Angiogenic potential of microvessel fragments established in three-dimensional collagen gels

Summary During angiogenesis, the microvasculature displays both vessel remodeling and expansion under the control of both cellular and extracellular influences. We have evaluated the role of angiogenic and angiostatic molecules on angiogenesis in anin vitro model that more appropriately duplicates the cellular and extracellular components of this process. Freshly isolated microvessel fragments from rat adipose tissue (RFMF) were cultured within three-dimensional collagen I gels. These fragments were characterized at the time of isolation and were composed of vessel segments observed in the microvasculature of fatin situ (i.e., arterioles, venules, and capillaries). Fragments also exhibited characteristic ablumenally associated cells including smooth muscle cells and pericytes. Finally, fragments were encased in an extracellular matrix composed of collagen type IV and collagen type I/III. The elongation of microvascular elements was subsequently evaluated using morphologic and immunocytochemical techniques. The proliferation, migration, and elongation of cellular elements in microvessel fragments from rat adipose tissue was dependent on initial fragment density, matrix density, and required serum. Inclusion of endothelial cell growth factors to microvessel fragments from rat adipose tissue 3-D cultures resulted in the accelerated elongation of tube structures and the expression of von Willebrand factor in cells constituting these tubes. Molecules with reported angiostatic capacity (e.g., transforming growth factor and hydrocortisone) inhibited vessel tube elongation. In vitro methods have been developed to evaluate numerous mechanisms associated with angiogenesis, including endothelial cell proliferation, migration, and phenotypic modulation. Microvascular endothelial cell fragments described in this study represent anin vitro population of cells that accurately duplicate thein vivo microcirculatory elements of fat. The proliferation of cells and elongation of microvascular elements subsequently observed in three-dimensional cultures provides anin vitro model of angiogenesis. Microvascular formation in this system results from pre-existing microvessel fragments unlike tube formation observed when cultured endothelial cells are placed in three-dimensional gels. This form of tube formation from cultured endothelium is more characteristic of vasculogenesis. Thus, the formation of microvascular elements from microvessel fragments provides the opportunity to examine the mechanisms regulating angiogenesis in anin vitro system amenable to precise experimental manipulation.     

Cellular responses to enteropathogenicEscherichia coli infection

EnteropathogenicEscherichia coli (EPEC), first described in the 1940's and 1950's, remain an important cause of severe infantile diarrhoea in many parts of the developing world. EPEC do not produce enterotoxins and are not invasive; instead their virulence depends upon exploitation of host cell signalling pathways and the host cell cytoskeleton both as a means of colonizing mucosal surfaces of the small intestine and causing diarrhoea. Following initial mucosal attachment, EPEC secrete signalling proteins and expresss a surface adhesin, intimin, to produce attaching & effacing lesions in the enterocyte brush border membrane characterised by localised destruction of brush border microvilli, intimate bacterial adhesion and cytoskeletal reorganisation and accretion beneath attached bacteria. The pathophysiology of EPEC diarrhoea is also complex and probably results from a combination of epithelial cell responses including both electrolyte secretion and structural damage.     

Long–term responses to factorial, NPK fertilizer treatment by Alaskan wet and moist tundra sedge species

At thirteen sites in northern and central Alaska, full factonal and partial factonal NPK fertilizer experiments were completed in wet and moist tundras The effects of the fertilizers on N and P concentrations in leaves, leaf mass per tiller, tilling, and flowering of the dominant sedge species ( Eriophorum vaginatum. E angustifolium, and Carex aquatilis ) were documented for 3–10 yr at each site Almost all sites showed at least some response to the fertilizer treatment, but the specific treatments and elements that caused the responses varied greatly among sites There also was no consistent difference in responses between wet and moist sites There was, however, a consistent temporal pattern to the responses observed, starting with increases in N and P concentration in leaves in the year that fertilizer was added, followed by growth and tilling responses in the second year, and increased flowering in the third year The increases in N concentration generally only appeared in the first year, while increased P concentrations were sustained for 3–4 yr Effects of fertilizer on flowering were still significant after 6 years in some cases Results are discussed in terms of the role of "nutrient limitation" arctic plant communities and detemuning their productivity following disturbance or fertilization     

Febrile Gastroenteritis Due to Salmonella thompson—Report of an Outbreak

Salmonella thompson, a common pathogen of poultry, has received scant attention as a cause of human gastroenteritis. At least 45 persons were infected with S thompson in Sacramento, California, after eating at a chicken restaurant and 38 became symptomatic. Ten required admission to hospital, and all were treated with antibiotics and improved. In 19 cases cultures of stool specimens for S thompson over a 60-day period showed slower but statistically insignificant differences in salmonellal elimination in 7 patients who received antibiotics when compared with 12 who were untreated. We report this outbreak to increase awareness of the virulence and prevalence of gastroenteritis due to S thompson.     

The effect of coenzyme A and structurally related thiols on the mammalian fatty acid synthetase

A comparison was made of the structural features of thiol compounds which can interact with the mammalian fatty acid synthetase. Three functional characteristics were examined: (i) the ability of the free thiols, at low concentrations, to satisfy the essential thiol requirement of the enzyme, (ii) the ability of the free thiols, at higher concentrations, to inhibit enzyme activity, and (iii) the ability of the malonyl esters of these thiol compounds to act as substrates for fatty acid synthesis. The relative effectiveness of the various thiols studied was identical in all three roles. Coenzyme A and N-hexanoylcysteamine were the most effective, pantetheine and N-butyrylcysteamine were less effective, and N-acetylcysteamine was totally ineffective. These results lend strong support to our hypothesis (A. Stern, B. Sedgwick, and S. Smith, 1982, J. Biol. Chem.257, 799–803) that the various effects of CoA and structurally related thiols are localized at one and the same site, namely, the site of transfer of substrates between coenzyme A ester form and enzyme-bound form.     

Parallel activities of fatty acid methyl esters and analogous phorbol diesters toward mouse lymphocytes

Linear saturated fatty acid methyl esters were comitogenic with lectins for mouse lymphocytes, the degree of comitogenicity being strongly dependent on the length of the acyl group, and maximal for methyl tetradecanoate. Lesser effects were found for analogs with 10, 12 or 16 acyl carbon atoms, whereas those with fewer than 10 or more than 16 were inactive. Analogous structure-function relationships have been described for various membrane-active and tumor-promoting phorbol diesters, where there is a similar dependence on ester acyl group length for many activities. The fatty acid esters may therefore represent simple model compounds for studying mechanistic aspects of phorbol diester activity.     

Gas exchanges by Phymatotrichum omnivorum in a closed,axenic system

Gas exchanges byPhymatotrichum omnivorum were studied in a closed, axenic system. The fungus liberated CO₂ and ethylene, and appeared to utilize N₂. Over a 44-day test period, CO₂ increased from 0.1 to 312.8 ml/liter. Oxygen decreased from 211 to 17.8 ml/liter and N₂ decreased from 789 to 669.5 ml/liter during the same period. The combined uptake of N₂ and O₂ was equal to the release of CO₂ in the ambient gas.A rapid increase in ethylene was observed 14 to 28 days after the flasks were inoculated (15 to 160 nliter/liter). Mycelial strands and sclerotial initials formed on the flask sides, but mature sclerotia did not develop.Supported in part by Cooperative Agreement 70-178 from Cotton Incorporated. A contribution of the Texas Agricultural Experiment Station.     

Inhibition of ion accumulation in maize roots by abscisic acid

Summary An inhibition of root growth, a decrease in the amount of potassium (as ⁸⁶Rb) and phosphate (³²P) accumulation by the root, and a partial depolarization of transmembrane electropotential were observed to develop with a similar time course and to a similar extent when intact maize (Zea mays L.) roots were treated with 10^-5 M abscisic acid (ABA). Potassium uptake was inhibited by ABA when excised, low-salt roots were bathed in KCl, KH₂PO₄, or K₂SO₄. ABA did not affect the ATP content of the tissues, the activity of isolated mitochondria, nor the activity of microsomal K⁺-stimulated ATPases.