Hypoventilation, as one of ventilatory disorders, decreases the electrical stability of the heart similarly as ischemia. If preconditioning by short cycles of ischemia has a cardioprotective effect against harmful influences of a prolonged ischemic period, then preconditioning by hypoventilation (HPC) can also have a similar effect. Anesthetized rats (ketamine 100 mg/kg + xylasine 15 mg/kg i.m., open chest experiments) were subjected to 20 min of hypoventilation followed by 20 min of reoxygenation (control group). The preconditioning (PC) was induced by one (1PC), two (2PC) or three (3PC) cycles of 5-min hypoventilation followed by 5-min reoxygenation. The electrical stability of the heart was measured by a ventricular arrhythmia threshold (VAT) tested by electrical stimulation of the right ventricle. Twenty-minute hypoventilation significantly decreased the VAT in the control and 1PC groups (p<0.05) and non-significantly in 2PC vs. the initial values. Reoxygenation reversed the VAT values to the initial level only in the control group. In 3PC, the VAT was increased from 2.32±0.69 mA to 4.25±1.31 mA. during hypoventilation (p<0.001) and to 4.37±1.99 mA during reoxygenation (p<0.001). It is concluded that cardioprotection against the hypoventilation/ reoxygenation-induced decrease of VAT proved to be effective only after three cycles of HPC., P. Švorc, I. Bračoková., and Obsahuje bibliografii
a1_A new concept of cardioprotection based on the exploitation of endogenous mechanisms is known as ischemic preconditioning (IPC). It has been hypothesized that substances released during brief ischemic stress (e.g. catecholamines) stimulate the receptors and trigger multiple cell signaling cascades. Opening of ATP-sensitive K+ channels [K(ATP)] has been suggested as a possible final step in the mechanisms of protection. In this study, the role of adrenergic activation was tested in Langendorff-perfused rat hearts subjected to test ischemia (TI; 30 min occlusion of LAD coronary artery) by: 1) mimicking IPC (5 min ischemia, 10 min reperfusion) with short-term (5 min) administration of norepinephrine (NE, 1 µM), 15 min prior to TI; 2) blockade with b- or a1-receptor antagonists, propranolol (10 µM) and prazosin (2 µM), respectively, applied 15 min prior to TI during IPC. The role of K(ATP) opening was examined by perfusion with a K(ATP) blocker glibenclamide (10 mM) during IPC. Both IPC and NE-induced PC effectively reduced the incidence of ventricular tachycardia (VT) to 33 % and 37 %, respectively, vs 100 % in the non-PC controls, whereby ventricular fibrillation (VF) was totally abolished by IPC and markedly suppressed by PC with NE (0 % and 10 %, respectively, vs 70 % in the non-PC hearts; P<0.05). The severity of arrhythmias (arrhythmia score, AS) was also markedly attenuated by both interventions (IPC: AS 1.7±0.4; NE-PC: AS 1.8±0.3 vs AS 4.1±0.2 in the controls; P<0.05). Protection was not suppressed by propranolol (VT 28 %; VF 14 %; AS 2.2±0.6), whereas prazosin reversed the protective effect of PC (VT 83 %; VF 67 %; AS 4.0±0.8). Antiarrhythmic protection afforded by NE-PC was abolished by pretreatment of rats with pertussis toxin (25 mg/kg, i.p.) given 48 h prior to the experiments., a2_Glibenclamide did not suppress the IPC-induced protection. In conclusion, the sensitivity of the rat heart to ischemic arrhythmias can be modulated by IPC. Protection is mediated via stimulation of a1-adrenergic receptors coupled with Gi-proteins but glibenclamide-sensitive K(ATP) channels do not appear to be involved in the mechanisms of antiarrhythmic protection in this model., T. Ravingerová, D. Pancza, A. Ziegelhoffer, J. Styk., and Obsahuje bibliografii
Our aim was to investigate whether hyperthermia before exercise protects against exercise-induced skeletal muscle damage. Two hyperthermia protocols were evaluated. In the first, male ICR mice were exposed to 30 min of whole-body heat in an environmental chamber at an ambient temperature of 42 °C. Heat-exposed and non-heat-exposed mice subsequently completed 60 min of downhill running on a treadmill, 24 h after exposure. Heat exposure significantly increased HSP70 and HSP25 content in the soleus muscle compared to controls. Plasma creatine kinase, muscle β-glucuronidase, and histochemical (hematoxylin and eosin stain) analysis demonstrated that muscle damage was lower in the heatexposed mice than in the non-heat-exposed mice. In the second, the effect of regional heating of the legs, by microwave diathermy, on the prevention of exercise-induced muscle damage was evaluated in male Wistar rats. Microwave-treated and nonmicrowave-treated rats again completed the running protocol 24 h after exposure. Microwave diathermy increased the muscle temperature to 40 °C, significantly increased HSP70 and HSP25 content in the soleus muscle, and significantly attenuated exercise-induced muscle damage. Therefore, hyperthermia before exercise increases skeletal muscle HSPs and attenuates the risk of exercise-induced muscle injury.
After ten years of experience, the authors present an overview of the possible clinical uses of precordial isopotential electrocardiographic mapping in patients with ischaemic heart disease. The resting Q wave and ST segment maps have most often been found useful in the early phases of myocardial infarction. They are a helpful tool for monitoring progression of the disease, the effect of drugs, or the therapeutic effect of fibrinolytic therapy, etc. R wave mapping provides an excellent opportunity for following up patients after orthotopic heart transplantation and monitoring cardiac rejection. Stress tests are usually performed under a workload; alternative loads may be mental, pharmacological, stimulation-induced or under hypoxaemic stress. To evaluate a test, resting values are compared with those obtained during exercise. It is mainly exercise ST segment maps which have proved to be most informative; their use in the chronic phase of ischaemic heart disease helps to make the diagnosis of coronary insufficiency more accurate. In clinical practice, stress tests are recommended mostly in the follow-up of drug therapy, monitoring of the therapeutic effect of cardiac surgery or coronary angioplasty.
Let $\mathcal G$ be an abstract class (closed under isomorpic copies) of left $R$-modules. In the first part of the paper some sufficient conditions under which $\mathcal G$ is a precover class are given. The next section studies the $\mathcal G$-precovers which are $\mathcal G$-covers. In the final part the results obtained are applied to the hereditary torsion theories on the category on left $R$-modules. Especially, several sufficient conditions for the existence of $\sigma $-torsionfree and $\sigma $-torsionfree $\sigma $-injective covers are presented.
Recently, Rim and Teply [8], using the notion of τ -exact modules, found a necessary condition for the existence of τ -torsionfree covers with respect to a given hereditary torsion theory τ for the category R-mod of all unitary left R-modules over an associative ring R with identity. Some relations between τ -torsionfree and τ -exact covers have been investigated in [5]. The purpose of this note is to show that if σ = (Tσ, Fσ) is Goldie’s torsion theory and Fσ is a precover class, then Fτ is a precover class whenever τ ≥ σ. Further, it is shown that Fσ is a cover class if and only if σ is of finite type and, in the case of non-singular rings, this is equivalent to the fact that Fτ is a cover class for all hereditary torsion theories τ ≥ σ.
Pollen and macroscopic analyses of two Upper Holocene spring fen sites in the vicinity of the Turček village in the south-western foothills of the Kremnické vrchy Mts (central Slovakia) revealed new and unique information on the precultural and natural climazonal forests, and the origin and development of local meadow fen vegetation. Pollen-analytical data indicate the prevalence of natural spruce (Picea abies) and fir (Abies alba) forests in this region. The mixed beech forests depicted on the geobotanical map of Slovakia must have, therefore occupied much smaller areas than previously thought. After human colonization of the region during the 13th and 14th centuries natural forests were transformed mainly into grasslands and pastures, and to a lesser extent into arable fields. These changes were connected with gold and silver mining in the vicinity of the nearby town of Kremnica, with Turček one of the important areas producing timber for the mining industry. The development of these fen mires is also connected with deforestation and transformation of the landscape. They originated as forest springs but after human colonization of the area they were transformed into treeless fen meadows by the direct or indirect effect of man cutting of trees, grazing livestock and mowing.
Macrolophus pygmaeus (Hemiptera: Miridae) is an important predator of pests of horticultural crops and here its ability as a predator of Acyrthosiphon pisum (Hemiptera: Aphididae) is addressed for the first time. The percentage predation of the different aphid instars and the number partially consumed were studied. Our results, obtained using choice and no-choice tests, revealed that M. pygmaeus caught and consumed more young than later instars of A. pisum, which confirms results of previous studies using other species of aphids. We also studied the interactions between predators (male/female) foraging in the same patch. When the prey/predator ratio is kept constant at 10 : 1 the average percentage of aphids completely consumed by individual females or males does not change with increase in the number of foraging predators. However, the number of partially consumed aphids decreased when females shared the same patch. In contrast, there was an increase in the number of aphids partially consumed when two males shared the same patch. The results were discussed in terms of potential predator foraging strategies since intraspecific competition is a key factor modulating the dynamics of prey-predator systems., Juliana Durán Prieto, Vincenzo Trotta, Paolo Fanti, Cristina Castañé, Donatella Battaglia., and Obsahuje bibliografii
We studied the predation behaviour of the "hunter fly" (Coenosia attenuata Stein) in the laboratory and greenhouse. In the laboratory, which was conducted at 25°C at 60-80% RH, with a 16L : 8D photoperiod, we examined the functional response of this species to three different pests, namely the sciarid fly (Bradysia sp.), the tobacco whitefly (Bemisia tabaci) and the leaf miner Liriomyza trifolii. In the greenhouse, we studied the population dynamics of the predator and its prey on pepper and water melon crops grown in southern Spain. Adult hunter flies were found to exhibit a type I functional response to adult sciarid flies and whiteflies, but a type II response to adult leaf miners. The type II response was a result of the greater difficulty in capturing and handling leaf miners compared to the other two species. The dynamics of the predator-prey interaction in the greenhouse revealed that the predator specializes mainly on adult sciarids and that the presence of the other prey can be supplemental, but is never essential for survival of the predator; this, however, is crop-dependent. The results on the dynamics of the predator-prey systems were obtained through a known population dynamics model with modifications.
The impact of predation by alien American mink (Mustela vison) on endangered stone crayfish (Austropotamobius torrentium) was examined in middle-sized streams in central and western Bohemia for the duration of two years. The most frequent food source of the American mink were crustaceans, followed by mammals, amphibians and fish. Crustaceans consisted entirely of one species, the stone crayfish, which was represented in 82% of all collected mink droppings. Analysis of the relative composition of summer and winter diet showed no significant differences between these periods. The identification of predation of the American mink on stone crayfish was based on the collection of prey remains during the period monitored. Predation rates at particular localities were highly variable (0.85–21.5%, average = 7.4%), and decreased significantly in winter periods. The use of crayfish seems to reflect their spatial availability, suggested by the good correspondence between the population density and the number of prey remains. Minks preyed selectively on sexually mature individuals, which increases the seriousness of their predation impact. This study suggests that alien mink could be an important mortality factor for stone crayfish populations on a local scale.