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Query: UMLS:C0009443 (cold)
 92,137 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We tested the hypothesis that forced-dived ducks experience a reduction in metabolic rate during prolonged submergence. Unidirectionally ventilated conscious ducks were subjected to forced dives by temporarily stopping the airflow in the ventilation system and simultaneously filling a face mask with cold water. A typical cardiovascular response to submergence was observed: bradycardia and maintained arterial blood pressure. Phosphorylated metabolite concentrations in the pectoral muscle were measured noninvasively by phosphorus magnetic resonance spectroscopy (31P-MRS). ATP content was constant, and phosphocreatine was depleted via the creatine kinase reaction at a rate similar to the resting rate of ATP turnover, which was estimated to be 0.9 mumol.min-1 x g-1 in resting perfused pectoral muscle of pentobarbital-anesthetized ducks. Oxygen from myoglobin supplied at most 12% of the ATP required by the resting muscle during dives. Whole animal postdive excess oxygen consumption and blood lactic acid accumulation suggested that the shortfall in aerobic metabolism during forced dives was compensated by an increase in anaerobic metabolism.
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PMID:Metabolic responses to forced dives in Pekin duck measured by indirect calorimetry and 31P-MRS. 148 44

In order to broaden the scope and increase the utility of differential scanning calorimetry, a theoretical model of calorimetric thermograms is presently proposed which facilitates their biophysical interpretation and accounts explicitly for their modifications induced by denaturing agents and/or pH. The model rests mainly on statistical-physical considerations, the denaturation-linked increase of the number of binding sites for denaturants (including H+) serving as the conceptual basis for thermogram modelling. Denaturants were envisioned as contributing indirectly to thermal denaturation by forming complexes preferentially with unfolded protein molecules, shifting thus the equilibrium towards the denatured phase. After postulating the probability of complex formation, mean numbers of the relevant molecular species were computed by ensemble averaging. Finally, an eight-parameter expression has been derived defining protein heat capacity as a function of both temperature and denaturant concentration (or pH), each of the eight parameters having a distinct biophysical meaning. The model has been tested by applying it to the prediction of the pH-dependence of thermograms. Four proteins have been considered (lysozyme, myoglobin, apomyoglobin, and ribonuclease A), each represented by a series of three to four published thermograms recorded under different pH conditions. Model equations, fitted simultaneously to all thermograms in a pH series, reproduced correctly experimental tracings. Parameter values obtained as best-fit requirements (particularly those representing the number of binding sites unmasked by denaturation and the free energy of ion binding) were in close agreement with empirical, mainly potentiometric, data from literature. The empirically established pH-independence of the total enthalpy of denaturation, the phenomenon of cold denaturation, the pH-dependence of the Gibbs free energy of denaturation, of the melting temperature and of the temperature of cold denaturation, were all correctly predicted by the model. Combined effects of multiple denaturants, including the effects of pH in the presence of denaturants other than protons, are also predictable by the model.
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PMID:Biophysical models of protein denaturation. II. Effects of denaturants and of pH. 166 34

The folding/unfolding transition of proteins is a highly co-operative process characterized by the presence of very few or no thermodynamically stable partially folded intermediate states. The purpose of this paper is to present a thermodynamic formalism aimed at describing quantitatively the co-operative folding behavior of proteins. In order to account for this behavior, a hierarchical algorithm aimed at evaluating the folding/unfolding partition function has been developed. This formalism defines the partition function in terms of multiple levels of interacting co-operative folding units. A co-operative folding unit is defined as a protein structural element that exhibits two-state folding/unfolding behavior. At the most fundamental level are those structural elements that behave co-operatively as a result of purely local interactions. Higher-order co-operative folding units are formed through interactions between different structural elements. The hierarchical formalism utilizes the crystallographic structure of the protein as a template to generate partially folded conformations defined in terms of co-operative folding units. The Gibbs free energy of those states and their corresponding statistical weights are then computed using experimental energetic parameters determined calorimetrically. This formalism has been applied to the case of myoglobin. It is shown that the hierarchical partition function correctly predicts the presence, energetics and co-operativity of the heat and cold denaturation transitions. The major contribution to the co-operative folding behavior arises from the solvent exposure of non-polar residues located in regions complementary to those that have undergone unfolding. This entropically uncompensated and energetically unfavorable solvent exposure characterizes all partially folded states but not the unfolded state, thus minimizing the population of partially folded intermediates throughout the folding/unfolding transition.
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PMID:Molecular basis of co-operativity in protein folding. 174 98

Myoglobins from rat, coho salmon (Oncorhynchus kisutch), buffalo sculpin (Enophrys bison) hearts, and yellowfin tuna (Thunnus albacares) red skeletal muscle were partially purified and their O2 binding affinities determined. Commercially prepared sperm whale myoglobin was employed as an internal standard. Tested at 20 degrees C, myoglobins from salmon and sculpin bound O2 with lower affinity than myoglobins from the rat or sperm whale. Oxygen binding studies at 12 degrees C and 37 degrees C suggest that this difference is adaptive, permitting myoglobins from cold-adapted fish to function at physiologically relevant temperatures. Taken together, purification and O2 binding data obtained in this study reveal a previously unrecognized diversity of myoglobin structure and function.
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PMID:Comparative oxygen affinity of fish and mammalian myoglobins. 276 Feb 86

The informative value of various functional and laboratory diagnostic methods was reviewed in 150 patients with unstable angina (UA). High informativeness (92%) and sensitivity (83%) of isometric hand grip under computerized electrocardiographic monitoring was demonstrated for the diagnosis and control of treatment in these patients. Isometric loading brought out a dramatically reduced coronary reserve, latent heart failure and electrical instability of the myocardium. The cold test with a small area of skin exposure is of low diagnostic value in UA cases and cannot be recommended for clinical use. Serial myoglobin assays add to the accuracy of diagnosis and have high predictive value.
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PMID:[Methods of diagnosing unstable stenocardia and monitoring its treatment]. 286 42

Myoglobin-specific, Iad-restricted cloned helper T cells and T hybridomas were found to directly kill Iad-bearing, myoglobin-pulsed B lymphoma targets and could also kill bystander targets, but only in the presence of antigen-pulsed antigen presenting cells (APC). The induction of the killing requires recognition of processed antigen in the context of class II major histocompatibility complex (MHC) molecules. Despite the specificity of induction, the bystander killing suggests a nonspecific lytic mechanism. The direct killing can be inhibited only by cold specific targets, whereas the bystander killing can be blocked by both specific and nonspecific targets. The cold target inhibition seems to be due to interference with effector-to-target contact or proximity rather than due to high-dose suppression of T-cell activation. Experiments using T-cell supernatants or cyclosporin A suggested that the helper T cells kill targets by synthesizing short-range soluble factor(s) with nonspecific killing activity de novo during the effector phase, but only while antigen-specific signal transduction is occurring. The mechanism of cold target inhibition appears to be absorption or consumption of a short-acting cytotoxic lymphokine by cells which must be able to interact closely with the effector cell. Normal spleen B cells, despite their capability for activating the helper T cells, cannot inhibit specific killing or be killed by helper T cells, even after lipopolysaccharide stimulation. Thus, although killing by helper T cells may play a negative feedback role in the normal immune response, our data raise the possibility that the helper T-cell-mediated killing may contribute to the immune surveillance against malignancy by virtue of the preferential killing of tumor cells either directly or indirectly.
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PMID:Cloned protein antigen-specific, Ia-restricted T cells with both helper and cytolytic activities: mechanisms of activation and killing. 295 81

Weanling male guinea pigs (Cavia porcellus), 2-3 weeks of age, with initial body weights of 207-271 g were exposed for 2-16 weeks to constant cold (6 degrees C) and hypoxia (PO2 = 85 Torr) equivalent to 4800 m above sea level. Their growth rates and body weights did not differ from those of control animals of the same age maintained under normoxic conditions (22 degrees C, PO2 = 133 Torr). After 2, 3, 4, 6, 10, or 16 weeks exposure the animals were sacrificed, the hearts were removed, the ventricles were separated and weighed, and myoglobin concentrations were determined. Total heart weight as well as both right and left ventricular weights increased linearly with age. By the second week of exposure of the guinea pigs to cold plus hypoxia the total heart and right ventricular weights were 25 and 50% greater than those of the normoxic control animals. Both weights increased at greater rates than those of the controls until Week 6 and then remained at 30 and 80% throughout the 16th week. The weights of the left ventricles in these animals were only slightly greater than those of the controls. In spite of the severe right ventricular hypertrophy these animals showed no clinical signs of right heart failure. Myoglobin concentrations were significantly greater in both ventricles for the cold-plus-hypoxic animals than for the controls.
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PMID:Ventricular weights in guinea pigs acclimated to cold plus hypoxia. 295 99

Clinical and experimental literature data reviewed by the author concern myoglobin structure, function and content in normal myocardium, skeletal muscles and serum. The assessment was aimed at elucidation of myoglobin diagnostic potential for a variety of pathologies. Its role in human and animal adaptation in exposure to cold, physical stress and high-altitude factors is demonstrated.
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PMID:[Myoglobin of the myocardium and skeletal musculature]. 328 13

Quantitative analysis of myoglobin (Mb) was established using the sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis in order to determine the influence of thermal acclimation on Mb levels in muscles. Myoglobin was measured in the red and white parts of quadriceps, soleus, diaphragm and heart of young adult male rats (11 weeks old). It was higher in the red muscle (0.92 +/- 0.043 mg/g fresh weight) than in the white muscle (0.08 +/- 0.007), and similar in the red muscle and soleus (1.17 +/- 0.117). Heart showed the highest level (1.52 +/- 0.073) among the tissues studied. The level in diaphragm (0.74 +/- 0.039) was intermediate between red muscle and heart. Cold acclimation (5 degrees C for 4 weeks, 11 weeks old) caused significant increases in Mb levels in white muscle (0.27 +/- 0.031, p less than 0.001), heart (1.95 +/- 0.094, p less than 0.01), and diaphragm (1.01 +/- 0.060, p less than 0.01), but not in red muscle and soleus. The rats reared in cold for many generations (20 generations at 5 degrees C, 11 weeks old) manifested significant increases in Mb levels of all tissues (p less than 0.05-0.001) examined. Heat acclimation (33 degrees C for 4 weeks, 11 weeks old) did not influence Mb levels of the tissues. The above findings suggest that skeletal muscle Mb may be partly involved in an enhanced thermogenesis in cold acclimation by favouring an oxidative capacity of muscles.
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PMID:Muscle myoglobin as determined by electrophoresis in thermally acclimated rat. 378 48

To assess renal function changes induced by marathon racing in asymptomatic runners, we studied them before, six hours after, and one week after warm and cold weather marathons (26.2 miles [42 km]). Standard serum electrolytes, creatine phosphokinase (CPK), urinalysis, urinary myoglobin, and renal function tests (para-aminohippurate [PAH], inulin, and true creatinine clearances) were performed. After rehydration to their prerace weight, the subjects showed no postrace change in serum electrolytes. The CPK rose postrace and was two to three times higher in the warm weather runners than in the cold weather runners. All postrace urinalyses were grossly abnormal. Urinary myoglobins were positive postrace in warm weather runners and negative in cold weather runners. Warm weather runners showed a 50% decline in inulin clearance postrace but maintained PAH clearance. At one week, inulin clearance returned to baseline but fractional excretion of creatinine was below unity. In contrast, cold weather runners showed no change in inulin and PAH clearances postrace or at one week, but fractional excretion or creatinine postrace was less than unity returning to baseline at one week. We conclude that renal function abnormalities occur in marathon runners and that the severity of the abnormality is temperature-dependent.
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PMID:Renal function abnormalities induced by marathon running. 731 36


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