褪黑素调控动物生殖内分泌的研究进展

褪黑素(MLT)是松果体分泌的一种神经内分泌激素,具有参与免疫反应、调节生命活动的节律性等多种生物学功能,并与生殖内分泌息息相关。目前对于褪黑素的研究主要集中在人类的癌症和植物等方面,而关于动物生殖内分泌的研究较少,深度较浅。研究表明,褪黑素可以调控动物下丘脑-垂体-性腺轴生殖相关激素的内分泌作用,抑制或促进促性腺激素释放激素(GnRH)、促卵泡素(FSH)、促黄体素(LH)、性腺激素的分泌。而在不同物种间,褪黑素作用效果却不同。论文综述了褪黑素对促性腺激素释放激素、促卵泡素、促黄体素、性腺激素以及其他与生殖相关激素的调控,为褪黑素调控动物生殖内分泌的的研究提供参考,以期对褪黑素在动物生殖调控中的作用更深入了解。     

促性腺激素细胞的研究进展

哺乳类和鱼类的促性腺激素(GTH)细胞都是位于腺垂体,所分泌的激素有促卵泡激素(FSH)和促黄体素(LH),促卵泡激素可以促成卵细胞和精子的生成,而促黄体素可以促进孕酮和睾酮的产生,关于促性腺激素细胞的来源有三种假说,在所有的对促性腺激素细胞调节控制的因素中,最重要的是促性腺激素释放激素(GnRH)。文章从促性腺激素细胞的定位、功能、源泉细胞,以及对其调节控制等方面的研究进展作一综述,以期为在实践中加强对动物生殖规律的人工调控提供参考。     

哺乳动物下丘脑-垂体-卵巢轴的研究进展

哺乳动物的下丘脑、垂体和卵巢分泌的激素在功能上相互作用,构成一个完整的神经内分泌生殖调节体系,即下丘脑垂体卵巢轴,它在生殖活动中起着主要的调节作用。下丘脑中分布的GnRH神经元可以分泌GnRH,GnRH调节垂体中促性腺激素细胞分泌促性腺激素FSH和LH,促性腺激素作用于卵巢受体,引起雌激素和孕酮分泌并影响生殖活动。从组织学角度上研究,下丘脑垂体卵巢轴中的结构,如GnRH神经元、促性腺激素细胞、卵泡随周期性变化而呈现出不同的形态结构和分泌特点。因此,对以上各种细胞的研究是探讨其所分泌激素的基础,而下丘脑垂体卵巢轴中的各种激素的研究则是了解和控制动物繁殖机能的关键。     

GnRH脉冲对体外原代培养大鼠GTH细胞中FSHβ mRNA表达水平的影响

为了从分子水平阐述不同脉冲频率促性腺激素释放激素(GnRH)对促性腺激素(GTH)分泌促卵泡素(FSH)的影响,采用细胞体外培养技术结合荧光定量PCR技术,研究体外培养大鼠原代垂体细胞在不同脉冲频率GnRH刺激下,细胞FSHβ mRNA的变化.在相同振幅条件下,低频刺激(120 min间隔)时,FSHβ mRNA表达水...     

生殖激素在畜牧生产中的应用（综述）

实践中一般把直接作用于生殖活动，与生殖机能关系密切的激素统称为生殖激素。这些激素有的来源于生殖器官之外的组织或器官，有的则是生殖器官本身所产生的。例如，下丘脑促性腺激素释放激素，来自垂体或胎盘的促性腺激素（促卵泡素、促黄体素、孕马血清促性腹激素、绒毛膜促性腺激素等）及两性性腺所产生的激素等。基于这些生殖激素在生产中有重要应用价值，我们根据这些生殖激素的来源和生理功能以及生产实践应用实例略谈几点。1神经激素（如下丘脑分泌的释放激素、催产素等）1．1促性腺激素释放激素（CnRH）。这种激素可以引起垂体促…     

类阿片肽对山羊生殖内分泌的调节Ⅱ．吗啡和纳洛酮在体外对促性腺激素的影响

利用含早卵泡期山羊血清或中黄体期山羊血清的培养液，对山羊腺垂体细胞进行２４ｈ体外培养，并在培养液中分别加入阿片受体兴奋剂——盐酸吗啡和其拮抗剂——盐酸纳洛酮，研究了类阿片肽对山羊垂体细胞分泌促性腺激素功能的影响。结果表明，在两种培养条件下，吗啡或纳洛酮对垂体促性腺激素的分泌均无显著影响（Ｐ＞０．０５）。因而认为，在山羊，类阿片肽对垂体细胞促性腺激素的分泌无直接调节作用。     

比格犬脑垂体远侧部细胞的电镜观察

透射电镜观察表明,比格犬(Beagle)脑垂体远侧部实质中含有6种细胞,即生长激素细胞、催乳激素细胞、促甲状腺激素细胞、促性腺激素细胞、促肾上腺皮质激素细胞和滤泡—星形细胞,它们各有其超微结构特征。生长激素细胞呈圆形;胞核为圆形;分泌颗粒很多,圆形,直径约233～465nm,催乳激素细胞多呈不规则形;胞核为不规则形;分泌颗粒很多,圆形,直径约310～620nm。促甲状腺激素细胞呈圆形或卵圆形;胞核为圆形或卵圆形;分泌颗粒较少,直径约78～232nm。促肾上腺皮质激素细胞呈圆形或卵圆形;胞核为圆形或卵圆形;分泌颗粒较多,圆形,直径约155～310nm,分布于细胞周边。促性腺激素细胞呈圆形或椭圆形;胞核为圆形或椭圆形;分泌颗粒较少,呈圆形、卵圆形、杵状或不规则形,长径约155～434nm。滤泡—星形细胞呈星形或不规则形,有突起伸入相邻细胞之间;胞核为圆形或卵圆形;胞质内无分泌颗粒。     

繁殖季节蒙古母马垂体促性腺激素细胞分泌颗粒与血清FSH、LH浓度的相关性

研究证实，动物垂体FSH和LH呈脉冲式分泌，在接受适当刺激后开始释放，又能在接受另一些信息后调整分泌量或停止分泌，并且其血清FSH和LH含量随着年龄和生理状态的变化而变化上，而与垂体促性腺激素细胞数量的相关性极低；但是，在繁殖季节蒙古利亚矮种母马垂体促性腺激素细胞分泌颗粒的形态学特性是否与血清FSH和LH浓度变化存在相关性，目前尚未见有报道。为此，     

GnRH的调控机制

ＧｎＲＨ由丘脑下部合成［１］,并以脉冲方式分泌进入丘脑下部垂体门脉血系统,到达垂体前叶发挥诱导促性腺激素释放的作用。ＧｎＲＨ除对垂体ＬＨ／ＦＳＨ分泌有强大的调控作用外,还与性腺和胎盘的生殖功能有关［２,３］。１ＧｎＲＨ信号转导途径ＧｎＲＨ调节垂体ＬＨ...     

动物促性腺激素的介绍

1垂体促性腺激素垂体是重要的神经内分泌器官,可以分泌多种蛋白质激素来调节动物的生长、发育、代谢,以及生殖活动。现已发现腺垂体至少分泌7种激素,即生长激素、促肾上腺皮质素、促甲状腺素、促乳素、促卵泡素、促黄体素、粗黑色细胞素。     

Dynamics of anterior pituitary immunoreactive gonadotrophs in moulted hens supplemented with protein,symbiotic and probiotics

The present work delineates redistribution patterns of the hormone‐producing cells of the anterior pituitary, after the phase of moulting. Two hundred single comb White Leghorn hens at the end of their first production cycle (Age = 70 week) were purchased from the commercial poultry farm and were induced to moult by high‐dietary zinc (3 g/kg feed/day) after 1 week of acclimatization, at the experimental research station, Department of Physiology and Pharmacology, University of Agriculture, Faisalabad. The moulted birds were equally (n = 50) and randomly allocated to their respective groups as G1 (control; CP (Crude protein) 16%, no supplement), G2 (CP18%, no other supplement), G3 (CP16%, symbiotic at does rate of 85 mg/l in drinking water daily) and G4 (CP16%, probiotic at dose rate of 85 mg/l in drinking water daily). Ten birds were slaughtered in each group at 5% and at peak of post‐moult production stage to collect their pituitary glands. An earlier post‐moult production recovery, sustained and lengthier production span was seen in the G2 as compared to all other groups. The lowest production and an earlier production decline were seen in G1. The cell diameter and area of follicle‐stimulating hormone (FSH) and luteinizing hormone (LH) gonadotroph increased (p ≤ 0.01) in G2 and G3 as compared to G1. The FSH gonadotroph nucleus diameter and area did increase (p ≤ 0.01) in G2 and G3, while LH gonadotroph nucleus diameter and area decreased (p ≤ 0.01) in G2 and G3 as compared to G1. The increased FSH and LH gonadotroph diameter in protein and symbiotic supplemented birds is accountable for the increased egg production in these groups.     

Histologic and immunohistochemical characterization of spontaneous pituitary adenomas in fourteen cynomolgus macaques (Macaca fascicularis)

Pituitary adenomas were identified in 14 of 491 (2.9%) cynomolgus macaques evaluated from 1994 to 2004. Cases included male (8) and female (6) cynomolgus macaques ranging from 18 to 32 years of age. Seven of the pituitary adenomas caused gross enlargement of the pituitary gland that was visible on postmortem examination, whereas the remaining 7 were multifocal microadenomas identified on histologic examination. A total of 35 adenomas were identified in the 14 macaques, 6 of which were being treated for diabetes mellitus. Mean (+/- SD) pituitary weight was 0.31 +/- 0.42 g, compared with 0.07 +/- 0.02 g for 430 historical control animals (P < 0.0001). Immunohistochemical staining for follicle-stimulating hormone, luteinizing hormone, prolactin, human growth hormone, thyroid-stimulating hormone, and adrenocorticotropic hormone was applied to pituitary tissue from all cases. Immunostaining revealed 22 of 35 (62.9%) lactotroph adenomas, 5 of 35 (14.3%) plurihormonal cell adenomas, 3 of 35 (8.6%) corticotroph adenomas, 2 of 35 (5.7%) null cell adenomas, 1 of 35 (2.9%) somatotroph adenomas, 1 of 35 (2.9%) mixed corticotroph-somatotroph adenomas, 1 of 35 (2.9%) mixed lactotroph-corticotroph adenomas, 0 of 35 gonadotroph adenomas, and 0 of 35 thyrotroph adenomas. This study represents the first extensive retrospective case series performed to evaluate the histologic and immunohistochemical characteristics of pituitary adenomas in cynomolgus macaques. Our findings indicated that macaque pituitary adenomas frequently had mixed histologic appearance and hormone expression, and that, similar to human pituitary adenomas, prolactin-secreting neoplasms were the most prevalent type.     

Changes in luteinizing hormone-containing gonadotrophs after moulting induced by fasting and zinc in laying hens (Gallus domesticus)

The purpose of the present study was to investigate egg production performance, immunohistochemical (IHC) identification, localization and morphological characterization of moulted hen’s pars distalis luteinizing hormone (LH) gonadotrophs. This system has been validated for chicken LH by immunodetection of purified hormones on dot blots, western blotting and by specific labelling of cells on sagittal sections of chicken pituitaries. This study showed that egg production and egg weight increased significantly after zinc-induced moult when compared with fasting-induced moult. Luteinizing hormone-gonadotrophs are of numerous shapes and distributed throughout the adenohypophysis, with densely populated regions on the margins of pars distalis. Moulting of laying hens was associated with a significant increase in immunoreactive LH gonadotroph cell count and cell size, which peaked at the subsequent production stages. Zinc-induced moulting also caused a significant increase in LH gonadotroph cell size as compared with fasting-induced moulting. The nuclear size of LH-positive cells was distinct during decreased egg production. Our results validate the use of ovine LHβ antibodies for the IHC localization of chicken LH gonadotrophs. This technology was further applied to the characterization of the shape and morphological changes of gonadotrophs as a function of the egg production status of the birds.     

Gonadotropin-releasing hormone targeting for gonadotroph ablation: an approach to non-surgical sterilization

Surgical sterilization is the mainstay of dog and cat population control, but its use is still often limited by the costs and effort involved, especially in developing countries. An ideal non-surgical sterilant that is safe, effective, permanent, administered as a single injection and capable of being manufactured inexpensively could have a significant impact on the world-wide dog and cat overpopulation problem. One approach towards developing such an agent is the targeting of pituitary gonadotrophic cells with cytotoxic agents using gonadotropin-releasing hormone (GnRH). GnRH is a peptide that binds to high-affinity receptors selectively expressed on gonadotrophs and some types of cancers. Both small molecules and proteins have been conjugated to GnRH analogues to generate targeted cytotoxic and imaging agents. Although most of these efforts have focused on development of human cancer therapeutics, available reproductive studies in rats and dogs suggest that current compounds do not have sufficient therapeutic windows for complete gonadotroph ablation, in part owing to poor stability of peptide targeting sequences. The only reported longer-term study of gonadotroph ablation in dogs reported suppression of serum testosterone for 8 months, but endocrine function then recovered, raising important questions about the mechanism of reproductive suppression and its recovery. Although studies to date suggest that this is a potentially attractive approach to non-surgical sterilization, ideal agents are yet to be developed, and important mechanistic questions remain to be answered.     

Effect of recombinant bovine tumor necrosis factor-α on hormone release in lactating cows

Tumor necrosis factor (TNF)‐α is a powerful macrophage cytokine released during infection, circulating in the blood to produce diverse effects in the organism. We examined the effect of recombinant bovine TNF‐α (rbTNF‐α) administration on hormone release in dairy cows during early lactation. Twelve non‐pregnant Holstein cows were treated subcutaneously with rbTNF‐α (2.5 µg/kg) or saline twice (at 11.00 and 23.00 hours). At 11.00 hours the next day, the cows were given growth hormone‐releasing hormone (GHRH, 0.25 µg/kg), thyrotrophin‐releasing hormone (TRH, 1.0 µg/kg), thyroid‐stimulating hormone (TSH, 10 µg/kg) or adrenocorticotropic hormone (500 µg/head) via the jugular vein. In the growth hormone‐releasing hormone challenge, the plasma growth hormone concentration was lower in the rbTNF‐α group than in the control (saline) group. The growth hormone and TSH responses to TRH were also smaller in the rbTNF‐α group than in the control. The plasma prolactin response to TRH was not affected by the rbTNF‐α treatment. In the TSH challenge, the rbTNF‐α‐treated cows had lower responses, as measured by plasma triiodothyronine and thyroxine, than the control cows. The rbTNF‐α treatment produced an increase in the basal plasma cortisol level, but the cortisol response to adrenocorticotropic hormone was the same level in both groups. The plasma concentrations of TNF‐α and interleukin‐1β in the cows were elevated by the rbTNF‐α treatment. The milk yield was reduced by the rbTNF‐α administration during 4 days. These data demonstrate that TNF‐α alters the secretion of pituitary and thyroid hormones in lactating cows. This effect may contribute to the suppression of the lactogenic function of the mammary gland observed in cases of coliform mastitis with high circulating TNF‐α levels.     

Endocrine and body growth traits in heifers exposed to testosterone-propionate during early fetal development

This study was conducted to determine the effects of testosterone-propionate exposure during fetal development on sexual differentiation and growth rates in heifers. Ten pregnant cows were given subcutaneous injections of testosterone-propionate (250 mg/injection) every other day during d 40 to 60 of gestation. Four cows aborted after the end of testosterone treatment, while four heifers (androgenized females) and two bulls (androgenized males) were produced from the six remaining pregnant, testosterone-propionate treated cows. Calves from cows that did not receive exogenous hormone treatment were used as controls. At 8 mo of age, the androgenized heifers and control heifers and control steers were challenged with 1 mg estradiol-17 beta to induce a preovulatory luteinizing hormone (LH) surge. Two weeks later, pituitary responsiveness to exogenous luteinizing hormone releasing hormone (LHRH; 75 micrograms) was evaluated in androgenized heifers and in control heifers and control steers. To monitor growth rates, all animals were weighed at 28-d intervals from birth to 380 d of age. Androgenized females exhibited a partially masculinized phenotype as well as internal male reproductive structures. Treatment with estradiol-17 beta first depressed (P less than .05) serum LH concentrations in all animals, then induced (P less than .05) a preovulatory-like LH surge in control and androgenized females. Control steers did not (P greater than .05) exhibit a preovulatory-like LH surge following administration of estradiol-17 beta. Exogenous LHRH treatment stimulated peak LH concentrations (P less than .05) to a greater extent in control and androgenized females than in control steers.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of cortisol on luteinizing hormone release during sexual behavior in the boar.

The effect of inhibiting the rise in cortisol concentrations that occurs at copulation upon luteinizing hormone release was studied in seven adult boars. Plasma samples were collected for assay of luteinizing hormone, testosterone and cortisol on a control day and before, during and after exposure to an estrous sow. The area under the curve was used to evaluate hormone production and treatment effects were evaluated by a paired Student's t-test. The 11 beta-hydroxylase inhibitor, metyrapone, was used to suppress glucocorticoid hormone production. Cortisol concentrations increased significantly (p less than 0.05) after breeding compared to values on the control day while treatment with metyrapone prior to breeding prevented the cortisol increase (p greater than 0.05). Although luteinizing hormone production increased significantly after copulation in both breeding experiments, metyrapone pretreatment resulted in a reduction of luteinizing hormone secretion (p less than 0.05). Testosterone production was also reduced in boars pretreated with metyrapone. The results suggest that the increased levels of cortisol occurring at copulation may enhance luteinizing hormone release in boars.     

Localization of leptin and leptin receptor in the bovine adenohypophysis

The present study was carried out to detail the cellular localization of leptin (Lep) and the leptin receptor (LepR) in the bovine adenohypophysis. Lep immunoreactivity (Lep-ir) was found in about 30% of adenohypophysial cells in the gland. Immunochemistry of Lep and specific hormones using serial sections revealed that Lep-ir was present in 60.4% of somatotrophs, 15.9% of gonadotrophs, 6.5% of mammotrophs, 6.5% of thyrotrophs and 2.4% of corticotrophs. Both the common short isoform (OBRa) and the long isoform (OBRb) of LepR mRNA were expressed in the bovine adenohypophysis. LepR immunoreactivity (LepR-ir) was found in only 2.8% of the adenohypophysial cells and over 50% of LepR-ir cells were gonadotrophs, in which most of the cells were distributed in the zona tuberalis. The findings on Lep and LepR in the adenohypophysial cells indicate that Lep may regulate gonadotroph function through autocrine/paracrine pathway in the bovine adenohypophysis.