Normal contact and friction of rubber with model randomly rough surfaces.

We report on normal contact and friction measurements of model multicontact interfaces formed between smooth surfaces and substrates textured with a statistical distribution of spherical micro-asperities. Contacts are either formed between a rigid textured lens and a smooth rubber, or a flat textured rubber and a smooth rigid lens. Measurements of the real area of contact A versus normal load P are performed by imaging the light transmitted at the microcontacts. For both interfaces, A(P) is found to be sub-linear with a power law behavior. Comparison with two multi-asperity contact models, which extend the Greenwood-Williamson (J. Greenwood and J. Williamson, Proc. Royal Soc. London Ser. A, 295, 300 (1966)) model by taking into account the elastic interaction between asperities at different length scales, is performed, and allows their validation for the first time. We find that long range elastic interactions arising from the curvature of the nominal surfaces are the main source of the non-linearity of A(P). At a shorter range, and except for very low pressures, the pressure dependence of both density and area of microcontacts remains well described by Greenwood-Williamson's model, which neglects any interaction between asperities. In addition, in steady sliding, friction measurements reveal that the mean shear stress at the scale of the asperities is systematically larger than that found for a macroscopic contact between a smooth lens and a rubber. This suggests that frictional stresses measured at macroscopic length scales may not be simply transposed to microscopic multicontact interfaces.

Diurnal change of thyroid-stimulating hormone mRNA expression in the rat pars tuberalis.

Thyroid-stimulating hormone (TSH)-producing cells (TSH cells), which account for a large fraction of the cells in the rat pars tuberalis (PT), have been found to express MT1 melatonin receptor and mammalian clock genes at high densities. Although these findings suggest that TSH production in the rat PT is regulated by melatonin and/or the biological clock, there have been no studies focusing on the diurnal change and regulation mechanism of TSH production in the rat PT. Therefore, in the present study, we examined diurnal changes of in TSH beta and alpha-glycoprotein subunit (alpha GSU) mRNA expression and TSH immunoreactivity (-ir) in the rat PT, and also examined the relationship between melatonin and TSH production in vivo. Both TSH beta mRNA expression and alpha GSU mRNA expression in the PT showed diurnal variations: the expression levels were lowest at the light phase [Zeitgeber time (ZT)4] and high at the dark phase (ZT12 and ZT20). TSH-ir in the PT showed the lowest level at ZT4, as was found for mRNA expression. Interestingly, TSH-ir, which was confined to the Golgi apparatus at ZT4, spread to the cytoplasm, and most of the TSH cells in the PT were uniformly immunostained in the cytoplasm at ZT20. Despite the fact that chronic administration of melatonin suppressed TSH beta and alpha GSU mRNA expression, TSH-ir in the PT was significantly enhanced. These findings results clearly show that there are diurnal changes in TSH expression and accumulation in rat PT-TSH cells and suggest that these fluctuations are regulated by melatonin.

Characterization of polyol pathway in Schwann cells isolated from adult rat sciatic nerves.

To elucidate the molecular mechanisms underlying the development of diabetic neuropathy, we isolated the Schwann cells from the sciatic nerves of adult rats and characterized the polyol pathway activity. Despite the presence of aldose reductase (AR) activity, no accumulation of sorbitol was observed in the cells cultured under 30 mM glucose conditions. Increased levels of sorbitol were detected in the medium conditioned by these cells. SNK-860 (fidarestat), an inhibitor of AR, decreased the sorbitol levels at 10(-6)M, while addition of SDI-158, an inhibitor of sorbitol dehydrogenase, did not affect the level in the cells grown in high glucose. These observations suggested that sorbitol produced by AR in the isolated Schwann cells may be predominantly excreted. In contrast, a significant increase in sorbitol level was observed in cells cultured under hyperosmotic conditions with 30 mM glucose. A significant correlation was observed between sorbitol level and AR activity (r = 0.998). The increase was suppressed by addition of SNK-860, while SDI-158 augmented sorbitol accumulation in a dose-dependent manner. These results suggested that the isolated Schwann cells may not accumulate sorbitol unless the activity of AR is augmented by some as yet undetermined mechanism under high glucose conditions, such as the hyperosmotic stress induced in this study.

Changes of hepatic vitronectin levels in patients with chronic hepatitis C treated with interferon alpha.

Hepatic vitronectin expression was assessed in 27 patients with chronic hepatitis C before and after interferon alpha treatment and in 7 control patients. Before interferon therapy, vitronectin was localized in the hepatocytes and in the portal and central venous regions. A high correlation was found for the vitronectin expression level with the histological grading and staging scores in the hepatocytes as well as in the portal region. After interferon therapy, the hepatic vitronectin was significantly decreased in the sustained and transient responders, but it was not as markedly decreased in the nonresponders and the non-treated group. A good correlation was found for the vitronectin expression with the staging scores but not with the grading scores in the portal region. These findings suggest that hepatic vitronectin is influenced by interferon therapy and that it may play an important role as a hepatic adhesion molecule through the improvement of inflammation, necrosis and fibrogenesis.

Significance of tangential views in lumbar discography.

In 64 patients with 69 herniated lumbar discs, craniocaudal or caudocranial tangential views were made in addition to conventional posteroanterior (PA) and lateral views in lumbar discography. Tangential views more clearly demonstrated details of annular tears and herniated discs in comparison with conventional views. The advantages of tangential views are as follows: precise demonstration of position, width, and shape of the hernial opening (main annular tear); precise demonstration of position and shape of the herniated mass; and a topographic display of disc degeneration. Dermal radiation absorbed during tangential views is less than that of computerized tomographic (CT) scans of discography. In addition, tangential views can be readily made at any hospital. The disadvantages of tangential views are that the X-ray tube direction must be chosen for each individual depending on whether there is a cranially or caudally migrated disc herniation; there is a tendency toward decreased sharpness of the exposure, especially when there are advanced degenerative discs; and, absorbed doses of gonadal radiation are higher during caudocranial tangential views than during CT discography in women.

Osteoma of the lateral pterygoid plate of the sphenoid bone.

A rare case is reported of an osteoma protruding into the pterygomandibular space from the lateral pterygoid plate of the sphenoid bone. The procedure of the diagnosis and treatment is described. In this case, computed tomography (CT) was the most useful in making a differential diagnosis. That the pulling force of the medial pterygoid muscle might be a causative agent in the growth of this osteoma is considered.

Biosynthesis of formycin. Incorporation and distribution of labeled compounds into formycin.

1. Two carbons, carbon-2 and one of carbons-3 to -5, of lysine seemed likely to be incorporated into one of carbon of the chromophore moiety of formycin. 2. From the results of radioisotopic studies with glutamate, gamma-amino-n-butyrate or organic acids related to tricarboxylic acid cycle, the important role of glutamate in the biosynthesis of formycin was strongly suggested. 3. The incorporation of nitrogen(s) of lysine into three nitrogens, including two nitrogens of pyrazole ring, of formycin was suggested by mass spectroscopy. 4. Ribose was estimated as a direct precursor moiety of formycin, whereas the biosynthesis of ribose was shown to occur via the pathway other than hexose monophosphate shunt or glucuronate pathway. 5. In replacement culture, the salvage synthesis of formycin from its chromophore moiety was not observed and it was also evident that the chromophore moiety or pyrazofurin (pyrazomycin) inhibited the biosynthesis of formycin.

Biosynthesis of formycin. Formation of formycin from formycin B.

1. In replacement culture with a formycin-producing strain. Steptomyces sp. MA406-A-1, exogenously added formycin B was quantitatively converted to formycin and the conversion was inhibited by adding the chromophore moiety of formycin. 2. The in vitro experiments revealed that the novel enzyme(s) catalyzing the formation and formycin from asparate and formycin B, but not from formycin B monophosphate, was present in this organism. The action of the partially purified enzyme(s) was also inhibited by the chromophore moiety of formycin, whereas the moiety showed no inhibitory effect on the actions of adenylosuccinate synthetase and adenylosuccinate lyase. 3. Adenine auxotrophs lacking either adenylosuccinate synthetase or adrenylosuccinate lyase were derived from strain MA406-A-1 and these auxotrophs were found to readily convert formycin B to formycin in replacement culture. From these results, it was estimated that, under the conditions of replacement culture, formycin B would be converted to formycin in vivo by the action of novel enzyme(s) rather than by the action of enzyme system including adenylosuccinate synthetase and adenylosuccinate lyase.