The effect of active immunization against inhibin on gonadotropin secretions and follicular dynamics during the estrous cycle in cows

The hypothesis of the present study is that active immunization of cows against inhibin would neutralize endogenous inhibin, increase circulating levels of follicle stimulating hormone, and subsequently affect follicular dynamics and the ovulation rate during the estrous cycle. Thirteen cows were immunized against inhibin alpha-subunit and, 6 cows were immunized with a placebo. Both groups were given 4 booster immunizations 7, 14, 21, and 34 weeks after the primary injection. Ovaries were examined daily after the 2nd, 3rd, and 4th booster immunizations by transrectal ultrasonography for 25 days. After the 4th booster immunization, blood samples were collected daily for one complete estrous cycle to measure FSH and LH. The results showed that the immunized cows generated antibodies against inhibin, and that they had higher FSH levels compared with the controls. The number of follicular waves during the estrous cycle was higher in the immunized cows (3 or 4 waves) than in the controls (2 or 3 waves). Moreover, the immunized cows had a greater number of follicles during the estrous cycle compared with the control cows. The maximum number of follicles was 14.8 +/- 1.7 vs 5.4 +/- 0.2 in inhibin-immunized and control cows, respectively, during the first follicular wave and 13.9 +/- 1.9 vs 5.6 +/- 0.7, respectively, during the ovulatory wave. Multiple ovulations were increased in the immunized cows. However, the ovulation rate varied greatly in the immunized animals. In conclusion, immunization against inhibin increased FSH secretions during the estrous cycle in the cows. Moreover, the immunized cows had a greater number of follicular waves during the estrous cycle and a greater number of follicles, and this could be used as a potential source of oocytes for use in IVF/embryo transfer programs.     

生殖激素控制卵泡细胞凋亡的研究进展

研究表明颗粒细胞凋亡是导致卵泡闭锁的重要原因，而颗粒细胞凋亡涉及许多因素，其中生殖激素，如GnRH、FSH、LH、P4、E、A、GH、Mel、inhibin、activin、follistatin等间接地和直接地对卵巢卵泡细胞凋亡发挥重要的综合控制作用，因此正确理解激素对体内、外卵泡及颗粒细胞发育和衰亡的调节网络具有很重要的理论和实践意义。     

Strain differences in the spontaneous incidence of sperm morphological abnormalities in Hatano rats

Two inbred strains of Hatano rats, which had been bred selectively on the basis for shuttlebox avoidance responses (high- and low-avoidance animals; HAA and LAA), were different in sperm motility. We have found that there are strain differences in the spontaneous incidence of sperm morphological abnormalities. The percentages of abnormalities were extraordinarily higher in the LAA rats, whose sperm motility was lesser. Since the high sperm abnormality was an exceptional case in rats, these rats may be useful models for sperm quality.     

Dynamic changes in plasma concentrations of gonadotropins, inhibin, estradiol-17beta and progesterone in cows with ultrasound-guided follicular aspiration

To elucidate the effects of ultrasound-guided transvaginal follicular aspiration, plasma concentrations of FSH, LH, inhibin, estradiol-17beta and progesterone, and folliculogenesis were examined in Holstein cows. Four clinically healthy cows with regular estrous cycles were scanned by ultrasound per rectum once a week for 9 weeks before the commencement of follicular aspiration. All visible follicles were divided into 3 categories based on their sizes (2 < or = small < 5 mm; 5 < or = medium < 10 mm, large > or = 10 mm). The follicular aspiration was started at random during the estrous cycle and conducted under epidural anesthesia induced with 5 ml of 2% lidocaine once a week for 6 weeks. The average number of total visible follicles > or = 2 mm in diameter at 7 days after aspiration (21.7 +/- 7.4, n = 24) was similar to that before starting aspiration (26.7 +/- 10.5, n = 36). Plasma inhibin and estradiol-17beta declined and fell to a trough on 1.5 days and returned to pre-aspiration values by 5 days after aspiration. Plasma concentrations of FSH increased and reached peak levels between 1 and 1.5 days after aspirations. Plasma concentrations of LH also increased and reached peak levels between 0.5 and 1.5 days after aspirations. Both plasma FSH and LH had returned to pre-aspiration levels by 5 days after aspirations. Plasma concentrations of progesterone did not change with the follicular aspiration. These results demonstrate that follicular aspiration decreases plasma concentrations of inhibin and estradiol-17beta, which in turn leads to a rise in plasma concentrations of FSH and LH. It is suggested that marked increases in plasma concentrations of FSH and LH after the aspiration stimulate the development and maturation of a new cohort of follicles within one week in cows.     

Follicular and hormonal dynamics during the estrous cycle in goats

Transrectal ultrasonography of ovaries was performed daily in 6 goats for 3 consecutive estrous cycles. Blood samples collected daily were measured for concentrations of FSH, inhibin A, and estradiol-17beta. Follicular and hormonal data were analyzed for associations between the follicular waves and hormonal concentrations. During the interovulatory intervals, follicular growth and regression occurred in a wave like pattern (2-5 waves), and the predominant patterns were three and four follicular waves. In addition, there was no significant difference among the diameters of dominant follicles during the growth phase of the follicular waves. The number of 3 mm follicles peaked on days 0, 7, and 11 in interovulatory intervals that had three follicular waves and on days -1, 5, 11, and 15 in those that had four follicular waves. Plasma concentrations of FSH increased around the day of follicular wave emergence and declined with the growth of follicles. Circulating FSH increased again concomitant with regression of dominant follicles in the anovulatory wave, whereas FSH levels remained low in the ovulatory wave. Inhibin A was negatively correlated with FSH, while it was positively correlated with estradiol-17beta, suggesting that inhibin A is a product of healthy growing follicles and that it contributes to the suppression of FSH secretion. In conclusion, the growth of ovarian follicles in goats exhibits a wave-like pattern, and follicular dominance is less apparent in goats. Moreover, inhibin A may be a key hormone for regulation of the follicular wave through suppression of FSH secretion in goats.     

Alterations in the ability of the bovine pituitary gland to secrete gonadotropins in vitro during the first follicle-stimulating hormone increase of the estrous cycle and in response to exogenous steroids

The objective was to determine if the endocrine status of the animal dictates the responsiveness of gonadotrophs to estradiol, activin, inhibin and follistatin; hormones implicated in the differential release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Bovine pituitaries were obtained at 13 (n=8), 30 (n=24) and 66 (n=8) h after the onset of estrus, corresponding to before, during and the end of the first FSH increase of the estrous cycle which follows the pre-ovulatory gonadotropin surge in heifers. Heifers slaughtered at 30 h received no treatment, or were treated with progesterone with or without estradiol before slaughter to suppress the first transient FSH increase. Secretion of FSH from cultured pituitary cells, reflecting the prior in vivo status, was greater (P<0.01) at 30 h than 13 or 66 h, whereas, LH secretion was less (P<0.01) at 13 h compared with 30 h. Treatment with exogenous steroids decreased (P<0.05) the pituitary gland's ability to subsequently secrete FSH and LH. Inhibin and, to a greater extent, estradiol decreased (P<0.01) mean FSH secretion but increased (P<0.05) mean LH secretion. These findings suggest that estradiol and inhibin both have the ability to differentially modulate basal gonadotropin secretion during the first FSH increase of the bovine estrous cycle. Differential regulation of LH and FSH is mediated via an alteration in gonadotropin biosynthesis and basal secretion. Furthermore, the secretory capability of cultured pituitary cells and basal gonadotropin secretion reflect the prior endocrine status of the animal from which pituitaries were obtained.     

Effect of active immunization of pony mares against recombinant porcine inhibin alpha subunit on ovarian follicular development and plasma steroids and gonadotropins

Two pony mares were immunized against recombinant porcine inhibin alpha subunit three times with 39 day intervals. Clinical findings and endocrinological changes before immunization were taken as the control. The first significant rise in the anti-inhibin titre (P<0.05) in the circulation was found 27 days after the first injection. Maximum binding activity was reached by the 12th day after the second booster dose. The number of small, medium and large sized follicles had increased significantly compared to before immunization (11.75 +/- 4.30, 2.75 +/- 0.69 and 2.51 +/- 0.63 vs 6.50 +/- 1.43, 1.83 +/- 0.44 and 1.33 +/- 0.38, respectively), but the ovulation rate remained unchanged after immunization. The average plasma concentration of FSH and estradiol-17beta during the estrous cycle increased significantly (P<0.05) after immunization. These results suggest that immunization against inhibin is a useful tool to increase the number of ovarian follicles during the estrous cycle of pony mares. Moreover, the present study supported the concept that inhibin plays a major role in the control of follicular growth through its inhibitory effect on FSH secretion synergistically with steroid hormones.     

Inhibin secretion in the golden hamster (Mesocricetus auratus) testis during active and inactive states of spermatogenesis induced by the restriction of photoperiod

Gonadal function in the male golden hamster (Mesocricetus auratus) was investigated during exposure to a short photoperiod condition. Within 3 weeks of exposure to the short photoperiod condition, FSH and testosterone in the plasma significantly decreased, and subsequently immunoreactive (ir)-inhibin significantly decreased. Testicular contents of ir-inhibin and testosterone, and pituitary contents of LH and FSH also significantly decreased by 3 weeks with regression of weight of testes, epididymis and seminal vesicles and sperm head count. Circulating LH varied but not significantly. Thereafter, all reproductive parameters and secretion of LH, FSH, ir-inhibin and testosterone gradually recovered after 17 weeks of exposure even though animals continued to be subjected to the short photoperiod condition. Plasma concentrations of inhibin B and inhibin pro-alphaC were detectable and were significantly decreased after 15 weeks of exposure to the short photoperiod, but their levels were still detectable. Immunopositive reaction of inhibin alpha and betaB subunits was found in Sertoli cells and Leydig cells in the regressed testes of animals subjected to short photoperiod as was also seen in animals before exposure to the short photoperiod. Although the spermatogenic cycle was suppressed like prepubertal animals, the present study showed that the testicular recovery, so-called refractoriness, is functionally different from the developing stage of immature animals, especially with regard to inhibin secretion. The present results showed that changes in FSH preceded changes in inhibin during the regression and recovery phases, indicating that FSH is a major regulatory factor of inhibin secretion in male golden hamsters. The present study also demonstrated that regressed testes still secrete a small amount of bioactive inhibin during exposure to a short-photoperiod condition.     

Changes in the peripheral concentrations of inhibin, follicle-stimulating hormone, luteinizing hormone, progesterone and estradiol-17beta during turnover of cystic follicles in dairy cows with spontaneous follicular cysts

Several studies have clarified that the follicular cysts degenerate and are replaced by newly growing follicles that develop into new follicular cysts without ovulation, i.e., turnover of ovarian follicular cysts in cows. However, the relativity of endocrinological changes, including the inhibin profile during turnover of spontaneous follicular cysts in dairy cows, is still unclear. In the present study, the relationship between turnover of follicular cysts and changes in the peripheral blood concentrations of progesterone (P), estradiol-17beta (E(2)), luteinizing hormone (LH), follicle stimulating hormone (FSH) and inhibin were examined in lactating dairy cows. Five cows diagnosed with follicular cysts (follicles of more than 25 mm in diameter in the absence of a corpus luteum) were investigated. Their ovarian dynamics were monitored using ultrasonography, and blood samples were collected at 2- or 3- day intervals throughout the experiment. The day when a follicle fated to become a follicular cyst reached more than 8 mm in diameter was defined as the start of a cystic follicular wave. Four of the 5 cows exhibited a similar patterns of cystic follicular changes and hormone profiles. The data from the 4 cows was used for analysis of the relationships between turnover of cystic follicles and the hormone profiles. Two or three new cystic follicular waves occurred in each cow during the experimental period. The mean diameter of the cystic follicles was more than 25 mm 13 to 15 days after the start of the cystic follicular wave, and it began to decrease 1 to 6 days before the start of the subsequent cystic follicular wave. The levels of E(2) and inhibin tended to decrease for 7 to 9 days before the start of a new cystic follicular wave and to increase concomitantly with new follicular cyst growth. The levels of FSH rose for 1 to 3 days before the start of a new cystic follicular wave. The present study clarified the relationship between FSH and inhibin during turnover of spontaneous follicular cysts in dairy cows and found that it was very similar to previous results for cows. The present results suggest that an increase in FSH secretion following a reduction in inhibin secretion triggers turnover of cystic follicles in cows with spontaneous follicular cysts.     

Expression of inhibin/activin subunits in the ovaries of fetal and neonatal mice

In the present study, the expression of inhibin/activin subunits in the mouse ovary from 13 days post-coitus (dpc) to 30 days postpartum (dpp) was investigated. Circulating FSH, LH, inhibin A, and inhibin B in neonatal to 30 dpp ovaries were measured. Inhibin/activin subunits (alpha, beta(A), beta(B) ) were weakly stained in 13 dpc ovarian stromal cells and increased with age. Inhibin alpha subunit was immunolocalized in follicular granulosa cells at each developmental stage. In 30 dpp ovaries, several large antral follicles were strongly stained for inhibin alpha subunit. Inhibin beta(A) subunit was weakly immunolocalized in granulosa cells until 20 dpp. Moreover, 2 to 3 antral follicles from 20 to 30 dpp were strongly stained for inhibin beta(A) subunit. There was relatively high immunoactivity for inhibin beta(B) subunit in neonatal to 30 dpp mouse ovaries. All three inhibin subunits were stained in theca-interstitial cells from 15 dpp onward. RIA data showed that a temporal increase in circulating FSH occurred around 10 dpp, while the plasma concentrations of LH were sustained at a relatively higher level from 8 to 15 dpp. Inhibin B was detectable in circulation early at 1 dpp (day of birth), and a clear increase in inhibin B occurred around 8 dpp. Circulating inhibin B gradually increased from 20 dpp to 30 dpp, indicating a negative correlation with FSH. Inhibin A levels were only measured on 25 and 30 dpp, and the levels were low. These results suggest that inhibins play an important role in early folliculogenesis in mice. In addition, inhibin B seems to be the main functional isoform from the neonatal to prepubertal stage in the mouse ovary.     

Use of Equine Chorionic Gonadotropin to Control Reproduction of the Dairy Cow: A Review

Equine chorionic gonadotropin (eCG) is a member of the glycoprotein family of hormones along with LH, FSH and thyroid‐stimulating hormone. In non‐equid species, eCG shows high LH‐ and FSH‐like activities and has a high affinity for both FSH and LH receptors in the ovaries. On the granulosa and thecal cells of the follicle, eCG has long‐lasting LH‐ and FSH‐like effects that stimulate oestradiol and progesterone secretion. Thus, eCG administration in dairy cattle results in fewer atretic follicles, the recruitment of more small follicles showing an elevated growth rate, the sustained growth of medium and large follicles and improved development of the dominant and pre‐ovulatory follicle. In consequence, the quality of the ensuing CL is improved, and thereby progesterone secretion increased. Based on these characteristics, eCG treatment is utilized in veterinary medicine to control the reproductive activity of the cow by i) improving reproductive performance during early post‐partum stages; ii) increasing ovulation and pregnancy rates in non‐cyclic cows; iii) improving the conception rate in cows showing delayed ovulation; and finally, iv) eCG is currently included in protocols for fixed‐time artificial insemination since after inducing the synchrony of ovulation using a progesterone‐releasing device, eCG has beneficial effects on embryo development and survival. The above effects are not always observed in cyclic animals, but they are evident in animals in which LH secretion and ovarian activity are reduced or compromised, for instance, during the early post‐partum period, under seasonal heat stress, in anoestrus animals or in animals with a low body condition score.     

Study on the Changes of Reproductive Hormone and Regulation of Follicle Development During the Reproductive Cycle of Yili Goose in Xinjiang

This experiment was aimed to study the changes of reproductive hormone and regulation of follicle development during the reproductive cycle of Yili goose in Xinjiang. 2 years old Yili goose were chosen which were in good health and similar weight. 32 samples were randomly selected to take blood samples for hormone detection during the laying, broodiness and ceased periods, and 15 samples were randomly selected to gather ovarian tissue for the observation of the development of ovary and follicular. The results showed that during the laying period, the GnRH of the Yili goose was extremely significantly higher than the broodiness and ceased periods of 16.78% and 58.29% (P<0.01);PRL was significantly lower than the broodiness period of 13.00% (P<0.05), and was extremely significantly higher than the ceased period of 28.94% (P<0.01); FSH was higher than the broodiness period of 6.98% (P>0.05),and was extremely significantly higher than the ceased period of 21.12% (P<0.01); LH was extremely significantly lower than the broodiness period of 8.38% (P<0.01),and was extremely significantly higher than the ceased period of 16.84% (P<0.01); E₂ were extremely significantly higher than that the broodiness and ceased periods of 29.80% and 112.40% (P<0.01); P₄ levels were extremely significantly higher than the broodiness and ceased periods of 28.89% and 30.34% (P<0.01). The ovary volume and weight of Yili goose were extremely significantly higher than that of broodiness and ceased periods (P<0.01). In the laying period, the mature follicles of Yili goose were significantly larger than that of the broodiness and resting periods, the number of secondary follicles was more and the number of primary follicles was lesser. Ovarian growth and mature follicle atresia, granule layer shrinkage, inward depression, cytoplasmic cavity, follicular atrophy at all levels in the broodiness period. The follicle cytoplasmic cavity of the ovary was larger in the ceased period than broodiness period, and inward concave further deeper, a large number of primordial follicles evenly arranged. Thus, during the laying period, the responses of GnRH, E₂ and LH of Yili goose were active and played a leading role on the development of ovarian and follicular. PRL and LH maintained a high level of secretion, cooperated to maintain the broodiness behavior during the broodiness period.     

Endocrine relationships of Meishan and White composite females after weaning and during the luteal phase of the estrous cycle

Endocrine differences between European crossbred and Chinese Meishan females have been somewhat modest. Indwelling jugular cannulas were placed in Meishan (n = 7) and White composite (n = 6) multiparous sows before weaning, and blood was sampled from 4 h before to 240 h after removal of litters. Temporal changes in FSH, triiodothyronine (T3), and tetraiodothyronine (T4) after weaning differed between Meishan and White composite sows. Plasma cortisol concentrations were higher in Meishan sows than in White composite sows (P < 0.01), but there were no temporal differences between breeds after weaning. Other hormones monitored (prolactin, GH, IGF-I, and inhibin) were not different between breeds. In the second experiment, Meishan gilts (n = 7) and sows (n = 7) and White composite sows (n = 9) were cannulated during the luteal phase of the estrous cycle and sampled after treatments consisting of GnRH (15 and 150 ng/kg BW), ovariectomy, estradiol cypionate challenge after ovariectomy (10 microg/kg BW), and GnRH antagonist. In response to GnRH challenge, White composite sows had elevated (P < 0.05) concentrations of gonadotropins compared with Meishan. Cortisol concentrations were elevated in Meishan as compared with White composite females (P < 0.01) but unaffected by GnRH treatment. After ovariectomy, LH concentrations increased 3 h sooner in White composite than in Meishan females. After GnRH antagonist, declines in gonadotropins were comparable in both breeds, but LH increased in Meishan females by 20 h but not until after 54 h in White composite females. White composite females demonstrated only a short decline in FSH in response to the GnRH antagonist, but Meishan females had a prolonged decline in FSH concentrations. Consistently elevated cortisol concentrations in Meishan females may positively impact ovarian function; thus, the assumption that high plasma cortisol concentration as an index of stress that impairs reproductive function should be reevaluated in swine. There were few endocrine differences that would relate to or explain increased ovulation rates found in the Meishan breed; thus, other mechanisms must exist to explain the increase in ovarian function in the Meishan breed.     

鹅就巢期卵巢特征及其内分泌机制的研究进展

鹅的就巢行为显著影响其产蛋量,就巢行为主要受下丘脑-垂体-性腺轴(HPG)分泌的相关激素调控。相关激素主要包括促性腺激素释放激素(GnRH)、催乳素(PRL)、促卵泡激素(FSH)、促黄体素(LH)、雌二醇(E_2)和孕酮(P_4),共同调控鹅的就巢行为。在就巢期,机体内PRL分泌浓度升高,能够抑制GnRH和FSH的分泌,导致大卵泡合成P_4、E_2速率下降,从而垂体分泌LH浓度降低。本文对鹅就巢期激素水平及卵巢形态变化进行阐述,以期通过调控鹅就巢行为来提高产蛋量的相关研究提供理论支持。     

Testosterone effects on gonadotropin response to GNRH: cows and pony mares

Effects of testosterone propionate (TP) treatment on plasma concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) before and after an injection of gonadotropin releasing hormone (GnRH) were studied using ovariectomized cows and pony mares. An initial injection of GnRH (1 microgram/kg of body weight) was followed by either TP treatment or control injections for 10 (cows) or 11 (ponies) d. A second GnRH injection was administered 1 d after the last TP or oil injection. Concentrations of LH and FSH were determined in samples of plasma taken before and after each GnRH injection. Control injections did not alter the response to GnRH (area under curve) nor the pre-GnRH concentrations of LH and FSH in ovariectomized cows or ponies. Testosterone treatment increased (P less than .01) the FSH release in response to GnRH in ovariectomized mares by 4.9-fold; there was no effect in cows, even though average daily testosterone concentrations were 59% higher than in pony mares. Testosterone treatment reduced the LH release in response to GnRH by 26% in ovariectomized mares (P less than .05) and by 17% in ovariectomized cows (P approximately equal to .051). These results are consistent with a model that involves ovarian androgens in the regulation of FSH secretion in the estrous cycle of the mare, but do not support such a model in the cow.     

Factors that affect ovarian follicular dynamics in cattle.

Studies of ovarian follicular dynamics in cattle may lead to methods for improving fertility, for synchronizing estrus with more precision, and for enhancing superovulatory responses. Within an estrous cycle, two or three large (> 10 mm) follicles develop during consecutive waves of follicular growth. The last wave provides the ovulatory follicle, whereas preceding wave(s) provide follicles that undergo atresia. The life span of large follicles seems to depend on the pulsatile secretion of LH; decreased frequency of LH pulses results in atresia of large follicles. Aromatase activity in the walls of the largest follicles is greatest during the first 8 d of the estrous cycle and decreases by d 12. Steroidogenesis of the largest and second-largest ovarian follicles differs on d 5, 8, and 12 of the estrous cycle. Follicular dynamics are altered by negative energy balance and lactation. The number of large follicles and concentration of estradiol during the preovulatory period differs between postpartum lactating and nonlactating cows. Dietary fats stimulate follicular growth when they are fed to increase energy balance. Administration of bovine somatotropin decreases energy balance and has a differential effect on ovarian follicular responses; growth of the largest follicle does not change, but growth of the second-largest follicle is stimulated by somatotropin. Studies of follicular dynamics in lactating cows demonstrate changes in ovarian function associated with energy balance that may be related to inefficient reproductive performance of cows producing high yields of milk.     

新疆伊犁鹅繁殖周期生殖激素变化及卵巢卵泡发育规律的研究

为探究新疆伊犁鹅繁殖周期中血浆主要生殖激素、卵巢形态及卵泡发育的变化规律,试验以健康状况良好、体重相近的2岁伊犁鹅为试验对象,分别在产蛋期、就巢期及休产期各随机选取32只,采集1次血样,测定激素水平;在各时期分别选取5只采集卵巢组织,观测卵巢及卵泡发育情况。结果表明,在产蛋期,伊犁鹅的GnRH分别极显著高于就巢期和休产期16.78%和58.29%（P<0.01）;PRL显著低于就巢期13.00%（P<0.05）,极显著高于休产期28.94%（P<0.01）;FSH高于就巢期6.98%（P>0.05）,极显著高于休产期21.12%（P<0.01）;LH极显著低于就巢期8.38%（P<0.01）,极显著高于休产期16.84%（P<0.01）;E₂水平分别极显著高于就巢期和休产期29.80%和112.40%（P<0.01）;P₄水平分别极显著高于就巢期和休产期28.89%和30.34%（P<0.01）。产蛋期伊犁鹅的卵巢体积和重量均极显著大于就巢期和休产期（P<0.01）。产蛋期伊犁鹅成熟卵泡与就巢期和休产期相比明显较大,次级卵泡数量较多,初级卵泡数量较少;就巢期卵巢上生长及成熟卵泡发生闭锁,颗粒胞层收缩,向内凹陷,胞质出现空腔,各级卵泡出现萎缩;与就巢期相比,休产期卵巢上卵泡胞质空腔变大,向内凹陷程度进一步加深,大量原始卵泡均匀排列。由此可见,在产蛋期,伊犁鹅的GnRH、E₂、LH反应活跃,对卵巢卵泡发育起主导作用;在就巢期,PRL、LH维持较高的分泌水平,协同维持就巢。     

Immunization of Sheep Against GNRH Early in Life: Effects on Gonadotropins,Follicular Growth and Responsiveness of Granulosa Cells To FSH and IGF-I in Two Breeds of Sheep With Different Prolificacy (Romanov and ILE-DE-France)

The prolific Romanov (R, ovulation rate = 3) and non-prolific Ile-de-France (IF, ovulation rate = 1) breeds were compared for their ovarian sensitivity to gonadotropins and IGF-I before puberty. For this purpose, the effects of in vivo immunization against GnRH on populations of ovarian follicles and in vitro sensitivity of granulosa cells to FSH and IGF-I were studied in prepuberal lambs from both breeds. Seventeen prepuberal lambs of each breed were actively immunized against GnRH between 3 wk and 6 mo of age. Relative to untreated lambs, FSH levels at 4, 5, and 6 mo of age were (respectively) 41%, 25%, and 29% for IF, and 43%, 24%, and 36% for R lambs. In a first experiment, histological analysis of ovaries was performed. Immunization treatment decreased the number of small (100–390 μm in diameter) and large size follicles (<1500 μm) in both breeds at 6 mo of age. In both breeds, gonadotropin (FSH - LH -hCG) treatment increased the number of large size follicles (<1500 μm in diameter) and induced the formation of preovulatory follicles in immunized as well as untreated lambs. The ovulation rate was less in immunized animals, but it was not different between breeds. In a second experiment, the effects of FSH and IGF-I were studied on granulosa cells from follicles between 1000 and 2000 μm in diameter. In both breeds, IGF-I increased granulosa cell proliferation, but enhanced progesterone secretion was observed only in R lambs after FSH and IGF-I stimulation. Granulosa cell response to FSH treatment was lost by immunization, whereas response to IGF-I remained unchanged in both breeds. These results indicate that long-term immunization of prepuberal lambs against GnRH reduced systemic concentrations of FSH, follicular development, and response to gonadotropins in vivo, similarly in the prolific R and the non-prolific IF breed. However, granulosa cells from R lambs had higher steroidogenic capacities and were more responsive to FSH. In addition, these results suggest that IGF-I could play an important role in regulating growth of small follicles both in immunized and non-immunized lambs.     

Pituitary and testicular responses of beef bulls to active immunization against inhibin alpha

Prepubertal crossbred beef bulls served as controls or were actively immunized against the N-terminal, 30-amino acid synthetic fragment of porcine inhibin alpha, pI alpha (1-30). Antibody titers were detected in sera (greater than 40% B/BO in sera diluted 1,000-fold) but not in rete testis fluid of 390-d-old bulls. Serum FSH and inhibin remained static during a 5-h intensive bleed; inhibin was not acutely affected by a 15-fold LH rise and a threefold FSH rise induced by exogenous GnRH. Serum FSH, but not LH or testosterone, was consistently elevated (P less than .05) in immunized bulls compared with control bulls. Neither pituitary weight, pituitary gonadotropin content nor pituitary FSH/LH ratios were affected (P greater than .10) by pI alpha(1-30) active immunization. Testicular sperm density was greater (60 x 10(6) vs 45 x 10(6) sperm/g testis; P less than .10) in immunized bulls, but testes weight, epididymides weight and total daily sperm production remained unchanged. These results suggest that inhibin is important for regulation of FSH secretion and testicular function. Immunization with suitable inhibin vaccines may improve bull fertility.     

生殖激素对禽类卵泡细胞凋亡的影响

从禽类生殖内分泌角度出发，依据近年来国内外的科学研究资料系统地综述了促性腺激素释放激素（Gonadotropin releasing hormone，GnRH）、促卵泡激素（Folicle-stimulating hormone，FSH）、雌激素（estrogen），孕激素（progestin）、促乳素（（Prolactin，PRL），褪黑素（Mel）、抑制素（Inhibin，IB）对禽类卵泡细胞凋亡的调控，为研究禽类繁殖性能及生殖毒理机制提供科学理论参考。