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PubMed2001

Ventilator-induced lung injury and the evolution of lung-protective strategies in acute respiratory distress syndrome.

Traditional ventilator management of acute respiratory distress syndrome (ARDS), emphasizing normalization of blood gases, promoted high rates of conventional barotrauma. Research revealed a broader range of ventilator-induced lung injury, physiologically and histopathologically indistinguishable from ARDS itself. It is now known that overdistention and cyclic inflation of injured lung can exacerbate lung injury and probably promote systemic inflammation, effects minimized by low tidal volumes/plateau pressures and by application of positive end-expiratory pressure. No compelling data suggest a safe interval for nonprotective ventilation in humans; historically defined "low" tidal volumes may remain excessive for certain patients. Protective ventilation, however, entails carbon dioxide accumulation ("permissive hypercapnia"). Despite extensive study, debate remains, even over whether consequent respiratory acidosis is harmful, tolerable with physiologic adaptation, or intrinsically adaptive. Its gross systemic effects seem generally tolerated by critically ill patients; however, subsets, including those with ischemic heart disease, left or right heart failure, pulmonary hypertension, or cranial injury, may be at higher risk. In controlled trials demonstrating mortality benefit from lung-protective ventilation, acidosis was more tightly controlled than in negative studies. Decreased acidosis-associated dyspnea probably explains reduced use of sedatives and paralytics noted in those trials. There may thus be disparate goals in ARDS management: rapid institution of a restrictive ventilatory strategy, and avoidance of significant acidosis. We review data pertaining to ARDS physiology, ventilator-induced lung injury, lung-protective ventilatory strategies, and the physiology of respiratory acidosis. Tracheal gas insufflation is considered as a means to reconcile the clinical goals of ventilatory reduction and control of acidosis.

Acidosis, Respiratory↗
PubMed1987

Adaptation by an urban population of the snail Helix aspersa to a diet contaminated with lead.

Two populations of the garden snail Helix aspersa, from an urban car park and from a semi-rural site, were fed a diet containing 500 microg g(-1) of Pb as PbSO(4). After 2 days, half of each population was removed to a Pb-free diet and half continued on the dosed food, both for 64 days. The snails from the contaminated site had a significantly lower uptake of Pb compared with those from the rural, uncontaminated site. The car park snails also lost Pb more rapidly from their tissues. A second experiment evaluated the effect of a previous exposure to a high Pb diet on Pb uptake. The results suggest that the differences between the two populations are not due to a physiological adaptation, but rather that the car park snails represent an ecotype adapted to a high Pb diet.

Journal Article↗
PubMed2005

Seasonal environmental changes regulate the expression of the histone variant macroH2A in an eurythermal fish.

Adaptation to cold and warm conditions requires dramatic change in gene expression. The acclimatization process of the common carp Cyprinus carpio L. in its natural habitat has been used to study how organisms respond to natural environmental changes. At the cellular level, adaptation to cold condition is accompanied by a dramatic alteration in nucleolar structure and a down regulation of the expression of ribosomal genes. We show that the enrichment of condensed chromatin in winter adapted cells is not correlated with an increase of the heterochromatin marker trimethyl and monomethyl K20H4. However, the expression of the tri methyl K4 H3 and of the variant histone macroH2A is significantly increased during the winter season together with a hypermethylation of CpG residues. Taking into account the properties of macroH2A toward chromatin structure and dynamics and its role in gene repression our data suggest that the increased expression of macroH2A and the hypermethylation of DNA which occurs upon winter-acclimatization plays a major role for the reorganization of chromatin structure and the regulation of gene expression during the physiological adaptation to a colder environment.

Acclimatization↗
PubMed2000

Characterisation of vasopressin V(1A), angiotensin AT(1) and AT(2) receptor distribution and density in normotensive and hypertensive rat brain stem and kidney: effects of restraint stress.

In the present study, we have examined neurochemical correlates that may be involved in the differential cardiovascular responses observed in normotensive and hypertensive rats during stress. Using a restraint stress paradigm, both normotensive Wistar Kyoto (WKY) and Spontaneously Hypertensive rats (SHR) underwent acute (1 h restraint in a perspex tube), chronic (1 h restraint for ten consecutive days) or no restraint (control) stress. Following cessation of restraint, rats were processed by incubating sections of brain stem and kidney with [125I]-HO-LVA (0.03 nM) or [125I]Sar(1)Ile(8)-AngiotensinII (0.5 nM), in the presence of PD123319 (10 microM) or losartan (10 microM), to determine the distribution and density of vasopressin V(1A), angiotensin AT(1) and AT(2) receptors, respectively. Analysis of autoradiograms indicated changes in the density of radioligand binding in acutely and chronically-stressed rats, as compared to controls. For example, V(1A) binding in the medial nucleus tractus solitarius (SolM) decreased in the WKY but increased in the SHR. AT(1) binding in SolM did not significantly change in the WKY but decreased in the SHR with repeated restraint. In kidney slices, AT(1) binding decreased with stress in the WKY (-17%) but increased in SHR (+10-15%). AT(2) binding in the kidney showed a pattern similar to that of AT(1) binding in SHR, but not WKY. Graded increases in V(1A) binding were measured in kidney medulla and cortex of both strains (+50-60% with chronic restraint). These results suggest that physiological adaptation to restraint is associated with specific changes in V(1A), AT(1) and AT(2) receptor density within brain nuclei and kidney.

Acute Disease↗
PubMed1978

Living with stress.

Explore the source record for details and available documents.

Adaptation, Physiological↗
PubMed1985

Morphology of physiologically identified slowly adapting lung stretch receptor afferents stained with intra-axonal horseradish peroxidase in the nucleus of the tractus solitarius of the cat. I. A light microscopic analysis.

The present series of experiments was designed to study the organization of preterminal processes and synaptic boutons of single physiologically identified slowly adapting receptor (SAR) pulmonary stretch afferent fibers. Intra-axonally injected horseradish peroxidase-wheat germ agglutinin (HRP-WGA) conjugate was used as the label. In the first paper, we describe the pattern of arborization of axon collaterals from single physiologically identified SAR afferent fibers evident in the various subnuclei of the nucleus of the tractus solitarius (nTS). In the second paper, details are presented regarding the ultrastructure of these synaptic boutons and axon collaterals. A number of significant findings resulted from this study: (1) A single lung stretch SAR afferent fiber arborized over a considerable distance rostrocaudally in the brain stem (1,700-2,100 microns). (2) A single lung stretch SAR afferent fiber terminated as hundreds of bouton terminals (650-1,180). (3) There was a remarkable consistency in the subnuclei of the nTS that received these terminal arborizations of SAR afferents. (4) The ventral (vnTS), intermediate (nI), ventrolateral (vlnTS), and interstitial (ni) subnuclei of the nTS were the only regions of the nTS receiving bouton terminals of SAR afferent fibers. (5) Under the light microscope the pattern of termination of SAR afferents was similar in all the axons studied in this series. (6) The injected parent axon in each case could be followed in the TS at all levels and remained consistent with regard to position and orientation and could be traced rostrally to levels as far as 3.5 mm rostral to the obex whereas the region of terminal arborization was located around 1.7-2.1 mm rostral to the obex. This pattern indicates that a single lung stretch SAR afferent fiber descends caudally upon entering the nTS. In the cat vagal afferent fibers are known to enter the medulla at levels between 0.5 mm and 3.2 mm rostral to the obex (Kalia and Mesulam, '80a). The results of the light microscopic analysis presented in this article indicate that lung stretch (SAR) afferents from the lungs and tracheobronchial tree have distinctly localized patterns of distribution in the nTS. In addition, these findings support the concept that representation of pulmonary afferents in the medulla is constituted by a differentiated distribution of nerve terminals in the various subnuclei of the nTS. Modality-specific localization (SAR afferents in this case) appears to be predominant in the nTS. The widespread rostrocaudal distribution of the terminal field of a single lung stretch SAR afferent is remarkable.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMed2005

Effects of season and low-level air pollution on physiology and element content of lichens from the U.S. Pacific Northwest.

Lichens were collected from three low-elevation sites in the western Cascade Range: HJ Andrews, OR (clean) and Bull Run, OR, and Pack Forest, WA (moderately enhanced nitrogen and sulfur deposition). The latter sites were within 50 km of Portland and Seattle/Centralia urban-industrial areas, respectively. Tissue concentrations of sulfur, nitrogen, and other macronutrients; rates of net carbon uptake; concentrations of photosynthetic pigments; and thallus density were correlated with season and seasonal changes in Platismatia glauca. Ion concentrations in precipitation and total wet deposition were measured from natural settings. Concentrations of depositional ions in precipitation, including NO3- and NH4+, were generally highest at Bull Run and Pack Forest; SO4(2-) concentrations and acidity were highest at Pack Forest. Total wet deposition was higher in the winter rainy season than the dry summer season at all three sites. Lichens adapted physiologically and morphologically to the higher light intensity and the warm, dry climate of summer through decreased optimal water content for CO2 uptake, increased concentrations of carotenoids and increased thallus density. Compared to the clean site, the sites with enhanced deposition were associated in P. glauca with year-round higher tissue concentrations of N, S, K, and Na; higher concentrations of total chlorophyll and carotenoids; higher OD435/415 ratios; higher CO2 uptake and lower thallus density in summer; and a general absence of other sensitive lichens. These results indicate that moderate levels of fertilizing air pollutants can stimulate carbon uptake and provide protection against chlorophyll degradation in air pollution-tolerant lichens of the Pacific Northwest, especially during the dry summer season.

Air Pollutants↗
PubMed1992

Effect of ambient oxygen concentration upon the acute toxicity of chlorophenols and heavy metals to the groundwater copepod Parastenocaris germanica (Crustacea).

Acute static toxicity experiments have been performed under normoxic and hypoxic conditions. The test animals used were adults of the groundwater-adapted copepod Parastenocaris germanica. The animals originated from a sandy, gravelly phreatic aquifer of the Meuse valley in The Netherlands. Toxicants applied were pentachlorophenol, 3,4-dichlorophenol, zinc, and cadmium. The results were statistically evaluated by a log-logistic model. LC50 and LC5 values with 95% confidence limits were calculated. Response models of application under both oxygen conditions were compared. The influence of ambient oxygen concentration on sensitivity appeared to be very small; only in the case of pentachlorophenol were hypoxic and normoxic models slightly but significantly different. Comparisons with the sensitivity of other organisms are made and the results are discussed against the specific physiological adaptations of the organisms to groundwater conditions.

Animals↗
PubMed1995

The 'cancell' theory of carcinogenesis: re-evolution of an ancient, holistic neoplastic unicellular concept of cancer.

The 'cancell' theory of carcinogenesis is based on four assumptions: 1. that there is early evolvement of neoplastic potentials in certain unicellular eukaryotes (so-called cancell lines) by adaptive response to the various carcinogens of the primitive Earth. The process that led to the neoplastic potential is called 'early carcinogenesis'; 2. that there is transition of cancell lines to multicellular forms; 3. that there is uptake of the basic genetics and epigenetics of the cancell concept into the genomic program of multicellular entities and their conservation even in human cells, and 4. the re-emergence of the ancient cancell concept in human somatic cells in a process called 'late carcinogenesis'. According to this theory, both processes of carcinogenesis, the early one and the late one, are thought to be the result of a physiological adaptive response to the various genotoxic and nongenotoxic carcinogens.

Animals↗
PubMed1993

Physiologic mechanisms effecting circulatory and body fluid losses in weightlessness as shown by mathematical modeling.

The mechanisms causing large body water losses in weightlessness are not clear. It has long been considered that a central volume expansion drives the physiologic adaptation to a reduced total blood volume, with normal blood composition eventually regained. However, inflight venous pressure measures suggest that central volume expansion in weightlessness may be very transient, or that considerable cardiovascular adaptation to fluid shifts occurs on the ground while astronauts wait in the semi-supine pre-launch position. If a central volume stimulus does not persist, other mechanisms must drive the adaptation of circulation to a reduced blood volume and account for body fluid losses. Recent results from the SLS-1 mission suggest that body fluid volumes do not simply decline to new equilibria but that they decrease to a low point, then undergo some recovery. Similar "under-shoots" of body fluid volumes have also been shown in computer simulations, providing confidence in the validity of the model. The purpose of this study was to examine the mechanisms which could explain the loss of body fluids in weightlessness and how a cardiovascular preadaptation countermeasure we previously tested ameliorated body fluid losses. It is assumed that the physiology of head down tilt (HDT) provides a reasonably accurate analog of weightless exposure.

Blood Viscosity↗
PubMed2005

New horizons for (p)ppGpp in bacterial and plant physiology.

A hyperphosphorylated guanosine nucleotide, (p)ppGpp, was initially identified as the effector molecule responsible for the stringent response in Escherichia coli. However, a rapidly growing number of reports proves that (p)ppGpp-mediated regulation is conserved in many bacteria and even in plants. It is now clear that (p)ppGpp acts as a global regulator during physiological adaptation of the organism to a plethora of environmental conditions. Adaptation is not only essential for surviving periods of stress and nutrient exhaustion but also for the interaction of bacteria with their eukaryotic host, as observed during pathogenesis and symbiosis, and for bacterial multicellular behaviour. Recently, there have been several new discoveries about the effects of (p)ppGpp levels, balanced by RelA-SpoT homologue proteins, in diverse organisms.

Arabidopsis↗
PubMed2000

Food intake-induced leptin secretion modulates hypothalamo-pituitary-adrenal axis response and hypothalamic Ob-Rb expression to insulin administration.

The mutation of the ob gene is known to induce a phenotype of obesity accompanied by symptoms including enhanced production of glucocorticoid. Chronic administration to ob/ob mice of leptin, the ob gene product, reverses hypercorticosteronemia. This establishes a clear relation between adipocyte and hypothalamo-pituitary-adrenal (HPA) axis functions. In the present study we investigated the acute modulatory effects of food intake-stimulated leptin secretion on HPA axis activity and hypothalamic leptin receptor (Ob-Rb) expression in 24-hour fasting, adult female, BALB/c mice after insulin-induced hypoglycemia. Our results indicate that: (1) food supply for 45 min to 24-hour fasting mice increased plasma glucose levels and reversed both hypercorticosteronemia and hypoleptinemia; (2) the insulin-induced hypoglycemia produced a marked HPA axis activation in animals with no access to food but this response was fully prevented by food intake and the consecutive increase in plasma leptin levels; (3) the inhibitory effect of leptin on the HPA axis response to insulin-induced hypoglycemia was corroborated by i.p. administration of murine leptin, and (4) fasting-induced hypothalamic Ob-Rb overexpression is not modulated by insulin itself but by leptin, since increase in leptin levels by food intake or by administration of exogenous leptin completely reversed this Ob-Rb overexpression. These results confirm the inhibitory effect of leptin on the HPA axis response to various stress stimuli. They clearly demonstrate that acute food intake in 24-hour fasting mice: (a) rapidly reduced fasting-induced hypercorticosteronemia by enhancing both spontaneous and insulin-elicited endogenous leptin secretion; (b) fully prevented HPA axis response to insulin administration, by rapidly increasing endogenous leptin secretion and probably also by diminishing the extent and the duration of insulin-induced hypoglycemia, and (c) abolished hypothalamic Ob-Rb overexpression induced by fasting itself combined with insulin treatment. The present data strongly suggests an inhibitory effect of endogenous leptin on insulin-induced HPA axis response, an interaction relevant to the physiological adaptation to starvation and caloric excess, and further supports the pivotal role played by the hypothalamus in restoring homeostasis in different allostatic states.

Adrenocorticotropic Hormone↗