Differences In Glucose Utilization Research Articles

Bulk isolation of renal PCT and PST. I. Glucose-dependent metabolic differences

A new procedure for separately isolating milligram quantities of rabbit renal proximal straight (PST) or convoluted (PCT) tubules is described, and the differential abilities of these segments to utilize glucose as a metabolic substrate are investigated. Separate dissection of the cortical cortices and the outer medullary stripe, followed by collagenase digestion and discontinuous Percoll centrifugation, provide enriched populations (greater than 98% pure) of PCT (37 mg) and PST (14 mg), respectively, per rabbit. The purity of PCT and PST fractions was quantitated morphologically and by comparing the enriched activity of the proximal tubular marker leucine aminopeptidase and deenriched activity of the distal marker hexokinase to previously published values reported from microdissection studies. To investigate glucose-dependent metabolic differences, PCT and PST suspensions (1 mg/ml) were preincubated in Dulbecco's modified Eagle's-Ham's F-12 medium for 1 h before being incubated for 30 min in buffer with or without glucose as the only available metabolic substrate. In glucose-containing buffer, PST segments maintained their oxygen consumption and ATP contents at levels significantly higher than PCT segments. These differential responses between PST and PCT were glucose-dependent because they were abolished when segments were incubated under glucose-free conditions. Because responses in PCT were glucose-independent, these results suggest that PCT cannot utilize glucose to support oxidative metabolism, whereas PST segments can oxidatively metabolize this substrate. These differences in glucose utilization do not correlate with the distribution of glycolytic enzyme activities, suggesting that differential metabolic regulation of these enzymes may determine the ability of each segment to utilize glucose.

Effect of high-intensity sound on local cerebral glucose utilization in fetal sheep

The effects of external noise on fetal sheep cerebral glucose utilization were determined with the [ 14C]deoxyglucose method. Seventeen animals were prepared at 130 days gestation with catheters and electrodes for assessing fetal behavioral state. Five to 7 days later, 7 animals were studied under normal laboratory sound conditions (65–70 dB), 5 animals were exposed to 105–120 dB broadband noise levels produced by two earphones applied to the abdomen of the ewe, and 5 fetuses were stimulated with an electronic artificial larynx (EAL), positioned on the abdomen directly over the fetal head. There were no significant differences between local cerebral glucose utilization in controls and earphone ewes, and no obvious alteration in behavioral states. However, there were marked, significant differences in glucose utilization along the central auditory pathway during EAL stimulation. These autoradiographs revealed isofrequency-like bands in medial geniculate body and irregular darkening of cortex of the temporal lobe. Total time spent in clearly defined high and low voltage electrocortical activity did not change during EAL stimulation.

Development of a fetal circadian rhythm after disruption of the maternal circadian system

The role of maternal circadian rhythms in the development of the fetal circadian system was investigated in the rat. Pregnant females were subjected to procedures known to disrupt circadian function, ablation of the maternal suprachiasmatic nuclei (SCN) or housing in constant illumination, on gestational day 10. Circadian function was assessed in fetuses at gestational day 22 by analysis of glucose utilization in hypothalamic slices in vitro using the 2-deoxyglucose method. Fetuses from control females exhibit a robust rhythm in glucose utilization in the SCN. In contrast, the SCN of fetuses from females with SCN lesions, or housed in constant illumination, show no significant day-night difference in glucose utilization. Analysis of individual brains indicates, however, that this apparent disruption in the development of circadian rhythmicity in metabolism in the fetal SCN is due to a desynchronization of individual fetuses resulting from the loss of maternal entraining influences. Thus, the fetal SCN is capable of developing a circadian rhythm in glucose utilization independent of the maternal circadian system.

Autoradiographic studies on glucose utilization in individual zones of the rat thymus.

Wistar rats were injected intraperitoneally with 2-(14C)deoxyglucose and their thymuses were processed for thaw-mount autoradiography after 5, 10 or 35 min. Highest levels of radioactivity were demonstrated in the thymic medulla (5-fold higher than in the cortex). Scanning of autoradiograms for regional differences in grain densities indicated particularly intense glucose utilization in the cortico-medullary zone. Differences in glucose utilization between individual thymic zones seem to reflect differences in cellular composition, i.e., ratio of stroma cells to thymocytes.

Local glucose utilization of the brain and pineal gland during stimulation of the cervical sympathetic trunk.

The quantitative autoradiographic 2-[14C]deoxyglucose method was employed to map the metabolic activity of the superior cervical ganglion and the entire brain during unilateral electrical stimulation of the cervical sympathetic trunk in the urethane-anesthetized rat. Stimulation of the cervical sympathetic trunk increased glucose utilization in the ipsilateral superior cervical ganglion (+95%) but did not produce side-to-side differences in glucose utilization in any of the brain structures examined in this study. Compared to the control nonstimulated animals, the rate of glucose metabolism in the pineal gland was increased 71% following stimulation of the cervical sympathetic trunk. The pineal gland was the only brain region out of 87 structures examined in which glucose utilization was increased by electrical stimulation of its sympathetic innervation.

Diurnal rhythmicity and hypothalamic deficits in glucose utilization in aged ovariectomized rats

Aging is associated with a loss of cyclic gonadotropin release in female animals. This deficit may reflect dampened circadian rhythmicity of neuroendocrine events and/or altered function in hypothalamic nuclei important to regulation of cyclic female reproduction. The purpose of this study was to determine if diurnal periodicity and glucose metabolism in the hypothalamus are altered with age and whether such changes could help to explain the age-related deficits in gonadotropin release. Young (3-4-month-old) and old (18-21-month-old) rats were ovariectomized and subjected to the 2-deoxy-D-1-14C-glucose technique to measure rates of cerebral glucose utilization (GU), an index of neural function (Sokoloff et al., 1977) in various brain areas and in the pineal gland. We measured GU during the light (1400 hours) and the dark (2200 hours) in 17 anatomical regions including the following hypothalamic areas: medial preoptic nucleus, suprachiasmatic preoptic nucleus, suprachiasmatic nucleus, paraventricular nucleus, arcuate nucleus, and median eminence. Serum concentrations of luteinizing hormone (LH) and prolactin were measured in the same rats to determine the effect of age on both of these hormones. Diurnal periodicity of GU was observed in the suprachiasmatic nucleus and the pineal gland in young and old rats. Although there was no age difference in GU of the pineal gland, GU was reduced during the light and dark in the suprachiasmatic nucleus and all other hypothalamic areas examined except the suprachiasmatic preoptic nucleus and the median eminence. Ovariectomy induced an attenuated increase in concentrations of LH in old, compared to young rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional neuroanatomic mapping of the rat striatum: regional differences in glucose utilization in normal controls and after treatment with apomorphine

Glucose utilization was measured in 5 regions of rat striatum within four anterior-posterior levels. Areas of minimal and maximal glucose utilization were identified. Density-window image analysis was used to visualize and to quantify areas of minimal and maximal glucose utilization, which were also apparent upon close visual inspection. In a normal control group, there were substantial regional variations in striatal glucose utilization (e.g. dorsal vs ventral; dorsomedial vs dorsolateral), revealing a detailed pattern, previously unavailable, which served as a baseline to study the effect of systemic apomorphine. The highest levels of glucose utilization were in small islands 0.01–0.25 mm 2, and in what appeared to be dense clusters of islands that formed larger zones. Apomorphine treatment decreased glucose utilization in dorsomedial regions, increased it in a ventromedial region, and did not change it in others. The findings emphasize the importance of regional analysis of striatum in functional and physiological studies, and provide a new baseline for analyses of striatal glucose utilization in studies of development and aging, drug effects, external stimuli, and rat models of movement disorders.

Glucose flux through the hexose monophosphate shunt and NADP(H) levels during in vitro ageing of human skin fibroblasts.

In cultured human skin fibroblasts the glucose flux through the hexose monophosphate shunt (HMS) amounts to 4% of the glucose flux through the glycolytic pathway. Upon in vitro ageing the rate of glucose utilization through the HMS is decreased more than 50%. This decrease in HMS was not caused by a limiting enzymatic capacity since glucose utilization through the HMS could be raised at least 30-fold in both 'young' and 'aged' fibroblasts upon stimulation with phenazine methosulphate. This effect of in vitro ageing upon glucose metabolism was also not due to differences in proliferation rate between 'young' and 'aged' human fibroblasts, since there was no difference in glucose utilization between proliferating and growth-inhibited (confluently cultured) fibroblasts. The NADPH/NADP ratio was found to be decreased by 12% in 'aged' cells.

Local cerebral glucose utilization during nitrous oxide and pentobarbital anesthesia in rats.

Local cerebral glucose utilization was measured in rats during nitrous oxide and pentobarbital anesthesia, using the 2-[14C]-deoxyglucose method. During nitrous oxide anesthesia, 67%, marked heterogeneity of glucose utilization was observed. During pentobarbital anesthesia (30 mg/kg), glucose utilization decreased, the decrease being pronounced in the structures where glucose utilization was high during nitrous oxide anesthesia. During combined use of nitrous oxide and pentobarbital (30 mg/kg), with an electroencephalogram (EEG) consisting of 4-6 Hz wave super-imposed by 10-15 Hz wave, glucose utilization was higher in many brain structures, including the midbrain reticular formation, than that observed during pentobarbital (30 mg/kg) anesthesia alone. With pentobarbital, 125 mg/kg, the EEG became nearly flat and a dose-related decrease in glucose utilization was observed in the cerebral cortices and inferior colliculus but not observed in any other structures. During the combined use of nitrous oxide and pentobarbital (125 mg/kg), the EEG was nearly flat, and no statistically significant differences in glucose utilization were observed as compared with those during pentobarbital (125 mg/kg) anesthesia in any of the structures examined. The results suggest that nitrous oxide and pentobarbital affect local cerebral glucose metabolism differently and that nitrous oxide acts as cerebral metabolic stimulant in the presence of cortical function during pentobarbital anesthesia.

Oxygen Consumption in Mice (I Strain) after Feeding

To determine if excess heat production can account for the lower fat accumulation in I strain mice, oxygen consumption, a measure of energy expenditure, was measured in I mice and C57BL mice (a control strain) to determine basal metabolic rate (BMR) and resting metabolic rate (RMR) and response to food consumption and acute cold exposure. Oxygen consumption was higher in the I strain than in the C57BL mice only after the dark cycle (feeding period). No difference between I and C57BL mice in spontaneous activity was found during the dark or light cycle. Body temperature was also not different in I and C57BL mice. Oxygen consumption in response to norepinephrine was similar in the two strains. These results indicate oxygen consumption is greater in I than C57BL mice only in response to feeding. Differences in glucose utilization by I and C57BL mice, including a lower glucose tolerance curve, greater deposition of glucose to muscle glycogen and lactate production in I mice also indicate differences in nutrient processing. Higher oxygen consumption after feeding in I mice than in C57BL mice indicates inefficient food utilization and accounts for their lower ability to store energy as fat.

Regional changes in brain glucose metabolism reflect cognitive impairments in aged rats

Aged rats (22 to 24 months) and young control rats (3 months) were tested in a battery of behavioral tests which included tests of learning, place navigation, sensorimotor integration, motor coordination, activity, and exploration. Following testing all animals were analyzed in an unanesthetized state for their local glucose utilization. Significant differences in glucose utilization were found between the aged and young groups on some behaviors and in some brain regions. There was considerable variability in the aged group in both their behavioral performance and their glucose utilization scores; thus, attempts were made to determine whether the variability in the degree of impairment within any particular behavioral test was correlated to the regional glucose utilization scores in any of the 45 brain regions analyzed. In two of the behavioral tests employed (i.e., one for learning and one for place navigation), the decline in performance correlated significantly with the decrement in regional glucose utilization. Moreover, the performance in these two tests showed significant correlation with glucose use in only five regions (dentate gyrus, medial septum-diagonal band area, hippocampal CA1, hippocampal CA3, and prefrontal cortex). These results show that the learning impairments in the aged rats are related to the extent of decrease in glucose utilization in restricted areas of the limbic system. In addition, the results show that the individual rats within an aged rat population develop cognitive impairments to a variable degree and that the aged rats with the most pronounced learning impairments are the ones exhibiting the most severe functional decrements, in terms of glucose utilization, in the septohippocampal system and the prefrontal cortex. This suggests that aging rats may be interesting not only for the study of the normal aging process, but also as a model of dementia.

Dietary Chromium and Interior Egg Quality

Effects of supplementing a corn-soy diet with chromium, vanadium and other ingredients on interior egg quality of caged layer hens were investigated. Although including 10 ppm chromium or 10% distillers dried grains with solubles (DDGS) significantly increased Haugh units in one experiment, no significant improvement was obtained by adding chromium to the basal diet in four subsequent experiments nor did DDGS show an improvement when included as a treatment in one of the latter experiments. In the first experiment, a combination of chromium and DDGS gave no further improvement in interior egg quality. No significant difference in glucose utilization was observed between hens fed diets with and without chromium.Vanadium significantly reduced Haugh unit values, but the marked deterioration of albumen quality caused by adding 10 or 20 ppm vanadium was significantly counteracted by adding chromium to the diet in all experiments. The effect of dietary zinc on Haugh units was not consistent.The results of these studies demonstrate that chromium is effective in counteracting the deleterious effect of vanadium on interior egg quality and indicate that chromium may be essential for maintenance of the normal physical state of egg albumen.

EPERYTHROZOON OVIS: THE DIFFERENCE IN CARBOHYDRATE METABOLISM BETWEEN INFECTED AND UNINFECTED SHEEP ERYTHROCYTES

The glucose utilization lactic and pyruvic acid production and oxygen uptake of normal and Eperythrozoon ovis infected sheep erythrocytes were measured under aerobic conditions. Infected cells showed marded increases in both glucose utilization and acid production as compared with controls. Uninfected erythocyte samples which included a percentage of reticulocytes comparable to that found in E. ovis infection showed no apparent difference in glucose utilization and lactic acid production form the normal control erythrocytes, although considerable increases in the oxygen uptake were recorded.

Effect of essential fatty acid deficiency on lipid metabolism in isolated fat cells of epididymal fat pads of rats.

AbstractLipogenesis, lipolysis, and stimulation of glucose conversion into lipid by insulin or prostaglandin E1 were studied in isolated fat cells of the epididymal fat pads of rats fed a fat‐free diet or this diet supplemented with 10% hydrogenated coconut oil or 10% safflower seed oil. Changes in fatty acid composition, characteristic of an essential fatty acid deficiency, were well advanced in the neutral lipid but had only started in the polar lipid of the fat cells of the epididymal fat pads of animals 3 months after weaning. Cellularity of the epididymal fat pads, as indicated by protein to lipid ratio of the fat cells, was influenced greatly by hydrogenated coconut oil in the diet irrespective of an essential fatty acid deficiency. Lipogenesis was increased in the fat cells of the animals fed the hydrogenated coconut oil diet 5 weeks after weaning but was not significantly different from that of the safflower fed animals 3 months after weaning. Incorporation of glucose into lipid, oxidation to CO2, and basal lipolysis were not significantly different in the fat cells of the essential fatty acid deficient animals from those fed safflower oil 3 months after weaning, except in animals of the fat‐free group based upon cell lipid. However, conversion of glucose to free fatty acid was significantly greater in the isolated fat cells of animals fed either the hydrogenated coconut oil or the fat‐free diet than in those of animals fed the safflower oil supplement. The incorporation of glucose into lipid by isolated fat cells was stimulated significantly by insulin in young animals fed a fat‐free diet, but the effect on lipogenesis appeared to be reversed in the fat cells of animals receiving safflower seed oil 3 months after weaning. Prostaglandin E1 also appeared to stimulate the incorporation of glucose into lipid in the fat cells of the older animals receiving safflower seed oil. Differences in osmolarity produced large differences in utilization of glucose and release of lipid from isolated fat cells, but no significant differences were observed between the cells from animals fed the fat‐free diet and those from the controls fed safflower oil. The results demonstrated the effects of diets containing fat or no fat on enzyme activities and membrane properties of fat cells of the epididymal fat pads of essential fatty acid deficient rats.

The Relation of Glucose Absorption to Respiration in Potato Slices

When plant tissue displays an indifference to one or another respiratory inhibitor, it is difficult to decide whether the respiration is truly resistant or whether the repression of an inhibitor-susceptible pathway elicits compensatory activity of a new or altered kind. Since resistance is in effect defined by the unimpaired utilization of 02 in the presence of the inhibitor, indirect means must be invoked to compare the respiratory behavior in the presence and absence of inhibitor in order to resolve the question. One way to estimate and characterize respiratory activity is to observe the utilization and disposition of radioactive substrate provided exogenously at levels sufficiently low so that hopefully the metabolite provided serves to label the endogenous metabolic pool without significantly altering the latter. It was early noted that when fresh and aged potato slices were compared with respect to the utilization of C14-labeled glucose, the evolution of C1402 differed very much more markedly than did gross glucose absorption (10, 19). Since a pronounced enhancement of salt absorbing capacity is known to accompany the respiratory rise which attends aging (12, 13), the question arose as to whether apparent differences in glucose utilization reflected distinctions related to glucose absorption. Consequently some attention was given the problem of glucose absorption per se. Absorption studies in turn served to answer in part the basic question regarding the meaning of inhibitor resistance. Potato slices, markedly cyanide-sensitive when freshly prepared, may become virtually cyanide-resistant in a day (7,14). By contrast, malonate-resistant fresh potato disks normally become increasingly malonate-sensitive with time (10, 19). However, when storage organ slices are aged in bicarbonate under 5 to 10 % CO2 in air, the respiration rises as normally but remains malonate-resistant (11). Thus a means is at hand to obtain metabolically active malonateresistant tissue. The experiments which follow examine the influence of malonate on both respiration and glucose absorption in malonate-sensitive and malonate-resistant potato slices, respectively. In addition, the effect of cyanide on the 2 processes is examined in cyanide-resistant tissue.