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(1/34186) The structlre of pili (fimbriae) of Moraxella bovis.

Cells from rough and smooth colonies of Moraxella bovis were examined by electron microscopy utilizing both shadowing and thin sectioning techniques. Pili were found on the surfaces of cells from rough but not smooth colonies. Pili had a peritrichoud distribution and appeared as delicate (6.5-8.5 nm in diameter), elongated unbranched filaments. When bacteria were sectioned pili did not contain central pores and appeared to originate from opacities on the surface of the cell wall.  (+info)

(2/34186) New perspectives on biliary atresia.

An investigation into the aetiology, diagnosis, and treatment of biliary atresia was carried out because the prognosis remains so poor.In an electron microscopical study no viral particles or viral inclusion bodies were seen, nor were any specific ultrastructural features observed. An animal experiment suggested that obstruction within the biliary tract of newborn rabbits could be produced by maternal intravenous injection of the bile acid lithocholic acid.A simple and atraumatic method of diagnosis was developed using(99) (m)Tc-labelled compounds which are excreted into bile. Two compounds, (99m)Tc-pyridoxylidene glutamate ((99m)Tc-PG) and (99m)Tc-dihydrothioctic acid ((99m)Tc-DHT) were first assessed in normal piglets and piglets with complete biliary obstruction. Intestinal imaging correlated with biliary tract patency, and the same correlation was found in jaundiced human adults, in whom the (99m)Tc-PG scan correctly determined biliary patency in 21 out of 24 cases. The (99m)Tc-PG scan compared well with liver biopsy and (131)I-Rose Bengal in the diagnosis of 11 infants with prolonged jaundice.A model of extrahepatic biliary atresia was developed in the newborn piglet so that different methods of bile drainage could be assessed. Priorities in biliary atresia lie in a better understanding of the aetiology and early diagnosis rather than in devising new bile drainage procedures.  (+info)

(3/34186) The isolation and partial characterization of the serum lipoproteins and apolipoproteins of the rainbow trout.

1. VLD (very-low-density), LD (low-density) and HD (high-density) lipoproteins were isolated from the serum of trout (Salmo gairdneri Richardson). 2. Each lipoprotein class resembled that of the human in immunological reactivity, electrophoretic behaviour and appearance in the electron microscope. Trout LD lipoprotein, however, was of greater density than human LD lipoprotein. 3. The trout lipoproteins have lipid compositions which are similar to those of the corresponding human components, except for their high contents of long-chain unsaturated fatty acids. 4. HD and LD lipoproteins were immunologically non-identical, whereas LD lipoproteins possessed antigenic determinants in common with VLD lipoproteins. 5. VLD and HD lipoproteins each contained at least seven different apoproteins, whereas LD liprotein was composed largely of a single apoprotein which resembled human apolipoprotein B. 6. At least one, and possibly three, apoprotein of trout HD lipoprotein showed features which resemble human apoprotein A-1.7. The broad similarity between the trout and human lipoprotein systems suggests that both arose from common ancestral genes early in evolutionary history.  (+info)

(4/34186) Assessment of hepatotoxic potential.

Philosophic concepts and pragmatic approaches toward improved understanding of the effect of drugs in the hepatocyte are reviewed. No set pattern of studies is advocated but rather observations are encouraged within the framework of studies that provide for varied exposure of the hepatocyte. Clinical usage should be imitated to provide earliest possible indications of toxicity in man. The need for definitive characterization through utilization of appropriate methodology derived from cross-fertilization of related disciplines is stressed. Both minimal and maximal dose effects should be established. Selected use of electron microscopy has become essential for characterizing responses of the liver to injury. The advantages of the toluidine blue-stained Epon "thick" sections are emphasized. Such observations are used to implement the utility of serial biopsies from the beagle dog prior to and during long-term study of potential hepatic injury. Examples of the critical effects of drug concentration within the hepatocyte are presented.  (+info)

(5/34186) Four dimers of lambda repressor bound to two suitably spaced pairs of lambda operators form octamers and DNA loops over large distances.

Transcription factors that are bound specifically to DNA often interact with each other over thousands of base pairs [1] [2]. Large DNA loops resulting from such interactions have been observed in Escherichia coli with the transcription factors deoR [3] and NtrC [4], but such interactions are not, as yet, well understood. We propose that unique protein complexes, that are not present in solution, may form specifically on DNA. Their uniqueness would make it possible for them to interact tightly and specifically with each other. We used the repressor and operators of coliphage lambda to construct a model system in which to test our proposition. lambda repressor is a dimer at physiological concentrations, but forms tetramers and octamers at a hundredfold higher concentration. We predict that two lambda repressor dimers form a tetramer in vitro when bound to two lambda operators spaced 24 bp apart and that two such tetramers interact to form an octamer. We examined, in vitro, relaxed circular plasmid DNA in which such operator pairs were separated by 2,850 bp and 2,470 bp. Of these molecules, 29% formed loops as seen by electron microscopy (EM). The loop increased the tightness of binding of lambda repressor to lambda operator. Consequently, repression of the lambda PR promoter in vivo was increased fourfold by the presence of a second pair of lambda operators, separated by a distance of 3,600 bp.  (+info)

(6/34186) Difference between mammary epithelial cells from mature virgin and primiparous mice.

Mammary epithelial cells from mature virgin mice are similar to those from primiparous mice in several respects. However, there is one known difference. The cells from the mature virgin must traverse the cell cycle in order to become competent to make casein and enzymatically active alpha-lactalbumin in vitro; those from the primiparous animal can make these proteins without first traversing the cycle. In this regard, cells from human placental lactogen- and prolactin-treated mature virgins are, after involution, similar to those from primiparous mice. The developemental block in the cells from the mature virgin, imposed by preventing cell cycle traversal, has been partially delineated. It does not appear to reside at the levels of ultrastructural maturation or the formation of casein messenger RNA. Rather, the lesion is postranscriptional and may be at the level of translation, or posttranslational modification, or both.  (+info)

(7/34186) Unsaturated fatty acid requirements for growth and survival of a rat mammary tumor cell line.

A cell line, the growth and survival of which is markedly affected by linoleic acid, has been established from a carcinogen-induced rat mammary tumor. The cells have been continuously passaged in 5% rat serum plus 10% fetal calf serum-supplemented medium. The rat serum component was found to be indispensalbe, for when it was omitted the growth rate rapidly declined and the cells died by 5 to 7 days. Removal of the rat serum from the growth medium also resulted in a dramatic loss of Oil Red O-positive droplets in the cells, suggesting that the lipid component of rat serum might be a major growth-promoting principle in rat serum. This is likely since the total lipid fraction, but not the delipidized protein fraction, could largely supplant requirement of the cells for rat serum. Pure linoleic acid was found to be effective in maintaining the cell growth in delipidized serum or in whole fetal calf serum-supplemented medium. Fatty acid analysis revealed a 19-fold higher amount of linoleic acid in rat serum than in fetal calf serum.  (+info)

(8/34186) Effect of desiccation on the ultrastructural appearances of Acinetobacter baumannii and Acinetobacter lwoffii.

An Acinetobacter baumannii isolate survived desiccation beyond 30 days and an Acinetobacter lwoffii isolate up to 21 days. For both species, desiccation resulted in a significant increase in the proportion of round cells (A baumannii, 40% to 80%; A lwoffii, 51% to 63%) and a significant decrease in rod shaped cells (A baumannii, 58% to 13%; A lwoffii, 46% to 34%). Electronmicroscopic examination showed that there was also a corresponding significant increase in the cell wall thickness (A baumannii, up to 53%; A lwoffii, up to 26%). Desiccated A baumannii cells became more electron-dense and had significantly thicker cell walls (x1.3) than those of A lwoffii. Cell wall structures of A baumannii strains with different abilities to resist desiccation deserve further study.  (+info)