促性腺激素抑制激素与生殖轴的关系

下丘脑的促性腺激素释放激素((GnRH)对调控促性腺激素释放十分重要.10年前在鸟类中首先发现了促性腺激素抑制激素(GnIH),它的鉴定提示GnRH不是唯一能直接影响垂体促性腺激素释放的下丘脑神经肤.GnIH及其同系肽广泛存在于鸟类及哺乳动物体内,GnIH在脑部与GnRH神经接触,GnIH可以直接抑制垂体促性腺激素的合成和释放,GnIH及其受体在鸟类和哺乳动物的生殖腺存在.因此GnIH可以在多个水平直接影响生殖轴:脑部、垂体、生殖腺.     

促性腺激素释放激素细胞模型研究进展

促性腺激素释放激素 (GnRH)神经元是哺乳动物中枢生殖调控体系的最终共同通路。然而 ,由于GnRH神经元在脑内数目稀少以及散在分布 ,长期以来给GnRH神经元的分离鉴定和功能研究带来了极大的困难。因此 ,科学家们一直致力于寻找理想的细胞模型。离体GnRH细胞株 (GT1)以及最近在体绿色荧光蛋白 GnRH(GnRH GFP)转基因小鼠的诞生 ,给生殖内分泌领域的研究创造了极好的条件 ,必将促进该领域的研究进程     

外源激素对雄性黄鳝性类固醇激素分泌的影响

硬骨鱼类促性腺激素(GTH)的分泌受到双重调控,即促性腺激素释放激素(GnRH)的刺激和促性腺激素释放抑制因子(GRIF)的抑制1.       

神经激肽B对哺乳动物GnRH脉冲发生器的调节

哺乳动物的生殖功能受体内状态和外部环境综合作用的影响,这种综合作用通过错综复杂的神经内分泌系统最终汇集于促性腺激素释放激素(GnRH)系统从而影响下丘脑-垂体-性腺(HPG)轴的状态。神经激肽B(NKB)目前被认为是除kisspeptin外,调控GnRH脉冲分泌的又一关键因子。大量研究证实,NKB能够影响GnRH和促黄体激素(LH)的分泌,进而影响青春期的启动和生殖功能。然而,NKB对LH分泌的影响是刺激作用还是抑制作用尚存在争论。此外,NKB如何作用于GnRH神经元的信号通路尚不清楚,性激素是否参与这一生理过程,是目前的研究热点问题之一。本文就NKB及其受体的分布、神经网络结构、NKB对GnRH脉冲发生器的作用进行了系统的阐述,并针对目前尚待解决的一些问题进行了探讨。     

奥利亚罗非鱼促性腺激素释放激素前体蛋白的克隆与表达

促性腺激素释放激素（gonadotropin—relying hormone,GnRH）是下丘脑分泌产生的神经激素,对脊椎动物生殖的调控起重要作用。为研究GnRH对性腺发育的作用,构建了GnRH cDNA的原核表达载体并进行融合表达。利用RT—PCR方法从奥利亚罗非鱼丘脑中扩增出长约400bp的目的序列GnRH基因,克隆至T载体中,经酶切鉴定和序列测定分析确认序列的正确性后将此片段克隆到表达载体pMAL—c2x中构建重组表达质粒pMAL—GnRH,并在大肠杆菌TB1中获得了高表达,目的蛋白约占菌体总蛋白的41．6％。菌体经溶菌酶裂解,制备无细胞抽提液,Amylose—sepharose柱层析后得到分子量为56kD单一条带的目的蛋白。目的蛋白经Factor Xa酶切裂解,Amylose—sepharose过柱纯化后得到纯化的GnRH前体蛋白。该研究为鱼类GnRH蛋白的控制性腺成熟和抗体制备打下了基础．是国内鱼类GnRH前体蛋白在原核细胞中成功表扶的首次报道．     

鱼类生殖内分泌学研究的进展及其在渔业生产中的应用

鱼类生殖活动的整个调节过程包括:感觉器官把外界环境的刺激(如温度、光照、降雨等)传送到脑,使下丘脑产生促性腺激素释放激素(GnRH)和促性腺激素释放的抑制因素(GRIF),激发或抑制脑垂体合成和释放促性腺激素(GtH);促性腺激素作用于性腺并促使它分泌     

青春期的内分泌调控网络

哺乳动物青春期发育受内分泌机制调控,促性腺激素释放激素(GnRH)脉冲释放增加是青春期启动的标志。这种增加依赖于GnRH神经网络中跨突触的和胶质神经元的相互作用,包括神经元及胶质兴奋性输入的增加和跨突触抑制的减少。这个调控网络的分子机制还不清楚,但应包括多级网络调控。本文将从调控青春期启动的GnRH网络的各个层次对调控因素进行综述。     

灵长类月经周期的调控

灵长类月经周期的调控与啮齿类不同,在下丘脑没有促性腺激素释放激素(GnRH)的周期性分泌中枢。排卵前促性腺激素(GTH)峰的出现无需下丘脑活动的增强和GnRH分泌的增加。GnRH对垂体GTH的周期性分泌不起控制作用,只起“允许作用”,起控制作用的是卵巢雌激素。雌二醇作用于垂体促性腺细胞的两个功能池,控制GnRH对它们的作用,完成调节GTH分泌的作用。     

芹菜素对雌性大鼠生殖轴的影响

目的：探讨芹菜素在10-9mol/L浓度时对雌性大鼠生殖功能的影响。方法：应用侧脑室注射方法观察芹菜素对雌性大鼠生殖轴激素含量的影响。在侧脑室注射后第3天取血浆,采用放免技术测定血浆中促性腺激素释放激素（GnRH）、卵泡刺激素（FSH）、黄体生成素（LH）、雌二醇（E2）、孕酮（P）的含量。结果：在给药后第3天血浆中促性腺激素释放激素（GnRH）、卵泡刺激素（FSH）、黄体生成素（LH）的含量增加而雌二醇（E2）、孕酮（P）的含量降低,差异有显著性。结论：芹菜素抑制雌二醇（E2）合成中芳香化酶的活性实现对雌二醇（E2）、孕酮（P）分泌的抑制。芹菜素通过影响雌激素受体而使下丘脑的促性腺激素释放激素（GnRH）和腺垂体的卵泡刺激素（FSH）、黄体生成素（LH）分泌增加。     

雌激素受体在垂体中的作用

垂体和性腺是生殖轴重要组成部分,两者之间的协同与制衡是动物维持正常生长发育的保证。性腺产生的雌激素可以反馈调控垂体神经内分泌活动。近年来,随着基因芯片和差异表达谱分析技术的发展,垂体内雌激素受体介导的基因调控网络不断取得进展,垂体生殖生理功能备受关注。通过综述雌激素及其受体在促性腺激素、催乳素、生长激素合成分泌中的调控作用,以及雌激素对垂体生长发育的影响,探讨雌激素受体通过垂体影响生殖过程,希望能为进一步研究雌激素及其受体的生殖生理作用开拓思路。     

Induction of estrus with intramuscular injections of GnRH or PMSG in lactating goats (Capra hircus ) primed with a progestagen during seasonal anestrus

In Experiment 1, goats in seasonal anestrus (n=154) were treated with sponges impregnated with 1 of 2 types of progestagen (MAP or FGA) followed by PMSG (400 IU im) 48 h before sponge removal. The type of progestagen used had no effect on kidding, abortion, pseudogestation, multiple births, stillbirths, number of live births per doe or gestation length. In Experiment 2, lactating goats (n=24) in seasonal anestrus were treated with progestagen sponges (MAP). At sponge removal they received one of the following treatments: 1 injection of PMSG (400 IU im), 1 injection of GnRH (125 mug im; GnRH-1), or 2 injections of GnRH (125 mug/injection im; GnRH-2) at a 48 h interval. Serum samples were taken at 6-h intervals for 96 h, starting 12 h after sponge removal. Heterologous radioimmunoassays were validated for the measurements of goat FSH, LH, E(2) and P(4). The onset of estrus (P=0.004), mean doe receptivity (P=0.0006), maximum preovulatory E(2) concentrations (P=0.0001) and LH peak concentrations (P=0.08) occurred significantly later for GnRH-1 and GnRH-2 than for PMSG treatment. The PMSG treatment induced a preovulatory LH peak in a greater number of goats (P=0.05) and gave a higher gestation rate than GnRH-1 and GnRH-2 treatments (57 vs 0 vs 12%; P=0.03). It is likely that the GnRH treatments administered did not reactivate the hypothalamo-pituitary-gonadal axis. Thus, intramuscular injections of GnRH in lactating goats primed with a progestagen were not as effective in regulating reproductive performance during seasonal anestrus as were injections of PMSG.     

Pharmacologic application of native GnRH in the winter anovulatory mare,II: Accelerating the timing of pregnancy

Onset of the winter anovulatory period in mares is associated with a marked diminution in adenohypophyseal synthesis and release of LH. Native GnRH, unlike its synthetic agonists, stimulates the synthesis and secretion of LH in mares without pituitary refractoriness. Herein we tested the hypotheses that (1) the average Julian day of pregnancy can be accelerated by up to 2 months in winter anovulatory mares treated continuously with native GnRH beginning on February 1 and (2) mares will sustain luteal function and pregnancy after treatment withdrawal. Forty-two winter anovulatory mares were stratified by age, body condition score, and size of the largest follicle across two locations in a randomized design and assigned to one of three groups (n = 14 per group): (1) Control: untreated, (2) GnRH-14: GnRH delivered subcutaneously in saline at a rate of 100 μg/h for 8 weeks (February 1–March 29) using four consecutive 14-day pumps (Alzet 2ML2), or (3) GnRH-28: GnRH delivered as in (2), but using two 28-day pumps (Alzet 2ML4). On development of a 35-mm follicle and expression of estrus, mares were bred the following day and treated with hCG. Pregnancies were confirmed using transrectal ultrasonography on Days 14, 24, 33, and 45, with blood samples collected to assess luteal function. Mares treated with GnRH (GnRH-14 and GnRH-28) did not differ reproductively in their responses and data were pooled for statistical comparisons. Mares treated with GnRH exhibited marked increases (P ≤ 0.04) in the frequency of development of a 35-mm follicle, submission rate for live cover and/or artificial insemination, ovulation, and pregnancy compared with control mares on treatment Day 56 (March 29). Interval to the first 35-mm follicle was 51.8 ± 4.9 and 19.3 ± 3.5 days (least square mean ± standard error of the mean) for control and GnRH-treated mares, respectively. Interval to pregnancy was 65.3 ± 6.7 and 28.6 ± 4.8 days (least square mean ± standard error of the mean) for control and GnRH-treated mares, respectively, excluding one GnRH-14 mare that failed to become pregnant over four cycles. By the end of the treatment period (March 29), only 21% of control mares were pregnant compared with 79% of GnRH-treated mares. Furthermore, mean serum concentrations of progesterone were similar to (GnRH-28; P = 0.26) or greater than (GnRH-14; P = 0.01) that of control mares from Day 0 to 46 postbreeding. Data illustrate that continuous administration of native GnRH is a highly efficient option for managing seasonal anovulation in mares and could be effectively used in the breeding industry if a user-friendly delivery option were available.     

Coordinate actions of arachidonic acid and protein kinase C in gonadotropin-releasing hormone-stimulated secretion of luteinizing hormone

The relative contributions of arachidonic acid and protein kinase C during GnRH-stimulated LH release were investigated in cultured rat anterior pituitary cells. Maximal or near-maximal concentrations of arachidonic acid or the phorbol ester, 12-O-tetradecanoylphorbol 13-acetate, were less effective than a maximal dose of GnRH in stimulating LH release. However, the effect of a combination of arachidonic acid and phorbol ester was equivalent with that of GnRH. The protein kinase C inhibitor, retinal, significantly reduced GnRH- and phorbol-induced, but not arachidonic acid-stimulated, LH release. The lipoxygenase inhibitors, 5,8,11,14-eicosatetraynoic acid and nordihydroguaiaretic acid, partially inhibited GnRH- and arachidonic acid-stimulated, but not phorbol-induced, LH secretion. Simultaneous addition of retinal and either lipoxygenase inhibitor completely abolished LH responses elicited by GnRH, as well as by combined treatment with arachidonic acid and the phorbol ester. These results suggest that hormone release is mediated by phospholipid-dependent mechanisms that are coordinated during the stimulation of LH secretion by GnRH.     

The effects of GnRH treatment at the time of AI and 12 days later on reproductive performance of high producing dairy cows during the warm season in northeastern Spain

It was hypothesized that gonadotropin-releasing hormone (GnRH) treatment at the time of insemination and 12 days later increases conception rates. The aim of the present study was to evaluate the effects of GnRH treatment at the time of insemination or at the time of insemination and 12 days later on reproductive performance during the warm season in high producing dairy cows. The effect of GnRH treatment on the incidence of subsequent twin pregnancies and pregnancy losses was also evaluated. Data were analyzed using logistic regression methods. Of the entire series of 1289 AI, 373 (29%) resulted in pregnancy. Three study groups were established to evaluate the effects of treatment on the conception rate: control (untreated cows, n=431), GnRH-0 (cows receiving GnRH at AI, n=429) or GnRH-0+12 (cows receiving GnRH at AI and at AI+12 days, n=429). Conception rates were 20.6% (89/431), 30.8% (132/429) and 35.4% (152/429) for animals receiving no treatment, GnRH at AI, and GnRH at AI and 12 days later, respectively. Based on the odds ratio, the probability of pregnancy was 0.80 and 0.46 times less likely for cows receiving treatment GnRH-0 and no treatment, respectively, than for cows receiving treatment GnRH-0+12 (reference). Of the 373 pregnant animals, 326 (87.4%) bore singletons and 47 (12.6%) carried twins. The effects of treatment on the dependent variables: twin pregnancy, additional corpus luteum and pregnancy loss were analyzed. Pregnancy loss between 38 and 90 days after insemination was registered in 30 (8%) cows: 17 (5.2%) in single and 13 (27.7%) in twin pregnancies. Fifty-six (15%) cows had an additional corpus luteum. No pregnancy losses were recorded in these cows. Treatment had no effect on the twin pregnancy rate. The treatment GnRH at AI and 12 days later increased the chances of an additional corpus luteum by a factor 3.7 (using the control group as reference). In conclusion, our results support the hypothesis that GnRH treatment at the time of insemination and 12 days later increases the conception rate in high producing dairy cows during the warm season. Although lower than double treatment, strong benefits were also registered following a single GnRH treatment at insemination. Under these conditions, treatment fails to affect the twin pregnancy rate yet increases the incidence of an additional corpus luteum in pregnant cows.     

Ovarian function in nutritionally induced anoestrous cows: effect of exogenous gonadotrophin-releasing hormone in vivo and effect of insulin and insulin-like growth factor I in vitro

Ovarian function of nutritionally induced anoestrus cows was evaluated in vivo (Expt 1) and in vitro (Expt 2). In Expt 1, 32 nutritionally induced anoestrous beef cows were divided into four treatment groups receiving: (1) saline infusions at one pulse every 4 h for 13 days (control); (2) 2 micrograms GnRH at one pulse every 4 h (2 micrograms infused in 1.8 ml saline over 5 min) for 13 days (GnRH-4); (3) 2 micrograms GnRH at one pulse every 1 h for 13 days (GnRH-1); and (4) continuous infusion of 2 micrograms GnRH (a total of 2 micrograms in 34 ml h-1) for 13 days (GnRH-C). On the last day of treatment, cows were killed, ovaries were removed and follicular fluid samples (n = 149) were collected. The percentage of cows with luteal activity on day 13 was significantly different (P < 0.01) among treatments (0, 25, 75 and 25% for control, GnRH-4, GnRH-1 and GnRH-C cows, respectively). Owing to the large percentage of ovulatory cows in the GnRH-1 group (n = 6), anovulatory cows (n = 2) were removed from this treatment group for statistical analysis, as were cows with luteal tissue from the GnRH-4 (n = 2) and GnRH-C (n = 2) groups. The numbers of small (1.0-4.9 mm) and medium plus large (> or = 5 mm) follicles were not affected (P > 0.10) by treatment. However, GnRH-4 cows (n = 6) had greater (P < 0.05) concentrations of oestradiol in follicular fluid than did control (n = 8) but not GnRH-1 (n = 6) or GnRH-C (n = 6) cows. Concentrations of insulin-like growth factor I were greater (P < 0.05) in the follicular fluid of GnRH-1 cows than in all other treatment groups. Concentrations of androstenedione and progesterone in follicular fluid were not affected (P > 0.10) by treatment or follicle size. The binding activity of insulin-like growth factor binding proteins was not affected by GnRH treatment. However, the binding activity of insulin-like growth factor binding protein 2, 29-32 kDa and 22 kDa insulin-like growth factor binding proteins were greater (P < 0.05) in small versus medium plus large follicles. In Expt 2, granulosa cells were collected from nutritionally anoestrous cows to determine whether ovarian cells from anoestrous cows have the capacity to respond to insulin-like growth factor I or insulin in vitro. Both insulin-like growth factor I (20 and 200 ng ml-1) and insulin (10, 100 and 1000 ng ml-1) increased (P < 0.05) granulosa cell proliferation and progesterone production. In conclusion, pulsatile infusion of 2 micrograms GnRH (every 1 or 4 h) for 13 days into nutritionally induced anoestrous cows results in increased intrafollicular oestradiol and insulin-like growth factor I concentrations and can stimulate ovulation without markedly affecting concentrations of androstenedione or progesterone, or the binding activity of insulin-like growth factor binding proteins, in follicular fluid. In addition, granulosa cells from nutritionally induced anoestrous cows have the capacity to respond to insulin-like growth factor I and insulin in vitro, indicating that the decrease in trophic factors observed with restricted feeding does not reduce the response of the ovary to insulin-like growth factor I and insulin.     

Comparison of follicular dynamics and hormone concentrations between the 7-day and 5-day CO-Synch + CIDR program in primiparous beef cows

The objectives were to compare follicular dynamics, preovulatory estradiol concentrations, and progesterone concentrations between the 7-day (7CO, n = 15) and 5-day (5CO, n = 13) CO-Synch + controlled internal drug release device (CIDR) program in primiparous suckled beef cows. On Day −7 (7CO) or Day −5 (5CO), GnRH (100 μg) was administered (GnRH-1) and a CIDR was inserted. On Day 0, hour 0, CIDR was removed and cows received PGF_2α (25 mg) at hours 0 and 12. Animals were administered GnRH (100 μg, GnRH-2) at either hour 60 (7CO) or 72 (5CO). Follicular growth and ovulation to both GnRH-1 and GnRH-2 were evaluated using ultrasonography. Concentrations of estradiol were determined in blood samples taken at hours 0, 36, 60, and 72 (5CO). Blood samples were collected on Days 5, 8, and 14 for progesterone quantification. Ovulation rate to GnRH-1 did not differ between the 7CO (11/15) and 5CO (8/13) treatments, and for all dependent variables the statistical model included treatment, ovulation to GnRH-1, and their interaction. Diameter (mm) of the ovulatory follicle did not differ between treatments (13.4 ± 0.3) but was greater (P < 0.05) in cows that responded to GnRH-1 (13.8 ± 0.3) than those did not (12.6 ± 0.6). Maximum estradiol concentrations tended (P = 0.06) to be greater in the 5CO (7.3 ± 0.5 pg/mL) than 7CO (6.1 ± 0.7 pg/mL) treatment and tended to be greater (P = 0.08) in cows that responded to GnRH-1 (7.1 ± 0.5 pg/mL) than those did not (5.6 ± 0.9 pg/mL). Three cows in the 7CO treatment failed to develop a CL after GnRH-2. There was a treatment by response to GnRH-1 interaction (P < 0.05) for progesterone concentrations. In cows that did not respond to GnRH-1 in the 7CO treatment, progesterone concentrations were less (P < 0.05) than in those that responded to GnRH-1 in the 7CO treatment and tended (P = 0.09) to be less than in cows in the 5CO treatment that did not respond to GnRH-1. In conclusion, these findings demonstrate that failure to respond to GnRH-1 is detrimental to estradiol and progesterone concentrations with a 7-day interval between GnRH-1 and PGF_2α but of little consequence when this interval is shortened to 5 days.     

Semaphorin 4D regulates gonadotropin hormone-releasing hormone-1 neuronal migration through PlexinB1-Met complex

In mammals, reproduction is dependent on specific neurons secreting the neuropeptide gonadotropin hormone–releasing hormone-1 (GnRH-1). These cells originate during embryonic development in the olfactory placode and migrate into the forebrain, where they become integral members of the hypothalamic–pituitary–gonadal axis. This migratory process is regulated by a wide range of guidance cues, which allow GnRH-1 cells to travel over long distances to reach their appropriate destinations. The Semaphorin4D (Sema4D) receptor, PlexinB1, is highly expressed in the developing olfactory placode, but its function in this context is still unknown. Here, we demonstrate that PlexinB1-deficient mice exhibit a migratory defect of GnRH-1 neurons, resulting in reduction of this cell population in the adult brain. Moreover, Sema4D promotes directional migration in GnRH-1 cells by coupling PlexinB1 with activation of the Met tyrosine kinase (hepatocyte growth factor receptor). This work identifies a function for PlexinB1 during brain development and provides evidence that Sema4D controls migration of GnRH-1 neurons.     

In vitro LH release and cAMP accumulation induced by synthetic GnRH derivatives

The LH-releasing activity of GnRH and nine synthetic GnRH derivatives was tested in pituitary monolayer cell culture prepared from female rats. D-amino acid-substituted analogs were found to be 12 to 18-fold as active as GnRH, while D-amino acid GnRH-[1-9]-ethylamide analogs showed 15 to 38-fold activity as compared to GnRH. Dehydroproline-GnRH was equipotent with the parent compound. Asp(A)6-GnRH-EA was less active than GnRH and it was a partial agonist only. All peptides stimulated intracellular cAMP content of the cultured cells at 1 hr and 4 hr of incubation. A nearly uniform 1.8 to 2-fold increase above basal cAMP could be observed with all peptides tested at their maximally active concentrations. However, no correlation could be established between the relative LH-releasing activities and cAMP-elevating potencies of the peptides. The findings suggest that cAMP may not be involved in overall LH-release by GnRH but leave the possibility open that cAMP could be involved in certain steps of mobilizing compartmentalized LH pools of pituitary gonadotrophs.