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 11,252 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Hypervitaminosis A and D is a potential cause of "hyena disease" in cattle, which results from premature growth-plate closure in long bones of calves. This study showed that vitamin A induced growth-plate closure if calves were given an intramuscular injection of vitamins A and D (2,000,000 IU and 300,000 IU, respectively) on the first day after birth and, in addition, vitamin A (30,000 IU/kg body weight) in a water dispersible form was added to the milk substitute daily. Gross lesions were observed in the proximal tibial growth plates of each of seven calves after 3 weeks of vitamin-A treatment. Microscopical examination showed commencing premature growth-plate closure in the proximal tibia at 2 weeks. After one week, the growth plate showed focal thinning, and there was premature endochondral ossification of columnar cartilage. Longitudinal bone growth was dramatically reduced before growth plate closure at one week (25 microns/day in a treated animal versus 136 microns/day in a control). Liver concentrations of retinol and retinyl palmitate became strikingly elevated at on week, and thereafter increased slowly until the third week. Elevation of plasma retinol and retinyl palmitate was rapid, reaching a maximum on day 10. Plasma all-trans-retinoic acid was undetectable in many samples from treated animals, but plasma concentrations of derivatives of retinoic acid (9-cis-retinoic acid, 13-cis-retinoic acid, 13-cis-4-oxoretinoic acid, and 9, 13 dicis-retinoic acid) were elevated. The vitamin-A intake required to induce growth-plate closure in calves was found to be exceedingly high. Vitamin-A toxicity must be considered as a potential cause of hyena disease, but it would seem likely that other factors also play a role.
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PMID:Vitamin (A and D)-induced premature physeal closure (hyena disease) in calves. 917 48

This experiment has clarified the ultrastructural pathology, by scanning (SEM) and transmission electron microscopy (TEM), induced by 1-naphthyl-N- methylcarbamate (carbaryl) in the gills of juvenile goldfish (Carassius auratus Linneaus). Carbaryl is a low toxicity pesticide commonly used in forestry and agriculture and for controlling aquatic weeds and crustacean predators of shellfish, and has been known to cause gill damage in fish and clams. A variety of cellular changes were observed after exposure of goldfish for 96 h to a sublethal dose of 10 mg carbaryl/l of water. SEM revealed secondary lamellar fusion, distortion, thinning, and mucus release. TEM responses included enlargement of subepithelial lymphatic spaces and mitochondrial disruption and distortion of the lamellar covering epithelium. Pillar cells became detached and chloride cells were vacuolated. Fish were able to withstand these changes in subacute experiments due to redundancy in gill surface area.
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PMID:Electron microscopic perspectives of gill pathology induced by 1-naphthyl-N-methylcarbamate in the goldfish (Carassius auratus Linnaeus). 922 46

We report on shear rheological measurements at 30&deg;C of fine oil-in-water emulsions (volume-surface average diameter < 0.5 &mgr;m) prepared at pH 6.8 with sodium caseinate as the sole emulsifier (1-6 wt%) and n -tetradecane as the dispersed phase (10, 35, or 45 vol%). Strong sensitivity of rheological behavior to total protein concentration was indicated by both steady-state viscometry and small-deformation oscillatory experiments. The behavior can be classified into three types, depending on the protein/oil ratio. (1) Emulsions containing insufficient protein for (near-) saturation protein surface coverage develop a time-dependent increase in low-stress apparent viscosity and associated shear-thinning behavior; this can be attributed to bridging flocculation. (2) Emulsions having full protein surface coverage but relatively little excess unadsorbed protein in the continuous phase are stable Newtonian liquids. (3) Emulsions containing a substantial excess of unadsorbed sodium caseinate exhibit considerable pseudoplasticity which can be attributed to depletion flocculation. Taken as a whole, the time-dependent rheological properties for this set of emulsions as a function of protein content and oil volume fraction are largely consistent with our previous results on the creaming stability and the particle gel microstructure for these same emulsion systems. In particular, the reversible flocculation of emulsion samples of high protein content is readily explicable in terms of depletion flocculation of droplets by unadsorbed protein existing in the form of approximately spherical caseinate submicelles.
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PMID:Rheology of Sodium Caseinate Stabilized Oil-in-Water Emulsions 924 Dec 17

Alpha-hydroxy acids (AHA) such as glycolic acid have recently been used extensively in cosmetic and dermatological formulas. In low concentration (2-5%) glycolic acid is believed to facilitate progressive weakening of cohesion of the intercellular material of the stratum corneum (SC), resulting in uniform exfoliation of its outermost layers (the stratum disjunctum). Since thinning of the SC as well as changes of intercellular lipids could theoretically compromise the barrier functions of the skin, we investigated the mode of AHA action on the SC to determine whether enhanced desquamation compromises the barrier structures of the SC and changes transepidermal water loss (TEWL) values. Electron microscopy of the epidermis biopsied from the volar forearm of human volunteers after 3 weeks of treatment with a 4% glycolic acid formulation twice daily was employed to evaluate 1) epidermal morphology and thickness of the SC, (2) the lamellar body and SC lipid bilayer organization, and (3) desquamative events based on degradation of desmosomes. TEWL values and SC hydration were recorded prior to and at the end of the study. Electron microscopy revealed no ultrastructural changes in the nucleated layers of the epidermis. The lamellar body (LB) secretory system in the stratum granulosum (SG), and intercellular lipid lamellae in the SC in both vehicle- and glycolic acid-treated samples were comparable to normal human SC. Within the SC, enhanced desmosomal breakdown, promoting loss of cohesion and desquamation, was restricted to the stratum disjunctum while desmosomes of the stratum compactum were unaffected. Treated areas displayed histologically, a more compact appearing SC. TEWL values remained unchanged in glycolic acid- and vehicle-treated skin. Our findings indicate that the barrier structures of the SC are not disrupted by glycolic acid formulations at the concentration used. One of the mechanism of action of AHA on the SC seemed to be a "targeted" desmosomal (corneosomal) action without compromising the barrier structures of the skin.
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PMID:Mode of action of glycolic acid on human stratum corneum: ultrastructural and functional evaluation of the epidermal barrier. 924 19

The respiratory flow of water over the gills of the cuttlefish Sepia officinalis at rest is produced by the alternate activity of the radial muscles of the mantle and the musculature of the collar flaps; mantle circular muscle fibres are not involved. Inspiration takes place as the radial fibres contract, thinning the mantle and expanding the mantle cavity. The rise in mantle cavity pressure (up to 0.15 kPa), expelling water via the siphon during expiration, is brought about by inward movement of the collar flaps and (probably) mainly by elastic recoil of the mantle connective tissue network 'wound up' by radial fibre contraction during inspiration. Sepia also shows a second respiratory pattern, in which mantle cavity pressures during expiration are greater (up to 0.25 kPa). Here, the mantle circular fibres are involved, as they are during the large pressure transients (up to 10 kPa) seen during escape jetting. Active contraction of the muscles of the collar flaps is seen in all three patterns of expulsion of water from the mantle cavity, electrical activity increasing with increasing mantle cavity pressures. Respiratory expiration in the resting squid Loligo vulgaris is probably driven as in Sepia, whereas in the resting octopus Eledone cirrhosa, the mantle circular musculature is active during expiration. The significance of these observations is discussed.
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PMID:On the respiratory flow in the cuttlefish sepia officinalis. 931 34

The Ohio State University (OSU) and the Cleveland Clinic Foundation (CCF) developed a 6 x 18 inch low velocity Rheologic Research Tunnel to do flow visualization and other experimental fluid studies, particularly on scaled-up models of cardiovascular devices, such as the CCF's Innovative Ventricular Assist System. The large test section (TS) permits detailed data to be obtained that would be inaccessible with a smaller test prototype. A particular feature of the OSU-CCF program is the use of a non-Newtonian blood analog (NNBA), so the effect of the shear-thinning behavior of blood on the local development of separation, stagnation, and flow patterns can be studied. The TS can simulate a pressure driven slit flow of 6 x 18 in., or the external flow around a vane or blade having an aspect ratio of 1. Maximum pressure is 8.5 psig, while the maximum velocity is 21.7 in/sec. The fluid supply tank has a capacity of 500 gal of NNBA and, with its associated filtration and circulation systems, can be adapted to studies of large transparent models better studied outside the TS. Using 2 pumps, flow rates of 98-610 gal/min can be provided. Instrumentation includes thermistors, a 48 port pressure scanner with pressure transducers, a data acquisition system, and a digital video camera. Dye and hydrogen bubble systems have been developed. Development of such a facility presents problems not encountered in more typical water tables or wind tunnels. These include fundamental issues such as providing a uniform flowfield; practical issues with respect to priming, operating, and obtaining data from the system; and safety considerations. For the very large volume of NNBA, a xanthan gum solution is used, whose shear-thinning behavior depends not only on concentration, but also on age and prior shear history. The lessons learned are presented, permitting others to efficiently develop systems suitable to their testing needs.
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PMID:Development of a 6 x 18 inch rheology tunnel for experimental fluid dynamics investigation. 936 Jan 20

These studies were done to determine the effects of fluoride (F) on the structure and function of the canine gastric mucosa and the possible protective effects of 16,16-dimethyl-prostaglandin E2 (dmPGE2). A portion of the stomach with its vascular supply intact was mounted in a two-compartment chamber, one side of which contained a control solution. Minor effects were caused by exposure to 1 mmol/liter F. Both 5 and 10 mmol/liter F caused marked increases in the fluxes of water and Na, K, and H ions; mucus secretion; and tissue swelling and redness. The extent of these changes did not increase appreciably upon exposure to 50 or 100 mmol/liter F. Histological findings included marked thinning of the surface cell layer, reduced uptake of PAS stain, localized exfoliation and necrosis of surface cells, acute gastritis, and edema. It was concluded that: (1) the threshold F concentration for effects on the structure and function of the gastric mucosa was approximately 1 mmol/liter; (2) the maximum or near-maximum effects were caused by 10 mmol/liter F; (3) the effects persisted for at least 6 hr after the exposure; and (4) dmPGE2 (0.5 microg/ml) did not attenuate the effects induced by F.
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PMID:Effects of fluoride on structure and function of canine gastric mucosa. 936 50

The mechanisms of three protocellular functions have been studied using molecular modeling techniques. These functions are (1) the transport of ions across membranes, (2) the formation of photoactivated proton gradient that could drive chemical synthesis in the protocell, and (3) the organization of small peptides necessary for catalytic activity. In all these processes, membranes play an essential role. The transfer of ions across the barrier formed by protocellular walls is facilitated by the formation of deep, thinning defects in the membrane. Membranes also form a barrier to charged species that allows for retaining proton gradients. These gradients can be generated by a simple transmembrane proton pump consisting of a proton source and two acceptors. The directionality of the pump is ensured by a "gate-keeping" mechanism involving a water molecule, conformational change of the primary acceptor or tautomerization of a histidine. The pump can be formed by two transmembrane helices but not one helix. They provide surfaces at which organic molecules concentrate and small peptides can organize into ordered, amphiphilic structures. In general, valuable information about the origins and evolution of protocells can be obtained from the knowledge of physical and chemical principles that govern functioning of contemporary cells.
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PMID:Molecular modeling of protocellular functions. 939 Feb 58

Coalescence of oil-in-water emulsion droplets in a simple shear flow produced by a Couette device is considered. A phase Doppler anemometer was used to measure the droplet size distribution as a function of time for shear rates ranging from 55 to 213 s-1 and for sodium chloride salt concentrations from 0.095 to 0.6 M. The initial droplet size distribution was log-normal. During the coalescence process, the size distribution was self-preserving in accordance with D. L. Swift and S. K. Friedlander's analysis [J. Colloid Sci. 19, 621 (1964)]. In the limiting case of negligible repulsive force due to the electric double layer, the calculated stability ratios, corrected for droplet polydispersity, agree well with the theoretical analyses of G. R. Zeichner and W. R. Schowalter [AIChE J. 23, 243 (1977)] and D. L. Feke and W. R. Schowalter [J. Fluid Mech. 133, 17 (1983)] for the case of solid particle aggregation. The good agreement between the stability ratios for the case of coalescence of droplets in the present study and those for aggregation of solid particles indicates that resistance to film deformation and thinning present in the case of coalescence is not important compared with the collision process. Copyright 1998 Academic Press. Copyright 1998Academic Press
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PMID:Self-Preservation of the Drop Size Distribution Function and Variation in the Stability Ratio for Rapid Coalescence of a Polydisperse Emulsion in a Simple Shear Field 946 44

Regulation of fluid flow through corneal stroma was investigated in the bullfrog. Corneal specimens were mounted by clamping their limbal sclera between the two chambers of a Ussing-type chamber. The epithelial surface was covered with Ringer's solution, while the endothelial surface was superfused with Ringer's solution at various pressures ranging from 0-60 mm Hg. At 0 mm Hg, the cornea swelled, while at 10 mm Hg the corneal thickness remained unchanged. Further elevation of the hydrostatic pressure of the endothelial superfusion solution caused a decrease in corneal thickness, suggesting that the hydrostatic pressure in the in vivo frog corneal stroma is about 10 mm Hg. At 10 mm Hg of endothelial superfusion pressure, piercing the epithelial cell layer with a 30-gauge needle caused only slight corneal swelling. Removing glucose from the epithelial perfusion solution induced a slowly progressing increase in corneal thickness. Iodoacetate did not interfere with the swelling of the pierced cornea after the removal of glucose from the epithelial perfusion solution. To examine the possibility that the interstitial fluid flows across the stroma-scleral boundary, corneal specimens having unclamped sclera were incubated in Ringer's solution containing 3 mmol/L dextran of various molecular weights ranging from 8800-162,000, and the volume of the preparation was monitored by sequential measurement of the weight. In the presence of dextran with a molecular weight higher than 70,000, the corneal volume decreased at the beginning of incubation, and after reaching the minimal volume it slowly increased, indicating that the stroma-scleral boundary is permeable to dextran of even a molecular weight of 162,000, although dextran molecules diffuse much more slowly than water, and the concentration of unfilterable solutes in the stroma is lower than 3 mmol/L. In experiments using the Ussing-type chamber at 10 mm Hg of endothelial superfusion pressure, a decrease of NaCl in the superfusing solution to 1/2 caused rapid corneal swelling followed by slow recovery. Adding NaCl to the 1/2 NaCl Ringer's solution caused a further corneal thinning in a concentration-dependent manner. The same extent of decrease in corneal thickness as induced by adding NaCl was achieved by the same concentration of glucose as of NaCl, implying that the value of the reflection coefficient of the endothelial cell layer to either Na+ or Cl- is about half that of glucose. Our results show that even a small difference in the concentration of low molecular weight solutes (e.g., Na+ and Cl-) exerts a force that draws water from the cornea.
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PMID:Regulation of fluid flow through corneal stroma in the bullfrog. 950 60


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