RESUMO
Opalized white tuff (OWT) with 40 µm average particle size and 39.3 m(2)/g specific surface area has been introduced into polyisoprene rubber (NR). Their reinforcing effects were evaluated by comparisons with those from precipitated silica (PSi). The cure characteristic, apparent activation energy of cross-link (E(ac)) and reversion (E(ar)), and mechanical properties of a variety of composites based on these rubbers were studied. This was done using vulcanization techniques, mechanical testing, and scanning electron microscopy (SEM). The results showed that OWT can greatly improve the vulcanizing process by shortening the time of optimum cure (t(c90)) and the scorch time (t(s2)) of cross-linked rubber composites, which improves production efficiency and operational security. The rubber composites filled with 50 phr of OWT were found to have good mechanical and elastomeric properties. The tensile strengths of the NR/OWT composites are close to those of NR/PSi composites, but the tear strength and modulus are not as good as the corresponding properties of those containing precipitated silica. Morphology results revealed that the OWT is poorly dispersed in the rubber matrix. According to that, the lower interactions between OWT and polyisoprene rubber macromolecules are obtained, but similar mechanical properties of NR/OWT (100/50) rubber composites compared with NR/PSi (100/50) rubber composites are resulted.
Assuntos
Butadienos/química , Resinas Compostas/química , Hemiterpenos/química , Pentanos/química , Borracha/química , Dióxido de Silício/química , Teste de Materiais , Fenômenos MecânicosRESUMO
Amyloid-beta peptide (Abeta) interacts with the vasculature to influence Abeta levels in the brain and cerebral blood flow, providing a means of amplifying the Abeta-induced cellular stress underlying neuronal dysfunction and dementia. Systemic Abeta infusion and studies in genetically manipulated mice show that Abeta interaction with receptor for advanced glycation end products (RAGE)-bearing cells in the vessel wall results in transport of Abeta across the blood-brain barrier (BBB) and expression of proinflammatory cytokines and endothelin-1 (ET-1), the latter mediating Abeta-induced vasoconstriction. Inhibition of RAGE-ligand interaction suppresses accumulation of Abeta in brain parenchyma in a mouse transgenic model. These findings suggest that vascular RAGE is a target for inhibiting pathogenic consequences of Abeta-vascular interactions, including development of cerebral amyloidosis.
Assuntos
Peptídeos beta-Amiloides/metabolismo , Barreira Hematoencefálica/fisiologia , Encéfalo/metabolismo , Receptores Imunológicos/metabolismo , Idoso , Idoso de 80 Anos ou mais , Peptídeos beta-Amiloides/farmacologia , Animais , Encéfalo/irrigação sanguínea , Circulação Cerebrovascular , Citocinas/genética , Citocinas/metabolismo , Antagonistas dos Receptores de Endotelina , Endotelina-1/efeitos dos fármacos , Endotelina-1/metabolismo , Humanos , Camundongos , Camundongos Transgênicos , Oligopeptídeos/farmacologia , Fragmentos de Peptídeos/farmacologia , Transporte Proteico/fisiologia , Receptor para Produtos Finais de Glicação Avançada , Receptor de Endotelina ARESUMO
The role of transport exchanges of neuroactive solutes across the blood-brain barrier (BBB) is increasingly recognized. To take full advantage of genetically altered mouse models of neurodegenerative disorders for BBB transport studies, we adapted a brain perfusion technique to the mouse. During a carotid brain perfusion with a medium containing sheep red blood cells and mock plasma, the physiological parameters in the arterial inflow, regional cerebral blood flow (14C-iodoantipyrine autoradiography), ultrastructural integrity of the tissue, barrier to lanthanum, brain water content, energy metabolites and lactate levels remain unchanged. Amyloid-beta peptides (Abeta) were iodinated by lactoperoxidase method. Non-oxidized mono-iodinated Abeta monomers were separated by HPLC (as confirmed by MALDI-TOF spectrometry) and used in transport measurements. Transport of intact 125I-Abeta40 across the BBB was time- and concentration-dependent in contrast to negligible 14C-inulin uptake. In 5-6 months old Alzheimer's Tg2576 mice, Abeta40 BBB transport was increased by >eight-fold compared to age-matched littermate controls, and was mediated via the receptor for advanced glycation endproducts. We conclude the present arterial brain perfusion method provides strictly controlled environment in cerebral microcirculation suitable for examining transport of rapidly and slowly penetrating molecules across the BBB in normal and transgenic mice.