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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Statistics and computing 2 (1992), S. 161-171 
    ISSN: 1573-1375
    Keywords: Asymptotic approximations ; bootstrap calibration ; coverage accuracy ; resampling ; saddlepoint methods ; tail probability approximations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Standard algorithms for the construction of iterated bootstrap confidence intervals are computationally very demanding, requiring nested levels of bootstrap resampling. We propose an alternative approach to constructing double bootstrap confidence intervals that involves replacing the inner level of resampling by an analytical approximation. This approximation is based on saddlepoint methods and a tail probability approximation of DiCiccio and Martin (1991). Our technique significantly reduces the computational expense of iterated bootstrap calculations. A formal algorithm for the construction of our approximate iterated bootstrap confidence intervals is presented, and some crucial practical issues arising in its implementation are discussed. Our procedure is illustrated in the case of constructing confidence intervals for ratios of means using both real and simulated data. We repeat an experiment of Schenker (1985) involving the construction of bootstrap confidence intervals for a variance and demonstrate that our technique makes feasible the construction of accurate bootstrap confidence intervals in that context. Finally, we investigate the use of our technique in a more complex setting, that of constructing confidence intervals for a correlation coefficient.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-136X
    Keywords: Key words Mannitol ; Fluorescein ; Permeability ; Salmon ; Posterior intestine ; Enhanced epithelial permeability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract This study characterised the permeability of the salmonid posterior intestine in vivo, to two hydrophilic markers of different molecular weight, both in the presence and absence of sodium deoxycholate (SDA), and determined the influence of mucosal secretions. The posterior intestine of chinook salmon was cannulated with a balloon catheter and the lumen infused with a solution of fluorescein and 14C-mannitol. In treated fish, the solution also contained 5.0 mmol · l−1 SDA. Blood samples from the dorsal aorta were taken at regular time intervals over 3 h. Clearances and volumes of distribution were assessed by intravenous administration of the markers to another group of fish. In the absence of SDA, low permeabilities were recorded for both markers; however, permeabilities for both were significantly greater in the treated groups. Both solutes had volumes of distribution similar to values reported elsewhere. Metabolism of fluorescein by the liver resulted in its plasma clearance. In contrast, elimination of mannitol was negligible during the study period, probably due to the lowered glomerular filtration rates observed in sea water adapted fish. Compared to in vitro investigations, in vivo mucus secretions were significantly lower and solute delivery across the epithelium was higher. Results from these in vivo investigations have implications for the oral delivery of peptides to salmonids.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-136X
    Keywords: Key words Proximal and distal intestine ; Mannitol flux ; Transepithelial electrical resistance ; Enhancement ; Salmon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The objective of this study was to assess regional variations in the permeability of the salmon posterior intestine and to evaluate the effect of permeability enhancers as a basis for oral delivery of biologically active peptides. Proximal and distal portions of the posterior intestine of the chinook salmon (Oncorhynchus tshawytscha) were removed, mounted as flat sheets in Ussing chambers and superfused with trout Ringer's. Intestinal permeability was assessed under short-circuit conditions by measurement of 14C-mannitol (mucosal to serosal) flux. Tissues were treated either with the mucolytic agent dithiothreitol (10 mmol · l−1), the permeability enhancer sodium deoxycholate (5.0 mmol · l−1) or both and compared to untreated controls. Both proximal and distal control tissues had low permeabilities, but the distal region had a lower transepithelial electrical resistance and produced significantly less mucus. Treatment with either dithiothreitol or sodium deoxycholate alone reduced mucus adhering to tissue in both regions but did not increase permeability or change transepithelial electrical resistance. In the distal region, sequential treatment with both agents significantly reduced adhering mucus, decreased transepithelial electrical resistance, and increased tissue permeability. The salmon posterior intestine can be divided into proximal and distal regions. The distal region is more likely to have the necessary permeability and responsiveness to enhancement for the successful delivery of peptides or polar drugs.
    Type of Medium: Electronic Resource
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