首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 0 毫秒
1.
2.
3.
4.
The interrelationships between vasopressin and the renin-angiotensin system are reviewed. Vasopressin can inhibit the release of renin by the kidney. This effect can occur at physiological plasma concentrations of vasopressin. Centrally administered angiotensin II can stimulate the release of vasopressin, a response that may be partially mediated by brain prostaglandins. The significance of this action of angiotensin II depends on whether there is an effective brain renin-angiotensin system and on whether peripherally generated or administered angiotensin can reach sites in the brain where it can act on vasopressin release. Peripherally administered angiotensin II can under certain, but not all, conditions stimulate vasopressin release. Peripheral angiotensin II can also potentiate the vasopressin response to an osmotic stimulus and to dehydration, but has little effect the release of vasopressin and renin, there is a failure to demonstrate any correlation between the two. Blockade of the renin-angiotensin system fails to modify the vasopressin response to a reduction in blood volume. In conclusion, the physiological significance of the interactions between the vasopressin and the renin-angiotensin system is not as yet clearly established.  相似文献   

5.
Electrically induced afterdischarge (ADs) were evoked in the cats' dorsal hippocampus. The action of the conditioning prestimulation of the pallidus nucleus on AD duration was studied. A significant facilitatory influence was observed when pallidal conditioning stimulation immediately preceded hippocampal test stimulation. The time course of the phenomenon showed a decrease of the conditioning action when the interval between the two stimulations increased : complete disappearance of the effect occurred after about 800 ms. Results are discussed as far as functional relationships between basal ganglia and rhinencephalic system are concerned.  相似文献   

6.
7.
8.
9.
10.
Understanding the relationships among immune components in free-living animals is a challenge in ecoimmunology, and it is important not only for selecting the immune assays to be used but also for more knowledgeable interpretation of results. In this study, we investigated the relationships among six immune defense indexes commonly used by ecoimmunologists and measured simultaneously in individual free-living tree swallows. Three main axes of variation in immune function were identified using a principal components analysis, representing variation in T-cell, B-cell, and innate immunity. Measures within each axis tended to be positively correlated among individuals, while measures in different axes were uncorrelated. A trade-off between T-cell function and B-cell function became apparent only when variation among individuals in body condition, age, and general quality was taken into account. Interestingly, the level of natural antibodies, a component of innate immunity, showed the strongest association with components of acquired B-cell function, possibly reflecting a common underlying genetic mechanism, as has been documented in poultry. Our results indicate that despite the complexity of the immune system, important insights can be gained by using the currently available assays but in a more comprehensive approach than has generally been used in the field of ecoimmunology.  相似文献   

11.
12.
13.
This communication introduces a simple method to determine the pKs of microscopic ionizations from complex titration curves. We used this approach to study the alkaline transition (pH-dependent ligand exchange) of mitochondrial cytochrome c. The linearization of titration curves permitted resolution of two to three limiting microscopic ionizations. By combining these data with studies of the temperature dependence of ligand-exchange equilibria, we found evidence that the alkaline transition comprises two chemically distinct processes: the deprotonation of the alternative ligands and the break of the iron-methionine ligation bond. We also noted that, in the horse and untrimethylated S. cerevisiae iso-1 cytochromes c, the permissible deprotonation of the epsilon-amino group of Lys(72) allows formation of an alkaline isomer at lower pH, with lesser stability, which leads to hysteresis in the titration curves. The linearization of the titration curves for different cytochromes c thus brings insight on the microscopic contributions to conformational stability.  相似文献   

14.
Relation of hemorheology and hemodynamics in healthy people and patients with hypertension of the 1st stage has been studied. A weak correlation between hemorheology and hemodynamics indices is observed in the group of healthy people. Closer relations between these indices begin establishing in patients with hypertension of the 1st stage, that testifies to the interaction of these systems.  相似文献   

15.
We studied a number of EEG parameters and indices of personality characteristics (evaluated with the use of the MMPI questionnaire) in sixty 44- to 73-year-old patients with Parkinson's disease (PD). According to the intensity of the symptoms, they were classified into groups 1 and 2, with an initial or moderate level of disease manifestation. In group-2 patients, the powers of the - and -range rhythms were greater, as compared with those in group 1. This was combined with higher indices in scales 2 (depression, D), 8 (individualism, Sc), and 0 (introversion/extraversion, Si). A clear correlations between the EEG parameters and indices of personality structure were found. There were positive correlations between the normalized power of 2-rhythm and values of a few MMPI scales: 1 (supercontrol, Hs), 2 (depression, D), 4 (impulsivity, Pd), 7 (anxiety, Pt), 8 (individualism, Sc), and 0 (introversion/extraversion, Si). We also found negative correlations between the frequency of -rhythm and indices of supercontrol and anxiety scales. Correlations between different EEG parameters and MMPI scale indices depended on the level of disease manifestation. Our results allow us to assume a certain generality of the neurophysiological mechanisms determining modifications of the integral electrical activity of the brain and formation of individual psychological characteristics in parkinsonian patients.  相似文献   

16.
17.
The intestinal microbiota of broiler chickens and the microbiota in the litter have been well studied, but the interactions between these two microbiotas remain to be determined. Therefore, we examined their reciprocal effects by analyzing the intestinal microbiotas of broilers reared on fresh pine shavings versus reused litter, as well as the litter microbiota over a 6-week cycle. Composite ileal mucosal and cecal luminal samples from birds (n = 10) reared with both litter conditions (fresh versus reused) were collected at 7, 14, 21, and 42 days of age. Litter samples were also collected at days 7, 14, 21, and 42. The microbiotas were profiled and compared within sample types based on litter condition using PCR and denaturing gradient gel electrophoresis (PCR-DGGE). The microbiotas were further analyzed using 16S rRNA gene clone libraries constructed from microbiota DNA extracted from both chick intestinal and litter samples collected at day 7. Results showed significant reciprocal effects between the microbiotas present in the litter and those in the intestines of broilers. Fresh litter had more environmental bacteria, while reused litter contained more bacteria of intestinal origin. Lactobacillus spp. dominated the ileal mucosal microbiota of fresh-litter chicks, while a group of bacteria yet to be classified within Clostridiales dominated in the ileal mucosal microbiota in the reused-litter chicks. The Litter condition (fresh versus reused) seemed to have a more profound impact on the ileal microbiota than on the cecal microbiota. The data suggest that the influence of fresh litter on ileal microbiota decreased as broilers grew, compared with temporal changes observed under reused-litter rearing conditions.The intestines of broiler chickens harbor a complex microbiota that plays an important role in the growth and health of the bird. Nurmi and Rantala (27) provided the first reported evidence that a healthy gut microbiota could protect broiler chicks against a challenge by enteric pathogens. That study led to the concept of “competitive exclusion.” Since then, the colonization of the intestines by beneficial bacteria has been shown to promote epithelial cell turnover (34), increase mucous production (26), upregulate expression of genes involved in several important intestinal functions (14), and help with reinforcement of the mucosal barrier, modulation of the immune system, and metabolism of nutrients by the host (46). Although studies conducted using either cultivation-based or molecular biology analyses have documented that the intestinal microbiota of mature broiler chickens is relatively stable (10, 24, 45), this microbiota is still dynamic and can be manipulated to a large extent (8, 31, 37).Commercial broiler flocks in the United States are primarily floor raised in enclosed, environmentally controlled facilities. Within these commercial broiler houses, poultry litter can be reused for a year or longer if managed well and maintained in a relatively dry state (6). At an estimated accumulation rate of 1.45 metric tons per 1,000 broilers, the U.S. poultry industry, which produces >8.5 billion broilers per year (39), produces >12.3 million metric tons of poultry litter annually (4). Management and disposal of such a large quantity of poultry litter are two of the greatest challenges faced by U.S. broiler producers (6). Reuse of poultry litter can help alleviate this challenge, but there is concern that the reused-litter environment, both biotic and abiotic, may negatively affect the intestinal microbiota of the bird, potentially resulting in poor health and reduced production efficiency.Poultry litter is primarily a mixture of bedding materials and bird excreta. In addition to variation in the physiochemical properties, reused poultry litter harbors microbes of typically intestinal origin that are not commonly present in fresh litter (23, 35). During a broiler growth cycle, a constant influx of nutrients and intestinal microbes results in a complex litter microbiota. With continued reuse, the litter environment becomes more complex, which may have a profound impact on flock growth performance and health. Recognizing the importance of the litter environment, especially in commercial broiler houses with high stocking densities, several research groups have investigated how the physiochemical properties of broiler litter affect the growth and health of the birds (15) and the microbiota in the litter, using either cultivation-based or molecular biology techniques (22, 23, 33). Early studies focused on the effect of litter on enteric pathogens, including Salmonella (35, 12, 28) and cellulitis-causing Escherichia coli (38). From analyzing 16S rRNA gene clone libraries, Lu et al. (23) showed that in broiler litter at various stages of reuse, low-G+C Gram-positive bacteria predominated. Recent studies have focused on the interplay between the unique physiochemical conditions within the litter and the endogenous microbiota (22, 29), as well as the occurrence and persistence of antibiotic resistance in poultry litter (13, 17), providing some insight into the litter microbiota and the intestinal microbiota in broiler chickens. However, the relationship between litter and intestinal microbiotas has not been investigated. Since chickens consume some litter materials, we hypothesized that the intestinal and litter microbiotas may affect each other with respect to their composition and diversity. Using PCR with denaturing gradient gel electrophoresis (PCR-DGGE) and 16S rRNA gene clone library analysis, we tested this hypothesis by examining the effect of the litter microbiota on the ontogeny of the intestinal microbiota in broilers over a 6-week growth cycle.  相似文献   

18.
19.
20.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号