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排序方式: 共有256条查询结果,搜索用时 171 毫秒
1.
B F BuSha B G Judd H L Manning P M Simon B C Searle J A Daubenspeck J C Leiter 《Journal of applied physiology》2001,90(6):2330-2340
Evidence of the Hering-Breuer reflex has been found in humans during anesthesia and sleep but not during wakefulness. Cortical influences, present during wakefulness, may mask the effects of this reflex in awake humans. We hypothesized that, if lung volume were increased in awake subjects unaware of the stimulus, vagal feedback would modulate breathing on a breath-to-breath basis. To test this hypothesis, we employed proportional assist ventilation in a pseudorandom sequence to unload the respiratory system above and below the perceptual threshold in 17 normal subjects. Tidal volume, integrated respiratory muscle pressure per breath, and inspiratory time were recorded. Both sub- and suprathreshold stimulation evoked a significant increase in tidal volume and inspiratory flow rate, but a significant decrease in inspiratory time was present only during the application of a subthreshold stimulus. We conclude that vagal feedback modulates respiratory timing on a breath-by-breath basis in awake humans, as long as there is no awareness of the stimulus. 相似文献
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Brett F BuSha Martha H Stella Harold L Manning J C Leiter 《Journal of applied physiology》2002,93(3):903-910
Imperceptible levels of proportional assist ventilation applied throughout inspiration reduced inspiratory time (TI) in awake humans. More recently, the reduction in TI was associated with flow assist, but flow assist also reaches a maximum value early during inspiration. To test the separate effects of flow assist and timing of assist, we applied a pseudorandom binary sequence of flow-assisted breaths during early, late, or throughout inspiration in eight normal subjects. We hypothesized that imperceptible flow assist would shorten TI most effectively when applied during early inspiration. Tidal volume, integrated respiratory muscle pressure per breath, TI, and TE were recorded. All stimuli (early, late, or flow assist applied throughout inspiration) resulted in a significant increase in inspiratory flow; however, only when the flow assist was applied during early inspiration was there a significant reduction in TI and the integrated respiratory muscle pressure per breath. These results provide further evidence that vagal feedback modulates breathing on a breath-by-breath basis in conscious humans within a physiological range of breath sizes. 相似文献
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Aging and glucose homeostasis in C57BL/6J male mice 总被引:2,自引:0,他引:2
Age-dependent changes in glucose homeostasis were assessed in specific pathogen-free C57BL/6J male mice. Increased islet size and pancreatic insulin content in old (21-25-month-old) mice were associated with lower nonfasting plasma glucose levels and improved clearance of either an oral or an i.p. administered glucose load in comparison with young, mature (4-5-month-old) males. The almost twofold increase in islet size correlated with a twofold increase of glucose-stimulated insulin secretion from perifused islets from 25-month-old males compared with 5-month-old males. These aging male mice did not become obese, and there were no fibrotic changes associated with the hyperplastic islets observed in the old males. Thus, the findings that glucose tolerance did not deteriorate with age, coupled with the lack of evidence for impaired beta cell responsiveness to glucose in old males, suggest that deterioration in glucose homeostasis is not an inevitable consequence of aging in the mouse. 相似文献
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The genetics of diabetes susceptibility in mice 总被引:12,自引:0,他引:12
E H Leiter 《FASEB journal》1989,3(11):2231-2241
The factors associated with a diabetes-susceptible genotype in mice exhibiting various forms of heritable glucose intolerance syndromes are discussed. Genetic models of insulin-dependent and non-insulin-dependent diabetes in mice are described. Although single gene mutations can be defined for each model that are major contributors to diabetogenic stress, polygenic interactions are required for the expression of a diabetic phenotype, and environmental factors are also contributory. Several strongly penetrant single gene mutations are capable of affecting obesity and insulin-resistant states. Analysis of inbred strain genomic interactions with one of these recessive obesity-producing genes, diabetes (db), suggests that development of a diabetic phenotype is dependent on the strength of an interaction between the db gene and sulfotransferase enzymes. Specifically, diabetes-susceptible vs. resistant inbred strain backgrounds can be distinguished by the extent to which the db mutation elicits an accelerated sequestration by sulfoconjugation of tissue estrogens while androgens remain free. In a male gender- (and Y chromosome-)associated model of transient glucose intolerance, stress as well as a requirement for both adrenal and testicular secretions are each components of the susceptibility background. In the obesity-associated diabetes models, autoimmunity, when it occurs, is a secondary reflection of pancreatic beta cell destruction. The nonobese diabetic (NOD) mouse, in contrast, represents a model in which autoimmunity against beta cells is a primary event in the development of insulin-dependent diabetes. In NOD mice, a gene that is either the unique class II gene in the major histocompatibility complex or is in linkage disequilibrium with this complex makes a major (recessivelike) contribution to diabetes susceptibility. However, diabetogenesis can be mediated only through a multifactorial interaction among this susceptibility locus and multiple unlinked genetic loci regulating immune responsiveness. In addition, the NOD mouse represents one of the best models of diabetes available for demonstrating a critical interaction between heredity and environmental factors. The polygenic nature of the various heritable forms of glucose intolerance syndromes in mice points to a comparable or even greater genetic heterogeneity underlying the major types of diabetes in humans. 相似文献
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Excess amino acid polymorphism in mitochondrial DNA: contrasts among genes from Drosophila, mice, and humans 总被引:13,自引:3,他引:10
Recent studies of mitochondrial DNA (mtDNA) variation in mammals and
Drosophila have shown an excess of amino acid variation within species
(replacement polymorphism) relative to the number of silent and replacement
differences fixed between species. To examine further this pattern of
nonneutral mtDNA evolution, we present sequence data for the ND3 and ND5
genes from 59 lines of Drosophila melanogaster and 29 lines of D. simulans.
Of interest are the frequency spectra of silent and replacement
polymorphisms, and potential variation among genes and taxa in the
departures from neutral expectations. The Drosophila ND3 and ND5 data show
no significant excess of replacement polymorphism using the
McDonald-Kreitman test. These data are in contrast to significant
departures from neutrality for the ND3 gene in mammals and other genes in
Drosophila mtDNA (cytochrome b and ATPase 6). Pooled across genes, however,
both Drosophila and human mtDNA show very significant excesses of amino
acid polymorphism. Silent polymorphisms at ND5 show a significantly higher
variance in frequency than replacement polymorphisms, and the latter show a
significant skew toward low frequencies (Tajima's D = -1.954). These
patterns are interpreted in light of the nearly neutral theory where mildly
deleterious amino acid haplotypes are observed as ephemeral variants within
species but do not contribute to divergence. The patterns of polymorphism
and divergence at charge-altering amino acid sites are presented for the
Drosophila ND5 gene to examine the evolution of functionally distinct
mutations. Excess charge-altering polymorphism is observed at the carboxyl
terminal and excess charge-altering divergence is detected at the amino
terminal. While the mildly deleterious model fits as a net effect in the
evolution of nonrecombining mitochondrial genomes, these data suggest that
opposing evolutionary pressures may act on different regions of
mitochondrial genes and genomes.
相似文献
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Wasicko M. J.; Giering R. W.; Knuth S. L.; Leiter J. C. 《Journal of applied physiology》1993,75(3):1395-1403