Pharmacological treatment of obesity has been neglected as a viable therapeutic option for many years. Recent long term studies with combinations of obesity drugs gives promise that drugs may play a role in weight maintenance, which classically has been the most difficult aspect of treating obesity. Currently available obesity drugs include centrally acting adrenergic agents and serotonin agonists. Drugs still in development include a lipase inhibitor that produces fat malabsorption, a combined adrenergic-serotonergic reuptake inhibitor, various gut-central nervous system peptides, and a number of beta-3 agonists. Any of these obesity drugs given alone produces modest weight loss, and for most, weight loss continues for as long as medication is given. The most successful drug regimens to date are combinations of phentermine and fenfluramine or of ephedrine, caffeine, and/or aspirin. The former combination produces reduction in body weight and complications of obesity for 2 to almost 4 years in clinical trials to date. More research is needed to document long term efficacy and particularly the long term safety of these and other combinations. 相似文献
Synopsis Juvenile salmonids,Oncorhynchus spp., commonly encounter conditions (e.g., during hatchery release and dam passage) that result in damage to the skin, scale, and slime complex. We conducted laboratory experiments to determine if descaling of juvenile chinook salmon,O. tshawytscha, increased their vulnerability to predation, and to assess the physiological stress responses elicited by descaling. Salmon were experimentally descaled on either 10% or 20% of their total body area. When offered equal numbers of control and descaled juvenile chinook salmon, northern squawfish,Ptychocheilus oregonensis, did not consume significantly more of either prey type (48–60% of consumed prey were descaled). Juvenile chinook salmon descaled on 10% of their body area did show significant physiological stress responses, however. Mean concentrations of plasma cortisol peaked 1 h after descaling, and returned to control levels by 12 h. Plasma glucose peaked 3 h post-treatment and remained elevated for 24 h. Plasma lactate increased immediately following treatment and returned to undisturbed control levels by 3 h. The osmoregulatory response of plasma potassium was highly variable, but plasma sodium decreased immediately and remained low for 24 h. The observed physiological responses suggest that descaling of juvenile chinook salmon could result in decreased resistance to disease and other stressors encountered in the field, possibly leading to reduced performance capacity and lowered survival. 相似文献
Erratic rainfall in rainfed lowlands and inadequate water supply in irrigated lowlands can results in alternate soil drying and flooding during a rice (Oryza sativa L.) cropping period. Effects of alternate soil drying and flooding on N loss by nitrification-denitrification have been inconsistent in previous field research. To determine the effects of water deficit and urea timing on soil NO3 and NH4, floodwater NO3, and N loss from added 15N-labeled urea, a field experiment was conducted for 2 yr on an Andaqueptic Haplaquoll in the Philippines. Water regimes were continuously flooded, not irrigated from 15 to 35 d after transplanting (DT), or not irrigated from 41 to 63 DT. The nitrogen treatments in factorial combination with water regimes were no applied N and 80 kg urea-N ha–1, either applied half basally and half at 37 DT or half at 11 DT and half at 65 DT. Water deficit at 15 to 35 DT and 41 to 63 DT, compared with continuous soil flooding, significantly reduced extractable NH4 in the top 30-cm soil layer and resulted in significant but small (<1.0 kg N ha–1) soil NO3 accumulations. Soil NO3, which accumulated during the water deficit, rapidly disappeared after reflooding. Water deficit at 15 to 35 DT, unlike that at 41 to 63 DT, increased the gaseous loss of added urea N as determined from unrecovered 15N in 15N balances. The results indicate that application of urea to young rice in saturated or flooded soil results in large, rapid losses of N (mean = 35% of applied N), presumably by NH3 volatilization. Subsequent soil drying and flooding during the vegetative growth phase can result in additional N loss (mean = 14% of applied N), presumably by nitrification-denitrification. This additional N loss due to soil drying and flooding decreases with increasing crop age, apparently because of increased competition by rice with soil microorganisms for NH4 and NO3. 相似文献
The exchange of ammonia between the atmosphere and the canopy of spring barley crops growing at three levels of nitrogen application (medium N, high N and excessive N) was studied over two consecutive growing seasons by use of micrometeorological techniques. In most cases, ammonia was emitted from the canopy to the atmosphere. The emission started around 2 weeks before anthesis, and peaked about or shortly after anthesis. The volatilization of ammonia only took place in the daytime. During the night-time, atmospheric ammonia was frequently aborbed by the canopy. Occasionally, plants in the medium and high N treatments also absorbed ammonia from the atmosphere during the daytime. Daytime absorption of ammonia never occurred in the excessive N canopy. The loss of ammonia from the canopy amounted in both years to 0.5–1.5 kg NH3-N ha?1 and increased with the N status of the canopy. In agreement with the small losses of ammonia, the content of 15N-labelled nitrogen in the plants did not decline during the grain-filling period. The experimental years were characterized by very favourable conditions for grain dry matter formation, and for re-utilization of nitrogen mobilized from leaves and stems. Consequently, a very high part of the nitrogen in the mature plants was located in grain dry matter (80–84% in 1989; 74–80% in 1990). The efficient re-utilization of nitrogen may have reduced the volatilization of ammonia. 相似文献
1. 1. The influence of ethnic differences is discussed with reference to the following issues.
2. 2. It has been found that total numbers of active sweat glands increase in tropical populations compared with people from northern latitudes.
3. 3. It has also been observed that the active sweat glands of Eskimos are fewer than those of Caucasians.
4. 4. The rate of the evaporated sweat loss was calculated by measuring body weight loss and it was found that the evaporated sweat loss of Caucasians is larger than that of Japanese in the same climate.
5. 5. Meteorological factors might have been responsible for the smaller loss in Japanese compared with that of Japanese-Americans.
6. 6. Under the same experimental conditions, it was observed that there were little or no differences between the Caucasians and Negros.
Long-term atmospheric CO2 concentration records have suggested a reduction in the positive effect of warming on high-latitude carbon uptake since the 1990s. A variety of mechanisms have been proposed to explain the reduced net carbon sink of northern ecosystems with increased air temperature, including water stress on vegetation and increased respiration over recent decades. However, the lack of consistent long-term carbon flux and in situ soil moisture data has severely limited our ability to identify the mechanisms responsible for the recent reduced carbon sink strength. In this study, we used a record of nearly 100 site-years of eddy covariance data from 11 continuous permafrost tundra sites distributed across the circumpolar Arctic to test the temperature (expressed as growing degree days, GDD) responses of gross primary production (GPP), net ecosystem exchange (NEE), and ecosystem respiration (ER) at different periods of the summer (early, peak, and late summer) including dominant tundra vegetation classes (graminoids and mosses, and shrubs). We further tested GPP, NEE, and ER relationships with soil moisture and vapor pressure deficit to identify potential moisture limitations on plant productivity and net carbon exchange. Our results show a decrease in GPP with rising GDD during the peak summer (July) for both vegetation classes, and a significant relationship between the peak summer GPP and soil moisture after statistically controlling for GDD in a partial correlation analysis. These results suggest that tundra ecosystems might not benefit from increased temperature as much as suggested by several terrestrial biosphere models, if decreased soil moisture limits the peak summer plant productivity, reducing the ability of these ecosystems to sequester carbon during the summer. 相似文献
Soil and atmospheric droughts increasingly threaten plant survival and productivity around the world. Yet, conceptual gaps constrain our ability to predict ecosystem-scale drought impacts under climate change. Here, we introduce the ecosystem wilting point (ΨEWP), a property that integrates the drought response of an ecosystem's plant community across the soil–plant–atmosphere continuum. Specifically, ΨEWP defines a threshold below which the capacity of the root system to extract soil water and the ability of the leaves to maintain stomatal function are strongly diminished. We combined ecosystem flux and leaf water potential measurements to derive the ΨEWP of a Quercus-Carya forest from an “ecosystem pressure–volume (PV) curve,” which is analogous to the tissue-level technique. When community predawn leaf water potential (Ψpd) was above ΨEWP (=−2.0 MPa), the forest was highly responsive to environmental dynamics. When Ψpd fell below ΨEWP, the forest became insensitive to environmental variation and was a net source of carbon dioxide for nearly 2 months. Thus, ΨEWP is a threshold defining marked shifts in ecosystem functional state. Though there was rainfall-induced recovery of ecosystem gas exchange following soaking rains, a legacy of structural and physiological damage inhibited canopy photosynthetic capacity. Although over 16 growing seasons, only 10% of Ψpd observations fell below ΨEWP, the forest is commonly only 2–4 weeks of intense drought away from reaching ΨEWP, and thus highly reliant on frequent rainfall to replenish the soil water supply. We propose, based on a bottom-up analysis of root density profiles and soil moisture characteristic curves, that soil water acquisition capacity is the major determinant of ΨEWP, and species in an ecosystem require compatible leaf-level traits such as turgor loss point so that leaf wilting is coordinated with the inability to extract further water from the soil. 相似文献