Feeding-induced increases in insulin do not suppress secretion of growth hormone     

McMahon CD  Chapin LT  Lookingland KJ  Radcliff RP  Tucker HA 《Domestic animal endocrinology》1999,17(4):439-447

Secretion of growth hormone (GH) is reduced for several hours after feeding when access to feed is restricted to a 2-hr period each day. We hypothesized that increased secretion of insulin after feeding inhibits release of GH from the anterior pituitary gland. Our objectives were to determine whether: 1) alloxan prevents concentrations of insulin from increasing after feeding steers; 2) concentrations of GH remain high after feeding alloxan-treated steers; and 3) GH-releasing hormone (GHRH) stimulates greater release of GH in alloxan-treated, than in control, steers after feeding. Steers were injected iv with either saline (control) or with alloxan (110 mg/kg) (n = 4 per group). Concentrations of insulin were not different (P = 0.61) between control and alloxan-treated steers before feeding (87.5 +/- 33.6 pmol/l). However, alloxan prevented insulin from increasing (P < 0.001) after feeding (131.8 pmol/1) compared with control steers (442.0 pmol/l) (pooled SEM = 47.5). Overall, GH was higher (P < 0.05) in alloxan-treated (6.4 ng/ml) than in control steers (3.7 ng/ml) (pooled SEM = 0.7), but GH decreased (P < 0.001) after feeding in both groups. Iv injection of GHRH stimulated release of GH 1 hr before, but not when injected 1 hr after feeding (P < 0.001). In addition, net areas under the GH curve were not significantly different between control and alloxan-treated groups. We conclude that increased concentrations of insulin after feeding do not mediate feeding-induced suppression of GH secretion in steers.  相似文献   

Linking habitat selection, emigration and population dynamics of freshwater fishes: a synthesis of ideas and approaches     

T. E. McMahon  W. J. Matter 《Ecology of Freshwater Fish》2006,15(2):200-210

Abstract –  The consequences of individual behaviour to dynamics of populations has been a critical question in fish ecology, but linking the two has proven difficult. A modification of Sale's habitat selection model provides a conceptual linkage for relating resource availability and individual habitat selection to exploratory behaviour, emigration and population-level responses. Whole-population experiments with pupfish Cyprinodon macularius that linked all factors along this resource to population continuum lend support to this conceptual model, and illustrate that emigration may be much more common in fish populations than considered in most individual- or population-based models. Accommodating emigration can enhance the ecological appropriateness of behavioural experiments and increase confidence in extrapolation of experimental observations to population-level effects. New experimental designs and advancing technologies offer avenues for assessing population consequences of habitat selection and emigration by individual fish. Emigration often is the key linkage between individual behaviour and population responses, and greater understanding of the underlying factors affecting this often-overlooked demographic parameter could offer new approaches for management and conservation of fishes.  相似文献   

Tricyclic Guanidine Alkaloids from the Marine Sponge Acanthella cavernosa that Stabilize the Tumor Suppressor PDCD4     

Tanja Grkovic  Johanna S. Blees  Magdalena M. Bayer  Nancy H. Colburn  Cheryl L. Thomas  Curtis J. Henrich  Megan L. Peach  James B. McMahon  Tobias Schmid  Kirk R. Gustafson 《Marine drugs》2014,12(8):4593-4601

A cell-based high-throughput screen that assessed the cellular stability of a tumor suppressor protein PDCD4 (Programmed cell death 4) was used to identify a new guanidine-containing marine alkaloid mirabilin K (3), as well as the known compounds mirabilin G (1) and netamine M (2). The structures of these tricyclic guanidine alkaloids were established from extensive spectroscopic analyses. Compounds 1 and 2 inhibited cellular degradation of PDCD4 with EC₅₀ values of 1.8 μg/mL and 2.8 μg/mL, respectively. Mirabilin G (1) and netamine M (2) are the first marine natural products reported to stabilize PDCD4 under tumor promoting conditions.  相似文献   

Forage nitrate analysis: laboratory performance study     

T L McMahon  H H Casper 《Journal of the Association of Official Analytical Chemists》1984,67(5):1026-1028

Four forage samples were analyzed by 16 laboratories for KNO3 content. Individual reported KNO3 values varied widely for each sample; coefficients of variation for the 4 samples were 36.0, 51.0, 12.8, and 55.0%. Recovery of KNO3 from the spiked sample averaged 105%. The analytical results, as a group, were unacceptable both statistically and for use in feeding recommendations. Three values reported could have resulted in feeding potentially toxic forage to livestock.  相似文献   

Pesticide residue levels in foods in the United States from July 1, 1969, to June 30, 1976: Summary     

R E Duggan  P E Corneliussen  M B Duggan  B M McMahon  R J Martin 《Journal of the Association of Official Analytical Chemists》1983,66(6):1534-1535

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The limb bud Shh-Fgf feedback loop is terminated by expansion of former ZPA cells     

Scherz PJ  Harfe BD  McMahon AP  Tabin CJ 《Science (New York, N.Y.)》2004,305(5682):396-399

Vertebrate limb outgrowth is driven by a positive feedback loop involving Sonic Hedgehog (Shh), Gremlin, and Fgf4. By overexpressing individual components of the loop at a time after these genes are normally down-regulated in chicken embryos, we found that Shh no longer maintains Gremlin in the posterior limb. Shh-expressing cells and their descendants cannot express Gremlin. The proliferation of these descendants forms a barrier separating the Shh signal from Gremlin-expressing cells, which breaks down the Shh-Fgf4 loop and thereby affects limb size and provides a mechanism explaining regulative properties of the limb bud.  相似文献   

Scaling stride frequency and gait to animal size: mice to horses   总被引：8，自引：0，他引：8  

N C Heglund  C R Taylor  T A McMahon 《Science (New York, N.Y.)》1974,186(4169):1112-1113

The stride frequency at which animals of different size change from one gait to another (walk, trot, gallop) changes in a regular manner with body mass. The speed at the transition from trot to gallop can be used as an equivalent speed for comparing animals of different size. This transition point occurs at lower speeds and higher stride frequencies in smaller animals. Plotting stride frequency at the trot-gallop transition point as a function of body mass in logarithmic coordinates yields a straight line.  相似文献   

A Fluted Point from the Uptar Site, Northeastern Siberia     

ML King  SB Slobodin 《Science (New York, N.Y.)》1996,273(5275):634-636

Lanceolate bifacial points, including one fluted specimen, have been collected from beneath an early Holocene tephra at the Uptar site, northeastern Siberia. Thus, the technology associated with the well-known Paleoindian tradition was not confined to the Americas. The Uptar collection does not compare readily with other Beringian complexes and demonstrates that there is greater diversity in the archaeological record of northeastern Siberia than traditional colonization models imply.  相似文献   

Rowing: a similarity analysis     

McMahon TA 《Science (New York, N.Y.)》1971,173(3994):349-351

The theory of models is employed for calculating the speed of geometrically similar racing shells. The theoretical prediction, that shells should have a speed proportional to the number of oarsmen raised to the 1/9 power, is in excellent agreement with observations. A significant implication for the proportions of lightweight and heavyweight eight-oared shells, indicating how both might attain the same speed, is developed.  相似文献   

Potent analgesic effects of GDNF in neuropathic pain states     

Boucher TJ  Okuse K  Bennett DL  Munson JB  Wood JN  McMahon SB 《Science (New York, N.Y.)》2000,290(5489):124-127

Neuropathic pain arises as a debilitating consequence of nerve injury. The etiology of such pain is poorly understood, and existing treatment is largely ineffective. We demonstrate here that glial cell line-derived neurotrophic factor (GDNF) both prevented and reversed sensory abnormalities that developed in neuropathic pain models, without affecting pain-related behavior in normal animals. GDNF reduces ectopic discharges within sensory neurons after nerve injury. This may arise as a consequence of the reversal by GDNF of the injury-induced plasticity of several sodium channel subunits. Together these findings provide a rational basis for the use of GDNF as a therapeutic treatment for neuropathic pain states.  相似文献