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981.
The circadian clock is a widespread cellular mechanism that underlies diverse rhythmic functions in organisms from bacteria and fungi, to plants and animals. Intense genetic analysis during recent years has uncovered many of the components and molecular mechanisms comprising these clocks. Although autoregulatory genetic networks are a consistent feature in the design of all clocks, the weight of evidence favours their independent evolutionary origins in different kingdoms. 相似文献
982.
Among individuals of many nontropical species, seasonal breeding is timed by tracking changes in the daily photoperiod. Transfer of rodents to short (< 12 h of light/day) day lengths for 6 to 14 weeks can induce regression of the testes mediated by apoptosis. After 16 to 20 weeks of short day exposure, reproductive function is "spontaneously" initiated, and testicular recrudescence is observed. The gonadal mechanisms that underlie testicular recrudescence are not fully understood. If the onset of testicular regrowth that occurs during spontaneous recrudescence reflects a down-regulation of apoptotic signals, then a decline in apoptosis should be noted concurrent with increased testis mass. This experiment sought to assess the role of apoptosis in the restoration of reproductive capacity to photoperiod-inhibited white-footed mice. Males were assigned to long (16:8 LD) or short (8:16 LD) photoperiods for 0, 14, 18, 22, 26, or 30 weeks. At each of these time points, testis mass and testosterone concentrations were assessed. In addition, apoptotic activity was measured using both in situ terminal deoxynucleotidyl transferase dNTP end labeling (TUNEL) and DNA laddering. Short photoperiod exposure induced maximal decreases in testicular parameters after 14 weeks (p < 0.05). After 26 weeks of short days, testis mass was no longer different between males housed in long days and those housed in short days. In contrast, the high incidence of apoptotic TUNEL labeling and DNA laddering observed at 14 weeks was reduced to long day values after 22 weeks of short day exposure. Together, our results establish that a decrease in testicular apoptosis coincides with testicular recrudescence in white-footed mice. The current study demonstrates a decline in the incidence of testicular cell death concomitant with changes in testis mass or length, elucidating a timeline of changes at the cellular level related to the onset of recrudescence. 相似文献
983.
Circadian variation of serum leptin in healthy and diabetic men 总被引:18,自引:0,他引:18
Kanabrocki EL Hermida RC Wright M Young RM Bremner FW Third JL Ryan MD Ayala DE Johnson M Nemchausky BA Shirazi P Scheving LE Olwin JH 《Chronobiology international》2001,18(2):273-283
Leptin, from the Greek leptos, meaning thin (in reference to its ability to reduce body fat stores), is a hormone secreted primarily by adipocytes. At one time, leptin was portrayed as a potential means of combating obesity. Recently, leptin has been identified as a potent inhibitor of bone formation, acting through the central nervous system. Since numerous studies clearly show that bone remodeling is circadian rhythmic with peak activity during sleep, it is of interest to explore circadian variability in serum leptin. Accordingly, circadian characteristics of serum leptin were examined in 7 clinically healthy men and 4 obese men with type II diabetes. Blood samples were collected for 24 h at 3 h intervals beginning at 19:00. The dark (sleep) phase of the light-dark cycle extended from 22:30 to 06:30, with brief awakening for sampling at 01:00 and 04:00. Subjects consumed general hospital meals (2400 calories) at 16:30, 07:30, and 13:30. Serum leptin levels were determined by a R&D Systems enzyme immunoassay technique. Data were analyzed by linear least-squares estimation using the population multiple components method. A statistically significant (P < .018) circadian rhythm modeled by a single 24 h cosine curve characterized the data of each group. The 24 h mean leptin level was statistically greater (P < .001) in the obese diabetic men than in the healthy men (9.47 +/- 0.66 ng/mL vs. 24.07 +/- 1.71 ng/mL, respectively). Higher leptin levels occurred between midnight and roughly 02:30, and lowest leptin levels occurred between noon and the early afternoon. The phasing of this rhythm is similar to the circadian rhythm in bone remodeling previously described. Our results suggest the findings from a single morning blood sampling for leptin may be misleading since it may underestimate the mean 24 h and peak concentrations of the hormone. 相似文献
984.
985.
Dokos S Smaill BH Young AA LeGrice IJ 《American journal of physiology. Heart and circulatory physiology》2002,283(6):H2650-H2659
We examined the shear properties of passive ventricular myocardium in six pig hearts. Samples (3 x 3 x 3 mm) were cut from adjacent regions of the lateral left ventricular midwall, with sides aligned with the principal material axes. Four cycles of sinusoidal simple shear (maximum shear displacements of 0.1-0.5) were applied separately to each specimen in two orthogonal directions. Resulting forces along the three axes were measured. Three specimens from each heart were tested in different orientations to cover all six modes of simple shear deformation. Passive myocardium has nonlinear viscoelastic shear properties with reproducible, directionally dependent softening as strain is increased. Shear properties were clearly anisotropic with respect to the three principal material directions: passive ventricular myocardium is least resistant to simple shear displacements imposed in the plane of the myocardial layers and most resistant to shear deformations that produce extension of the myocyte axis. Comparison of results for the six different shear modes suggests that simple shear deformation is resisted by elastic elements aligned with the microstructural axes of the tissue. 相似文献
986.
We determined the effect of aromatic aminoacid stimulation of the human extracellular Ca2+-sensingreceptor (CaR) on intracellular Ca2+ concentration([Ca2+]i) in single HEK-293 cells. Additionof L-phenylalanine or L-tryptophan (at 5 mM)induced [Ca2+]i oscillations from a restingstate that was quiescent at 1.8 mM extracellular Ca2+concentration ([Ca2+]e). Each[Ca2+]i peak returned to baseline values, andthe average oscillation frequency was ~1 min1 at37°C. Oscillations were not induced or sustained if the[Ca2+]e was reduced to 0.5 mM, even in thecontinued presence of amino acid. Average oscillation frequency inresponse to an increase in [Ca2+]e (from 1.8 to 2.5-5 mM) was much higher (~4 min1) than thatinduced by aromatic amino acids. Oscillations in response to[Ca2+]e were sinusoidal whereas those inducedby amino acids were transient. Thus both amino acids andCa2+, acting through the same CaR, produce oscillatoryincreases in [Ca2+]i, but the resultantoscillation pattern and frequency allow the cell to discriminate whichagonist is bound to the receptor. 相似文献
987.
A slowly growing microaerophilic Helicobacter strain was isolated from the ceca and fecal pellets of Korean wild mice (Mus musculus molossinus). This bacterial strain possessed a pair of nonsheathed bipolar flagella, was positive for urease, catalase and oxidase, and reduced nitrate to nitrite. It proved susceptible to nalidixic acid and resistant to cephalodine, and did not hydrolyze hippurate. On the basis of phenotypic characteristics and 16S rRNA gene sequence analysis, the isolate represents a new species of the genus Helicobacter, for which the name Helicobacter muricola sp. nov. is proposed; the type strain of the new species is w-06T. 相似文献
988.
Won YS Kwon HJ Oh GT Kim BH Lee CH Park YH Hyun BH Choi YK 《Microbiology and immunology》2002,46(9):629-632
Coagulase negative staphylococci (CNS) are significant pathogens, particularly in medical device related infections and in immunocompromised patients. Five CNS strains were isolated from 5 NOS2 knockout mice with dermatitis. Histologically, granulomatous dermatitis was found in the skin around the ear with epidermal ulceration. Dermal lesions included pustules, necrosis, and accumulations of neutrophils and macrophages. Isolates of the bacterial strains were identified to be Staphylococcus xylosus by the API STAPH kit and 16S-23S intergenic transcribed spacer-PCR. These results demonstrate the potential of this organism to be an opportunistic pathogen in immunocompromised mice. 相似文献
989.
Otsuki T Young DB Sasaki DT Pando MP Li J Manning A Hoekstra M Hoatlin ME Mercurio F Liu JM 《Journal of cellular biochemistry》2002,86(4):613-623
Fanconi anemia (FA), a genetic disorder predisposing to aplastic anemia and cancer, is characterized by hypersensitivity to DNA-damaging agents and oxidative stress. Five of the cloned FA proteins (FANCA, FANCC, FANCE, FANCF, FANCG) appear to be involved in a common functional pathway that is required for the monoubiquitination of a sixth gene product, FANCD2. Here, we report that FANCA associates with the IkappaB kinase (IKK) signalsome via interaction with IKK2. Components of the FANCA complex undergo rapid, stimulus-dependent changes in phosphorylation, which are blocked by kinase-inactive IKK2 (IKK2 K > M). When exposed to mitomycin C, cells expressing IKK2 K > M develop a cell cycle abnormality characteristic of FA. Thus, FANCA may function to recruit IKK2, thus providing the cell a means of rapidly responding to stress. 相似文献
990.