A Dramatic Accumulation of Glycogen in the Brown Adipose Tissue of Rats Following Recovery from Cold Exposure
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During starvation, muscle glycogen in Boleophthalmus boddaerti was utilized preferentially over liver glycogen. In the first 10 days of fasting, the ratio of the active‘a’form of glycogen phosphorylase to total phosphorylase present in the liver was small. During this period, the active‘I’form of glycogen synthetase increased in the same tissue. In the muscle, the phosphorylase‘a’activity declined during the first 7 days and increased thereafter while the total glycogen synthetase activity showed a drastic decline during the first 13 days of fasting. The glycogen level in the liver and muscle of mudskippers starved for 21 days increased after refeeding. After 6 and 12 h refeeding, liver glycogen level was 8·5 ± 2·3 and 6·9 ± 4·5 mg·g wet wt 1 , respectively, as compared to 5·8 ± l·6mg·g wet wt 1 in unfed fish. Muscle glycogen level after 6 and 12 h refeeding was 0·96±0·76 and 0·82 ± 0·50 mg·g wet wt 1 , respectively, as opposed to 0·21 ± 0·12 mg·g wet wt 1 in the 21‐days fasted fish. At the same time, activities of glycogen phosphorylase in the muscle and liver increased while the active‘I’form of glycogen synthetase showed higher activity in the liver. Since glycogen was resynthesized upon refeeding, this eliminated the possibility that glycogen depletion during starvation was due to stress or physical exhaustion after handling by the investigator. Throughout the experimental starvation period, the body weight of the mudskipper decreased, with a maximum of 12% weight loss after 21 days. Liver lipid reserves were utilized at the onset of fasting but were thereafter resynthesized. Muscle proteins were also metabolized as the fish were visibly thinner. However, no apparent change in protein content expressed as per gram wet weight was detected as the tissue hydration state was maintained constant. The increased degradation of liver and muscle reserves was coupled to an increase in the activities of key gluconeogenic enzymes in the liver (G6Pase, FDPase, PEPCK, MDH and PC). The increase in glucose synthesis was possibly necessary to counteract hypoglycemia brought about by starvation in B. boddaerti.
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Changes induced in liver and striated muscle glycogen and glycogen enzymes (glycogen synthetase, glycogen phosphorylase and alpha-amylase) by hypothyroidism and hyperthyroidism in rats have been determined. There were no changes in liver glycogen synthetase, phosphorylase and amylase activities in the hypothyroid group. Hyperthyroid rats showed lower liver glycogen synthetase, phosphorylase a and amylase activities. In muscle, hypothyroid rats had lower phosphorylase activity. In the hyperthyroid group glycogen synthetase was increased.--The results presented do not completely agree with the glycogen levels found in both tissues studied, and they are obviously more related to other factors such as glucose availability. It can be concluded that under the conditions studied, the glycogen enzyme levels could not alone explain the variations of glycogen levels.
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Optimum conditions were established for the assay of glycogen, glycogen synthase, glycogen phosphorylase, phosphoglucomutase, and glucose-6-phosphatase in rabbit fetal heart, lung, and liver. Using these methods, the pattern of appearance of glycogen and the above four enzymes was established from day 18 of gestation to day 8 after birth. The results indicate that total tissue glycogen reaches maximum levels between days 22 and 24 in the heart, days 24 and 26 in the lung, and days 30 and 31 in the liver. In all three tissues, the rapid rise or depletion of glycogen is coincident with a corresponding increase in glycogen synthase and glycogen phosphorylase activities. However, substantial amounts of glycogen synthase are present both prior to and after the accumulation of glycogen. Similarly, considerable amounts of glycogen phosphorylase are present early in gestation, yet deposition of glycogen occurs. Both the I and D forms of glycogen synthase are present in the three tissues, the major being the physiologically inactive D form. Similarly both the a and b forms of glycogen phosphorylase are present, with the a form (active form) making up about 30–60% of the total phosphorylase activity. Glucose-6-phosphatase was absent in fetal heart and lung throughout the period of gestation investigated. Low levels of this enzyme were detectable in fetal liver near term. The phosphoglucomutase activity increased progressively from day 22 of gestation in all three tissues and continues to increase after birth. The disappearance of fetal lung glycogen occurs between days 27 and 28 at a time when surfactant phospholipids first appear. These findings indicate that the breakdown of glycogen is providing the fetal lung cells with energy necessary for surfactant phospholipid biosynthesis.
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Although brown adipose tissue in infants and young children is important for regulation of energy expenditure, there has been considerable debate on whether brown adipose tissue normally exists in adult humans and has physiologic relevance in this population. In the last decade, radiologic studies in adults have identified areas of adipose tissue with high 18F-fluorodeoxyglucose (18F-FDG) uptake, putatively identified as brown fat. This radiologic study assessed the presence of physiologically significant brown adipose tissue among 1972 adult patients who had 3640 consecutive 18F-FDG positron-emission tomographic and computed tomographic whole-body scans between 2003 and 2006. Brown adipose tissue was defined as areas of tissue that were more than 4 mm in diameter, had the CT density of adipose tissue, and had maximal standardized uptake values of 18F-FDG of at least 2.0 gm per mL. A sample of 204 date-matched patients without brown adipose tissue served as the control group. Using these criteria, positron-emission tomographic and computed tomographic scans identified brown adipose tissue in 106 of the 1972 patients (5.4%). The most common location for substantial amounts of brown adipose tissue was the region extending from the anterior neck to supraclavicular region. Immunohistochemical staining for uncoupling protein 1 in this region confirmed the identity of immunopositive, multilocular adipocytes as brown adipose tissue. More brown adipose tissue was detected in women (7.5% {lsqb;76/1013{rsqb;) than in men (3.1% {lsqb;30/959{rsqb;); the female:male ratio was 2.4:1.0 (P < 0.001). The mass and activity of brown adipose tissue was also greater in women than in men. The probability of having substantial brown adipose tissue decreased with increasing age (<50–>64) (P < 0.001), short-term or long-term use of beta-blockers (P < 0.001), increasing mean outdoor temperature at the time of the scan (P < 0.02), and increasing tissue and increasing body mass index among patients in the top third for age (>64 years) (P for trend = 0.007). These findings show that functional brown adipose tissue is prevalent in adult humans, and significantly more frequently in women. The inverse correlation of body mass index with the amount of brown adipose tissue, especially in older patients, suggests to the investigators a possible role of brown adipose tissue in protecting against obesity.
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Abstract Glycogen synthetase and phosphorylase activities were quantitatively determined for the first time in glycogen body tissue from late embryonic and neonatal chicks. For comparative purposes, these enzyme activities were examined also in skeletal muscle and liver from pre‐ and post‐hatched chicks. The present data show that the forms of glycogen synthetase which exist in the chick glycogen body are similar to those found in both liver and muscle, while glycogen body phosphorylases more closely resemble those forms characteristic of skeletal muscle.
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Abstract Cytometric analysis was made on the adult adipose tissue of sectioned abdomens of normal and experimentally treated adult Drosophila melanogaster . The adipose cells of two week old males and females are equal in size. The male cells contain 72% glycogen and 7% lipid, whereas the female cells contain 60% glycogen and 23% lipid. The adipose tissue of males containing a mature, transplanted ovary is similar to the female adipose tissue with regard to the cell size and amounts of lipid and glycogen. The adipose cells of castrated females are about 1.4 times larger than those of normal females, but the amount of lipid and glycogen per cell remains somewhat feminine. The adipose cells of genetically sterile, fes , females are about 1.4 times larger than those of normal females, but the amount of lipid and glycogen per cell remains somewhat feminine. The adipose cells of genetically sterile, fes , females are about 1.5 times larger than normal cells and are similar to normal male cells with regard to the proportions of reserve substances. The adipose cells of fes females containing a transplanted, normal ovary shrink to the same size as those of normal flies; and are similar to those of the normal females with respect to amount of glycogen, but are similar to those of normal males with respect to the amount of lipid. The ovary's stimulatory effect on the growth of the larval and repressive effect on the growth of the adult tissue is discussed.
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Summary. The distributions of glycogen, phosphorylase and glycogen synthetase were studied in the testes and ductuli efferentes of hamsters aged 1 to 99 days (body weight 3 to 130 g). Glycogen was also determined quantitatively. From Stages IV to VIII of spermatogenesis, the seminiferous tubules of adult hamsters contain considerable amounts of glycogen (0·15 to 0·2% of testicular weight), localized in the Sertoli cells and in the lumen of the tubules. Phosphorylase and glycogen synthetase are also present in tubules containing glycogen. The appearance of glycogen in the seminiferous tubules during the 4th week of life (45-g animals) coincides with the appearance of spermatocytes. Up to the establishment of spermatogenesis (usually 5th or 6th week; 50 to 60-g animals), a progressive increase in the glycogen content (0·05 to 0·07%) and phosphorylase activity is observed. Glycogen synthetase activity appears at this stage. A sharp rise in glycogen concentration as well as an increase in activity of phosphorylase and glycogen synthetase occurs at puberty. From the 3rd month, the enzyme activities diminish considerably, though the content and cyclic distribution of glycogen remains unchanged. Rete testis epithelium, though devoid of glycogen, contains phosphorylase at all the stages of development. In the adult, the intratesticular rete testis lumen contains a trace of glycogen and phosphorylase. The proximal portion of the ductuli efferentes is characterized by a massive glycogen accumulation in the epithelium (ciliated cells) as well as in the lumen. Both phosphorylase and glycogen synthetase have a high activity in this organ. Glycogen synthesis in the ductuli efferentes occurs earlier than in the seminiferous tubules. It seems probable that spermatogenesis and glycogen synthesis are independent of each other.
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Liver and muscle glycogen content, and the activities of glycogen synthetase, glycogen phosphorylase and alpha-amylase have been measured in fed and 24 hours fasted rats. Muscle and liver glycogen account for similar amounts of glycosyl residues liberated in this period of food deprivation. With fasting, liver glycogen synthetase activity decreases somewhat, increasing the I versus total ratio; the liver phosphorylase activity decreases considerably and amylases remain constant. In muscle, total synthetase remains constant with fasting, but the I versus total ratio decreases; phosphorylase activity decreases very considerably and alpha-amylase activity increases to almost thrice the values found in fed animals. These changes reflect a tendency towards conservation of glycogen primers with a preparation to increase glycogen synthesis when glucose would be available. In muscle also, the amylase increase in activity would be tentatively explained as a partial replacement of phosphorylase activity as a means of glucose mobilization from glycogen.
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