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At least 217 records · Page 12Linked to original sources
PubMed1987

Physiological adaptations of anaerobic bacteria to low pH: metabolic control of proton motive force in Sarcina ventriculi.

Detailed physiological studies were done to compare the influence of environmental pH and fermentation end product formation on metabolism, growth, and proton motive force in Sarcina ventriculi. The kinetics of end product formation during glucose fermentation in unbuffered batch cultures shifted from hydrogen-acetate production to ethanol production as the medium pH dropped from 7.0 to 3.3. At a constant pH of 3.0, the production of acetate ceased when the accumulation of acetate in the medium reached 40 mmol/liter. At a constant pH of 7.0, acetate production continued throughout the entire growth time course. The in vivo hydrogenase activity was much higher in cells grown at pH 7.0 than at pH 3.0. The magnitude of the proton motive force increased in relation to a decrease of the medium pH from 7.5 to 3.0. When the organism was grown at pH 3.0, the cytoplasmic pH was 4.25 and the organism was unable to exclude acetic acid or butyric acid from the cytoplasm. Addition of acetic acid, but not hydrogen or ethanol, inhibited growth and resulted in proton motive force dissipation and the accumulation of acetic acid in the cytoplasm. The results indicate that S. ventriculi is an acidophile that can continue to produce ethanol at low cytoplasmic pH values. Both the ability to shift to ethanol production and the ability to continue to ferment glucose while cytoplasmic pH values are low adapt S. ventriculi for growth at low pH.

Acids↗
PubMed1981

Relation between QT interval and heart rate. New design of physiologically adaptive cardiac pacemaker.

The relation between QT interval and heart rate has been studied in a group of patients undergoing physiological exercise, in a group undergoing atrial pacing without exercise, and in a group with complete heart block undergoing exercise at a fixed ventricular rate controlled by cardiac pacing. The expected shortening in QT interval during physiological exercise is only in part the result of the intrinsic effect of increased rate, since patients undergoing atrial pacing to comparable rates show only a small decrease in measured QT interval and patients exercising at fixed rates in heart block exhibit a decreasing QT interval related to the independent atrial rate. QT interval changes appear mainly to be governed by factors extrinsic to heart rate. The physiological control of QT interval has been used to construct a cardiac pacemaker which senses the interval between the delivered stimulus and the evoked T wave, and uses the stimulus-evoked T wave interval to set the subsequent pacemaker escape interval. Thus physiological control of cardiac pacing rate, independent of atrial activity, using conventional unipolar lead systems is possible.

Cardiac Pacing, Artificial↗
PubMed1983

Specificity of physiologic adaptations resulting from ice-hockey training.

The specificity of the metabolic and cardiorespiratory responses to varied seasonal training programs and to varied testing modalities and protocols were investigated in two groups of college hockey players. Training consisted of either ice hockey (IH) or a combination of ice hockey and prolonged low-intensity cycling (IH-C). Measurement of training-induced adaptations were determined during maximal and submaximal ice skating, and during maximal and submaximal cycling. Ice hockey training caused no change in VO2max, maximal heart rate (HRmax), and maximal ventilation (VEmax) during maximal ice skating. During submaximal ice skating following IH training, however, reductions (P less than 0.05) in blood lactate (La), VE/VO2, and respiratory exchange ratio (R) were observed. When maximal and submaximal cycling was employed as the test modality, no training-induced alteration was found. The IH-C training program (ice hockey-cycling) resulted in adaptations similar to those observed during submaximal ice skating following the IH training. In addition, a reduction (P less than 0.05) in heart rate was observed during submaximal cycling exercise. From these findings it appeared that the adaptive response to training may be specific to the type of work used in training, the type of ergometry used to evaluate training, and to specific physiological processes. In addition, these results suggested a dissociation between local and central adaptations.

Adult↗
PubMed1983

Behavioral, but not physiological, adaptation to repeated separation in mother and infant primates.

Mother and infant squirrel monkeys were subjected to a series of brief separations in order to evaluate how behavioral and physiological responses change following multiple exposures to stress. Beginning when the infants reached three months of age, their behavioral and hormonal responses were assessed during six 1-hr separations; and additional five dyads served as controls for the effect of repeated disturbance. The separated infants showed a marked and progressive decrease in distress calling across time, but no change was observed in the high levels of agitated activity or the plasma cortisol response to separation. This finding questions the traditional use of distress vocalizations as a measure of stress and indicates that certain types of behavior can change independently of physiological arousal responses, which may continue to occur even after repeated exposures to stress.

Adaptation, Psychological↗
PubMedDate not supplied

Neandertal cold adaptation: physiological and energetic factors.

European Neandertals employed a complex set of physiological cold defenses, homologous to those seen in contemporary humans and nonhuman primates. While Neandertal morphological patterns, such as foreshortened extremities and low relative surface-area, may have explained some of the variance in cold resistance, it is suggested the adaptive package was strongly dependent on a rich array of physiological defenses. A summary of the environmental cold conditions in which the Neandertals lived is presented, and a comparative ethnographic model from Tierra del Fuego is used. Muscle and subcutaneous fat are excellent "passive" insulators. Neandertals were quite muscular, but it is unlikely that they could maintain enough superficial body fat to offer much cold protection. A major, high-energy metabolic adaptation facilitated by modest amounts of highly thermogenic brown adipose tissue (BAT) is proposed. In addition, Neandertals would have been protected by general mammalian cold defenses based on systemic vasoconstriction and intensified by acclimatization, aerobic fitness, and localized cold--induced vasodilation. However, these defenses are energetically expensive. Based on contemporary data from circumpolar peoples, it is estimated that Neandertals required 3,360 to 4,480 kcal per day to support strenuous winter foraging and cold resistance costs. Several specific genetic cold adaptations are also proposed--heat shock protein (actually, stress shock protein), an ACP*1 locus somatic growth factor, and a specialized calcium metabolism not as yet understood.

Acclimatization↗
PubMed1995

Mathematical model of oxygen transport: a teaching aid for normal physiology adaptable to extracorporeal oxygenation circuits.

The ultimate aim of most intensive care therapies is to improve tissue oxygen delivery; consequently, a detailed knowledge of this area of physiology is important to a wide range of Critical Care Staff. We describe a simple mathematical model of oxygen transport that was initially written as a training aid for extracorporeal oxygenation training. The model has subsequently proved useful for explaining the determinants of oxygen transport to a broader audience. It is based on simple linear equations and is easily displayed with a standard computer spreadsheet. Apart from its teaching value, the model can also generate a graph of oxygen saturation vs. inspired oxygen fraction for different degrees of pulmonary shunt. This provides a noninvasive method for determining the magnitude of pulmonary venous admixture and may also prove to have some clinical value.

Biological Transport, Active↗
PubMed1988

Physiological adaptations to thermal stress in tropical Asians.

Young sedentary adult males of Malay, Indian, and Chinese origin who had established continuous residence in tropical Malaysia and presumed to be naturally acclimatized to heat, were studied to evaluate their physiological responses to a standard heat stress test. The Malay and Indian races have evolved in hot and humid geographical zones, whereas the Chinese originated from a temperate area. Subjects exercised at 50% VO2max alternating 18 minutes walking and 2 min rest during a 2-h exposure to an ambient of 34.9 degrees C dry bulb and 32.1 degrees C wet bulb. Heart rates, core and skin temperatures, sweat rates, and oxygen uptakes were measured during the heat exposure. The subjects of Malay origin exhibited the least circulatory stress of the three ethnic groups. The data obtained on these long-term residents of a hot-wet climate and who were considered acclimatized to this environment were compared to experimental data obtained by other investigators and other ethnic groups.

Acclimatization↗
PubMedDate not supplied

Discordance between genetic structure and morphological, ecological, and physiological adaptation in Lake Magadi tilapia.

The Magadi tilapia (Alcolapia grahami, formerly Oreochromis alcalicus grahami) is a remarkable example of teleost life in an extreme environment. Typical conditions include water pH=10, titration alkalinity>300 mM, osmolality=525 mOsm, temperatures ranging from 23 degrees to 42 degrees C, and O(2) levels fluctuating diurnally between extreme hyperoxia and anoxia. A number of relatively small tilapia populations are present in various thermal spring lagoons around the margin of the lake separated by kilometers of solid trona crust (floating Na(2)CO(3)) underlain by anoxic water. Despite the apparent isolation of different populations, annual floods may provide opportunities for exchange of fish across the surface of the trona and subsequent gene flow. To assess the question of isolation among Lake Magadi populations, we analyzed the variable control region of the mitochondrial DNA (mtDNA) from six lagoons. A total of seven mtDNA haplotypes, including three common haplotypes, were observed in all six populations. Several of the Lake Magadi populations showed haplotype frequencies indicative of differentiation, while others showed very little. However, differentiation among lagoon populations was discordant with their geographical distribution along the shoreline. All populations exhibited the unusual trait of 100% ureotelism but specialized morphological and physiological characteristics were observed among several of the lagoon systems. In addition, distinct differences were observed in the osmolality among the lagoons with levels as high as 1,400-1,700 mOsm kg(-1), with corresponding differences in the natural levels of whole-body urea. These levels of osmotic pressure proved fatal to fish from less alkaline systems but remarkably were also fatal to the fish that inhabited lagoons with this water chemistry. Upon more detailed inspection, specific adaptations to differential conditions in the lagoon habitat were identified that allowed survival of these cichlids. Additional evidence against potential for gene flow among lagoons despite the sharing of common mtDNA haplotypes was that the osmolality of floodwaters following a heavy rain showed lethal levels exceeding 1,700 mOsm kg(-1). In isolation, different mtDNA haplotypes would be predicted to go to fixation in different populations due to rapid generation times and the small effective population sizes in a number of lagoons. We propose a model of balancing selection to maintain common mtDNA sequences through a common selection pressure among lagoons that is based on microhabitats utilized by the tilapia.

Adaptation, Biological↗
PubMed2004

An ffh mutant of Streptococcus mutans is viable and able to physiologically adapt to low pH in continuous culture.

Previously, we described in Streptococcus mutans strain NG8 a 5-gene operon (sat) that includes ffh, the bacterial homologue of the eukaryotic signal recognition particle (SRP) protein, SR54. A mutation in ffh resulted in acid sensitivity but not loss of viability. In the present study, chemostat-grown cells of the ffh mutant were shown to possess only 26% and 39% of the parental membrane F-ATPase activity and 55% and 75% of parental glucose-phosphotransferase (PTS) activity when pH-7 and pH-5-grown cells, respectively, were assayed. Two-dimensional-gel electrophoretic analyses revealed significant differences in protein profiles between parent and ffh-mutant strains at both pH 5 and pH 7. It appears that the loss of active SRP (Ffh) function, while not lethal, results in substantial alterations in cellular physiology that includes acid tolerance.

Acclimatization↗
PubMed1980

Physiological adaptations in response to environmental stress during an n(2)-fixing anabaena bloom.

Anabaena spiroides has the ability to maintain intense biomass production for extensive periods in the epilimnion of a small eutrophic lake characterized by conditions shown to cause photooxidative death in a number of other phytoplankton. By the enhancement of carotenoid synthesis chlorophyll a was protected from photooxidation and prevented from catalyzing other photooxidative reactions within the cells. By temporally separating CO(2) and N(2) fixation, maximum utilization of photosynthetically active radiation was achieved. Because CO(2) fixation was more sensitive than N(2) fixation to a high oxygen concentration, the former was maximized during morning hours, before the afternoon buildup of dissolved oxygen. The diurnal partitioning of carbon and N(2) fixation has two additional advantages; possible competition for reductant-generating compounds is minimized, and adequate endogenous pools of carbon skeletons are assured to accept newly fixed ammonia. Hence, Anabaena, far from undergoing photooxidative death, appears to utilize a physiological strategy which allows optimization of radiant energy use for reductive processes and dominance of surface waters and shading of deeper phytoplankton during summer blooms.

Journal Article↗
PubMed2000

[Blood physiological resources and their role in physiological adaptation of the body to blood loss (based on the experimental data and calculations)].

In white rats, loss of about 66 +/- 3% of the blood volume results in an abrupt drop of the BP and arrest of the lung respiration. Introduction of a plasma substitute in the volume equal to the lost blood resulted in an increase of the BP and restoration of rhythmical respiration in 9 out of 14 experimental rats. Haematocrit after the blood loss and subsequent administration of the substitute was about 15%. Previously obtained data show that the Ht of about 15% decreases the oxygen transport to tissues. However, an increase in the lung ventilation, a shift of the haemoglobin dissociation curve to the right, an increase of oxygen extraction from the blood, and an increase in the minute blood volume by 50-100%, allow a sufficient oxygen transport to the organism tissues to be ensured at the Ht of about 15%. Thus, the reserve of the blood respiration function of the blood remaining after a life-threatening blood loss plays an important physiological role in replenishing the volume of the lost blood with the plasma substitute and in survival of the organism.

Animals↗
PubMed1991

Regulation of cardiac gene expression during myocardial growth and hypertrophy: molecular studies of an adaptive physiologic response.

Studies from both in vivo and in vitro model systems have provided an initial skeleton of the potential signaling pathways that might regulate cardiac genes during growth and hypertrophy. One of the first detectable changes in cardiac gene expression is the activation of a program of immediate early gene expression, which is distinct for the hypertrophic response, and is conserved in multiple models of both in vivo and in vitro hypertrophy. Diverse and distinct hormonal stimuli have been documented to activate several features of the hypertrophic response, including several autocrine and paracrine factors. Although the signaling mechanisms that link these factors with the activation of cardiac gene expression are unclear, recent studies suggest that the activation of protein kinase C may represent one of the most proximal common events in this signaling cascade. The activation of cardiac target genes induces a program of embryonic gene expression, including the atrial natriuretic factor (ANF) gene. The cis sequences that mediate cardiac-specific and inducible expression of an embryonic marker gene (ANF) can be segregated by studies in both cultured cell models and in vivo models of hypertrophy in transgenic mice, suggesting that specific sets of regulatory elements may exist for inducible expression of this class of cardiac gene responses. However, the induction of a constitutively expressed contractile protein gene (MLC-2) is mediated by a set of conserved elements that regulate both cardiac-specific and inducible expression. Finally, a subset of cardiac muscle genes appears to be noninducible during in vivo or in vitro hypertrophy in myocardial cells, demonstrating specificity of transcriptional activation during the hypertrophic process. The development of a bona fide in vivo pressure overload model of hypertrophy in a small animal model that can be genetically manipulated, such as the in vivo murine model recently described, should allow a rigorous analysis of the role of these specific signaling mechanisms in the activation of the responses of cardiac genes during the hypertrophic process in vivo.

Adaptation, Biological↗
PubMed1993

Some aspects of perinatal maturation and adaptation.

Physiological challenges facing the perinatal individual are huge. This is partly because of the marked and abrupt change from the intrauterine to the extrauterine environment, but also because the physiological responses to that change depend upon systems whose maturation is affected markedly by birth. Perinatal maturation appears, therefore, both to precede and accompany the physiological adaptations required for neonatal survival. This review does not provide a comprehensive coverage of perinatal physiology but directs attention towards evaluating constraints on foetal and neonatal thermogenesis, especially those imposed by post-natal availability of metabolic fuels in body reserves deposited before birth and acquired in colostrum and milk after birth. The relative importance of the supply of carbohydrate from body reserves and colostrum is examined. Carbohydrate is the major rate-limiting substrate with respect to heat production. It is shown that in the normal birth environments of several species, including the horse, colostral supply of lactose is not adequate to meet the entire carbohydrate needs of the neonate. It must, therefore, draw on its body glycogen reserves to sustain the required rates of heat production during the first day after birth. Gastrointestinal maturation and growth play a major part in the initial and continued provision of substrates for general metabolism and growth. Pre-natal and post-natal development of the stomach and intestines in a number of species are considered, including their disproportionately large growth compared with the body as a whole during the first 1-3 days after birth. Possible contributions to gastro intestinal growth and body growth of milk-borne growth factors such as epidermal growth factors and the insulin-like growth factors are considered. The role, as a possible significant stimulus to gastrointestinal growth and maturation immediately after birth, of the high levels of these growth factors in colostrum is evaluated.

Adaptation, Physiological↗
PubMed1997

Molecular aspects of oxygen sensing in physiological adaptation to hypoxia.

Oxygen is an essential substrate in aerobic metabolism for most eukaryotic organisms. Thus organisms and cells have developed numerous immediate and long-term compensatory mechanisms for dealing with oxygen deprivation. Adaptation to hypoxia at the organismal level includes reflex hyperventilation, polycythemia and angiogenesis, which lead to increased O2 delivery to the tissues. Adaptation at the cellular level involves a shift from oxidative phosphorylation to anaerobic glycolysis, increased glucose metabolism, and expression of hypoxic stress-related proteins. Regulation of many proteins participating in adaptation to hypoxia occurs at the level of gene expression. The most widespread molecular mechanism of hypoxia-dependent regulation is transcriptional induction via the binding of a transcription factor, hypoxia-inducible factor-1 (Hif-1), to the specific sequences on the regulated genes. Long-term induction of many proteins also requires an increase in mRNA stability, which is mediated by the binding of regulatory proteins to specific sequences within the mRNAs. The current theories of coupling between the O2 sensor and mechanisms controlling gene expression are discussed.

Animals↗