Blunted Sensitivity to Sucrose in Autoimmune MRL-lpr Mice: A Curve-Shift Study

Lupus-prone MRL-lpr mice show an autoimmunity-associated behavioral syndrome that has many features similar to the effects of chronic stress. The present study evaluated whether autoimmune MRL-lpr mice show reduced responsiveness to sucrose, as observed in normal animals exposed to chronic mild stress. Sixteen-week old MRL-lpr mice and their age-matched congenic MRL +/+ controls were given 0%, 0.5%, 1%, 2%, 4%, 8%, or 16% sucrose solution to drink every 48 h in a one-bottle test. The MRL-lpr mice drank less than controls at all concentrations, except at 16%. The amount of sucrose consumed vs. solution concentration followed a saturation curve. Estimates were obtained for the concentration yielding the half-maximum response (X₅₀) and the response at saturating concentration of sucrose (R_max). The X₅₀ was significantly higher in MRL-lpr than in MRL +/+ mice, indicating a shift to the right of the concentration-intake curve. The R_max did not differ significantly between substrains, suggesting that the autoimmune process did not affect performance capacity. Pretreatment with the immunosuppressant cyclophosphamide diminished the substrain difference in X₅₀, suggesting that reduced sensitivity to sucrose is related to autoimmune/inflammatory factors. These results support the similarity between autoimmunity-associated behavioral syndrome and behavioral changes produced by chronic stress, and suggest common neuroendocrine mechanisms. Because reduced sensitivity to palatable stimulus may reflect blunted hedonic responsiveness (“anhedonia”), it is hypothesized that an autoimmune/inflammatory factor(s) produces the depression found in human lupus, and some cases of affective disorder. Copyright © 1996 Elsevier Science Inc.     

Brain uptake of mannitol and sucrose after cerebral ischemia: Effect of hyperglycemia

The effect of 10 min cerebral ischemia on blood-brain barrier permeability to mannitol and sucrose was evaluated in normo-and hyperglycemic rats. In the period immediately after ischemia (1–4 min) the PS (permeability-surface area product) for mannitol was 159%± 75 of control (0.17 ± 0.02 ml/100g min) in the normoglycemic rats (plasma glucose 8mM) and 204%± 30 of control (0.09 ± 0.02ml/100g min) in the hyperglycemic rats (plasma glucose 28mM). Two hours after ischemia, PS for mannitol returned to the control levels in the normoglycemic rats and remained elevated in the hyperglycemic animals. The mannitol/sucrose ratios—2.3 ± 0.4 in normoglycemic rats and 2.6 p± 0.I in hyperglycemic rats—remained unchanged after ischemia. As there was no significant difference in the effects of ischemia on normo-and hyperglycemic rats, it was concluded that the deleterious effect of hyperglycemia on clinical recovery after cerebral ischemia in rats (Siemkowicz & Hansen 1978) is not related to enhancement of BBB damage.     

The global obesity epidemic: snacking and obesity may start with free meals during infant feeding

Feeding is vital for survival. The brain has strong hunger and reward mechanisms that ensure optimal food intake for adequate nutrition. The drive for feeding is particularly strong in humans whose large brains require large energy support. This starts immediately after birth; the newborn child being able to taste sucrose and suck the sweet and fat from its mother's milk. At present, mothers are generally advised to breastfeed children as often as they like, which may be up to 15 times a day. At the same time, childhood obesity is rapidly developing. One reason for the rapidly increasing prevalence of childhood obesity may be overfeeding with snack food.

Conclusion: We hypothesize that non-rule breastfeeding favours the development of snacking throughout the day during childhood, a habit which in turn favours the development of obesity.     

Kiss-and-Run Quantal Secretion in Frog Nerve-Muscle Synapse

Electrophysiological and optical methods were used to study exo- and endocytosis of synaptic vesicles underlying secretion of the neurotransmitter from motor nerve terminals in frog sternocutaneous muscle. Increase in extracellular concentration of K+ or sucrose produced similar increase in the frequency of miniature endplate currents recorded by extracellular microelectrode. Fluorescent microscopy revealed bright spots in nerve terminal during stimulation of secretion with high-potassium solutions in the presence of endocytosis marker FM1-43. These spots corresponded to clusters of synaptic vesicles that passed through the cycles of exo- and endocytosis. Subsequent high-potassium stimulation of exocytosis in normal Ringer solution led to disappearance of marker spots, while in hyperosmotic saline the spots were preserved. No spots were seen after stimulation of neurotransmitter secretion with sucrose in the presence of FM1-43. It is concluded that quantal secretion of the neurotransmitter in frog motor nerve endings can be realized via both complete exocytosis of synaptic vesicles with subsequent endocytosis and kiss-and-run mechanism with the formation of a temporary pore.     

Determination of Glass Transition Temperature and in Situ Study of the Plasticizing Effect of Water by Inverse Gas Chromatography

Purpose. To use an inverse gas chromatographic (IGC) method to determine the glass transition temperature (Tg) of some amorphous pharmaceuticals and to extend this technique for the in situ study of the plasticizing effect of water on these materials. Methods. Amorphous sucrose and colyophilized sucrose-PVP mixtures were the model compounds. Both IGC and differential scanning calorimetry (DSC) were used to determine their Tg. By controlling the water vapor pressure in the IGC sample column, it was possible to determine the Tg of plasticized amorphous phases. Under identical temperatures and vapor pressures, the water uptake was independently quantified in an automated water sorption apparatus. Results. The Tg of the dry phases, determined by IGC and by DSC, were in very good agreement. With an increase in the environmental relative humidity (RH), there was a progressive decrease in Tg as a result of the plasticizing effect of water. Because the water uptake was independently quantified, it was possible to use the Gordon-Taylor equation to predict the Tg values of the plasticized materials. The predicted values were in very good agreement with those determined experimentally using IGC. A unique advantage of this technique is that it provides complete control over the sample environment and is thus ideally suited for the characterization of highly reactive amorphous phases. Conclusions. An IGC method was used (a) to determine the glass transition temperature of amorphous pharmaceuticals and (b) to quantify the plasticizing effect of water on multicomponent systems.     

Reversibility of Heat-Induced Denaturation of the Recombinant Human Megakaryocyte Growth and Development Factor

Purpose. The present study was performed to examine the effect of solution conditions on the reversibility of the thermal denaturation of megakaryocyte growth and development factor (rHuMGDF). Methods. Changes in the far U V CD spectra of rHuMGDF with temperature were used to monitor the thermal denaturation of the protein, and the recovery of folded protein following a return to room temperature. The effect of protein concentration, scan rate, and buffer composition on thermal denaturation and on the reversibility were determined. Surface tension measurements were used to determine the effect of this unfolding reaction on the surface adsorption of the protein. Sedimentation velocity was used to assess recovery of native monomer and the size of soluble aggregates. In addition, monomeric protein remaining in solution after incubation at 37°C for 2 weeks in either 10 mM imidazole of 10 mM phosphate was determined. Results. In phosphate buffer the rHuMGDF irreversibly precipitates upon unfolding under all the conditions examined. In imidazole the unfolding is at least partially reversible, with no visible precipitate seen; the degree of reversibility increased by lowering both protein and salt concentrations, and the amount of time spent at elevated temperature. In order to compare thermal unfolding occuring with different degrees of reversibility, the melting temperature was defined as the temperature at which melting begins. The melting temperature itself is relatively independent of the buffer composition, or experimental conditions. At low protein concentrations the protein stabilizer sucrose had a marginal effect on the thermal transition of rHuMGDF, while at protein concentrations of about 2 mg/ml the inclusion of sucrose increased the apparent melting temperature by about 4°C, to that seen at low protein concentrations, but had little effect on the reversibility of denaturation. Inclusion of 1 or 2 M urea did not affect the reaction. Surface tension measurements of rHuMGDF solutions showed little difference before and after melting, and in the presence or absence of sucrose. When unfolding is irreversible, the MGDF appears to form soluble aggregates of tetramers to 14-mers, while under reversible conditions native monomer is recovered. More monomeric MGDF remained in solution following storage for 2 weeks at 37°C in imidazole than in phosphate, in both the presence and absence of sucrose. Conclusions. These results can be explained by assuming that thermal denaturation proceeds as a two-step reaction, the first step being the equilibrium between folded and unfolded states, while the second step is a slow irreversible aggregation. The different buffer systems affect the rate of the aggregation step, but not the intrinsic thermal stability nor the rate of the unfolding step.     

Evaluating the Fracture Toughness of Sucrose Crystals Using Microindentation Techniques

The brittleness of pharmaceutical crystals influences their ability to form compacts of acceptable quality. While many macroscopic methods are available to elucidate the fracture behavior of materials, the porosity, inhomogeneity, and anisotropy of pharmaceutical compacts render it difficult to interpret the results of these tests. Microindentation techniques may be used to evaluate both the flow and the fracture characteristics of small crystals, so that it is not necessary to test compacts. The flow and fracture behavior of sucrose, the model substance used in this study, were anisotropic. The fracture surface energy, derived from the average fracture toughness value, is of the same order of magnitude as the surface free energy, indicating that sucrose fractures in a brittle manner.     

不同冷冻保护剂对人类精子冷冻复苏后活动能力的影响

目的:比较添加葡萄糖或蔗糖的冷冻保护剂对人类精子冷冻复苏后活动力的影响。方法:将50例志愿者的精液标本分别采用添加葡萄糖或蔗糖的保护剂冷冻,比较精子复苏后的活动力。结果:冷冻前,前向活动精子百分率为(58.4±5.7)%,活动率为(63.4±6.1)%,采用添加葡萄糖的冷冻保护剂冷冻复苏后的前向活动精子百分率为(43.8±7.6)%,活动率为(48.4±7.6)%;采用添加蔗糖的冷冻保护剂冷冻复苏后的前向活动精子百分率为(42.6±8.9)%,活动率为(48.0±8.5)%。冷冻前后精子的前向活动百分率和总活动率差异有统计学意义(P<0.01),采用2种不同的冷冻保护剂冷冻复苏后的精子前向活动百分率和总活动率没有统计学差异(P>0.05)。结论:冷冻对精子活动力损伤明显,添加蔗糖作为精子冷冻的保护剂是可行的。     

Effect of fructose or sucrose feeding with different levels on oral glucose tolerance test in normal and type 2 diabetic rats

This study was designed to determine whether acute fructose or sucrose administration at different levels (0.05 g/kg, 0.1 g/kg or 0.4 g/kg body weight) might affect oral glucose tolerance test (OGTT) in normal and type 2 diabetic rats. In OGTT, there were no significant differences in glucose responses between acute fructose- and sucrose-administered groups. However, in normal rats, the AUCs of the blood glucose response for the fructose-administered groups tended to be lower than those of the control and sucrose-administered groups. The AUCs of the lower levels fructoseor sucrose-administered groups tended to be smaller than those of higher levels fructose- or sucrose-administered groups. In type 2 diabetic rats, only the AUC of the lowest level of fructose-administered (0.05 g/kg body weight) group was slightly smaller than that of the control group. The AUCs of fructose-administered groups tended to be smaller than those of the sucrose-administered groups, and the AUCs of lower levels fructose-administered groups tended to be smaller than those fed higher levels of fructose. We concluded from this experiment that fructose has tendency to be more effective in blood glucose regulation than sucrose, and moreover, that smaller amount of fructose is preferred to larger amount. Specifically, our experiments indicated that the fructose level of 0.05 g/kg body weight as dietary supplement was the most effective amount for blood glucose regulation from the pool of 0.05 g/kg, 0.1 g/kg and 0.4 g/kg body weights. Therefore, our results suggest the use of fructose as the substitute sweetener for sucrose, which may be beneficial for blood glucose regulation.