共查询到20条相似文献，搜索用时 93 毫秒
1.
Stimulation of gonadotropin release by a non-GnRH peptide sequence of the GnRH precursor 总被引：1，自引：0，他引：1
The human gonadotropin-releasing hormone (GnRH) precursor comprises the GnRH sequence followed by an extension of 59 amino acids. Basic amino acid residues in the carboxyl terminal extension may represent sites of processing to biologically active peptides. A synthetic peptide comprising the first 13 amino acids (H X Asp-Ala-Glu-Asn-Leu-Ile-Asp-Ser-Phe-Gln-Glu-Ile-Val X OH) of the 59-amino acid peptide was found to stimulate the release of gonadotropic hormones from human and baboon anterior pituitary cells in culture. The peptide did not affect thyrotropin or prolactin secretion. A GnRH antagonist did not inhibit gonadotropin stimulation by the peptide, and the peptide did not compete with GnRH for GnRH pituitary receptors, indicating that the action of the peptide is independent of the GnRH receptor. The GnRH precursor contains two distinct peptide sequences capable of stimulating gonadotropin release from human and baboon pituitary cells. 相似文献
2.
[目的]研究促性腺激素释放激素（GnRH）在青年摩杂一代水牛下丘脑-垂体-卵巢轴的免疫组化定位。[方法]采用免疫组织化学SuperPicTure^TM二步法检测5头青年摩杂一代水牛下丘脑、垂体和卵巢中GnRH的分布情况,研究GnRH在下丘脑、垂体及卵巢的分布上的联系,进而了解GnRH在下丘脑、垂体及卵巢三者之间分泌释放的途径。[结果]GnRH存在于青年摩杂一代水牛下丘脑-垂体-卵巢轴的各个环节。青年摩杂一代水牛下丘脑中各主要核团都有GnRH免疫阳性神经元的分布,尤其以视上核、视前核、室旁核分布较多。对于垂体,GnRH免疫阳性产物只存在于青年摩杂一代水牛的腺垂体中。青年摩杂一代水牛卵巢中生殖上皮细胞、颗粒细胞和黄体细胞发现有GnRH免疫阳性产物。[结论]为进一步研究GnRH在生殖中的生理和作用机制提供形态学依据,并对青年摩杂一代水牛的繁殖育种起到参考指导作用。 相似文献
3.
Homologous regulation of gonadotropin-releasing hormone receptors in cultured pituitary cells 总被引：3，自引：0，他引：3
Specific receptors for gonadotropin-releasing hormone (GnRH) in cultured rat pituitary cells were increased by subnanomolar concentrations of GnRH agonists and decreased by high concentrations of these peptides. The antagonist [D-Phe2, Pro3, D-Phe6]GnRH did not alter GnRH binding capacity and blocked the increase in sites induced by GnRH. These findings provide direct evidence for the homologous regulation of GnRH receptors by physiological concentrations of the hypothalamic peptide, an action that could mediate the cyclical and postcastration increases in GnRH receptors and responsiveness of the pituitary gonadotrophs. 相似文献
4.
During activation of visceral smooth muscle there is an increase in cytosolic-free calcium, but the source (intracellular calcium release or calcium influx), kinetics, and stoichiometry of this increase have not been determined. Here, the fluorescent indicator, quin2-acetoxymethyl ester, was used to measure directly cytosolic-free calcium during contraction of isolated stomach muscle cells induced by the two neuropeptides cholecystokinin-octapeptide and Met-enkephalin as well as acetylcholine. An increase in cytosolic-free calcium was seen that was (i) dependent on the concentration of contractile agonist, (ii) derived from intracellular sources (that is, not significantly affected by removal of ambient calcium or addition of a calcium channel blocker), and (iii) kinetically and stoichiometrically related to net calcium efflux and contraction. In contrast, the increase in cytosolic-free calcium induced by depolarizing concentrations of potassium was caused by influx of calcium through voltage-dependent calcium channels. 相似文献
5.
The plant hormone cytokinin stimulates asymmetrical division in target cells of the protonema of the moss Funaria hygrometrica, leading to bud formation. The initial division can be induced in the absence of cytokinin by the calcium ionophore A23187 in medium containing calcium. These findings suggest that increases in the concentration of intracellular calcium are essential to bud initiation. Therefore mitotic regulation by cytokinin may be due, at least in part, to the modulation of intracellular calcium ion concentration. 相似文献
6.
促性腺激素释放激素在不同品种母牛垂体中的免疫组化定位 总被引：1，自引：1，他引：0
为了掌握促性腺激素释放激素（GnRH）及其受体在不同品种母牛垂体中的变化规律,采用免疫组化SP染色法分别对广西沼泽型水牛、摩拉杂交水牛、荷斯坦奶牛、广西本地黄牛垂体中GnRH的分布表达进行对比研究。结果表明,不同品种母牛垂体中均发现有呈棕黄色或黄褐色的GnRH阳性物质存在,经Image-Pro Plus 6.0软件统计发现,摩拉杂交母水牛的GnRH免疫阳性细胞较其他3个品种的大（P〈0.05）,而平均光密度值介于荷斯坦母奶牛和广西本地母黄牛之间（P〉0.05）。在神经垂体中仅发现GnRH免疫阳性纤维,而未发现GnRH免疫阳性细胞;在腺垂体远侧部的细胞均呈GnRH免疫反应阳性,阳性物质主要分布在腺垂体远侧部嫌色细胞和嗜色细胞胞质内。说明GnRH对腺垂体激素分泌的调节可能是直接通过神经调节,而神经垂体可能只是GnRH调节过程的通路。 相似文献
7.
Prolonged Ca2+-dependent afterhyperpolarizations in hippocampal neurons of aged rats 总被引：3，自引：0，他引：3
The possibility that calcium is elevated in brain neurons during aging was examined by quantifying afterhyperpolarizations induced by spike bursts in CAl neurons of hippocampal slices from young and aged rats. The afterhyperpolarizations result from Ca2+-dependent K+ conductance increases and are blocked in medium low in Ca2+ and prolonged in medium high in Ca2+. The afterhyperpolarization and associated conductance increases were considerably prolonged in cells from aged rats, although inhibitory postsynaptic potentials did not differ with age. Since elevated intracellular Ca2+ can exert deleterious effects on neurons, the data suggest that altered Ca2+ homeostasis may play a significant role in normal brain aging. 相似文献
8.
The kinetics of calcium release by inositol 1,4,5-trisphosphate (IP3) in permeabilized rat basophilic leukemia cells were studied to obtain insight into the molecular mechanism of action of this intracellular messenger of the phosphoinositide cascade. Calcium release from intracellular storage sites was monitored with fura-2, a fluorescent indicator. The dependence of the rate of calcium release on the concentration of added IP3 in the 4 to 40 nM range showed that channel opening requires the binding of at least three molecules of IP3. Channel opening occurred in the absence of added adenosine triphosphate, indicating that IP3 acts directly on the channel or on a protein that gates it. The channels were opened by IP3 in less than 4 seconds. The highly cooperative opening of calcium channels by nanomolar concentrations of IP3 enables cells to detect and amplify very small changes in the concentration of this messenger in response to hormonal, sensory, and growth control stimuli. 相似文献
9.
Divalent cations directly affect the conductance of excised patches of rod photoreceptor membrane 总被引：2，自引：0，他引：2
Phototransduction in rod cells is likely to involve an intracellular messenger system that links the absorption of light by rhodopsin to a change in membrane conductance. The direct effect of guanosine 3',5'-monophosphate (cGMP) on excised patches of rod outer segment membrane strongly supports a role for cGMP as an intracellular messenger in phototransduction. It is reported here that magnesium and calcium directly affect the conductance of excised patches of rod membrane in the absence of cGMP and that magnesium, applied to intact rod cells, blocks a component of the cellular light response. The divalent cation-suppressed conductance in excised patches showed outward rectification and cation-selective permeability resembling those of the light-suppressed conductance measured from the intact rod cell. The divalent cation-suppressed conductance was partly blocked by a concentration of the pharmacological agent L-cis-diltiazem that blocked all of the cGMP-activated conductance. Divalent cations may act, together with cGMP, as an intracellular messenger system that mediates the light response of the rod photoreceptor cell. 相似文献
10.
Endothelin: a novel peptide in the posterior pituitary system 总被引：21，自引：0，他引：21
T Yoshizawa O Shinmi A Giaid M Yanagisawa S J Gibson S Kimura Y Uchiyama J M Polak T Masaki I Kanazawa 《Science (New York, N.Y.)》1990,247(4941):462-464
Endothelin (ET), originally characterized as a 21-residue vasoconstrictor peptide from endothelial cells, is present in the porcine spinal cord and may act as a neuropeptide. Endothelin-like immunoreactivity has now been demonstrated by immunohistochemistry in the paraventricular and supraoptic nuclear neurons and their terminals in the posterior pituitary of the pig and the rat. The presence of ET in the porcine hypothalamus was confirmed by reversed-phase high-pressure liquid chromatography and radioimmunoassay. Moreover, in situ hybridization demonstrated ET messenger RNA in porcine paraventricular nuclear neurons. Endothelin-like immunoreactive products in the posterior pituitary of the rat were depleted by water deprivation, suggesting a release of ET under physiological conditions. These findings indicate that ET is synthesized in the posterior pituitary system and may be involved in neurosecretory functions. 相似文献
11.
In this study, the direct effects of exterior abscisic acid （ABA） on both calcium distribution of mesophyll cells and cytosolic calcium concentration of guard cells were examined. The distribution of Ca^2＋ localization were observed with calcium antimonate precipitate-electromicroscopic-cyto-chemical methods after treated with ABA and pretreated with ethylene glycol-bis-（2-aminoethylether）-N,N,N＇,N＇-tetraacetic acid （EGTA）, verapamil （Vp）, and trifluoperazine （TFP）. The laser scanning confocal microscopy was used to measure the cytosolic calcium concentrations of guard cells under different treatments. The results showed that the cytosolic Ca^2＋ concentration of mesophyll ceils was induced to increase by ABA, but to decrease in both outside cell and the vacuoles within 10 rain after treatments. The cytosolic calcium concentration of guard cells was increased gradually with the lag in treatment time. However, both EGTA and TFP could inverse those effects, indicating that the increase of cytosolic calcium induced by exterior ABA was mainly caused by calcium influx. The results also showed that calmodulin could influence both the calcium distribution of mesophyll cells and calcium concentration of guard cells. It shows that calmodulin participates in the process of ABA signal transduction, but the mechanism is not known as yet. The changes both calcium distribution of mesophyll cells and calcium concentration of guard cells further proved that the variations of cytosolic Ca^2＋ concentration induced by ABA were involved in the stomatal movements of maize seedlings. 相似文献
12.
Intracellular calcium: its movement during pentylenetetrazole-induced bursting activity 总被引：1，自引：0，他引：1
The intracellular calcium concentration in the cytoplasm decreased and the calcium concentration near the cell membrane increased during bursting activity induced by pentylenetetrazole in snail neuron. Incubation in medium containing cobalt chloride or lanthanum chloride did not change this tendency, which suggests that this calcium distribution change is due to the stored calcium in the subcellular structure moving toward the cell membrane. 相似文献
13.
生物体内源性的昼夜节律使其能够预测周边环境周期性的变化,使机体的内在代谢和周边环境保持一致。在禽类卵泡的成熟、排卵和蛋的形成过程中,不同生理进程在时间上的吻合显示了机体自身以及机体与环境之间的协调统一。动物对营养物质的摄入、内分泌激素的生成、能量代谢等一系列的行为和生理过程都有生物钟参与调控。文章从光照和营养两种因素入手,综述了生物钟在神经内分泌、能量摄入和能量代谢中的调控作用,揭示了蛋鸡的排卵和产蛋机制。1.光信号通过调控生物钟影响下丘脑-垂体-性腺轴(HPG轴),从而调控机体的繁殖活动。在光信号刺激下,位于禽类视交叉上核(SCN)和松果体的中枢生物钟作用于下丘脑,使下丘脑定时性释放促性腺激素释放激素(Gn RH)和促性腺激素抑制激素(Gn IH),Gn RH和Gn IH继而作用于垂体调节释放促性腺激素-促黄体生成素(LH)和促卵泡激素(FSH),卵巢中存在的外周生物钟接受中枢的同步化信号来维持生物节律,促使禽类的卵泡成熟和定时排卵;2.除了受到HPG的神经内分泌调控之外,蛋鸡的排卵-产蛋过程还受到机体能量代谢的影响。中枢和外周的生物钟基因能够调控食欲调节系统,从而影响能量摄入;生物钟能够通过调控代谢过程中重要限速酶的表达、整合核受体和营养信号蛋白、调节代谢感受器和代谢物、影响肠道微生物等途径来调节能量代谢,影响卵黄前体物质的合成、转运和沉积;禽类松果体分泌的褪黑素可通过介导降钙素、甲状旁腺素(PTH)及雌激素分泌,节律性地调节体内钙代谢,影响蛋壳的形成。能量摄入的时间和行为、机体能量代谢和能量状态也可以通过腺苷酸活化蛋白激酶(AMPK)、过氧化物酶体增殖物激活受体α(PPARα)等一些与食欲调控和能量代谢相关的细胞因子反过来调控生物钟。营养-生物钟-能量代谢三者之间相互作用,使生物体适应环境的能力增强,能量利用达到最优。因此,通过调整进食时间和食物组分(如饲料能量水平和钙水平),能够改变能量代谢从而调节生物钟的功能。将环境(光照管理)和营养(饲喂时间、饲料配方)综合研究并加以运用,使机体生物钟成为连接外部环境信号和内部能量代谢的纽带,既能响应外界环境刺激,又能同时调控机体能量代谢进程,从而使各项生理功能得到更好地发挥,这将为蛋鸡的产蛋调控机制研究提供新的视角。 相似文献
14.
Fura-2 calcium imaging in the cricket omega neuron revealed increased intracellular free calcium ion concentration in response to simulated cricket calling songs and other sound stimuli. The time course of the increase and decrease in intracellular calcium coincided with the time course of forward masking, a time-dependent modulation of auditory sensitivity. The buffering of calcium transients with high concentrations of a kinetically fast calcium buffer eliminated the post-stimulus hyperpolarization associated with forward masking, whereas the uncaging of calcium inside the neuron produced a hyperpolarization. The results suggest that sound-stimulated intracellular calcium accumulation acts by means of a calcium-activated hyperpolarizing current to produce forward masking. These findings underscore the importance of chemical dynamics in neural computation by demonstrating a behaviorally relevant role of calcium dynamics in vivo. 相似文献
15.
Ca(2+)-induced Ca2+ release in sea urchin egg homogenates: modulation by cyclic ADP-ribose 总被引：19，自引：0，他引：19
Calcium-induced calcium release (CICR) may function widely in calcium-mediated cell signaling, but has been most thoroughly characterized in muscle cells. In a homogenate of sea urchin eggs, which display transients in the intracellular free calcium concentration ([Ca2+]i) during fertilization and anaphase, addition of Ca2+ triggered CICR. Ca2+ release was also induced by the CICR modulators ryanodine and caffeine. Responses to both Ca2+ and CICR modulators (but not Ca2+ release mediated by inositol 1,4,5-trisphosphate) were inhibited by procaine and ruthenium red, inhibitors of CICR. Intact eggs also displayed transients of [Ca2+]i when microinjected with ryanodine. Cyclic ADP-ribose, a metabolite with potent Ca(2+)-releasing properties, appears to act by way of the CICR mechanism and may thus be an endogenous modulator of CICR. A CICR mechanism is present in these nonmuscle cells as is assumed in various models of intracellular Ca2+ wave propagation. 相似文献
16.
17.
The role of sodium-calcium exchange at the sarcolemma in the release of calcium from cardiac sarcoplasmic reticulum was investigated in voltage-clamped, isolated cardiac myocytes. In the absence of calcium entry through voltage-dependent calcium channels, membrane depolarization elicited release of calcium from ryanodine-sensitive internal stores. This process was dependent on sodium entry through tetrodotoxin-sensitive sodium channels. Calcium release under these conditions was also dependent on extracellular calcium concentration, suggesting a calcium-induced trigger release mechanism that involves calcium entry into the cell by sodium-calcium exchange. This sodium current-induced calcium release mechanism may explain, in part, the positive inotropic effects of cardiac glycosides and the negative inotropic effects of a variety of antiarrhythmic drugs that interact with cardiac sodium channels. In response to a transient rise of intracellular sodium, sodium-calcium exchange may promote calcium entry into cardiac cells and trigger sarcoplasmic calcium release during physiologic action potentials. 相似文献
18.
The regulation of intracellular calcium concentration in single smooth muscle cells was investigated by simultaneously monitoring electrical events at the surface membrane and calcium concentration in the cytosol. Cytosolic calcium concentration rose rapidly during an action potential or during a voltage-clamp pulse that elicited calcium current; a train of voltage-clamp pulses caused further increases in the calcium concentration up to a limit of approximately 1 microM. The decline of the calcium concentration back to resting levels occurred at rates that varied with the calcium concentration in an apparently saturable manner. Moreover, the rate of decline at any given calcium concentration was enhanced after a higher, more prolonged increase of calcium. The process responsible for this enhancement persisted for many seconds after the calcium concentration returned to resting levels. Thus, the magnitude and duration of a calcium transient appear to regulate the subsequent calcium removal. 相似文献
19.
Yeast mating pheromone activates mammalian gonadotrophs: evolutionary conservation of a reproductive hormone? 总被引：2，自引：0，他引：2
alpha-Factor, a tridecapeptide mating pheromone of yeast (Saccharomyces cerevisiae), has extensive sequence homology with the hypothalamic decapeptide gonadotropin-releasing hormone (GnRH). Both synthetic and natural preparations of alpha-mating factor were found to bind specifically to rat pituitary GnRH receptors and to stimulate the release of luteinizing hormone from cultured gonadotrophs. The ability of the yeast pheromone to reproduce the biological actions of GnRH in the mammalian pituitary gland indicates that the structural and functional properties of GnRH-related peptides may have been highly conserved during evolution. 相似文献
20.
Angiotensin II-induced calcium mobilization in oocytes by signal transfer through gap junctions 总被引：5，自引：0，他引：5
K Sandberg M Bor H Ji A Markwick M A Millan K J Catt 《Science (New York, N.Y.)》1990,249(4966):298-301
Angiotensin II (AII) stimulates rapid increases in the concentration of cytosolic calcium in follicular oocytes from Xenopus laevis. This calcium response was not present in denuded oocytes, indicating that it is mediated by AII receptors on the adherent follicular cells. The endogenous AII receptors differed in their binding properties from mammalian AII receptors expressed on the oocyte surface after injection of rat adrenal messenger RNA. Also, the calcium responses to activation of the amphibian AII receptor, but not the expressed mammalian AII receptor, were blocked reversibly by octanol and intracellular acidification, treatments that inhibit cell coupling through gap junctions. In addition, AII increased the rate of progesterone-induced maturation. Thus, an AII-induced calcium-mobilizing signal is transferred from follicle cells to the oocyte through gap junctions and may play a physiological role in oocyte maturation. 相似文献