid succession during the year at Varanasi, India. Ovarian recrudescence was observed during September, and antral follicles were first observed during the month of October. Circulating androstenedione concentration showed an increase beginning in October, reaching a peak in December. This increase in androstenedione concentration correlated with the period of heavy accumulation of adipose tissue and increase in body mass. Antral follicles grow slowly during the period of high circulating androstenedione concentration from October to December. There was a sharp decline in androstenedione concentration during January. Simultaneously with the decline in androstenedione concentration, a sharp increase in size of the antral follicle and circulating estradiol concentration was noticed. Soon thereafter, one of the follicles ruptures, followed by fertilization and the commencement of the first pregnancy. During the second pregnancy, antral follicles first appeared during late pregnancy in March in the contralateral ovary that lacked the corpus luteum. One follicle developed rapidly and quickly attained a preovulatory stage in April. This is reflected in a sharp increase in estradiol concentration during this period. Ovulation was observed immediately following the first pregnancy in May. During this period, androstenedione concentration remained low. The results of the present study suggest that high androstenedione concentration during October to December (winter dormancy) may be responsible for slow follicular development and delays ovulation in T. longimanus. It is further hypothesized that the geographical variation in reproductive pattern of T. longimanus could be due to variation in the duration of fat storage and associated changes in the androstenedione concentration.

Proliferative activity of follicles and serum steroid concentration in Scotophilus heathi (vespertilionid bat) during periods of delayed ovulation

Follicular kinetics were studied using immunocytochemical localization of proliferating cell nuclear antigen (PCNA) and changes in circulating steroid concentrations to investigate the cause of prolonged survival of Graafian follicles and delayed ovulation in the vespertilionid bat Scotophilus heathi. PCNA immunoreactivity was limited to the granulosa cells and varied with stage of follicular development and reproductive phase. Two waves of follicular growth appear to be initiated in October and February. The first wave resulted in the appearance of some late antral follicles in November. These antral follicles grew slowly and differed from typical mammalian Graafian follicles, as the cells of their cumulus oophoricus were large and hypertrophied. The second wave of follicular development resulted in fresh recruitment and selection of dominant follicles in February. The steroid-hormone profile showed an unusually high concentration of circulating androstenedione from October to December. The estradiol concentration showed two peaks coinciding with two peaks of PCNA immunoreactivity. The results show that the unusually high androstenedione concentration might be responsible for the development of non-ovulatory Graafian follicles with hypertrophied granulosa cells, which survive for a prolonged period. The decline in androstenedione concentration allows the development of ovulatory follicles in S. heathi.

Mechanism of delayed ovulation in a vespertilionid bat, scotophilus heathi: role of gonadotropin, insulin, and insulin-like growth factor-1

The aim of this study was to evaluate the effects of luteinizing hormone (LH), follicle-stimulating hormone (FSH), insulin, and insulin-like growth factor-1 (IGF-1) on ovarian androstenedione synthesis to understand the mechanism responsible for delayed ovulation in Scotophilus heathi. We found that LH stimulated a dose-dependent increase in androstenedione synthesis by the ovary in vitro. This study also showed a clear seasonal variation in the ability of the ovary to produce androstenedione in vitro in response to LH and FSH stimulation. In response to LH and FSH, maximum quantities of androstenedione were produced during recrudescence in November. The same doses of gonadotropins during the preovulatory period in February stimulated comparatively low androstenedione secretion by the ovary. On the basis of these data, we suggest that in S. heathi, ovarian responsiveness to LH and FSH peaks during recrudescence. This study also showed a seasonal variation in the effects of insulin and IGF-1 on ovarian androstenedione production in vitro. Peak ovarian responsiveness to insulin and IGF-1 was observed during quiescence in September. It is hypothesized that increased insulin/IGF-1 sensitivity during September may be responsible for increased responsiveness to LH. Increased LH release, if coincident with the period of enhanced ovarian responsiveness to LH, may result in the excessive androstenedione production responsible for delayed ovulation in S. heathi.

Possibility of inhibin as a regulator of androstenedione production by the ovary during the period of delayed ovulation in a vespertilionid bat, Scotophilus heathi

The aim of the present study was to evaluate the role of inhibin in regulating androstenedione production by the ovary of Scotophilus heathi during the period of delayed ovulation. Inhibin alone increased the androstenedione synthesis in vitro by the ovary during all reproductive phases, but augmented the hCG induced androstenedione production only during November. The follicles produced significantly higher androstenedione as compared to the stromal or granulosa cell in response to both hCG and inhibin. However, inhibin augmented hCG stimulated androstenedione in the stromal cell only. Immunoreactivity of inhibin subtype alpha, betaA and betaB were mainly localized in the thecal and interstitial cell from September to November and then declined during the preovulatory period. However, in granulosa cells weak to moderate immunoreactivity of all inhibin subtype was observed during these phases. These results indicate the possible role of inhibin in regulating androstenedione synthesis by the ovary and thus. may be indirectly responsible for causing delayed ovulation in S. heathi.