Effects of square-wave and simulated natural light-dark cycles on hamster circadian rhythms.
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Circadian rhythms of activity (Act) and body temperature (Tb) were recorded from male Syrian hamsters under square-wave (LDSq) and simulated natural (LDSN, with dawn and dusk transitions) light-dark cycles. Light intensity and data sampling were under the synchronized control of a laboratory computer. Changes in reactive and predictive onsets and offsets for the circadian rhythms of Act and Tb were examined in both lighting conditions. The reactive Act onset occurred 1.1 h earlier (P < 0.01) in LDSN than in LDSq and had a longer alpha-period (1.7 h; P < 0.05). The reactive Tb onset was 0.7 h earlier (P < 0.01) in LDSN. In LDSN, the predictive Act onset advanced by 0.3 h (P < 0.05), whereas the Tb predictive onset remained the same as in LDSq. The phase angle difference between Act and Tb predictive onsets decreased by 0.9 h (P < 0.05) in LDSN, but the offsets of both measures remained unchanged. In this study, animals exhibited different circadian entrainment characteristics under LDSq and LDSN, suggesting that gradual and abrupt transitions between light and dark may provide different temporal cues. (+info)
Thermal heterogeneity within human atherosclerotic coronary arteries detected in vivo: A new method of detection by application of a special thermography catheter.
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BACKGROUND: Activated macrophages play an important role in the pathogenesis of acute ischemic syndromes. It has been postulated that detection of heat released by activated inflammatory cells of atherosclerotic plaques may predict plaque rupture and thrombosis. Previous ex vivo studies have shown that there is thermal heterogeneity in human carotid atherosclerotic plaques. METHODS AND RESULTS: To measure the temperature of human arteries in vivo, we developed a catheter-based technique. Ninety patients (45 with normal coronary arteries, 15 with stable angina [SA], 15 with unstable angina [UA], and 15 with acute myocardial infarction [AMI]) were studied. The thermistor of the thermography catheter has a temperature accuracy of 0.05 degrees C, a time constant of 300 ms, and a spatial resolution of 0.5 mm. Temperature was constant within the arteries of the control subjects, whereas most atherosclerotic plaques showed higher temperature compared with healthy vessel wall. Temperature differences between atherosclerotic plaque and healthy vessel wall increased progressively from SA to AMI patients (difference of plaque temperature from background temperature, 0. 106+/-0.110 degrees C in SA, 0.683+/-0.347 degrees C in UA, and 1. 472+/-0.691 degrees C in AMI). Heterogeneity within the plaque was shown in 20%, 40%, and 67% of the patients with SA, UA, and AMI, respectively, whereas no heterogeneity was shown in the control subjects. CONCLUSIONS: Thermal heterogeneity within human atherosclerotic coronary arteries was shown in vivo by use of a special thermography catheter. This heterogeneity is larger in UA and AMI, suggesting that it may be related to the pathogenesis. (+info)
Changes in core temperature compartment size on induction of general anaesthesia.
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A two-compartment model of temperature distribution estimates the core compartment to occupy 66% of body mass at rest, while the peripheral compartment comprises the remainder. General anaesthesia impairs thermoregulation by central and peripheral actions. Peripheral vasodilatation accelerates heat transfer from the core to peripheral compartment causing the core compartment to cool and expand in size. Core hypothermia may be a significant cause of postoperative morbidity. This undocumented change in the size of the core compartment on induction of anaesthesia can be calculated. Core size increased from the established value of 66% before induction of general anaesthesia to 71.2 (SD 6)% of body mass, 20 min after induction of anaesthesia (P = 0.0001). On induction of general anaesthesia, the core compartment cools and expands while the peripheral compartment warms and contracts by a corresponding amount. Measurement of the magnitude of changes in core:periphery heat distribution on induction of anaesthesia contribute to a clearer understanding of the pathophysiology of perioperative hypothermia. (+info)
Thermogenic effects of sibutramine and its metabolites.
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1. The thermogenic activity of the serotonin and noradrenaline reuptake inhibitor sibutramine (BTS 54524; Reductil) was investigated by measuring oxygen consumption (VO2) in rats treated with sibutramine or its two pharmacologically-active metabolites. 2. Sibutramine caused a dose-dependent rise in VO2, with a dose of 10 mg kg(-1) of sibutramine or its metabolites producing increases of up to 30% that were sustained for at least 6 h, and accompanied by significant increases (0.5-1.0 degrees C) in body temperature. 3. Based on the accumulation in vivo of radiolabelled 2-deoxy-[3H]-glucose, sibutramine had little or no effect on glucose utilization in most tissues, but caused an 18 fold increase in brown adipose tissue (BAT). 4. Combined high, non-selective doses (20 mg kg(-1)) of the beta-adrenoceptor antagonists, atenolol and ICI 118551, inhibited completely the VO2 response to sibutramine, but the response was unaffected by low, beta1-adrenoceptor-selective (atenolol) or beta2-adrenoceptor-selective (ICI 118551) doses (1 mg kg(-1)). 5. The ganglionic blocking agent, chlorisondamine (15 mg kg(-1)), inhibited completely the VO2 response to the metabolites of sibutramine, but had no effect on the thermogenic response to the beta3-adrenoceptor-selective agonist BRL 35135. 6. Similar thermogenic responses were produced by simultaneous injection of nisoxetine and fluoxetine at doses (30 mg kg(-1)) that had no effect on VO2 when injected individually. 7. It is concluded that stimulation of thermogenesis by sibutramine requires central reuptake inhibition of both serotonin and noradrenaline, resulting in increased efferent sympathetic activation of BAT thermogenesis via beta3-adrenoceptor, and that this contributes to the compound's activity as an anti-obesity agent. (+info)
Effect of breed (Angus vs Simmental) on immune function and response to a disease challenge in stressed steers and preweaned calves.
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Two experiments were conducted with feeder steer calves and preweaned calves to determine the effects of breed on immune response. In Exp. 1, newly weaned Angus (n = 24) and Simmental (n = 24) steer calves were blocked by weight within breed and randomly assigned to 12 pens with four calves per pen. The basal diet consisted of 87% corn silage (DM basis) and 13% of a soybean meal-mineral-vitamin supplement. Steers were allowed ad libitum access to feed throughout the study. On d 2 following weaning, calves received an intranasal inoculation of infectious bovine rhinotraecheitis virus (IBRV; 2.7 x 10(8) CCID50). Rectal temperatures in response to the IBRV were higher (P < .05) in Angus calves. On d 9, calves were injected i.m. with 10 mL of a 25% pig red blood cell (PRBC) suspension. Total immunoglobulin (Ig) and IgM titers against PRBC were higher (P < .05) for the Angus calves. Breed did affect cell-mediated immune response to phytohemagglutinin (PHA). In Exp. 2, preweaned (16 Angus and 16 Simmental) calves were selected based on breed, body weight, and sex. On 0 d, all selected calves were injected i.m. with 10 mL of a 25% PRBC suspension. Total Ig and IgG titers against PRBC were higher (P < .05) for Angus calves. On d 28, lymphocytes were isolated from peripheral blood obtained from eight calves per breed. Peripheral lymphocytes from the Angus calves had a greater (P < .07) blastogenic response to 6.25 microg/mL of PHA than lymphocytes from Simmental calves. Results indicate that the immune response of Angus and Simmental calves may differ. (+info)
Treatment in a combined acute and rehabilitation stroke unit: which aspects are most important?
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BACKGROUND AND PURPOSE: We have previously shown that treatment of acute stroke patients in our stroke unit (SU) compared with treatment in general ward (GWs) improves short- and long-term survival and functional outcome and increases the possibility of earlier discharge to home. The aim of the present study was to identify the differences in treatment between the SU and the GW and to assess which aspects of the SU care which were most responsible for the better outcome. METHODS: Of the 220 patients included in our trial, only 206 were actually treated (SU, 102 patients; GW, 104 patients). For these patients, we identified the differences in the treatment and the consequences of the treatment. We analyzed the factors that we were able to measure and their association with the outcome, discharge to home within 6 weeks. RESULTS: Characteristic features in our SU were teamwork, staff education, functional training, and integrated physiotherapy and nursing. Other treatment factors significantly different in the SU from the GW were shorter time to start of the systematic mobilization/training and increased use of oxygen, heparin, intravenous saline solutions, and antipyretics. Consequences of the treatment seem to be less variation in diastolic and systolic blood pressure (BP), avoiding the lowest diastolic BP, and lowering the levels of glucose and temperature in the SU group compared with the GW group. Univariate analyses showed that all these factors except the level of glucose were significantly associated with discharge to home within 6 weeks. In the final multivariate Cox regression model, shorter time to start of the mobilization/training and stabilized diastolic BP were independent factors significantly associated with discharge to home within 6 weeks. CONCLUSIONS: Shorter time to start of mobilization/training was the most important factor associated with discharge to home, followed by stabilized diastolic BP, indicating that these factors probably were important in the SU treatment. The effects of characteristic features of an SU, such as a specially trained staff, teamwork, and involvement of relatives, were not possible to measure. Such factors might be more important than those actually measured. (+info)
Magnitude of functional adaptation after intestinal resection.
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Intestinal adaptation after resection has been much studied, but rarely examined in an integrative context. Hence we assessed the effects of resection and subsequent adaptation on the quantitative relationship between dietary glucose load and gut capacity to transport glucose. The ratio of capacity to load is termed the "safety factor." Our objectives were to determine 1) the time course of intestinal adaptation after resection, 2) whether adaptation is quantitatively complete, 3) whether survival requires maintaining a safety factor of at least 1.0 for glucose transport, 4) the effect of altered energy demands on adaptation, and 5) the relationship between the amount of tissue removed and the magnitude of functional adaptation. We performed 80% resection of the small intestine on Sprague-Dawley rats and measured small intestinal glucose uptake capacity, dietary glucose load, and gut gross morphology at 1, 5, and 10 wk postsurgery. Nearly all aspects of adaptation were complete by 1 wk postsurgery. After resection, remnant small intestine mass increased by over fivefold within 1 wk, to reach 50-70% of its preresection value. However, mass-specific glucose uptake activity was reduced, so that intestinal regeneration restored uptake capacity to only 33% of control values. Increased energetic demands had only modest effects on intestinal adaptation. Although the safety factor for small intestinal glucose uptake remained <1.0 (i.e., capacity < load) after adaptation to resection, nearly all rats survived. Hindgut fermentation of nonabsorbed nutrients appeared to contribute to that survival, despite inadequate small intestinal capacity. After less massive resection surgeries (25, 50, and 75% resections), the percent increase in glucose uptake capacity increased with the amount of tissue removed. (+info)
Heat acclimation increases the basal HSP72 level and alters its production dynamics during heat stress.
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It has been previously shown that heat acclimation leads to an elevated basal level of 72-kDa heat shock protein (HSP72). Augmented expression of HSP72 is considered as a cytoprotective response. This led us to hypothesize that alterations in the heat shock protein (HSP) defense pathway are an integral part of the heat acclimation repertoire. To investigate this, we studied the temporal profile of basal HSP expression upon acclimation and the dynamics of their accumulation subsequent to acute heat stress (HS). In parallel, HSP72 mRNA level before and after HS was measured. For comparison, HSC mRNA [the constitutive member of 70-kDa HSP (HSP70) family] was measured in similar conditions. Heat acclimation was attained by continuous exposure of rats to 34 degrees C for 0, 1, 2, and 30 days. HS was attained by exposure to 41 or 43 degrees C for 2 h. Thermoregulatory capacity of the rats was defined by rectal temperature, heating rate, and the cumulative heat strain invoked during HS. HSP72 and HSP70 gene transcripts were measured in the left ventricle of the heart by means of Western immunoblotting and semiquantitative RT-PCR, respectively. The resultant acclimatory change comprised a higher resting level of the encoded 72-kDa protein (Delta175%, P < 0.0001). After HS, peak HSP72 mRNA level was attained, 40 and 20 min post-HS at 41 and 43 degrees C, respectively, vs. 60 and 40 min in the nonacclimated group. The subsequent HSP synthesis, however, was dependent on the severity of the cumulative heat strain. At the initial phase of heat acclimation, augmented HSP72 transcription unaccompanied by HSP synthesis was observed. It is concluded that upon heat acclimation, the HSP defense pathway is predisposed to a faster response. At the initial phases of heat acclimation, inability to elevate the HSP cytosolic level rules out their direct cytoprotective role. (+info)