Glucose oxidation in white adipose tissue from BIO 14.6 dystrophic hamsters

In studies of glucose oxidation in white retroperitoneal adipose tissue of BIO 14.6 dystrophic and F1B normal hamsters aged 55-67 and 368-379 days, no difference was found in the basal state of radiolabelled 14CO2 production using either D-[6-14C]glucose or D-[1-14C]glucose. When C6-labelled glucose was used, insulin induced a slightly greater increase in glucose oxidation in dystrophic adipose tissue at both ages. When C1-labelled glucose was used, insulin enhanced glucose oxidation in dystrophic tissue more than twice normal in tissues from young animals and five times normal in tissues from the old ones. The increase in oxidation with D-[1-14C]glucose likely represents enhanced activity of the pentose phosphate pathway, which has also been observed in certain tissues of other animals with inherited skeletal-muscle degeneration. The change can probably be classified as being compensatory, an attempt by tissues to maintain functional integrity.     

Characterization of lipolytic responses of isolated white adipocytes from hamsters.

1. Lipolysis by isolated white adipocytes from hamsters, as measured by glycerol production, was stimulated by corticotropin, isopropylnorepinephrine (INE), norepinephrine, or epinephrine (EPI), in a dose-dependent fashion. 2. Lipolysis was stimulated by five inhibitors of cyclic 3',5'-adenosine monophosphate phosphodiesterase: caffeine, theophylline, 1-methyl-3-isobutyl xanthine, 1-ethyl-4-(isopropylidenehydrazine)-1H-pyrazolo-(3,4,-b)-pyridine-5-carboxylic acid ethyl ester (SQ 20009), and 4-(3,4-dimethoxybenzyl)-2-imidazolidinone (Ro 7-2956). Caffeine-stimulated lipolysis consistently attained higher rates than did hormone-stimulated lipolysis. However, when cells were stimulated by both caffeine and a hormone, lipolytic rates were consistently lower than those attained under the influence of caffeine alone. 3. Isolated white adipocytes from hamsters were sensitive to both alpha- and beta-adrenergic antagonists. The beta-adrenergic antagonist propranolol could completely inhibit norepinephrine-stimulated glycerol production. The alpha-adrenergic antagonist phentolamine, on the other hand, had a biphasic effect on the cells. At 5-10(-7) M or 5-10(-6) M, phentolamine enhanced norepinephrine-stimulated lipolysis, while concentrations higher than 5-10(-5) M caused inhibition. 4. The effects of two different concentrations of six antilipolytic agents, prostaglandin E1, nicotinic acid, phenylisopropyladenosine, 5-methylpyrazole-3-carboxylic acid, adenosine and insulin, were measured. With the exception of insulin, all of these agents showed much more potent inhibition of caffeine-stimulated lipolysis than of hormone-stimulated lipolysis. Insulin, in contrast, showed only modest inhibition of hormone-stimulated lipolysis and virtually no inhibition of caffeine-stimulated lipolysis.     

A longitudinal study on BIO14.6 hamsters with dilated cardiomyopathy: micro-echocardiographic evaluation

Background

Acute myocarditis may mimic myocardial infarction, since affected patients complain of "typical" chest pain, the ECG changes are identical to those observed in acute coronary syndromes, and serum markers are increased. We describe a case series of presumptive myocarditis with ST segment elevation on admission ECG.

Methods and Results

From 1998 to 2009, 21 patients (20 males; age 17-42 years) were admitted with chest pain, persistent ST segment elevation, serum enzyme and troponine release. All but one patients had fever and flu-like symptoms prior to admission. No abnormal Q wave appeared in any ECG tracing, and angiography did not show significant coronary artery disease. Patients remained asymptomatic at long term follow-up, except 2 who experienced a late relapse, with the same clinical, electrocardiographic and serum findings as in the first clinical presentation.

Conclusion

Presumptive myocarditis of possible viral origin characterized by ST elevation mimicking myocardial infarction, good short term prognosis and some risk for recurrence is relatively frequent in young males and appears as a distinct clinical condition.     

Thermoregulatory responses of dystrophic hamsters to changes in ambient temperatures

The ability of dystrophic hamsters to maintain their body temperature despite abnormal muscle and brown adipose tissue, two organs involved in thermoregulation, was evaluated. Dystrophic hamsters (CHF 146) between the ages of 30 and 160 days kept at 21 degrees C had core (rectal) temperatures (TR) that were 0.5-1.5 degrees C lower than Golden Syrian controls. The reduced core temperatures of dystrophic hamsters were unlikely the result of an incapacity to generate heat since the dystrophic hamsters were able to maintain their TRs during 3 h of acute cold stress (4 degrees C) and to adapt to prolonged cold exposure. However, TRs of cold-acclimated dystrophic hamsters were still 1 degree C below TRs of cold-acclimated control animals. By contrast, increasing the ambient temperature raised TRs of both normal and dystrophic hamsters. When kept at 32 degrees C overnight, the TRs of dystrophic hamsters remained significantly below those of control animals. When heat-exposed dystrophic hamsters were returned to 21 degrees C, their TRs returned to values significantly lower than those of control hamsters. Thus, dystrophic hamsters showed a capacity to thermoregulate, like control hamsters, but appeared to do so at a lower temperature. The reduced core temperatures of dystrophic hamsters kept at 21 degrees C cannot be explained by a reduction in metabolic activity since newborns and 30- and 140-day-old dystrophic hamsters had rates of oxygen consumption (VO2) and carbon dioxide production (VCO2) that were similar to those of controls. These results suggest that the thermoregulatory set point may be altered in dystrophic hamsters.     

Metabolic integrity and stability of isolated rat brown adipocytes

Using rats previously anesthetized with pentobarbital and with subtle modifications to existing procedures, rat brown adipocytes of good yield, viability, and stability were consistently obtained. The metabolic integrity of the cells, indicated by an 8–11 fold norepinephrine-dependent stimulation of respiration, was reproducible between cell preparations and maintained even after 3–5 hours of cell storage at room temperature. The ATP content of freshly isolated and stored cells per mg DNA (using a modified DNA assay) closely reflected the in vivo content determined from freeze clamped tissue.     

Analysis of erythrocyte membrane proteins from dystrophic hamsters

To search for potentially mutant proteins, we have investigated erythrocyte ghost proteins from normal and dystrophic hamster by two-dimensional gel electrophoresis. No significant differences are observed between dystrophic and normal erythrocytes in their peptide patterns on SDS-polyacrylamide gel electrophoresis while on two-dimensional gels a protein spot of approximate Mr 20 000 with an approximate isoelectric point of 4.5 is found in erythrocytes from dystrophic animals and is consistently absent in normal erythrocytes. A large population of erythrocyte (60%) from dystrophic hamsters shows distorted shape as visualized by scanning electron microscopy. The nature of this protein and its relevance in hamster muscular dystrophy are at present not known.     

Modulation by insulin and glucagon of noradrenaline-induced activation of isolated brown adipocytes from the rat

1. The effects of insulin (2 nM and 4 nM) upon oxygen consumption (VO2), lipolysis rates and indirectly derived rates of fatty acid utilization, by isolated brown adipocytes from warm-acclimated (W cells) and cold-acclimated (C cells) animals, induced by noradrenaline and glucagon separately and conjointly, are reported. 2. Changes in interrelationships (coupling) between the parameters under different treatment regimes were assessed using bivariate regression analyses. 3. Administration of glucagon with noradrenaline increased lipolysis/fatty acid utilization coupling without concomitant increase of VO2 suggesting that glucagon may increase re-esterification through glycogenolytic generation of glycerol 3-phosphate, trapping intracellular fatty acid in excess of the capacity of disposal mechanisms, thus conserving respiratory substrate. 4. W cells were unresponsive to glucagon in terms of lipolysis and VO2, C cells responded to glucagon with parallel increases in lipolysis rate and VO2. Both cell types responded to noradrenaline alone and conjointly with glucagon; C cells were more sensitive to these agonists than W cells. 5. Lipolysis/VO2 coupling was reduced in C cells suggesting that in cold acclimation, noradrenaline-induced lipolysis rates are in excess of the capacity of cellular oxidation/re-esterification mechanisms. 6. Insulin inhibited noradrenaline and glucagon-induced lipolysis, simultaneously increasing VO2, supporting the hypothesis that glucose may be a thermogenic substrate in brown adipase tissue, permitting concurrent thermogenesis and lipogenesis. C cells were more insulin-sensitive than W cells. 7. The data indicate that insulin may mediate its effects (additively with noradrenaline) by activation of pyruvate dehydrogenase, generating glycolytic flux and, in the presence of noradrenaline-inhibited lipogenesis, generate additional oxaloacetate, permitting increased beta-oxidation.     

Microcalorimetric measurements of heat production in isolated rat brown adipocytes.

Heat production, oxygen consumption, and lipolysis in isolated interscapular brown adipocytes from the rat were investigated. Epinephrine, norepinephrine, and isoproterenol increased heat production in a concentration-dependent manner, showing, about 6-, 4-, and 5-fold higher effects than controls, respectively. The concentration of isoproterenol for threshold heat production and glycerol release were 10(-10) M and 10(-9) M, respectively. The fact that 10(-9) M isoproterenol increased heat production by about 3-fold while glycerol release had no effect at all indicates that calorimetry is more appropriate for investigation of brown adipocytes. At least the method is more sensitive than that of measuring glycerol release.     

Effects of fasting and food restriction on brown adipose tissue composition in normal and dystrophic hamsters

Fasting for 36-48 h or food restriction (30% reduction of daily food intake for 6 weeks) caused brown adipose tissue (BAT) atrophy in hamsters. Fasting-induced atrophy was characterized by reductions in tissue mass, DNA, protein, and thermogenin. By contrast, food restriction had no effect on tissue cellularity (DNA) but markedly reduced the tissue protein and thermogenin contents. The concentration of thermogenin in isolated mitochondria was unchanged by fasting or food restriction. Dystrophic hamsters had a reduced BAT mass when compared with weight-matched control hamsters. This resulted from a reduction in tissue cellularity since BAT DNA, protein and thermogenin contents were all reduced. The extent of binding of [3H]guanosine diphosphate to isolated mitochondria and their content of thermogenin were similar in normal and dystrophic hamsters. In response to cold exposure, as in normal hamsters, BAT of dystrophic hamsters grew and the tissue thermogenin increased, but the mitochondrial concentration of thermogenin did not change. In response to fasting, in contrast with normal hamsters, there was no significant reduction in BAT DNA in dystrophic animals and the loss of tissue protein was reduced. However, the relative changes in BAT composition during chronic food restriction were similar in normal and dystrophic animals. Thus, reduction in hamster BAT thermogenic capacity during food deprivation may occur by loss of cells and (or)reduction in the tissue protein and thermogenin contents. The extent of protein and (or) DNA loss may be dependent upon the original tissue mass and the severity of food deprivation.     

Protein synthesis in muscles from normal and dystrophic hamsters.

Homogenates of hindleg muscle were obtained from control and dystrophic male hamsters, 30 and 190 days of age, and were used to prepare the postmicrosomal pH5-supernatant fraction. The activity of this fraction in the incorporation of [14C]phenylalanyl-tRNA into peptides was increased in the dystrophic-muscle preparations. No such increase was found in brain or liver preparations from dystrophic hamsters. The increased capacity for aminoacyl-tRNA binding that was observed in preparations from dystrophic animals is discussed.     

Electrophysiological observations on diaphragm muscle from normal and dystrophic hamsters

The cellular electrical activity of diaphragm from F1B normal and BIO 14.6 dystrophic hamsters has been investigated using microelectrodes. Resting membrane potentials and action potentials were recorded from control muscles and from muscles exposed to 2,4-dinitrophenol. The action potentials of normal and dystrophic diaphragms were similar in amplitude and configuration. Treatment with 2,4-dinitrophenol caused the action potential amplitude of both diaphragms to decline by similar amounts. The control resting membrane potential of diaphragm from dystrophic hamsters is not significantly different from that of normal hamsters. Treatment with 2,4-dinitrophenol caused a linear decrease in the resting membrane potentials of both groups of muscles. Dystrophic muscle, however, showed a more rapid decline in excitability when exposed to 2,4-dinitrophenol. This suggests that adenosine triphosphate production in dystrophic muscle is partially inhibited as has been suggested by other workers.