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271.
A priming effect of gonadotrophin releasing hormone on luteinizing hormone secretion in the boar.
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The possibility that gonadotrophin releasing hormone (GnRH) can prime the anterior pituitary to a second dose of GnRH resulting in a greatly enhanced secretion of luteinizing hormone was examined in three adult boars. Four experiments were conducted: saline injection followed one hour later by a second saline injection (control); 1 microgram of synthetic GnRH injection followed one hour later by saline injection; saline injection followed one hour later by GnRH injection; GnRH injection followed one hour later by a second GnRH injection. Immunoassayable levels of plasma luteinizing hormone resulting from GnRH plus GnRH treatment were significantly greater than the sum obtained when values from GnRH plus saline and saline plus GnRH were added. Testosterone values in plasma reached maximal concentrations about 60 minutes after peak values of luteinizing hormone were achieved. The results suggest that the first dose of GnRH, in addition to stimulating release of luteinizing hormone can also sensitize the gonadotrophs to a second dose of GnRH causing a significantly greater release of luteinizing hormone. 相似文献
272.
Brad J. Argue Steve M. Arce Shaun M. Moss 《Journal of the World Aquaculture Society》2000,31(1):119-122
Abstract.— The correlation between market weight (20–25 g) and broodstock weight (> 35 g) in Pacific white shrimp Litopenaeus vannamei has not been determined. Breeders may assume that the largest brood-stock shrimp were also the largest market shrimp. In this study, 120 market shrimp were individually tagged and grown to broodstock in an earthen pond. There was a significant relationship between market and broodstock weight ( P < 0.001) but it was not highly correlated ( r = 0.42). There was no correlation between market weight and post-market weight gain ( P = 0.477; r = 0.08). Of the largest 20 broodstock, only seven were among the top 20 at market weight. If the goal of a breeding program is to select the fastest growing individuals to market, shrimp should be individually selected at market weight and not as broodstock. 相似文献
273.
Dayton M. Lambert Brad J. Argue Zhanjiang Liu Rex A. Dunham 《Journal of the World Aquaculture Society》1999,30(1):80-89
The primary objective was to compare thyroid hormones and levels of carp pituitary extract for the artificial production of female Ictalurus punctatus × male I. furcatus hybrid catfish. The effects of different carp pituitary extract dosage rates (5, 6, 9, and 10 mg/kg), carp pituitary extract (6 and 10 mg/kg) supplemented with the thyroid hormones thyroxine (T4 ) and triiodothyronine (T3 ), or pregnenolone (DHP) were determined for inducing ovulation of female channel catfish, fertilization of channel catfish eggs with male blue catfish sperm, and hatching rate of these embryos. Hormone treatments thyroxine and tri-iodothyronine with carp pituitary extract, carp pituitary extract alone, and pregnenolone with carp pituitary extract used to artificially produce hybrid catfish were not different in terms of ovulation rates, eggs/kg, fry/kg body weight of female channel catfish, fertilization rates, or hatching rates (P > 0.05). These findings suggest that lower amounts of carp pituitary extract may be used to induce spawn of female channel catfish for production of channel-blue catfish hybrids and the addition of thyroid and steroid hormones is ineffective at the rates used in this study. 相似文献
274.
Complexity in modelling forest ecosystems: How much is enough? 总被引:1,自引:0,他引:1
James P. Kimmins Juan A. Blanco Brad Seely Clive Welham Kim Scoullar 《Forest Ecology and Management》2008
The levels-of-integration concept in ecology suggests that while the population and community levels of biological organization provide understanding, they do not provide an adequate basis for predicting future states of populations, communities or ecosystems. Empirical models of populations and communities are implicitly ecosystem level because they are based on measures of the results of all past determinants that affected the populations and communities in question. They can be good predictors under unchanging conditions, but they are not able to predict for changing conditions, which requires the explicit representation of those ecological processes that are anticipated to change. The question addressed in this paper is: how does the performance of a “simple” stand-level model change as representations of these processes are added, and how much complexity is enough? Examples are given of change in performance of the ecosystem management model FORECAST run as a light competition model as nutrient regulation of growth and understory interactions are added singly or in combination. These examples are framed in comparisons of simulations for a white spruce stand in the in boreal mixedwood region in northern British Columbia, for a long-term thinning-fertilization trial in a Douglas-fir stand on southern Vancouver Island, and for yield decline in Chinese fir in south eastern China. It is concluded that the effect of adding complexity on the predictions of this model depends on the time scale of the simulation and the management or natural disturbance regime that is being simulated. The results supported Occam's razor: that models should be as simple as possible but as complex as necessary. 相似文献
275.
Talitha C. Santini Brad P. Degens Andrew W. Rate 《Water, air, and soil pollution》2010,209(1-4):251-268
Deep drains used to manage shallow saline water tables in the Western Australian agricultural region discharge acidic, saline drainage water with high concentrations of metals. The activity of sulfate-reducing bacteria can treat these waters by generating alkalinity in the form of bicarbonate and by generating sulfide, which removes metals from solution as sulfide precipitates. Bacterial sulfate reduction was strongly influenced by the organic carbon substrate provided for bacterial consumption. Mixtures of lupin compost, wheat chaff, oil mallee distillate wastes, straw, ethanol, and sheep manure were compared to determine which substrate was most effective in promoting the activity of sulfate-reducing bacteria and the contribution of this to bioremediation of acidic saline drainage. Mesocosm treatment systems containing reactive mixtures and acidic saline drainage were operated for a 50-day establishment period and subsequent 27-day “batch flow” period. Effluent from the treatment systems was analyzed for pH, sulfate, metals, and nutrients over the period of operation. Effluents from all reactive mixtures showed increased pH (to 5.1–5.9) and decreased sulfate and metal concentrations compared with untreated drainage water. Straw with ethanol appeared to be the most effective substrate for treatment of low pH and high metal concentrations, followed equally by both lupin compost and wheat chaff. The latter are likely to be more suitable for use in a field scale low-maintenance bioreactor or composting wetland. 相似文献
276.
White BJ Hanzlicek G Sanderson MW Anderson DE Larson RL 《The Canadian veterinary journal. La revue veterinaire canadienne》2010,51(9):1016-1018
Mollicutes nasal swab culture status and potential associations with health outcomes were determined in beef feeder calves. Mollicutes culture was positive in 7.6% (22/291) of calves at arrival and in 26.2% (34/130) of calves at first disease treatment. Positive Mollicutes culture at first treatment was associated with increased odds for subsequent retreatment or death. 相似文献
277.
Barnett BP Hwang Y Taylor MS Kirchner H Pfluger PT Bernard V Lin YY Bowers EM Mukherjee C Song WJ Longo PA Leahy DJ Hussain MA Tschöp MH Boeke JD Cole PA 《Science (New York, N.Y.)》2010,330(6011):1689-1692
Ghrelin is a gastric peptide hormone that stimulates weight gain in vertebrates. The biological activities of ghrelin require octanoylation of the peptide on Ser(3), an unusual posttranslational modification that is catalyzed by the enzyme ghrelin O-acyltransferase (GOAT). Here, we describe the design, synthesis, and characterization of GO-CoA-Tat, a peptide-based bisubstrate analog that antagonizes GOAT. GO-CoA-Tat potently inhibits GOAT in vitro, in cultured cells, and in mice. Intraperitoneal administration of GO-CoA-Tat improves glucose tolerance and reduces weight gain in wild-type mice but not in ghrelin-deficient mice, supporting the concept that its beneficial metabolic effects are due specifically to GOAT inhibition. In addition to serving as a research tool for mapping ghrelin actions, GO-CoA-Tat may help pave the way for clinical targeting of GOAT in metabolic diseases. 相似文献
278.
Matthew G. Hamilton Brad M. Potts Bruce L. Greaves Greg W. Dutkowski 《Annals of Forest Science》2010,67(5):511-511
279.
280.
We estimate the cosmic production rate of helium relative to metals (DeltaY/DeltaZ) using K dwarf stars in the Hipparcos catalog with accurate spectroscopic metallicities. The best fitting value is DeltaY/DeltaZ = 2.1 +/- 0.4 at the 68% confidence level. Our derived value agrees with determinations from H II regions and with theoretical predictions from stellar yields with standard assumptions for the initial mass function. The amount of helium in stars determines how long they live and therefore how fast they will enrich the interstellar medium with fresh material. 相似文献