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许多革兰氏阴性细菌借助于细菌的分泌系统来发挥其毒性。革兰氏阴性细菌有5种类型蛋白分泌系统(Protein secretion system),即Ⅰ~Ⅴ型。其中,Ⅲ型分泌系统与细菌的致病性密切相关。Ⅲ型分泌系统广泛存在于动、植物致病菌中。在动物致病菌中,胞外菌利用Ⅲ型分泌系统黏附在宿主细胞表面,然后跨越胞膜将特异性蛋白注入宿主细胞内,而存在于空泡中的细菌也利用此系统穿越空泡膜注入蛋白质,从而来调节宿主细胞的功能。研究该分泌系统可能会发现新药的靶子,理解该分泌途径可能对于高毒性的或不稳定的成分的靶向运输等都有重要意义,Ⅲ型分泌系统正日益受到微生物学者的重视。 相似文献
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《中国预防兽医学报》2016,(12)
正蛋白分泌在调控细菌与周围环境的互相作用中起着重要的作用。革兰氏阴性菌的分泌涉及内膜和外膜的跨膜转运,已知的6种蛋白分泌系统均显示出相当可观的多样性。而革兰氏阳性菌除了部分蛋白通过其中的几种分泌系统来分泌外,其还进化、发展出了一种特殊的蛋白分泌系统,就是Ⅶ型分泌系统(TypeⅦSecretion System,简称 相似文献
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病原体在感染的过程中,不仅要努力寻找外在的基本营养物质,又要避免被宿主免疫系统清除.这些过程大多都依赖于某些特殊的蛋白质,这些蛋白质由细菌自身合成及释放,或存在于细菌表面,或释放到细菌的外环境中,或者是注入到宿主细胞内.这些蛋白质参与了细菌的各种重要生命活动,包括菌毛和鞭毛等细胞器的生物合成、营养物质的获取、对宿主细胞的毒力以及对药物抵抗力的形成等.因此,充分了解这些蛋白质从细胞内膜(IM)、细胞周质和外膜(OM)到达细菌表面的运输过程是了解宿主和病原菌之间联系的关键.分子微生物学已经揭示了革兰氏阴性细菌分泌生物学活性外蛋白的多种不同机制,目前备受关注6个分泌系统即Ⅰ,Ⅱ,Ⅲ,Ⅳ,V,Ⅵ及Ⅶ型分泌系统[1].所有的分泌系统均持有特殊的成分来介导效应蛋白穿过细菌不同的膜结构(即IM、细胞周质和OM).这些分泌途径可以分为两个主要组群:Sec依赖性和非Sec依赖性[ 2].其中Ⅱ型分泌系统(T2SS)和V型分泌系统(T5SS)用Sec转移酶和氨基端信号肽运输其效应蛋白,Ⅰ型(TlSS)、Ⅲ型(T3SS)、Ⅳ型(T4SS)和Ⅵ型(T6SS)则采用的不依赖Sec转移酶的机制.Ⅵ和Ⅶ(T7SS)型分泌系统是最近被发现的分泌系统[3-5],还不清楚T7SS的机理,但已知T6SS被认为是许多革兰氏阴性致病菌的潜在毒力决定因子,能够促进细菌病原体之间,以及细菌病原体和宿主之间的相互作用.虽然现在对其机制的研究还很缺乏,但已经在不同的动物感染模型中观察到了T6SS表型. 相似文献
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<正>细菌为了在宿主体内生存、繁殖和扩散,必须分泌一些毒力因子。革兰氏阳性细菌(G+)具有单一胞浆膜,胞浆膜外是一层由肽聚糖组成的细胞壁;革兰阴性细菌(G-)则有两层生物膜,分为内膜(胞浆膜)和外膜,内膜和外膜之间为一层肽聚糖层和外周质间隙。毒力蛋白质的分泌需要跨膜,蛋白质跨膜所依赖的分泌通路称为分泌系统[1]。截至目前,已经在细菌中发现了5种主要类型的分泌系统：Ⅰ型分泌系统(TypeⅠsecretory system,T1SS)、Ⅲ型分泌系统(TypeⅢsecretory system,T3SS)、Ⅳ型分泌系统(TypeⅣsecretory system,T4SS)、Ⅴ型分泌系统(TypeⅤsecretory system,T5SS)和Ⅵ型分泌系统(TypeⅥsecretory system,T6SS)[2-4]。 相似文献
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对五个鸭舍环境中气载内毒素浓度与气载需氧革兰氏阴性菌浓度进行了测定,并对二者之间的数量关系进行了统计分析,同时对需氧革兰氏阴性菌的成分进行了研究。在测量的鸭舍中革兰氏阴性菌菌群占优势的是肠杆菌,其中大肠杆菌最为常见。气载内毒素与气载需氧革兰氏阴性活菌含量和气载需氧活菌总数在数值上存在弱的正相关,此结果表明不能通过测定气载需氧革兰氏阴性细菌或需氧细菌总数来估计气载内毒素的含量。舍内气载内毒素的含量介于0.19~20.08103EU/m3之间;气载需氧革兰氏阴性活菌的含量介于1.69~90.37103CFU/m3之间;气载需氧活菌含量介于1.01~55.72104CFU/m3之间。 相似文献
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Abomasal secretion has been collected from Grosskopftype pouches prepared in five adult Karrakul ewes. Feeding caused a marked increase in volume, acidity and pepsin activity, whereas these factors were reduced by starvation. Both insulin-induced hypoglycaemia and electrical stimulation of the vagal nerve supply to the pouch increased the volume, total acid and pepsin secretion. It is concluded that vagal activity is an important factor in the control of abomasal secretion in sheep. 相似文献
12.
In order to interact with their host, pathogenic strains of E. coli need to secrete some virulence factors which can modify the metabolism of host cells, contributing to disease. Since E. coli is a Gram-negative bacteria, this secretion process involves the crossing of both the inner and the outer membranes. E. coli uses mainly four secretion mechanisms called type I, type II, type III and type IV secretion systems. In the type I secretion system, the secretion machinery is composed of three proteins forming a channel through the inner and outer membranes. It is a one-step mechanism. The secretion signal is present in the carboxyterminal region of the secreted protein but without proteolytic cleavage. In E. coli, the best studied type I secreted protein is haemolysin. In type II and type IV secretion systems, the crossing of the inner membrane involves the sec machinery with the cleavage of an aminoterminal signal sequence. The crossing of the outer membrane involves the formation of a pore either by other proteins (type II) or by the carboxyterminal region of the protein (type IV). The A-B toxins, such as heat labile enterotoxin, are secreted by the first mechanism and members of the IgA proteases are secreted by the second. The type III secretion system involves at least 20 proteins including cytoplasmic, inner membrane and outer membrane proteins. The originality of this system is the ability to inject secreted bacteria into the cytosol of the host cells. Such a system is found in attaching and effacing E. coli and in diffusely adhering E. coli. 相似文献
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《Domestic animal endocrinology》1997,14(1):25-38
The role of prolactin on luteal function in dogs was investigated in vivo. The function of prolactin in mid-luteal phase was compared in pregnant and nonpregnant dogs. A dopamine agonist, cabergoline, known for its prolactin secretion inhibitory effects, was injected subcutaneously at a dose of 5 μg/kg body weight in five pregnant and five nonpregnant Beagle bitches. Mean plasma prolactin and progesterone were dramatically suppressed for 4 to 5 days after injection in both groups when compared with control pregnant and non-pregnant animals, whereas no effect on luteinizing hormone (LH) secretion was observed. The decline in plasma progesterone occurred after that in prolactin, suggesting plasma progesterone was impaired by inhibition of prolactin secretion. These results confirm the luteotropic importance of prolactin in pregnant bitches, and also demonstrate its importance in luteal phase of the nonpregnant dog.Second, to demonstrate that the effects of cabergoline were mediated by prolactin inhibition and not by a direct action on the corpus luteum, concomitant administration on Day 30 of cabergoline and prolactin (375 μg IV twice daily on Days 30 and 31) or cabergoline and LH (750 μg IV twice daily on Days 30 and 31) was affected in two groups of five pregnant animals each. Results showed that only prolactin was able to reverse the negative effects of cabergoline on circulating progesterone. This confirms the indirect mode of action of the dopamine agonist, cabergoline on corpus luteum function.Third, further investigation on the precise luteotropic role of prolactin was made by IV injection of 375 μg pure canine prolactin twice daily in five pregnant bitches on Days 30 and 31, and in five pregnant bitches on Days 40 and 41. No direct stimulatory effect of prolactin on plasma progesterone secretion occurred. Nor was there a noticeable effect on plasma LH secretion. These results suggest that prolactin is unable to directly stimulate progesterone secretion by the corpus luteum of pregnancy.The results of this study suggest that prolactin is an essential luteotropin in the dog from mid-luteal phase in both pregnant and nonpregnant animals. However, it appears to act by sustaining corpus luteum lifespan and function rather than by direct stimulatory effects on progesterone secretion. 相似文献
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Bruno B. Chomel Henri-Jean Boulouis Edward B. Breitschwerdt Rickie W. Kasten Muriel Vayssier-Taussat Richard J. Birtles Jane E. Koehler Christoph Dehio 《Veterinary research》2009,40(2)
Bartonella spp. are facultative intracellular bacteria that cause characteristic host-restricted hemotropic infections in mammals and are typically transmitted by blood-sucking arthropods. In the mammalian reservoir, these bacteria initially infect a yet unrecognized primary niche, which seeds organisms into the blood stream leading to the establishment of a long-lasting intra-erythrocytic bacteremia as the hall-mark of infection. Bacterial type IV secretion systems, which are supra-molecular transporters ancestrally related to bacterial conjugation systems, represent crucial pathogenicity factors that have contributed to a radial expansion of the Bartonella lineage in nature by facilitating adaptation to unique mammalian hosts. On the molecular level, the type IV secretion system VirB/VirD4 is known to translocate a cocktail of different effector proteins into host cells, which subvert multiple cellular functions to the benefit of the infecting pathogen. Furthermore, bacterial adhesins mediate a critical, early step in the pathogenesis of the bartonellae by binding to extracellular matrix components of host cells, which leads to firm bacterial adhesion to the cell surface as a prerequisite for the efficient translocation of type IV secretion effector proteins. The best-studied adhesins in bartonellae are the orthologous trimeric autotransporter adhesins, BadA in Bartonella henselae and the Vomp family in Bartonella quintana. Genetic diversity and strain variability also appear to enhance the ability of bartonellae to invade not only specific reservoir hosts, but also accidental hosts, as shown for B. henselae. Bartonellae have been identified in many different blood-sucking arthropods, in which they are typically found to cause extracellular infections of the mid-gut epithelium. Adaptation to specific vectors and reservoirs seems to be a common strategy of bartonellae for transmission and host diversity. However, knowledge regarding arthropod specificity/restriction, the mode of transmission, and the bacterial factors involved in arthropod infection and transmission is still limited. 相似文献
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The Modulation of Gonadotrophic Hormone Action on the Ovary by Paracrine and Autocrine Factors 总被引：3，自引：0，他引：3
B. K. Campbell 《Anatomia, histologia, embryologia》1999,28(4):247-251
It has been hypothesized that the physiological basis of follicle selection is the differential expression of factors, which modulate the action of gonadotrophins on follicular cells, at key points during the process of follicle development. The aim of this research was to test this hypothesis by identifying factors that can enhance or attenuate the action of the gonadotrophins in stimulating follicle development using both in vivo and in vitro models. Experiments in vivo utilized sheep with an ovarian autotransplant to allow intra-arterial infusion of putative local factors and exposure of the ovary to high local concentrations. Experiments in vitro utilized physiological serum-free cell culture systems for both granulosa and theca cells that allow gonadotrophin-induced differentiation in vitro. The putative local factors tested included insulin-like growth factor-I (IGF-I LR3 analogue), transforming growth factor alpha (TGF alpha) or epidermal growth factor (EGF) and inhibin A. IGF-I stimulated both cellular proliferation and hormone production by both granulosa and theca cells in vitro and similarly stimulated ovarian follicle development and ovarian androgen and oestradiol secretion in vivo. Both TGF alpha and EGF stimulated granulosa and thecal cell proliferation in vitro in a dose-responsive manner and concomitantly inhibited hormone production, whereas intra-arterial infusion of TGF alpha in vivo resulted in induction of atresia in large antral follicles and an acute fall in ovarian hormone secretion. Inhibin A in vitro augmented gonadotrophin stimulated androgen and oestradiol production by thecal and granulosa cells, respectively, but had no effect on cell number. Paradoxically, intra-arterial infusion of inhibin A resulted in an acute depression in ovarian steroid secretion. This depression, however, was also associated with an acute depression in circulating FSH concentrations. In conclusion, these data provide strong support for the hypothesis that factors can modulate the action of gonadotrophins on follicular cells to augment (IGF-I, inhibin A) or inhibit (TGF alpha/EGF) granulosa and thecal cell differentiation. The challenge for the future in this area of research is to understand how these factors interact to enable one follicle to be selected from an ovulatory cohort. 相似文献
16.
胰腺外分泌功能调节的研究进展 总被引：2，自引：0，他引：2
胰腺外分泌(主要指胰液)对食物的消化、吸收起着十分重要的作用。胰液分泌紊乱会导致动物消化、吸收异常,影响动物生长发育,给生产带来很大损失。影响胰腺外分泌的因素很多,主要包括以迷走神经为主的神经调节和以激素为主的体液调节。在神经和体液综合调节下,使得胰液分泌维持在一个正常水平,确保动物的生长发育。除这些自身调节机制外,还有很多外界因素影响其分泌。健脾消食类中药因其具有健脾益气、助消化、促生长的作用,在临床应用较多。因此,有必要了解这些中药对胰腺外分泌的调节作用。文章从神经、体液及中药调节方面综述了胰腺外分泌诸因素,为进一步研究和开发健脾消食中药添加剂提供理论基础。 相似文献
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Saline solution or dexamethasone (DXM, 35 micrograms/kg bodyweight) was injected intramuscularly twice daily for four days into five ovariectomized sows and five castrated boars. Blood samples from an indwelling jugular vein catheter were taken at 15 min intervals for 12 h prior to DXM injection and on the fourth day of treatment in order to compare the effect on variables describing the pulsatile secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH). Dexamethasone treatment caused a decrease (p less than 0.05) in the number of pulsatile episodes of LH secretion in both gonadectomized boars and sows resulting in a significant decrease in mean concentrations. Follicle stimulating hormone secretion parameters appeared to be unaffected by DXM injection in both groups of animals. It is concluded that previously described differences in LH suppression in boars and sows given glucocorticoids may be attributed to the influence of gonadal hormones. 相似文献
18.
Growth hormone (GH) is essential for postnatal somatic growth, maintenance of lean tissue at maturity in domestic animals and milk production in cows. This review focuses on neuroregulation of GH secretion in domestic animals. Two hormones principally regulate the secretion of GH: growth hormone-releasing hormone (GHRH) stimulates, while somatostatin (SS) inhibits the secretion of GH. A long-standing hypothesis proposes that alternate secretion of GHRH and SS regulate episodic secretion of GH. However, measurement of GHRH and SS in hypophysial-portal blood of unanesthetized sheep and swine shows that episodic secretion of GHRH and SS do not account for all episodes of GH secreted. Furthermore, the activity of GHRH and SS neurons decreases after steers have eaten a meal offered for a 2-h period each day (meal-feeding) and this corresponds with reduced secretion of GH. Together, these data suggest that other factors also regulate the secretion of GH. Several neurotransmitters have been implicated in this regard. Thyrotropin-releasing hormone, serotonin and gamma-aminobutyric acid stimulate the secretion of GH at somatotropes. Growth hormone releasing peptide-6 overcomes feeding-induced refractoriness of somatotropes to GHRH and stimulates the secretion of GHRH. Norepinephrine reduces the activity of SS neurons and stimulates the secretion of GHRH via alpha(2)-adrenergic receptors. N-methyl-D,L-aspartate and leptin stimulate the secretion of GHRH, while neuropeptide Y stimulates the secretion of GHRH and SS. Activation of muscarinic receptors decreases the secretion of SS. Dopamine stimulates the secretion of SS via D1 receptors and inhibits the secretion of GH from somatotropes via D2 receptors. Thus, many neuroendocrine factors regulate the secretion of GH in livestock via altering secretion of GHRH and/or SS, communicating between GHRH and SS neurons, or acting independently at somatotropes to coordinate the secretion of GH. 相似文献
19.
R J Kemppainen T P Clark J L Sartin C A Zerbe 《American journal of veterinary research》1992,53(12):2355-2358
Pituitary cells, collected from five healthy dogs, were cultured and treated with various doses of ovine corticotropin-releasing hormone (CRH), arginine vasopressin (AVP), oxytocin (OT), or angiotensin II (AII) to determine which of these hypothalamic peptides affected adrenocorticotropin (ACTH) secretion. Of the 4 peptides, only CRH significantly increased ACTH secretion from cultured canine anterior pituitary cells. The lowest dose of CRH tested, 0.01 nM, significantly stimulated ACTH release. Co-addition of AVP, OT, or AII with CRH did not increase ACTH secretion beyond that caused by addition of CRH alone. Similarly, neither co-addition of AVP with OT, AVP with AII, or OT with AII significantly stimulated ACTH secretion. These results support a role for CRH in the physiologic regulation of ACTH secretion from the canine anterior pituitary, but do not support regulatory roles for AVP, OT, or AII. 相似文献
20.
This paper examines the validity of a model that is embedded in a computer-based decision support system to assess the welfare status of pregnant sows in housing and management systems. The so-called SOWEL (SOw WELfare) model was constructed using a formalized procedure to identify and weight welfare-relevant attributes of housing systems in relation to the animal's needs, and evidenced by scientific statements collected in a database. The model's predictions about welfare scores for 15 different housing systems and weighting factors for 20 attributes were compared with expert opinion, which was solicited using a written questionnaire for pig-welfare scientists. The experts identified tethering and individual housing in stalls as low welfare systems. The group of midwelfare systems contained indoor group-housing systems and an individual-housing system with additional space and substrate. The five best systems were all systems with outdoor access and the provision of some kind of substrate such as straw. The highest weighting factors were given for the attributes "social contact," "health and hygiene status," "water availability," "space per pen," "foraging and bulk," "food agonism," "rooting substrate," "social stability," and "movement comfort." The degree of concordance among the experts was reasonable for welfare scores of housing systems, but low for weighting factors of attributes. Both for welfare scores and weighting factors the model correlated significantly with expert opinion (Spearman's Rho: 0.92, P < 0.001, and 0.72, P < 0.01, respectively). The results support the validity of the model and its underlying procedure to assess farm-animal welfare in an explicit and systematic way based on available scientific knowledge. 相似文献