Biomedical subjects

S Azhar

Publications and source records attributed to S Azhar.

At least 73 records · Page 4Linked to original sources

PubMed1993

Effect of okadaic acid on hepatocyte structure and function.

The aim of this study with rat hepatocytes was to describe the effect of okadaic acid (OKA) (a potent and specific inhibitor of protein phosphatases) on the biosynthesis, processing and/or secretion of various lipid and protein molecules. Gel radioautograms indicated that low concentrations of okadaic acid (100 nM) induced hyperphosphorylation of a number of hepatocyte phosphoserine/threonine residues in the Mr range of 35-220 kDa. The effects of okadaic acid on the morphology of the hepatocytes was time and dose-dependent; early changes included cell rounding, loss of typical Golgi staining of beta COP, and fragmentation of the Golgi compartment at the EM level. General hepatocyte cell functions such as protein synthesis, lactate dehydrogenase activity, and ATP levels were unchanged with 100 nM okadaic acid as were all hepatocyte functions carried out in the endoplasmic reticulum of these cells. As such, incubation with okadaic acid did not alter the biosynthesis of phosphatidylcholine (from labeled choline), or very low density lipoproteins (VLDL) from labeled fatty acids or glycerol. Likewise, the biosynthesis of various endoplasmic reticulum synthesized proteins (transferrin, albumin, apolipoprotein E, and HMG CoA Reductase) continued normally in the presence of okadaic acid. However, incubation with okadaic acid led to major changes in all hepatocyte functions normally carried out in the Golgi compartment; i.e., the incorporation of labeled ceramide into sphingomyelin was profoundly reduced, as was the Golgi-required packaging and secretion of various proteins synthesized in the endoplasmic reticulum. These findings point to the Golgi compartment as an specific target for okadaic acid and suggest that one or more okadaic acid-sensitive phosphoproteins may be involved in maintaining its normal structure and function.

Animals↗

PubMed1992

Reconstitution of the lipoprotein cholesteryl ester transfer process using isolated rat ovary plasma membranes.

Steroidogenic cells are able to utilize lipoprotein-derived cholesteryl esters for steroidogenesis without internalizing intact lipoproteins. In the current report, we provide evidence that an early step in this process may be the selective extraction of cholesteryl esters at the cell (plasma membrane) surface. We have used a highly purified plasma membrane preparation from rat luteinized ovaries for incubation with rat- and human-derived high density (HDL) and low density (LDL) lipoproteins. The lipoproteins were modified with residualizing [125I]apoprotein or [3H]cholesteryl ester markers. Following trypsin treatment to remove intact surface-bound apoprotein particles, the membranes were analyzed for transferred radioactive labels. The results show that all the lipoproteins tested could serve as cholesteryl ester donors. Although far more [3H]cholesteryl ester than [125I]apoprotein radioactivity was transferred to plasma membranes in each case, and varied with the ligand used, the total (net) mass of cholesteryl ester transferred was comparable with the different lipoproteins. These data were confirmed using direct chemical methodology. Transfer was found to be specific for cholesteryl esters or ethers and did not involve other lipoprotein core lipids tested. Endomembranes from the same tissue could not substitute for plasma membranes as the primary cholesteryl ester acceptor. These results provide evidence that a reconstituted lipoprotein-plasma membrane system can simulate the cholesteryl ester extraction process described in situ and suggest uses for this methodology in future experiments designed to understand the transfer process.

Animals↗

PubMed1992

Alterations in glucose and protein metabolism in animals subjected to simulated microgravity.

Reduction of physical activity due to disease or environmental restraints, such as total bed rest or exposure to spaceflight, leads to atrophy of skeletal muscle and is frequently accompanied by alterations in food intake and the concentration of metabolic regulatory hormones such as insulin. Hindlimb suspension of laboratory rats, as a model for microgravity, also shows marked atrophy of gravity dependent muscles along with a reduced gain in body weight. Suspended rats exhibit enhanced sensitivity to insulin-induced glucose uptake when compared with normal control rats and resistance to insulin action when compared with control rats matched similarly for reduced body weight gain. These changes are accompanied by decreased insulin binding and tyrosine kinase activity in soleus but not plantaris muscle, unchanged glucose uptake by perfused hindlimb and decreased sensitivity but not responsiveness to insulin-induced suppression of net proteolysis in hindlimb skeletal muscle. These findings suggest that loss of insulin sensitivity during muscle atrophy is associated with decreased insulin binding and tyrosine kinase activity in atrophied soleus muscle along with decreased sensitivity to the effects of insulin on suppressing net protein breakdown but not on enhancing glucose uptake by perfused hindlimb.

Animals↗

PubMed1992

Prolonged activation of alpha 1 adrenoceptors induces down-regulation of protein kinase C in vascular smooth muscle.

Sustained exposure of vascular smooth muscle to catecholamines results in desensitization of alpha 1-adrenoreceptor-mediated vascular smooth muscle contraction. The present study was designed to determine the effects of prolonged exposure of blood vessels to catecholamines on protein kinase C (PKC) activity. Incubation of rat aortic smooth muscle with 10 microM norepinephrine (NE) for 4 h resulted in a threefold decrease in sensitivity of the contractile response of rat aortic smooth muscle to the phorbol ester 4 beta-phorbol 12,13-dibutyrate (PDBu); this loss in sensitivity was dependent on the presence of endothelium. NE induced a 45% decrease in enzymatic activity of the soluble and particulate forms of PKC. With [3H]PDBu used to label phorbol ester receptor binding sites in the aorta, there was a 34% decrease in [3H]PDBu binding sites in NE-treated blood vessels without change in binding affinity for the ligand. To determine whether this loss in enzymatic activity and [3H]PDBu binding resulted from a decrease in the quantity of the enzyme, Western blot analyses were performed using a monoclonal antibody (MoAb) against PKC. This approach confirmed the presence of an 80-Kd immunoreactive PKC in the soluble fraction of rat aortic smooth muscle and demonstrated a 44% decrease in the amount of PKC in blood vessels after sustained exposure to catecholamines. Our results demonstrate that prolonged activation of alpha-adrenoceptors in blood vessels leads to down-regulation of PKC which may contribute to desensitization of contraction mediated by vasoconstrictors.

Animals↗

PubMed1992

Inactivation of endothelial derived relaxing factor by oxidized lipoproteins.

Endothelial cell derived relaxing factor (EDRF) mediated relaxation of blood vessels is impaired in vessels exposed to lipoproteins in vitro and in arteries of hyperlipidemic humans and animals. To investigate the mechanism by which lipoproteins impair the effects of EDRF, which is likely nitric oxide (NO) or a related molecule, we have bioassayed EDRF/NO activity by measuring its ability to increase cGMP accumulation in rat fetal lung cultured fibroblasts (RFL-6 cells). Low density lipoprotein modified by oxidation (ox-LDL) induced a concentration-dependent inhibition of EDRF activity that had been released from bovine aortic endothelial cells (BAEC) stimulated with bradykinin or the calcium ionophore A23187. In addition, lipoproteins directly impaired authentic NO-induced stimulation of cGMP accumulation in the detector cells; stimulation by sodium nitroprusside was unaffected. Ox-LDL or oxidized HDL3 were highly potent in blocking NO-stimulated cGMP accumulation with EC50's of approximately 1 microgram/ml. Lipid extracted from ox-LDL blocked NO-stimulated cGMP accumulation to about the same extent as intact ox-LDL, while the protein component of ox-LDL did not inhibit the cGMP response. These results suggest that the lipid component of oxidized lipoproteins inactivate EDRF after its release from endothelial cells.

Animals↗

PubMed1992

Lactate production and pyruvate dehydrogenase activity in fat and skeletal muscle from diabetic rats.

This study was initiated to explore the possibility that an increase in the supply of gluconeogenic precursors contributes to the overproduction of glucose by the liver in NIDDM patients. To address this issue, a form of experimental NIDDM was produced in rats by injecting a low dose (38 mg/kg) of STZ and comparing lactate and alanine production and PDH activity in skeletal muscle and isolated adipocytes from normal and diabetic rats. Skeletal muscle lactate production was measured by using a hindlimb perfusion technique and was significantly greater (P < 0.01) in the diabetic rats compared with two groups of control rats: one perfused at normal glucose levels and the other perfused at glucose concentrations comparable with those observed in diabetic rats. Alanine production by hindlimb from diabetic rats was 46% greater than hindlimbs from control rats perfused at normal glucose levels (P < 0.01) but was not significantly greater than control rats perfused at diabetic glucose levels. The percentage of glucose converted to lactate by muscle from both control groups was 4-5%, significantly lower than the 18% conversion rate observed in diabetic animals (P < 0.001). An increase in the ratio of lactate produced/glucose transport by isolated adipocytes from diabetic rats also was observed when measured in both the basal state (0.65 +/- 0.12 vs. 0.15 +/- 0.03, P < 0.01) and in the presence of maximal amounts of insulin (0.15 +/- 0.02 vs. 0.04 +/- 0.01, P < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗

PubMed1991

Okadaic acid interferes with lipoprotein-supported corticosterone production in adrenal cells.

Rat adrenocortical cells in culture respond to stimulation by ACTH alone (15 fold over basal) and to ACTH + added lipoproteins (as an exogeneous source of cholesterol), with an additional 25-30 fold rise in steroidogenesis. With the addition of okadaic acid (OKA, 100 nM), a potent protein phosphatase inhibitor, the lipoprotein-induced rise in steroidogenesis is blocked. If 20 alpha-hydroxycholesterol is provided instead of lipoprotein-cholesterol, OKA has no effect suggesting that OKA affects only actively transported cholesterol. Since the OKA block is preceded by specific morphological changes in the cell (i.e., the loss of Golgi-associated microtubules followed by the disruption of the Golgi apparatus itself), it is hypothesized that some OKA-sensitive phosphoprotein associated with the microtubule/Golgi network of adrenocortical cells is critical for lipoprotein-derived cholesterol uptake and/or transport during steroidogenesis.

Adrenal Cortex↗

PubMed1991

Characterization of insulin receptor kinase activity and autophosphorylation in different skeletal muscle types.

We have examined insulin binding, autophosphorylation, and tyrosine kinase activity in detergent-solubilized and wheat germ agglutinin-purified insulin receptor preparations from four rat muscles of different fiber composition (i.e., tensor fascia latae, soleus, vastus intermedius, and plantaris). Insulin binding activity was similar in three of the four muscles but lower in tensor fascia latae. No significant differences were noted in the affinity of insulin for its receptor from various muscle types. Insulin receptor tyrosine kinase activity measured in the absence (basal) and presence of insulin (0.3-300 nM) was comparable in all muscle types (normalized to the amount of insulin bound). Insulin sensitivity, measured as the dose of insulin required for half-maximal activation of kinase activity, was also similar in all muscle types. Likewise, incubation of receptor preparations with [gamma-32P]ATP, Mn2+, and insulin (0.25-100 nM) resulted in a dose-dependent autophosphorylation of the beta-subunit (relative molecular weight approximately 95 kDa) with similar kinetics in all muscle types. In conclusion, these results show that the functional behavior of the insulin receptor autophosphorylation-kinase system (in vitro) is not changed by alterations in muscle fiber composition, indicating that differences in insulin sensitivity between different skeletal muscle types is probably not due to modulation of the insulin receptor phosphorylation system.

Adenosine Triphosphate↗

PubMed1991

Differences in insulin action as a function of original anatomical site of newly differentiated adipocytes obtained in primary culture.

Stromal vascular cells were isolated from adipose tissue obtained from three different anatomical locations: epididymal (EPI), retroperitoneal (RP), and dorsal subcutaneous (SC), and allowed to differentiate in primary tissue culture. Cell number, protein concentration, glycerophosphate dehydrogenase, and lipoprotein lipase activity were similar in cells obtained from the EPI, RP, and SC regions, as were total insulin binding and the affinity of insulin for its receptor. However, both maximal insulin receptor tyrosine kinase activity and insulin-stimulated phosphorylation of the insulin receptor were significantly lower (P less than 0.05) in cells cultured from the SC region. In addition, newly differentiated adipocytes from the SC region were less sensitive to the ability of insulin to stimulate glucose uptake, and maximal insulin-stimulated glucose uptake by these cells was also significantly lower (P less than 0.05) when compared to cells obtained from the two other regions. Since these studies were performed on adipocyte precursor cells, allowed to differentiate to a similar degree in primary culture, the observed differences in insulin receptor phosphorylating activity, as well as the ability of insulin to stimulate glucose uptake appear to be intrinsic to adipose tissue from the three sites.

Adipose Tissue↗

PubMed1990

Uptake and utilization of lipoprotein cholesteryl esters by rat granulosa cells.

Earlier studies have shown that rat granulosa cells grown in serum-free medium are exquisitely responsive to exogenously provided lipoprotein cholesterol. In this study we compare the amount of cholesterol (cholesteryl ester) actually delivered from various homologous and heterologous cholesterol-rich lipoproteins and examine the intracellular pathways used in the delivery system. Granulosa cells were incubated for 5 or 24 h with 125I-labeled human (h) HDL3, rat (r) HDL or hLDL equipped with non-releasable apoprotein and cholesteryl ether tags which accumulate within cells, even after degradation. We show that all the tested lipoproteins were similarly efficient in cholesteryl ester delivery; i.e., based on cholesterol: protein ratios of the starting ligands, each delivered approximately the same cholesteryl ester mass and evoked a similar progestin response. However, each lipoprotein was processed quite differently by the granulosa cells: hHDL3-cholesteryl ester was taken up almost exclusively by an non-endocytic pathway, hLDL-cholesteryl ester almost exclusively by an endocytic pathway and rHDL-cholesteryl ester by both pathways. In general, there was no correlation between the total amount of lipoprotein bound or apoprotein internalized and/or degraded by the cells with the amount of cholesteryl ester received or the level of the progestin response. Hormone stimulation upregulated the preferred pathway for each lipoprotein.

Animals↗

PubMed1990

Interaction of lipoproteins with isolated ovary plasma membranes.

Plasma membranes of ovarian luteal and adrenal cortical cells from "microvillar channels," a unique extracellular compartment formed by the close apposition of flattened microvillar surfaces. Microvillar channels have unusual affinity for cholesterol-rich lipoproteins, and, in vivo, may provide an increased surface area for these particles. In this research, we have isolated a plasma membrane-enriched fraction from rat luteinized ovaries, in which closely apposed membrane (i.e. microvillar channels) comprise about 30% of the preparation. Following in vitro incubations (approximately 1 h) of this plasma membrane fraction with different plasma lipoproteins, the closely apposed plasma membrane surfaces widen and become filled with lipoprotein particles (up to about 30 nm), whereas other membranes of the fraction show little binding. Competition experiments show that rat high density lipoproteins have the highest affinity for binding to the plasma membrane fraction. Radiolabeled plasma lipoprotein and the tissue-specific hormone, human chorionic gonadotropin, showed specific and saturable binding to the plasma membrane fraction, whereas other macromolecules used as controls did not. Radioautographic analyses of 125I-labeled lipoproteins and human chorionic gonadotropin indicate that binding occurs predominantly to the closely apposed plasma membranes (i.e. microvillar channels of the fraction). These studies show that microvillar channels of steroid-secreting cells entrap large numbers of plasma lipoproteins, particularly high density lipoproteins particles, presumably functioning in the delivery of cholesterol to these cells.

Animals↗

PubMed1990

Structural plugs at microtubule ends may regulate polymer dynamics in vitro.

Microtubules contain in their lumens distinct structures (plugs) that influence their dynamic behavior in vitro. As observed by electron microscopy, plugs are stain-occluding structures 10-30 nm in length that occur along the lengths and at the ends of microtubules. Plugs occur at a frequency of 20-40% at the ends of microtubules assembled from cycled microtubule protein containing MAPs. While the composition of plugs is not known, preliminary evidence suggests that they are accretions of tubulin, that they are labile, and that they are more common in preparations containing MAPs. When polymers are induced to depolymerize by endwise subunit dissociation, the frequency of plugged microtubule ends increases transiently, suggesting that plugs temporarily stabilize microtubules. The functional significance of plugs may be that they prevent the sudden complete loss of microtubules through catastrophic disassembly. It is possible that plugs, by slowing the rate of disassembly, enable a polymer to add GTP-tubulin subunits, thereby forming a stabilizing GTP-cap. These observations suggest that plugs may stabilize polymers and account for the frequent transitions from shortening to growing phases that characterize dynamic instability.

Animals↗

PubMed1990

Effects of insulin on carbohydrate and protein metabolism in voluntary running rats.

The goal of this study was to assess the effects of voluntary running activity in rats on various aspects of carbohydrate and protein metabolism. After 6 wk of exercise training, rats (ET) were rested for 24 h and their hindquarters, along with those from sedentary control (SC) and dietary control (DC) rats, were perfused with 0, 60, 250, or 6,000 microU/ml insulin. At 0 insulin, glucose clearance was similar for all groups, and it was increased with added insulin. However, the insulin effect was 20-40% greater for ET rats at all insulin concentrations (P less than 0.05). Muscle glycogen deposition also increased with added insulin but showed muscle-specific differences. Specifically, glycogen content of the plantaris muscle was significantly higher in ET compared with SC or DC rats, whereas this pattern was reversed in soleus muscle. In plantaris muscle, insulin stimulated glucose 6-phosphate (G-6-P)-independent (-G-6-P) glycogen synthase activity only in SC and DC rats and increased its affinity for G-6-P at 250 microU/ml in all groups. In contrast, the -G-6-P synthase activity was not increased in soleus muscle and was actually decreased in all groups at 6,000 microU/ml. Tyrosine release was suppressed by insulin in all groups, but this effect was significantly greater at insulin levels of 60 microU/ml (P less than 0.02) in hindquarters from ET rats compared with SC and DC rats. Neither insulin nor exercise training decreased 3-methylhistidine release from perfused hindquarters.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Differences in insulin-induced glucose uptake and enzyme activity in running rats.

To evaluate the relationship between enhanced insulin action and level of exercise training, in vivo glucose uptake was assessed in the absence of added insulin and during insulin-stimulated conditions for three activity levels of voluntarily trained rats (low 2-5 km/day, medium 6-9 km/day, high 11-16 km/day). After rats rested for 24 h and fasted overnight, glucose uptake was estimated by comparing steady-state serum glucose (SSSG) levels at low insulin (SSSI) concentrations achieved during an insulin suppression test. In the absence of added insulin, SSSI averaged approximately 20 microU/ml and glucose uptake was similar for high runners and younger weight-matched controls. However, with insulin added to sustain SSSI at approximately 35 microU/ml, SSSG was significantly reduced in all runners (P less than 0.02), with the lowest value attained in high runners. Fasting serum triglycerides were also reduced in all runners (P less than 0.05), with the lowest values seen in medium and high runners. The concentration of glycogen in liver and select skeletal muscles at the start of the study was not different between trained and control rats, suggesting that enhanced insulin-stimulated glucose uptake was not the result of lower glycogen levels. In addition, glycogen synthase and succinate dehydrogenase activities in biceps femoris muscle were only elevated for high runners, but glycogen synthase activity was not enhanced in plantaris muscle and was decreased in soleus muscle. These findings indicate that enhanced insulin-stimulated glucose uptake and reduced serum triglyceride concentrations induced in exercise-trained rats at varying activity levels are dissociated from changes in glycogen synthase and oxidative enzyme activity for skeletal muscle.

Animals↗

PubMed1989

Differences in uptake of high-density lipoproteins by rat adrenals using in vivo vs. in situ perfusion techniques.

This study describes the effect of the delivery route of high-density lipoproteins (HDL) on the ultimate fate of the lipoprotein in the intact rat adrenal. Equal amounts of human (h)-derived affinity-purified apoE-free 125I-labeled HDL3 was given to ethinyl estradiol-treated (i.e., lipoprotein-deficient) rats either intravenously (in vivo route) or by non-recycling perfusion (in situ perfusion route). After 60-90 min, the adrenals were either excised and assessed for uptake of radioactivity, or perfusion-fixed with glutaraldehyde and prepared for autoradiograms at the electron microscope level. The results show that hHDL3 circulated in vivo binds 9-times more readily to adrenal tissues than the same quantity of ligand delivered by perfusion. Also, when the lipoprotein is administered in vivo, it is 5-times more likely to be interiorized as an intact particle by zona fasciculata (corticosterone-secreting) cells via an endocytic pathway than when delivered by perfusion. Similar differences between the in vivo and in situ routes were not seen when 125I-labeled rat HDL was the ligand delivered. Whereas the starting hHDL3 ligand was free of apoE, there was a substantial (7-fold) conversion of the HDL3 to apoE-containing HDL3 following in vivo circulation of the ligand, as shown by sodium phosphotungstate-MgCl2 precipitation or heparin-Sepharose column chromatography. These results show that the route of lipoprotein delivery to specific tissues can play a major role in determining both the binding and the processing of the ligand by the tissue in question. With hHDL3, acquisition of apoE during only 1 h of recirculation in lipoprotein-deficient rats was sufficient to totally alter the fate of the ligand in the adrenal cortex.

Adrenal Cortex↗

PubMed1989

Calcium-activated phospholipid-dependent protein kinases from rat liver: characterization of purified isoenzymic forms.

1. This report describes characteristics of the three isoenzymic forms of protein kinase C purified in our laboratory from rat liver. 2. All three C-kinases phosphorylated several histone preparations, and to a much lesser degree, other protein substrates and had similar Km values for ATP and histones. 3. Each isoenzyme demonstrated an absolute requirement for Ca2+ and negatively charged phospholipids. 4. Among various phospholipids tested, phosphatidylserine from bovine brain was most effective with approximately 220 fold stimulation over basal activity. 5. Both diolein and 12-O-tetradecanoylphorbol-13-acetate decreased the Ca2+ requirement of the isoenzymes and also directly stimulated C-II and C-III enzymes in the presence of suboptimal concentrations of Ca2+ and phosphatidylserine.

Adenosine Diphosphate↗

PubMed1989

Effects of exercise training on the relationship between insulin binding and insulin-stimulated tyrosine kinase activity in rat skeletal muscle.

The effect of exercise training on insulin binding and insulin receptor tyrosine kinase activity was studied using detergent solubilized wheat germ agglutinin (WGA)-agarose purified receptor preparations from rat biceps femoris (BF) and tensor fascia lata (TFL) muscles. Insulin receptor activity, as assessed by A14 [125I] insulin binding, was significantly elevated in BF of exercise-trained rats when compared with similar preparations from a sedentary control group. This increase in binding activity was due to change in Bmax not KD. In contrast, neither the Bmax nor the KD of insulin binding to TFL changed with exercise training. The structure of insulin receptors isolated from BF or TFL was unaltered by exercise training as determined by affinity labeling (alpha-subunit, molecular weight (mol wt) approximately 131 kilodaltons [kDa]) and electrophoretic mobility of the alpha- and beta-subunit. Furthermore, basal tyrosine kinase activity was not affected by exercise training in extracts from either BF or TFL. However, the insulin dependent increase in maximal tyrosine kinase activity (Vmax) of the BF, but not TFL, was enhanced by exercise training. Specifically, insulin stimulated phosphorylation of both the beta-subunit of the insulin receptor (auto phosphorylation) and of a synthetic peptide (exogenous phosphorylation) were increased over control values in BF from exercise-trained rats, whereas both measurements of tyrosine kinase activity of TFL from the two experimental groups were similar. In contrast, both insulin-stimulated autophosphorylation and tyrosine kinase activity were significantly decreased in BF of exercise-trained rats when normalized to insulin binding activity. This disassociation was only seen in BF from exercise-trained rats, and was not true of TFL. These data indicate that exercise training can lead to increases in insulin receptor number and tyrosine kinase activity, as well as modifying the relationship between these two variables. The changes noted are not observed in all exercising muscles, and their development seems to depend upon the fiber composition. These results emphasize the complex relationship that exists in the regulation of insulin action at the level of its receptor.

Adenosine Triphosphate↗

PubMed1989

Prevention of insulin resistance by environmental manipulation as young rats mature.

This study was initiated in an attempt to see if the insulin resistance associated with maturation in young rats could be prevented by environmental manipulation. Consequently, seven week-old rats were either housed in standard laboratory cages and fed a calorie-restricted diet or placed individually in exercise wheel cages and allowed to eat chow ad lib. A control group of rats was housed in standard laboratory cages from seven weeks to five months of age, and also allowed to eat chow ad lib. When studied at five months of age, the chow-fed rats weighed more (624 +/- 8 g) than either the calorie restricted (479 +/- 9 g) or exercise trained (485 +/- 13 g) rats. Insulin action was compared in the three groups by assessing the steady-state serum glucose (SSSG) and insulin (SSSI) concentrations achieved during a continuous intravenous infusion of glucose and exogenous insulin. The results of these studies indicated that SSSG concentration was significantly higher (P less than 0.001) in chow-fed rats than in the two experimental groups. Since SSSI concentrations were the same in all three groups, lower SSSG concentrations in calorie-restricted and exercise trained rats indicates that insulin-stimulated glucose uptake was preserved in these two groups as compared to the chow-fed population. In an attempt to understand why exercise training and calorie restriction prevented the development of insulin resistance, muscle glycogen synthase activity and muscle capillary density were compared in the three groups of five month-old rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗