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991.
The structural elucidation of six new related polyoxypregnane glycosides, gymnepregosides A (1), B (2), C (3), D (4), E (5) and F (6), together with two known compounds, from the roots of Gymnema alternifolium (Asclepiadaceae) was achieved through on a detailed study of 1H- and 13C-NMR spectral data and chemical means. The results obtained for new compounds, 1-6, show that they are (20S)-pregn-6-ene-3 beta,5 alpha,8 beta,12 beta,14 beta,17 beta,20-heptaol or sarcostin 3-O-glycosides, and all the sugars at C-3 are beta(1-->4)-linked. Some of them possessed benzoyl, cinnamoyl and tigloyl residues as the ester linkages located at C-12 and/or C-20 of the aglycon.  相似文献   
992.
Several cerebral pathologic processes thought to result from derangements in vascular autoregulatory mechanisms show reversible abnormalities on computed tomographic and magnetic resonance images. The hypertensive encephalopathies are characterized by intracranial abnormalities due to subacutely elevated blood pressure; these entities include hypertensive encephalopathy, preeclampsia and eclampsia, and cyclosporine toxicity. Imaging studies reveal symmetric confluent lesions with mild mass effect and patchy enhancement centered in the immediate subcortical white matter of the occipital lobes. The uremic encephalopathies are characterized by intracranial abnormalities due to an elevated level of blood urea nitrogen; these entities include uremia and glomerulonephritis, hemolytic-uremic syndrome, and thrombotic thrombocytopenic purpura. Imaging studies reveal multiple areas of symmetric edema in the basal ganglia; in severe cases, focal infarcts with or without hemorrhage can be seen. As radiologists become more familiar with these entities, cases can be recognized earlier in the disease process, allowing more timely initiation of appropriate therapy.  相似文献   
993.
994.
Adolescents grow at the greatest rate of any age group after infancy and accumulate 37% of their total bone mass during this growth spurt. Because maximum bone mass is acquired during adolescence, the calcium deposited during adolescence determines the risk of osteoporosis and fracture in adulthood. Bone mass is dependent on calcium intake, growth and pubertal development, exercise, and genetic and racial factors. Unfortunately, during this time of tremendous calcium need, most adolescents eat a diet that is very deficient in calcium. Girls are twice as likely to be deficient as boys (85% vs 43%). Other factors contributing to poor bone mineralization include adolescent pregnancy, anorexia nervosa, excessive exercise, and various chronic medical conditions. To avoid osteoporosis in later life, adequate dietary calcium intake should be recommended and calcium supplementation considered in all adolescent patients.  相似文献   
995.
Risk factors for early onset disease (EOD) caused by Group B streptococci (GBS) that are the foundation of prevention guidelines were identified in studies conducted in a few hospital centers. We investigated cases of EOD identified through laboratory-based active surveillance during 1991 and 1992 in a multistate population of 17 million. Ninety-nine cases were compared with 253 controls matched for hospital, date of birth and birth weight. Prematurity (< 37 weeks of gestation) was present in 28% of cases; 53% of case mothers had rupture of membranes > 12 hours; and 48% reported intrapartum fever. The incidence of EOD in each surveillance area was higher among blacks. By multivariate analysis, case mothers were more likely than controls to have rupture of membranes before labor onset (adjusted odds ratio 8.7, P < 0.001), intrapartum fever (adjusted odds ratio 11.9, P < 0.001), and history of urinary infection during pregnancy (adjusted odds ratio 4.3, P < 0.05). Young maternal age was also associated with risk of disease. Three-fourths of case mothers had intrapartum fever, < 37 weeks of gestation and/or prolonged rupture of membranes, indicators previously used to select high risk women for intrapartum chemoprophylaxis. Our findings extend data from single hospitals and suggest prenatal screening and selective intrapartum chemoprophylaxis of high-risk mothers could potentially prevent the majority of EOD in the United States.  相似文献   
996.
The solution structure and backbone dynamics of the recombinant, ferrous CO-ligated form of component IV monomeric hemoglobin from Glycera dibranchiata (GMH4CO) have been characterized by NMR spectroscopy. Distance geometry and simulated annealing calculations utilizing a total of 2550 distance and torsion angle constraints yielded an ensemble of 29 structures with an overall average backbone rmsd of 0.48 A from the average structure. Differences between the solution structure and a related crystal structure are confined to regions of lower precision in either the NMR or X-ray structure, or in regions where the amino acid sequences differ. 15N relaxation measurements at 76.0 and 60.8 MHz were analyzed with an extended model-free approach, and revealed low-frequency motions in the vicinity of the heme, concentrated in the F helix. Amide proton protection factors were obtained from H-D amide exchange measurements on 15N-labeled protein. Patterns in the backbone dynamics and protection factors were shown to correlate with regions of heterogeneity and disorder in the ensemble of NMR structures and with large crystallographic B-factors in the X-ray structures. Surprisingly, while the backbone atoms of the F helix have higher rmsds and larger measures of dynamics on the microsecond to millisecond time scale than the other helices, amide protection factors for residues in the F helix were observed to be similar to those of the other helices. This contrasts with H-D amide exchange measurements on sperm whale myoglobin which indicated low protection for the F helix (S. N. Loh and B. F. Volkman, unpublished results). These results for GMH4 suggest a model in which the F helix undergoes collective motions as a relatively rigid hydrogen-bonded unit, possibly pivoting about a central position near residue Val87.  相似文献   
997.
There has been a considerable improvement in the media available for the culture of preimplantation mouse embryos during the 40 years since mouse embryos were first cultured and successfully transferred to uterine foster mothers. Two new media, KSOM and mMTF, are becoming more commonly used. The history of the development of these media, including recent work on KSOM and mMTF, is reviewed. A major artefact in the earlier work was the two-cell block. The causes of the two-cell block and the methods by which it has been overcome are reviewed. It is concluded that even the best available media inevitably cause imbalances in the environment in which the embryos are forced to develop, because they consist of only a small subset of the compounds present in the natural environments. As a result, the embryos must adapt to these abnormal conditions if they are to survive. The implications of these conclusions on the choice of media for specific purposes are discussed.  相似文献   
998.
Knowledge of the response of cytochrome P450 1B1 (CYP1B1) to exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in both humans and rodents is limited. To improve the analysis of CYP1 proteins, specific CYP1B1 and CYP1A1 polypeptides were expressed as hexahistidine-tagged fusion proteins in Escherichia coli, purified to homogeneity and used to produce polyclonal antibodies in rabbits. Immunoblot analyses showed that these antibodies were specific and sensitive, detecting both the human and rat forms of the respective isozymes and exhibiting negligible cross-reactivity between the two known CYP1 subfamilies. We show that CYP1B1, CYP1A1 and CYP1A2 protein levels were induced in the livers of female Sprague-Dawley rats following either acute (single dose of 25 microg TCDD/kg) or chronic (125 ng TCDD/kg/day for 30 weeks) exposure to TCDD. CYP1B1 protein exhibited a dose-response to TCDD that was different from those of CYP1A1 and CYP1A2. CYP1B1 induction appeared to be less sensitive to TCDD exposure, with induction occurring at higher doses of TCDD than that required for induction of CYP1A1 or CYP1A2. Immunohistochemical analysis showed that in animals chronically exposed to TCDD (35 ng/kg/day for 30 weeks), CYP1B1 was induced only in centrilobular hepatocytes, a pattern of expression similar to that of CYP1A1 and CYP1A2. These observations of cellular co-localization of the CYP1 cytochromes in livers of TCDD-treated rats and apparent differences in both protein amounts and dose-response are indicative of both common and unique regulation of CYP1 induction.  相似文献   
999.
Evidence from both clinical studies and animal models suggests that the local anesthetic, lidocaine, is neurotoxic. However, the mechanism of lidocaine-induced toxicity is unknown. To test the hypothesis that toxicity results from a direct action of lidocaine on sensory neurons we performed in vitro histological, electrophysiological and fluorometrical experiments on isolated dorsal root ganglion (DRG) neurons from the adult rat. We observed lidocaine-induced neuronal death after a 4-min exposure of DRG neurons to lidocaine concentrations as low as 30 mM. Consistent with an excitotoxic mechanism of neurotoxicity, lidocaine depolarized DRG neurons at concentrations that induced cell death (EC50 = 14 mM). This depolarization occurred even though voltage-gated sodium currents and action potentials were blocked effectively at much lower concentrations. (EC50 values for lidocaine-induced block of tetrodotoxin-sensitive and -resistant voltage-gated sodium currents were 41 and 101 microM, respectively.) At concentrations similar to those that induced neurotoxicity and depolarization, lidocaine also induced an increase in the concentration of intracellular Ca++ ions ([Ca++]i; EC50 = 21 mM) via Ca++ influx through the plasma membrane as well as release of Ca++ from intracellular stores. Finally, lidocaine-induced neurotoxicity was attenuated significantly when lidocaine was applied in the presence of nominally Ca(++)-free bath solution to DRG neurons preloaded with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA). Our results indicate: 1) that lidocaine is neurotoxic to sensory neurons; 2) that toxicity results from a direct action on sensory neurons; and 3) that a lidocaine-induced increase in intracellular Ca++ is a mechanism of lidocaine-induced neuronal toxicity.  相似文献   
1000.
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