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81.
The work-to-fracture of canine femoral bone has been measured using the technique of Tattersall and Tappin (1966). The work required to fracture a specimen in three point bending by slow crack propagation through a triangular cross section is obtained from the load-deformation curve. The area of the resulting fracture surface is measured by macrophotographic techniques, and the work-to-fracture is calculated as work per unit area. The values of fracture “toughness” measured in this way ranged from 5.36 × 103 J/m2 to 1.55 × 104 J/m2 in the samples tested with a mean of 9.03 × 103 J/m2 and a standard deviation of 3.27 × 103 J/m2. The work-to-fracture was found to vary with transverse variation in location in the femoral shaft. Scanning electron microscope photographs of the fracture surfaces indicate that the nature of the failure is similar to that of fiber reinforced composite materials. Samples which failed by catastrophic crack propagation were characterized by smooth fracture surfaces and had larger osteons than those which failed by slow crack propagation. 相似文献
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85.
Evidence for two independent pathways in the stimulation of steroidogenesis by luteinizing hormone involving chloride channels and cyclic AMP 总被引:1,自引:0,他引:1
The possible role of chloride channels in luteinizing hormone (LH) action on steroidogenesis in rat Leydig cells had been investigated. A chloride channel blocker, SITS (4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid), inhibited LH-stimulated steroidogenesis at low (less than or equal to 1 ng/ml), but not at high (100 ng/ml) LH concentrations. In addition, dibutyryl cyclic AMP- and forskolin-stimulated steroidogenesis was unaffected by SITS. The removal of extracellular chloride potentiated steroidogenesis stimulated by submaximal but not maximal doses of LH. These results suggest that at low levels of LH, steroidogenesis depends on chloride channels whereas with high levels, cyclic AMP is the mediator of LH action. 相似文献
86.
Human growth hormone-variant demonstrates a receptor binding profile distinct from that of normal pituitary growth hormone 总被引:2,自引:0,他引:2
J Ray H Okamura P A Kelly N E Cooke S A Liebhaber 《The Journal of biological chemistry》1990,265(14):7939-7944
We have recently established that the human growth hormone-variant (hGH-V) gene is functional in vivo by documenting its expression in the placenta. We have subsequently generated transformed murine cell lines stably expressing the genes for normal pituitary growth hormone (hGH-N), hGH-V, and each of two chimeric genes generated by exon 3 exchanges, hGH-NV3 and hGH-VN3. In the present study, we utilize these cell lines as sources of hormone to characterize and compare the receptor binding profiles of hGH-N with hGH-V. hGH-V was found to displace 125I-ovine prolactin bound to rat liver microsomes (lactogen binding) and to displace 125I-hGH bound to rabbit liver microsomes (somatogen binding). Therefore, hGH-V would be predicted to display both somatogenic and lactogenic bioactivity, a dual specificity previously thought to be unique to hGH-N. The concentrations of hormone necessary to displace 50% (IC50) of the 125I-hGH from somatogen receptors and 125I-ovine prolactin from lactogen receptors was expressed as a ratio, IC50 somatogen: IC50 lactogen, for each hormone tested. A 7.4-fold difference in this ratio was observed for hGH-N compared to hGH-V, suggesting significantly greater selectivity by hGH-V in binding to the somatogen receptor. The intermediate binding ratios of the hGH-NV3 and hGH-VN3 chimeric proteins confirmed the distinct receptor binding profiles of the two parent hormones and served to identify three amino acids of potential importance in defining their respective receptor binding specificities. 相似文献
87.
Morphological and biochemical alterations in reproductive tracts of neonatal female mice treated with the pesticide methoxychlor 总被引:1,自引:0,他引:1
Effects of estradiol-17 beta and the estrogenicity of different doses of the technical grade pesticide methoxychlor were compared in the vagina, uterus, and oviducts of neonatal mice. Beginning within 24 h of birth, neonates received 10 daily i.p. injections of sesame oil vehicle, 10.0 micrograms estradiol, or 0.05, 0.1, 0.5, or 1.0 mg methoxychlor. Estradiol injections induced precocious vaginal opening, complete vaginal cornification, and increased total reproductive tract weight and its DNA content. In comparison to the controls, the three highest methoxychlor doses also significantly increased the weights of the reproductive tracts and stimulated their development. The two highest doses (0.5 and 1.0 mg) also induced precocious vaginal opening and complete vaginal cornification. In addition, the same two doses produced atypical cells in the uterus and oviducts that may be indicative of early dysplasia; similar atypia were not recorded following estradiol treatments. Total DNA content in various reproductive organs increased with increased methoxychlor dosages. Dose-response changes were observed in the oviduct and uterus but not vagina. In summary, methoxychlor stimulated the development of neonatal female reproductive tracts, even at concentrations not previously reported to be biologically active. Furthermore, the higher doses induced abnormalities that were not seen following estradiol treatment; these abnormalities may represent precursors of pathological changes. 相似文献
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89.
The extracellular mucilage from Beijerinckia mobilis, a member of the Azotobacteriaceae, after removal of contaminating protein, was separated into a neutral polysaccharide (N-2, 10%); a neutral, dialysable fraction (N-1, 5%), consisting of glucose and oligosaccharides containing glucose, arabinose, and rhamnose; and an acidic polysaccharide (85%). N-2 (mol. wt, 1900) was highly branched and comprised glucopyranose, mannopyranose, and arabinofuranose residues (1:1:1). The various linkages were determined. The acid fraction was a polymer of high molecular weight composed of L-guluronic acid (65%), D-glucose (15%), and D-glycero-D-mannoheptose (20%), together with acetic and pyruvic acids. From the results of methylation, periodate oxidation, and partial hydrolysis, a branched molecule with a backbone of guluronic acid and heptose, and side chains of glucose and guluronic acid is proposed. Pyruvic acid was found to be acetal-linked to 2?5% of the heptose residues. The similarities between this polysaccharide and that from the related species Azotobacter indicum are discussed. 相似文献
90.
Actin purified from amoebae of Dictyostelium discoideum polymerizes into filaments at 24 degrees upon addition of KCl, as judged by a change in optical density at 232 nm and by electron microscopy. The rate and extent of formation of this supramolecular assembly and the optimal KCl concentrations (0.1 M) for assembly are similar to those of striated muscle actin. The apparent equilibrium constant for the monomer-polymer transition is 1.3 muM for both Dictyostelium and muscle actin. Although assembly of highly purified Dictyostelium actin monomers into individual actin filaments resembles that of muscle actin, Dictyostelium actin but not muscle actin was observed to assemble into two-dimensional nets in 10 mM CaCl2. The Dictyostelium actin also forms filament bundles which are 0.1 mum in diameter and which assemble in the presence of 5 mM MgCl2. These bundles formed from partially purified Dictyostelium actin preparations but not from highly purified preparations, suggesting that their formation may depend on the presence of another component. These actin bundles reconstituted in vitro resemble the actin-containing bundles found in situ by microscopy in many non-muscle cells. 相似文献