Metabolic Differentiation of Distinct Muscle Types at the Level of Enzymatic Organization

Summary.Specimens of human adipose tissue were cultured for one week with or without the addition of insulin. The basal as well as the noradrenaline-stimulated lipolysis were enhanced in the explants cultured with insulin, showing that the long-term effect of the hormone is lipolytic. However, an acute antilipolytic effect of insulin could be demonstrated in these explants in the subsequent short-term incubations. The basal rate of glucose incorporation into the lipids was enhanced in the explants cultured with insulin. When insulin was added in the short-term incubations these explants did not further respond to the hormone while this was the case with the explants cultured without insulin. Thus, it seems that prolonged exposure to insulin leads to a diminished acute effect of the hormone on glucose metabolism. However, the same explants responded to the antilipolytic effect showing that insulin was able to bind itself to the membrane. The activities of hexokinase (HK), glucose-6-phosphate dehydrogenase (G6PDH), pyruvate kinase (PK) and lactate dehydrogenase (LDH) were increased in large fat cells both in freshly excised tissue and in the cultured explants. However, the activity of phosphofructokinase (PFK) did not correlate with the cell size. The presence of insulin during the culture period enhanced the activities of G6PDH, PK, and LDH, while this was not found for HK or PFK. The data thus suggest that the metabolic capacity of human fat cells is enhanced by long-term exposure to insulin. Although enzyme induction could be shown for G6PDH, PK and LDH it seems unlikely that this is of importance for the increased rates of glucose metabolism in these explants since the rate-limiting enzymes, HK and PFK, were not increased. Most probably, *Part of these data were presented at the First International Congress on Obesity in London, England on 9-11 October, 1974. then, this stimulating effect of insulin is exerted on the membrane and the rate of glucose transport.

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“…Hexokinase (E.C.2.7.1.1) was determined according to the method of Bass et al [15]. For the other enzymes the assay mixtures were:…”

Section: Enzyme Determinationsmentioning

confidence: 99%

Human adipose tissue in culture V. Studies on the metabolic effects of insulin

1976

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“…After these measurements, the rats were anesthetized with pentobarbital sodium (40 mg/kg body wt ip), and transthoracic echocardiography was performed with an echocardiographic systems (model SSD-900, Aloka; Tokyo, Japan) equipped with a 7.5-MHz convex scan probe (VST-987-7.5, Aloka) as described in our previous papers (20,33). We determined the left ventricular end-diastolic dimension (LVEDD), left ventricular end-systolic dimension (LVESD), left ventricular fractional shortening (LVFS), which was calculated according to the following formula: LVFS (%) ϭ [(LVEDD Ϫ LVESD)/LVEDD]ϫ100, and stroke volume (SV), which was calculated according to the following formula (Pombo method): SV ϭ (LVEDD) 3 Ϫ (LVESD) 3 .…”

Section: Animals and Protocolmentioning

confidence: 99%

Aging-induced decrease in the PPAR-α level in hearts is improved by exercise training

Iemitsu

Miyauchi

Maeda

et al. 2002

American Journal of Physiology-Heart and Circulatory Physiology

155

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Peroxisome proliferator-activated receptor (PPAR)-␣, a transcriptional activator, regulates genes of fatty acid (FA) metabolic enzymes. To study the contribution of PPAR-␣ to exercise training-induced improvement of FA metabolic capacity in the aged heart, we investigated whether PPAR-␣ signaling and expression of its target genes in the aged heart are affected by exercise training. We used hearts of sedentary young rat (4 mo old), sedentary aged rat (23 mo old), and swim-trained aged rat (23 mo old, training for 8 wk). The mRNA and protein expression of PPAR-␣ in the heart was significantly lower in the sedentary aged rats compared with the sedentary young rats and was significantly higher in the swim-trained aged rats compared with the sedentary aged rats. The activity of PPAR-␣ DNA binding to the transcriptional regulating region on the FA metabolic enzyme genes, the mRNA expression of 3-hydroxyacyl CoA dehydrogenase (HAD) and carnitine palmitoyl transferase-I, which are PPAR-␣ target genes, and the enzyme activity of HAD in the heart altered in association with changes of the myocardial PPAR-␣ mRNA and protein levels. These findings suggest that exercise training improves aging-induced downregulation in myocardial PPAR-␣-mediated molecular system, thereby contributing to the improvement of the FA metabolic enzyme activity in the trained-aged hearts.peroxisome proliferator-activated receptor-␣; swimming training; aged rat; fatty acid THE HEART is known for its ability to produce energy from fatty acids (FA) because of its important ␤-oxidation equipment, but it can also derive energy from several other substrates, including glucose and lactate (10, 23). On a physiological condition, FA is considered to account for 60-70% of oxygen consumption for energy production in the heart (23). However, FA metabolic capacity in the heart is reduced by aging (19, 32).It has been reported that exercise training improved an aging-induced decrease of FA metabolic capacity in the heart (7, 18, 25, 32). However, the mechanisms for improving FA metabolic capacity in the heart by exercise training are unclear.Peroxisome proliferator-activated receptor (PPAR)-␣ is a member of the nuclear receptor transcription factor superfamily and is mainly expressed in the heart, liver, and kidney (2,13,29). The recent studies indicated that PPAR-␣ plays a critical role in the expression of genes involved in FA metabolism (13). PPAR-␣ heterodimerizes with the retinoid X receptor (RXR-␣) to bind to peroxisome proliferator-response elements (PPRE) in the upstream regions of a number of genes involved in metabolic homeostasis (13,29). PPAR-␣ regulates target genes encoding FA metabolic (␤-oxidation) enzymes and FA transporters such as FA binding protein, carnitine palmitoyl transferase-I (CPT-I), acyl-CoA synthase, 3-hydroxyacyl CoA dehydrogenase (HAD), apolipoproteins, and so on, suggesting that PPAR-␣ plays an important role in FA metabolic homeostasis (2,5,17,29). However, it is unknown whether the aging and subsequent exercise training affect...

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“…Glycolytic potential was calculated according to Monin et al (1987) The activity of phosphorylase was measured spectrophotometrically (absorbance 340 nm, Perkin Elmer Lambda 2 spectrometer, Űberlingen, Germany) according to Bass et al (1969) following the release of glucose-1-phosphate from glycogen with L-cystein, NaDP (N8129, Sigma-Aldrich, St. Luis, USA), glucose-1,6-diphosphate, AMP, phosphoglucomutase (rabbit muscle, 79440, Fluga Chemie GmbH, Buchs, Switzerland) and glucose-6-phosphatedehydrogenase (127671, Roche, Indiapolis, USA).…”

Section: Biochemical Analysesmentioning

confidence: 99%

The significance of the activity of glycogen debranching enzyme in glycolysis in porcine and bovine muscles

2006

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The purpose of the study was to examine the activity of glycogen debranching enzyme, GDE, in porcine and bovine muscles differing in rate of contraction and in oxidative capacity. The activity of GDE, the activity of phosphorylase, total glucose content, lactate content and pH were measured from meat samples taken 35 min post-mortem and ultimate pH 24 or 48 h post-mortem.Both GDE and phosphorylase are needed for the complete degradation of glycogen. In porcine muscles the activities of these glycogen degrading enzymes were higher than in bovine muscles. The activities were increasing with the increasing fast twitch and glycolytic character of a muscle of a given species. However, the increase in the activity of phosphorylase was greater than the increase in the activity of GDE. It was concluded that the GDE may restrict the rate of glycolysis in fast twitch muscles.

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Metabolic Differentiation of Distinct Muscle Types at the Level of Enzymatic Organization

Cited by 624 publications

References 46 publications

Human adipose tissue in culture V. Studies on the metabolic effects of insulin

Human adipose tissue in culture V. Studies on the metabolic effects of insulin

Aging-induced decrease in the PPAR-α level in hearts is improved by exercise training

The significance of the activity of glycogen debranching enzyme in glycolysis in porcine and bovine muscles

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