肾素－血管紧张素系统──应激激素反应系统

各种急性与慢性应激时,循环血中及脑、心血管、肾腺等组织中血管紧张素Ⅱ（ＡⅡ）显著增多;人剧烈运动后血浆ＡⅡ与皮质醇一样均剧烈增加,在慢性应激性高血压动物循环及组织中,ＡⅡ含量持续地增高。还发现高浓度ＡⅡ对肾上腺糖皮质激素的分泌有直接的刺激作用,而组织ＡⅡ增多又受肾上腺素能β受体的激发。根据近年来的系列工作,并结合文献,我们认为ＡⅡ是一种重要的应激激素;肾素－血管紧张素系统是一个应激激素反应系统;它与经典的应激激素反应系统,下丘脑－垂体－肾上腺皮质系统及交感－肾上腺髓质系统也存在着密切的关系。     

Reproductive responses of Iphiseius degenerans and Neoseiulus teke (Acari: Phytoseiidae) to changes in the density of the cassava green mite, Mononychellus tanajoa (Acari: Tetranychidae)

We assessed the reproductive responses of adult female Iphiseius degenerans and Neoseiulus teke to increasing density of three stages of their prey, Mononychellus tanajoa, on cassava leaf discs under laboratory conditions. The oviposition rates increased with number of prey consumed per predator per day with a maximum of approximately two eggs per day for I. degenerans and four eggs per day for N. teke. The oviposition rate of N. teke was higher when consuming eggs than other prey stages. Neoseiulus teke was more efficient than I. degenerans in converting consumed prey into egg production. The data were adequately described by simple mathematical models.     

Influence of 50 Hz electric and magnetic fields on the pulse rate of human heart

This investigation studied the effects of 50 Hz electric and magnetic fields on the pulse rate of the human heart. The ECG (electrocardiograms) of 41 male volunteers were recorded with a Holter recorder. Twenty-six subjects were measured in and outside real fields, and 15 subjects were measured in and outside “sham” fields. The blood pressure and EEG (electroencephalogram) were also measured, but this article presents only the results of ECG recordings. The measurements took 3 h. The subjects were first sitting for 1 h outside the fields, then 1 h in the real or “sham” fields, and then, again, 1 h outside the fields. The electric field strength varied from 3.5 to 4.3 kV/m and the magnetic flux density from 1.4 to 6.6 μT. An analysis of the ECG recordings showed that the subjects' pulse rates were the same in and outside the fields. No response occurred when the subjects were exposed to real or “sham” fields. © 1994 Wiley-Liss, Inc.     

SR141716A, a potent and selective antagonist of the brain cannabinoid receptor

SR141716A is the first selective and orally active antagonist of the brain cannabinoid receptor. This compound displays nanomolar affinity for the central cannabinoid receptor but is not active on the peripheral cannabinoid receptor. In vitro, SR141716A antagonises the inhibitory effects of cannabinoid receptor agonists on both mouse vas deferens contractions and adenylyl cyclase activity in rat brain membranes. After intraperitoneal or oral administration SR141716A antagonises classical pharmacological and behavioural effects of cannabinoid receptor agonists. This compound should prove to be a powerful tool for investigating the in vivo functions of the anandamide/cannabinoid system.     

The effects of selection for gain in mice on the direct-maternal genetic correlation

Components of genetic variation for postweaning growth traits were estimated for both control and growth stocks of mice. The effect of phenotypic selection for gain, which genetically combines selection for additive direct and maternal effects, on additive genetic variance components, heritability, and additive genetic correlationsis discussed. Quantitative genetic theory predicts that simultaneous selection for two metric traits in the same direction will cause the genetic correlation between the two traits to become more negative. The results presented in this paper conflict with this theory. The direct-maternal additive genetic correlation was more negative in the control line (with 356 mice) than in the growth-selected line (with 320 mice) for the three traits analyzed (0.310 vs 0.999 for 21-day weight, 0.316 vs 1.000 for 42-day weight, and 0.506 vs 1.000 for gain from 21–42 days). Estimates were obtained by restricted maximum likelihood (REML) computed under a derivative free algorithm (DFREML).     

Acclimation of photosynthesis to increasing atmospheric CO2: The gas exchange perspective

The nature of photosynthetic acclimation to elevated CO₂ is evaluated from the results of over 40 studies focusing on the effect of long-term CO₂ enrichment on the short-term response of photosynthesis to intercellular CO₂ (the A/C_i response). The effect of CO₂ enrichment on the A/C_i response was dependent on growth conditions, with plants grown in small pots (< 5 L) or low nutrients usually exhibiting a reduction of A at a given C_i, while plants grown without nutrient deficiency in large pots or in the field tended to exhibit either little reduction or an enhancement of A at a given C_i following a doubling or tripling of atmospheric CO₂ during growth. Using theoretical interpretations of A/C_i curves to assess acclimation, it was found that when pot size or nutrient deficiency was not a factor, changes in the shape of A/C_i curves which are indicative of a reallocation of resources within the photosynthetic apparatus typically were not observed. Long-term CO₂ enrichment usually had little effect or increased the value of A at all C_i. However, a minority of species grown at elevated CO₂ exhibited gas exchange responses indicative of a reduced amount of Rubisco and an enhanced capacity to metabolize photosynthetic products. This type of response was considered beneficial because it enhanced both photosynthetic capacity at high CO₂ and reduced resource investment in excessive Rubisco capacity. The ratio of intercellular to ambient CO₂ (the C_i/C_a ratio) was used to evaluate stomatal acclimation. Except under water and humidity stress, C_i/C_a exhibited no consistent change in a variety of C₃ species, indicating no stomatal acclimation. Under drought or humidity stress, C_i/C_a declined in high-CO₂ grown plants, indicating stomata will become more conservative during stress episodes in future high CO₂ environments.Abbreviations A net CO₂ assimilation rate - C_i (C_a) intercellular (ambient) partial pressure of CO₂ - operational C_i intercellular partial pressure of CO₂ at a given ambient partial pressure of CO₂ - g_s stomatal conductance - normal CO₂ current atmospheric mole fraction of CO₂ (330 to 355 mol mol^–1) - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase     

Inspection and evaluation of host plant by the butterfly Mechanitis lysimnia (Nymph., Ithomiinae) before laying eggs: a mechanism to reduce intraspecific competition

Parasites of all kinds affect the behaviour of their hosts, often making them more susceptible to predators. The associated loss in expected future reproductive success of infected hosts will vary among individuals, with younger ones having more lose than older ones. For this reason, young hosts would benefit more by opposing the effects of parasites than old ones. In a laboratory study, the effects of the trematode Telogaster opisthorchis on the anti-predator responses of the upland bully (Gobiomorphus breviceps) and of the common river galaxias (Galaxias vulgaris) were examined in relation to fish age. In a bully population where parasites were very abundant, the magnitude of the fish's anti-predator responses decreased as the number of parasites per fish increased, and this effect was significantly more pronounced in age 2 + and, to a lesser extent, age 3 + fish than in age 1 + fish. In another bully population where parasites were 10 times less abundant, similar effects were noticeable but not significant, whereas no effects of parasites on the responses of galaxiids to predators were apparent. Differences in the abundance of parasites and in their sites of infection in fish may explain the variability among host populations or species. However, in the bully population with high parasite abundance, parasitism has age-dependent effects on responses to predators, providing some support for the prediction that young fish with high expected future reproductive success invest more energy into opposing the effects of parasites than do older fish.