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101.
Age-related changes in secretion of luteinizing hormone and metabolism of hypothalamic amines in bull calves prior to puberty 总被引:1,自引:0,他引:1
Effects of age and castration on secretion of luteinizing hormone (LH) and metabolism of hypothalamic monoamines were determined in Holstein bulls. Calves were assigned to be intact or castrated and killed at 8, 12, or 24 wk of age. Animals were castrated and bled every 10 min for 6 h at 96 and 24 h prior to slaughter, respectively. The stalk median eminence (SME), medial basal (MBH), and anterior-preoptic (AHA-POA) hypothalamic regions were obtained at slaughter and assayed for norepinephrine (NE), dopamine (DA), dihydroxy-phenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5-HT), and 5-hydroxyindole-acetic acid (5-HIAA) using high performance liquid chromatography with electrochemical detection (HPLC-EC). Concentrations of LH and testosterone in plasma were determined by radioimmunoassay (RIA). In intact calves, LH pulse frequency (pulses/6 h) increased between 8 and 12 wk (1.4 vs. 3.4) and then declined (1.6 at 24 wk of age). Frequency of LH discharges did not change during the first 72 h post-castration in calves 8 (1.4 vs 1.0) and 12 (3.4 vs. 3.8) wk of age, but increased in 24-wk-old calves during this time (1.6 vs. 6.4). The amplitude of LH pulses increased with age (p less than 0.05) and after castration (p less than 0.05). There were marked regional differences in concentrations of monoamines. However, effects of age and castration on concentrations of monoamines were observed only within the SME where DA, DOPAC and NE increased significantly with age. Plasma concentrations of testosterone were correlated with concentrations of NE and DOPAC within the SME. Changes in 5-HT with age were biphasic; at each age, 5-HT increased after castration. From these data, it is concluded that 1) different mechanisms regulate LH pulse frequency and amplitude in calves as early as 8 wk of age, and 2) differences in hypothalamic metabolism of monoamines may be related to maturational changes in secretion of LH in bull calves. 相似文献
102.
Studies on the role of transferrin and endocytosis in the uptake of Fe3+ from Fe-nitrilotriacetate by mouse duodenum 总被引:2,自引:0,他引:2
R J Simpson K R Osterloh K B Raja S D Snape T J Peters 《Biochimica et biophysica acta》1986,884(1):166-171
Addition of iron-binding proteins (human serum transferrin, mouse serum transferrin, human lactoferrin) to the luminal fluid in tied-off segments of mouse intestine in vivo led to reduced 59Fe3+ absorption from 59Fe3+-nitrilotriacetate when compared to 59Fe3+-nitrilotriacetate alone. Assay of transferrin in luminal fluid from tied segments revealed only trace amounts of immunoreactivity. The levels of luminal transferrin are unaltered in chronic hypoxia where iron absorption is significantly enhanced. Studies in vitro revealed that NH4Cl, dansylcadavarine, para-chloromercuribenzoate and trinitrobenzenesulphonate have no effect on initial 59Fe3+ uptake rates from 59Fe3+-nitrilotriacetate, while N-ethylmaleimide (1 mM) caused a 40% inhibition. In vivo 59Fe3+ uptake was unaffected by preincubation of tied-off segments with colchicine (5 mM) for up to 2 h. These results suggest that receptor-mediated endocytosis of transferrin is not a significant mechanism in the uptake of luminal Fe3+ by mouse duodenum. 相似文献
103.
W H Peters P L Jansen H T Cuypers R A de Abreu H Nauta 《Biochimica et biophysica acta》1986,873(2):252-259
Evidence was found for UDPglucuronyltransferase-catalysed deconjugation of p-nitrophenol-, 4-methylumbelliferone- and phenolphthalein-glucuronides. The evidence is based on the following observations: 1, deconjugation is UDP-dependent and the reactions show Michaels-Menten kinetics with respect to UDP and glucuronide saturability; 2, UDP-glucuronic acid was identified as reaction product; 3, all studies were done in the presence of a beta-glucuronidase inhibitor; 4, induction profiles, using 3-methylcholanthrene and phenobarbital as inducing agents, were identical for conjugation and deconjugation reactions. Optimal deconjugation rates for p-nitrophenol- and 4-methylumbelliferone-glucuronides were at pH 5.1 and for phenolphthalein-glucuronide at pH 6.5. Only conjugation reactions showed latency; the corresponding deconjugation reactions were not latent. UDPglucuronyltransferase is a group of oligomeric isoenzymes with different molecular masses. The molecular masses of the isoenzyme species catalysing the forward and reverse reactions were determined by radiation-inactivation analysis. The molecular masses of the isoenzyme species mediating the catalyses of deconjugation reactions were significantly smaller than those mediating catalyses of conjugation reactions: 66 +/- 4 kDa vs. 109 +/- 7 kDa for p-nitrophenol; 82 +/- 8 kDa vs. 105 +/- 6 kDa for 4-methylumbelliferone; and 74 +/- 8 kDa vs. 159 +/- 14 kDa for phenolphthalein. This suggests that for catalyses of deconjugation reactions only part of a UDPglucuronyltransferase isoenzyme is needed, whereas for forward reactions the complete isoenzymes are required. 相似文献
104.
P M Peters J R Ortaldo M R Shalaby L P Svedersky G E Nedwin T S Bringman P E Hass B B Aggarwal R B Herberman D V Goeddel 《Journal of immunology (Baltimore, Md. : 1950)》1986,137(8):2592-2598
Highly purified populations of large granular lymphocytes (LGL) have been shown to mediate natural killer (NK) cell activity. The mechanism of target cell killing by NK cells is as yet undefined; however, it has been postulated that such killing may involve soluble cytotoxic factors produced and secreted by NK cells. The data presented show that NK-sensitive, but not NK-resistant, tumor cell lines induce highly purified populations of human LGL to produce factors with cytotoxic and/or cytostatic activities. We have identified one of these factors as tumor necrosis factor-alpha (TNF-alpha), and have shown that production of this factor is enhanced by recombinant human interferon-gamma (rHuIFN-gamma). We have also examined the role of TNF-alpha in the cytotoxic function of NK cells. The data show that although highly purified LGL populations produce low levels of TNF-alpha, the cytotoxic/cytostatic activity of this lymphokine on tumor target cells does not correlate with the cytotoxic activity of highly purified populations of LGL on tumor target cells. Furthermore, NK cell-mediated cytotoxicity is not reliably inhibited by antibodies directed against various epitopes of recombinant human TNF-alpha and/or recombinant TNF-beta (lymphotoxin) or rHuIFN-gamma. These data show that although TNF-alpha is produced by highly purified NK-containing LGL cell populations, this factor does not appear to be responsible for NK cell cytotoxicity against classical NK target cells such as Molt-4 or K562. We suggest that NK function can be attributed to a combination of factors rather than to a single factor alone, and that at least two major phenomena are involved in LGL function: the rapid cytotoxic events which lead to the cell lysis measured in classical in vitro NK assays such as against K562; and the release of factors such as TNF-alpha with cytotoxic/cytostatic activities which would inhibit the growth of invading tumor cells in vivo. 相似文献
105.
Brant J. Bassam Barry G. Rolfe Michael A. Djordjevic 《Molecular & general genetics : MGG》1986,203(1):49-57
Summary A 6.7 kb HindIII fragment from the Sym-plasmid of strain NGR234 was found to code a nodD-like gene flanked by two loci which were required for siratro host range. Transfer of the 6.7 kb fragment from NGR234 to R. trifolii strain ANU843 conferred extended host range ability to this strain on siratro plants but not to other plants normally nodulated by strain NGR234. Tn5 mutagenesis of the 6.7 kb fragment showed that insertions located into loci flanking the nodD-like gene abolished the extended host range phenotype. A hybridization probe spanning one of the host specificity loci was shown to hybridize to three specific bands in the NGR234 genome. Complementation and DNA hybridization data showed that the nodD-like gene of strain NGR234 was functionally similar to that in R. trifolii. The introduction to R. trifolii of the 6.7 kb HindIII fragment containing Tn5 insertions located in the nodD-like gene did not abolish the ability to extend the host range of R. trifolii to siratro plants. However, transfer of the 6.7 kb HindIII to R. trifolii derivatives containing Tn5 insertions into either nodA, B or C or other R. trifolii nod genes failed to confer siratro nodulation to these recipients. Reconstruction experiments showed that the 6.7 kb fragment from strain NGR234 and the 14 kb nodulation region of R. trifolii could induce the nodulation of siratro plants when introduced together into Sym-plasmid-cured Rhizobium strains. 相似文献
106.
Michael Ward Barry Wilkinson Geoffrey Turner 《Molecular & general genetics : MGG》1986,202(2):265-270
Summary An allele (oliC31) of the A. nidulans oliC gene has been cloned using homology with the equivalent gene from N. crassa. OliC31 codes for an oligomycin-resistant, triethyltin-hypersensitive form of subunit 9 of the mitochondrial ATP synthase complex. Direct selection for oligomycin-resistance was possible following transformation of A. nidulans with the oliC31 gene. The phenotypes of transformants cultured in the presence of oligomycin were indicative of the position of integration of the transforming plasmid within the genome. Subsequent recombination events involving the integrated oliC31 gene were also apparent from altered levels of resistance to oligomycin or triethyltin. This gene should prove useful as a marker for transformation of strains lacking auxotrophic lesions and in gene replacement or disruption experiments. 相似文献
107.
Summary N2-fixing cyanobacteria occur in symbiotic associations with fungi (ascomycetes) as lichens and with a few green plants. The associated cyanobacterium is always a species ofNostoc orAnabaena. Only a small number of plant genera are involved but there is a remarkable range of host diversity. Associations occur with several bryophytes (e.g.Anthoceros, Blasia, Cavicularia), a pteridophyte (Azolla), cycads (nine genera includingMacrozamia andEncephalartos) and an angiosperm (Gunnera). Except forGunnera, where the cyanobacterium penetrates the plant cells, the cyanobacteria are extracellular with specialized morphological modifications and/or structures of the host plant organs providing an environment which facilitates interaction with the prokaryote.Salient aspects of current knowledge pertaining to the establishment, perpetuation, and functioning of the individual symbioses are summarized. Where possible this includes information concerning recognition and specificity, mode(s) of infection, morphological modifications/adaptations of the host plant and a synopsis of morphological, physiological and biochemical changes common to the symbiotic cyanobacteria. The latter encompasses heterocyst frequencies, enzymes involved in ammonia assimilation, photosynthetic capability and metabolic interaction with the host.TheAzolla-Anabaena symbioses, which have potential agronomic significance as an alternative nitrogen source and maintain continuity with the endophyte through the sexual cycle, are emphasized. 相似文献
108.
Local application of K+ via micropressure-ejection, coupled with in vivo electrochemical detection, was used to study stimulated release from monoaminergic nerve terminals in the striatum of anesthetized rats and mice. K+-evoked releases were reversible, reproducible, and dose-dependent. In contrast, releases of electroactive species could not be evoked by local ejection of Na+. The magnitudes and time courses of K+-evoked releases recorded from the caudate nucleus of mice were greater than those seen in rats. Local application of nomifensine, a putative catecholamine reuptake blocker, augmented the magnitudes and time courses of K+-evoked releases. Releases were also recorded from brain regions adjacent the striatum; these signals were always smaller than those seen in the caudate nucleus and had amplitudes that showed good correspondence to the relative degree of dopaminergic input to these areas. These data, taken together with other information in the literature, suggest that this new technique is well suited for in situ studies of monoamine release and reuptake in intact animals. 相似文献
109.
gamma-Glutamyltransferase has been purified from rat kidney by a novel procedure using phenyl boronate affinity chromatography. The highly purified enzyme has been studied with respect to acceptor specificity for a number of amino acids, amino acid analogues, dipeptides and tripeptides. The acceptor activity is specific for L-amino acids. The amino acids and the majority of the essential amino acids are poor acceptors while the sulphur-containing amino acids are the best acceptors. The acceptor activity is modulated by the substitution of the amino acid side chain. Substitution of the side chain at the delta, gamma or beta positions results in a proportionally decreasing ability to act as acceptor. The carbonyl moiety of the gamma-carboxy group of the acceptor appears to be essential for acceptor activity, absence of an alpha-carboxy carbonyl group increases the Kappm of the acceptor approximately 100-fold. 相似文献
110.
Dieter Stefan Peters 《Acta biotheoretica》1985,34(2-4):157-164
A reconstruction of the anagenetic transformations from fins to tetrapod limbs is represented considering the self-evident mechanical constraints which must have limited the construction and thus the function and the transformation. 相似文献