Biomedical subjects

M J Pagliassotti

Publications and source records attributed to M J Pagliassotti.

At least 19 recordsLinked to original sources

PubMed2001

A high-sucrose diet increases gluconeogenic capacity in isolated periportal and perivenous rat hepatocytes.

A high-sucrose (SU) diet increases gluconeogenesis (GNG) in the liver. The present study was conducted to determine the contribution of periportal (PP) and perivenous (PV) cell populations to this SU-induced increase in GNG. Male Sprague-Dawley rats were fed an SU (68% sucrose) or starch (ST, 68% starch) diet for 1 wk, and hepatocytes were isolated from the PP or PV region of the liver acinus. Hepatocytes were incubated for 1 h in the presence of various gluconeogenic substrates, and glucose release into the medium was used to estimate GNG. When incubated in the presence of 5 mM lactate, which enters GNG at the level of pyruvate, glucose release (nmol x h(-1) x mg(-1)) was significantly increased by the SU diet in both PP (84.8 +/- 3.4 vs. 70.4 +/- 2.6) and PV (64.3 +/- 2.5 vs. 38.2 +/- 2.1) cells. Addition of palmitate (0.5 mM) increased glucose release from lactate in PP cells by 11.6 +/- 0.5 and 20.6 +/- 1.5% and in PV cells by 11.0 +/- 4.4 and 51.1 +/- 9.1% in SU and ST, respectively. When cells were incubated with 5 mM dihydroxyacetone (DHA), which enters GNG at the triosephosphate level, glucose release was significantly increased by the SU diet in both cell types. In contrast, glucose release from fructose (0.5 mM) was significantly increased by the SU diet in PV cells only. These changes in glucose release were accompanied by significant increases in the maximal specific activities of glucose-6-phosphatase (G-6-Pase) and phosphoenolpyruvate carboxykinase (PEPCK) in both PP and PV cells. These data suggest that the SU diet influences GNG in both PP and PV cell populations. It appears that SU feeding produces changes in GNG via alterations in at least two critical enzymes, G-6-Pase and PEPCK.

Animals↗

PubMed2001

Inherent capacity for lipogenesis or dietary fat retention is not increased in obesity-prone rats.

Obesity results from positive energy balance and, perhaps, abnormalities in lipid and glycogen metabolism. The purpose of this study was to determine whether differences in lipogenesis, retention of dietary fat, and/or glycogenesis influenced susceptibility to dietary obesity. After 1 wk of free access to a high-fat diet (HFD; 45% fat by energy) rats were separated on the basis of 1 wk body weight gain into obesity-prone (OP; > or =48 g) or obesity-resistant groups (OR; < or =40 g). Rats were either studied at this time (OR1, OP1) or continued on the HFD for an additional 4 wk (OR5, OP5). Weight gain and energy intake were greater (P < or = 0.05) in OP vs. OR at both 1 (53 +/- 2 vs. 34 +/- 1 g; 892 +/- 27 vs. 755 +/- 14 kcal) and 5 (208 +/- 7 vs. 170 +/- 7 g; 4,484 +/- 82 vs. 4,008 +/- 72 kcal) wk, respectively. Rats were injected with (3)H(2)O and were either provided free access to an HFD meal containing labeled fatty acids (fed; n = 10 or 11/group) or were fasted (n = 10/group) overnight. The amount of food or (14)C tracer eaten overnight was equivalent between OP and OR rats. In liver, the fraction of (3)H retained in glycogen or lipid was not significantly different between OR and OP groups. Retention of dietary fat in the liver was not increased in OP rats. In adipose tissue, retention of (3)H was approximately 49% greater (P < or = 0.05) in OP1 vs. OR1 and approximately 30% greater in OP5 vs. OR5, but retention of dietary fat was not elevated in OP vs. OR. At the same time, fat pad weight (sum of epididymal, retroperitoneal, mesenteric) was 49% greater in OP1 rats vs. OR1 rats and 65% greater in OP5 vs. OR5 rats (P < or = 0.05). Thus a greater capacity for lipogenesis or retention of dietary fat does not appear to be included in the OP phenotype. The characteristic increase in energy intake associated with OP rats appears to be necessary and critical to accelerated weight and fat gain.

Adipose Tissue↗

PubMed2001

Increased pyruvate flux capacities account for diet-induced increases in gluconeogenesis in vitro.

High-fat (HF) and high-sucrose (SU) diets increase gluconeogenesis. The present study was designed to determine the contributions of pyruvate dehydrogenase, pyruvate carboxylase, phosphoenolpyruvate carboxykinase (PEPCK), and pyruvate kinase fluxes to this accelerated gluconeogenesis (GNEO) in the absence and presence of fatty acids. Male Sprague-Dawley rats were fed an HF, SU, or starch (ST) diet for 1 wk, and hepatocytes or mitochondria were isolated. In the absence of palmitate, the tracer estimated rates of GNEO (nmol. min(-1). mg(-1)) were elevated in hepatocytes isolated from SU (32.3 +/- 1.8) and HF (35.4 +/- 1.8) vs. ST (22.8 +/- 1.5). Pyruvate carboxylase and PEPCK flux rates (nmol. min(-1). mg(-1)) were increased in the SU (47.5 +/- 2.2 and 34.8 +/- 1.5) and HF (49.4 +/- 1.8 and 38.2 +/- 1.8) groups compared with the ST group (32.8 +/- 3.2 and 44.3 +/- 2.0). Palmitate (250-1,000 microM) stimulation of these fluxes was not significantly different among groups. Bromopalmitate, an inhibitor of fat oxidation, abolished differences in GNEO, pyruvate carboxylase, and PEPCK fluxes in HF and SU vs. ST. In isolated mitochondria, pyruvate carboxylation and palmitoyl carnitine oxidation were not significantly different among groups. The results of this study suggest that the increased gluconeogenic flux observed with HF and SU diets is associated with an increased pyruvate flux through pyruvate carboxylase and PEPCK. Moreover, the ability of bromopalmitate to normalize gluconeogenic fluxes suggests that endogenous fatty acids contribute to diet-induced increases in GNEO.

Animals↗

PubMed2001

Hyperglycemia compensates for diet-induced insulin resistance in liver and skeletal muscle of rats.

High-fat and high-sucrose diets increase the contribution of gluconeogenesis to glucose appearance (glc R(a)) under basal conditions. They also reduce insulin suppression of glc R(a) and insulin-stimulated muscle glycogen synthesis under euglycemic, hyperinsulinemic conditions. The purpose of the present study was to determine whether these impairments influence liver and muscle glycogen synthesis under hyperglycemic, hyperinsulinemic conditions. Male rats were fed a high-sucrose, high-fat, or low-fat, starch control diet for either 1 (n = 5-7/group) or 5 wk (n = 5-6/group). Studies involved two 90-min periods. During the first, a basal period (BP), [6-3H]glucose was infused. In the second, a hyperglycemic period (HP), [6-3H]glucose, [6-14C]glucose, and unlabeled glucose were infused. Plasma glucose (BP: 111.2 +/- 1.5 mg/dl; HP: 172.3 +/- 1.5 mg/dl), insulin (BP: 2.5 +/- 0.2 ng/ml; HP: 4.9 +/- 0.3 ng/ml), and glucagon (BP: 81.8 +/- 1.6 ng/l; HP: 74.0 +/- 1.3 ng/l) concentrations were not significantly different among diet groups or with respect to time on diet. There were no significant differences among groups in the glucose infusion rate (mg x kg(-1) x min(-1)) necessary to maintain arterial glucose concentrations at approximately 170 mg/dl (pooled average: 6.4 +/- 0.8 at 1 wk; 6.4 +/- 0.7 at 5 wk), percent suppression of glc R(a) (44.4 +/- 7.8% at 1 wk; 63.2 +/- 4.3% at 5 wk), tracer-estimated net liver glycogen synthesis (7.8 +/- 1.3 microg x g liver(-1) x min(-1) at 1 wk; 10.5 +/- 2.2 microg x g liver(-1) x min(-1) at 5 wk), indirect pathway glycogen synthesis (3.7 +/- 0.9 microg x g liver(-1) x min(-1) at 1 wk; 3.4 +/- 0.9 microg x g liver(-1) x min(-1) at 5 wk), or tracer-estimated net muscle glycogenesis (1.0 +/- 0.3 microg x g muscle(-1) x min(-1) at 1 wk; 1.6 +/- 0.3 microg x g muscle(-1) x min(-1) at 5 wk). These data suggest that hyperglycemia compensates for diet-induced insulin resistance in both liver and skeletal muscle.

Analysis of Variance↗

PubMed2001

Sucrose diets increase glucose-6-phosphatase and glucose release and decrease glucokinase in hepatocytes.

A high-sucrose diet (SU) decreases insulin action in the liver (Pagliassotti MJ, Shahrokhi KA, and Moscarello M. Am J Physiol Regulatory Integrative Comp Physiol 266: R1637-R1644, 1994). The present study was conducted to characterize the effect of SU on glucagon action in isolated periportal (PP) and perivenous (PV) hepatocytes by measuring glucagon-stimulated glycogenolysis and glucose release. Male rats were fed a SU (68% sucrose) or starch diet (ST, 68% starch) for 1 wk, and hepatocytes were isolated from PP or PV regions (n = 4/diet/cell population). Hepatocytes were incubated for 1 h in the presence of varying concentrations of glucagon (0-100 nM). In PP and PV cells, glucagon stimulation of glucose release and glycogenolysis (sum of glucose release and lactate accumulation) was not significantly different between SU and ST cells. However, in the SU PP cells, glucose release was increased compared with ST PP cells, both in the absence of glucagon (76.1 +/- 4 vs. 54.8 +/- 3 nmol x h(-1) x mg cell wet x wt(-1)) and at all glucagon concentrations. In SU-fed PV cells, glucose release was increased compared with ST PV cells in the absence of glucagon (79.3 +/- 5 vs. 56.4 +/- 5 nmol x h(-1) x mg cell wet x wt(-1)) and at low glucagon concentrations. Maximal glucose-6-phosphatase activity (in nmol x min(-1) x mg protein(-1)) was elevated in SU compared with ST cells (61.4 +/- 3 vs. 37.5 +/- 4 in PP and 37.5 +/- 4 vs. 29.5 +/- 3 in PV cells). In contrast, maximal glucokinase activity (in nmol x min(-1) x mg protein(-1)) was elevated in ST compared with SU cells (15.9 +/- 2 vs. 12.1 +/- 1 in PP and 19.4 +/- 2 vs. 14.2 +/- 1 in PV cells). These data demonstrate that SU increases the capacity for glucose release in both PP and PV hepatocytes, in part because of reciprocal changes in glucose-6-phosphatase and glucokinase.

Animals↗

PubMed2000

Quantitative assessment of pathways for lactate disposal in skeletal muscle fiber types.

Quantifying the contribution of the various skeletal muscle fiber types toward lactate disposal has proven elusive. In part, this can be attributed to the lack of adequate preparations for the study of all potential metabolic pathways involved. Toward this end our laboratory developed several perfused muscle preparations that are homogeneous for specific fiber types. This paper briefly reviews our findings regarding the influence of fiber type on lactate disposal in resting skeletal muscle and the metabolic pathways involved. Perfusing over a range of lactate concentrations, 1-12 mM, all fiber types were shown to switch from net production at low lactate concentrations to net consumption at higher concentrations. This transition occurred at lower lactate concentrations for Type I and IIa fibers, when compared with IIb fibers. For Type I and IIa fibers oxidation was observed to be the primary route of disposal accounting for approximately 50% of the lactate removed. For all fiber types, transamination was a significant pathway for the disposal of lactate carbon, whereas glyconeogenesis was the primary pathway for disposal in Type IIb fibers. The glyconeogenic capacity was quantitatively similar for Type IIa and IIb fibers but was negligible for Type I fibers. The pathway for glyconeogenesis in skeletal muscle was shown to be substantially different from that employed in hepatic glyconeogenesis. Results indicated that neither the TCA cycle nor phosphoenolpyruvate carboxykinase is involved in skeletal muscle glyconeogenesis. Our findings suggested that PEP formation in skeletal muscle glyconeogenesis occurs by "reversal" of the pyruvate kinase reaction.

Animals↗

PubMed2000

Fat oxidation, lipolysis, and free fatty acid cycling in obesity-prone and obesity-resistant rats.

Defects in fat metabolism may contribute to the development of obesity, but what these defects are and where they occur in the feeding/fasting cycle are unknown. In the present study, basal fat metabolism was characterized using a high-fat diet (HFD)-induced model of obesity development. Male rats consumed a HFD (45% fat, 35% carbohydrate) ad libitum for either 1 or 5 wk (HFD1 or HFD5). After 1 wk on the HFD, rats were separated on the basis of body weight gain into obesity-prone (OP, > or =48 g) or obesity-resistant (OR, </=40 g) groups. Twenty-four-hour-fasted rats were studied either at this time (OP1, OR1) or after 5 wk (OP5, OR5). Fat pad weight (sum of epididymal, retroperitoneal, and mesenteric fat pads) at HFD1 was 26% greater and at HFD5 was 43% greater (P</=0.05) in OP vs. OR. Free fatty acid rates of appearance (FFA R(a)) and oxidation were not significantly different between OP and OR at 1 or 5 wk. Glycerol R(a), when expressed in absolute terms (micromol/min), increased from 1 to 5 wk of HFD feeding in both OP and OR, but significantly so only in OP. Likewise, increased rates of intracellular FFA cycling [estimated as (3 x glycerol R(a)) - FFA R(a)] were observed in both OP and OR rats from 1 to 5 wk of HFD feeding, but significantly so in OP rats only. When expressed relative to fat cell volume (micromol. pl(-1). min(-1)), neither lipolysis nor intracellular cycling was significantly different between OP and OR, regardless of time on HFD. These data suggest that 1) if low rates of fat oxidation contribute to obesity development in OP rats, the contribution does not occur at times when fat oxidation is at or near maximum rates (i.e., 24-h fasted conditions), and 2) between 1 and 5 wk of HFD feeding, basal lipolysis and reesterification may work to expand fat cell volume and increase fat pad weight in both OP and OR rats, although more so in OP rats.

Adipocytes↗

PubMed2000

Developmental stage modifies diet-induced peripheral insulin resistance in rats.

In the present study, the effects of age and diet on glucose disappearance and tissue-specific glucose uptake (R'g) were examined under basal or hyperinsulinemic, euglycemic conditions in male Sprague-Dawley rats. Rats were equicalorically fed either a high-starch diet (68% of kcal), high-fat diet (HFD; 45% of kcal), or high-sucrose diet (68% of kcal), beginning at either 5 (W; weanling), 10 (Y; young), 18 (M; mature), or 58 wk (O; older) of age for 5 wks (n = 6-9. group(-1) x diet(-1)). Body weight gain was not significantly different among dietary groups within a given age. Significant (P< 0.05) age effects were observed on basal and clamp free fatty acid concentrations. Significant diet effects were observed on basal and clamp triglyceride concentrations. There were significant diet and age effects on basal skeletal muscle R'g. This interaction was primarily due to an age-associated increase in basal R'g microg x g(-1). min(-1)) in HFD (gastrocnemius R'g: 0.9+/-0.2 in W, 1.1+/-0.2 in Y, 1.8+/-0.2 in M, 2.5+/-0.2 in O). Both age and diet significantly decreased insulin-stimulated muscle R'g. However, whereas age-associated reductions in both glucose-6-phosphate concentration and glycogen synthase activity were observed, significant diet effects were observed on glucose-6-phosphate concentrations only. Age significantly reduced basal and clamp adipose tissue R'g when expressed per gram of tissue but significantly increased R'g when expressed per total fat pad mass. These data suggest that diet-induced changes in peripheral glucose metabolism are modulated by age.

Adipose Tissue↗

PubMed2000

Hyperthermia impairs liver mitochondrial function in vitro.

The effects of temperature on the relationships among the rates of pyruvate carboxylation, O(2) uptake (J(o)), oxidative phosphorylation (J(p)), and the free energy of ATP hydrolysis (G(p)) were studied in liver mitochondria isolated from 250-g female rats. Pyruvate carboxylation was evaluated at 37, 40, and 43 degrees C. In disrupted mitochondria, pyruvate carboxylase maximal reaction velocity increased from 37 to 43 degrees C with an apparent Q(10) of 2.25. A reduction in ATP/ADP ratio decreased enzyme activity at all three temperatures. In contrast, in intact mitochondria, increasing temperature failed to increase pyruvate carboxylation (malate + citrate accumulation) but did result in increased J(o) and decreased extramitochondrial G(p). J(p) was studied in respiring mitochondria at 37 and 43 degrees C at various fractions of state 3 respiration, elicited with a glucose + hexokinase ADP-regenerating system. The relationship between J(o) and G(p) was similar at both temperatures. However, hyperthermia (43 degrees C) reduced the J(p)/J(o) ratio, resulting in lower G(p) for a given J(p). Fluorescent measurements of membrane phospholipid polarization revealed a transition in membrane order between 40 and 43 degrees C, a finding consistent with increased membrane proton conductance. It is concluded that hyperthermia augments nonspecific proton leaking across the inner mitochondrial membrane, and the resultant degraded energy state offsets temperature stimulation of pyruvate carboxylase. As a consequence, at high temperatures approaching 43 degrees C, the pyruvate carboxylation rate of intact liver mitochondria may fail to exhibit a Q(10) effect.

Adenosine Triphosphate↗

PubMed2000

Comparison of the effects of sucrose and fructose on insulin action and glucose tolerance.

The purpose of the present study was to determine whether fructose is the nutrient mediator of sucrose-induced insulin resistance and glucose intolerance. Toward this end, male rats were fed a purified starch diet (68% of total calories) for a 2-wk baseline period. After this, rats either remained on the starch (ST) diet or were switched to a sucrose (SU, 68% of total calories), fructose/glucose (F/G, 34/34% of total calories), or fructose/starch (F/ST, 34/34% of total calories) diet for 5 wk. Rats then underwent either an intravenous glucose tolerance test (n = 10/diet) or a euglycemic, hyperinsulinemic clamp (n = 8 or 9/diet). Incremental glucose and insulin areas under the curve in SU, F/G, and F/ST were on average 61 and 29% greater than ST, respectively, but not significantly different from one another. During clamps, glucose infusion rates (mg. kg(-1). min(-1)) required to maintain euglycemia were significantly lower (P < 0.05) in SU, F/G, and F/ST (13.4 +/- 0.9, 9. 5 +/- 1.7, 11.3 +/- 1.3, respectively) compared with ST (22.8 +/- 1. 1). Insulin suppression of glucose appearance (mg. kg(-1). min(-1)) was significantly lower (P < 0.05) in SU, F/G, and F/ST (5.6 +/- 0.5, 2.2 +/- 1.2, and 6.6 +/- 0.7, respectively) compared with ST (9.6 +/- 0.4). Insulin-stimulated glucose disappearance (mg. kg(-1). min(-1)) was significantly lower (P < 0.05) in SU, F/G, and F/ST (17. 9 +/- 0.6, 16.2 +/- 1.3, 15.3 +/- 1.8, respectively) compared with ST (24.7 +/- 1.2). These data suggest that fructose is the primary nutrient mediator of sucrose-induced insulin resistance and glucose intolerance.

Adipose Tissue↗

PubMed2000

Effects of high fat or high sucrose diets on rat femora mechanical and compositional properties.

Diets high in fat and/or sucrose decrease whole bone mechanical properties and mineralization. This study examines the impact on rat bone mechanical properties and composition of age and diets (a) low in fat, (b) high in sucrose, and (c) high in fat. Sprague-Dawley rats aged 3 weeks (weanling [W]; n = 42), 8 weeks (young [Y]; n = 42), 16 weeks (teenage [T]; n = 39) and 56 weeks (old [O]; n = 40) were randomly assigned to groups: low fat, high sucrose and high fat with n = 12-16 per group. All animals were fed a purified low-fat, high starch diet for two weeks, and fed a low fat (STD), high sucrose (HSD), or high-fat (HFD) for five additional weeks. After sacrifice, the femurs were harvested and non-osseous tissue was removed. The bones were dried at 25 degrees C for 48 hours. Length and the periosteal minimum and maximum diameter (D-min and D-max) at the mid-diaphysis of the femurs were measured with Vernier calipers. The femurs were rehydrated and tested via three-point flexure. Bones were weighed after drying at 105 degrees C (48 hours; Dry-M) and 800 degrees C (24 hours; Ash-M). Percent mineralization (%Min) was calculated as Ash-M/Dry-M X 100%. Length, D-min and D-max, Dry-M and Ash-M all significantly (p < 0.05) increased with age (W < Y < T < O) within each group. %Min and stiffness were significantly greater in [O] than in the younger femurs. No significant results were seen in any age group due to varying diet. These results indicate that five weeks of high fat or high sucrose diet feeding does not affect whole bone size, composition or mechanical properties. Whether a longer dietary period or different diet composition would elicit changes requires further study.

Animals↗

PubMed1999

The head arterial glucose level is not the reference site for generation of the portal signal in conscious dogs.

Experiments were performed on twelve 42-h-fasted, conscious dogs to determine whether the head arterial glucose level is used as a reference standard for comparison with the portal glucose level in bringing about the stimulatory effect of portal glucose delivery on net hepatic glucose uptake (NHGU). Each experiment consisted of an 80-min equilibration, a 40-min control, and two 90-min test periods. After the control period, somatostatin was given along with insulin (7.2 pmol. kg(-1). min(-1); 3.5-fold increase) and glucagon (0.6 ng. kg(-1). min(-1); basal) intraportally. Glucose was infused intraportally (22.2 micromol. kg(-1). min(-1)) and peripherally as needed to double the hepatic glucose load. In one test period, glucose was infused into both vertebral and carotid arteries (HEAD(G); 22.2 +/- 0.8 micromol. kg(-1). min(-1)); in the other test period, saline was infused into the head arteries (HEAD(S)). One-half of the dogs received HEAD(G) first. When all dogs are considered, the blood arterial-portal glucose gradients (-0.52 +/- 0.07 vs. -0.49 +/- 0.03 mM) and the hepatic glucose loads (339 +/- 14 vs. 334 +/- 20 micromol. kg(-1). min(-1)) were similar in HEAD(G) and HEAD(S). NHGU was 24.1 +/- 3.8 and 25.1 +/- 4.6 micromol. kg(-1). min(-1), and nonhepatic glucose uptake was 46.1 +/- 4.2 and 48.8 +/- 7.0 micromol. kg(-1). min(-1) in HEAD(G) and HEAD(S), respectively. The head arterial glucose level is not the reference standard used for comparison with the portal glucose level in the generation of the portal signal.

Animals↗

PubMed1999

Effects of a high-fat diet and voluntary wheel running on gluconeogenesis and lipolysis in rats.

The purpose of the present study was to determine the effects of diet composition and exercise on glycerol and glucose appearance rate (Ra) and on nonglycerol gluconeogenesis (Gneo) in vivo. Male Wistar rats were fed a high-starch diet (St, 68% of energy as cornstarch, 12% corn oil) for a 2-wk baseline period and then were randomly assigned to one of four experimental groups: St (n = 7), high-fat (HF; 35% cornstarch, 45% corn oil; n = 8), St with free access to exercise wheels (StEx; n = 7), and HF with free access to exercise wheels (HFEx; n = 7). After 8 wk, glucose Ra when using [3-3H]glucose, glycerol Ra when using [2H5]glycerol (estimate of whole body lipolysis), and [3-13C]alanine incorporation into glucose (estimate of alanine Gneo) were determined. Body weight and fat pad mass were significantly (P < 0.05) decreased in exercise vs. sedentary animals only. The average amount of exercise was not significantly different between StEx (3,212 +/- 659 m/day) and HFEx (3,581 +/- 765 m/day). The ratio of glucose to alanine enrichment and absolute glycerol Ra (micromol/min) were higher (P < 0.05) in HF and HFEx compared with St and StEx rats. In separate experiments, the ratio of 3H in C-2 to C-6 of glucose from 3H2O (estimate of Gneo from pyruvate) was also higher (P < 0.05) in HF (n = 5) and HFEx (n = 5), compared with St (n = 5) and StEx (n = 5) rats. Voluntary wheel running did not significantly increase estimated alanine or pyruvate Gneo or absolute glycerol Ra. Voluntary wheel running increased (P < 0.05) glycerol Ra when normalized to fat pad mass. These data suggest that a high-fat diet can increase in vivo Gneo from precursors that pass through pyruvate. They also suggest that changes in the absolute rate of glycerol Ra may contribute to the high-fat diet-induced increase in Gneo.

Adipose Tissue↗

PubMed1998

A high-sucrose diet alters the lipid composition and fluidity of liver sinusoidal membranes.

Impaired insulin suppression of hepatic glucose production and accumulation of hepatic triglycerides occur after 1 week on a high-sucrose diet. The purpose of this study was to ascertain whether changes in structural lipids, fatty acid composition and/or fluidity occur after 1 week on a high-sucrose diet, and therefore might contribute to the sucrose-induced impairment in hepatic glucose metabolism. Male Wistar rats (n=28) were fed a purified high starch (68% of energy) diet for a 2-week baseline period. Fourteen animals were then switched to a high sucrose (68% of energy) diet for 1 (n=7) or 5 (n=7) weeks. Analyses were performed on liver sinusoidal membranes (due to this membrane's involvement in nutrient transport) from overnight fasted rats. The degree of saturation of sinusoidal membrane phospholipids and liver triglyceride fatty acids was significantly greater in sucrose vs. starch at 1 and 5 weeks. This resulted in significantly lower sinusoidal membrane fluidity at 1 and 5 weeks in the sucrose group. In contrast, hepatic sinusoidal membrane cholesterol content (0.60+/-0.05 vs. 0.42+/-0.04 micromol/mg protein) and the cholesterol to phospholipid molar ratio (0.66+/-0.04 vs. 0.50+/-0.03) were significantly greater in sucrose vs. starch animals at 5 weeks only. Minimal differences were observed in individual phospholipid species between groups. These data suggest that changes in fatty acid composition and fluidity may contribute to the development of sucrose-induced hepatic insulin resistance.

Animals↗

PubMed1998

Hepatic glucose disposition during concomitant portal glucose and amino acid infusions in the dog.

The effect of concomitant intraportal infusion of glucose and gluconeogenic amino acids (AA) on net hepatic glucose uptake (NHGU) and glycogen synthesis was examined in 42-h-fasted dogs. After a basal period, there was a 240-min experimental period during which somatostatin was infused continuously into a peripheral vein and insulin and glucagon (at 3-fold basal and basal rates, respectively) and glucose (18.3 mumol.kg-1.min-1) were infused intraportally. One group (PoAA, n = 7) received an AA mixture intraportally at 7.6 mumol.kg-1.min-1, whereas the other group (NoAA, n = 6) did not receive AA. Arterial blood glucose concentrations and hepatic glucose loads were the same in the two groups. NHGU averaged 4.8 +/- 2.0 (PoAA) and 9.4 +/- 2.0 (NoAA) mumol.kg-1.min-1 (P < 0.05), and tracer-determined hepatic glucose uptake was 4.6 +/- 1.6 (PoAA) and 10.0 +/- 1.7 (NoAA) mumol.kg-1.min-1 (P < 0.05). AA data for PoAA and NoAA, respectively, were as follows: arterial blood concentrations, 1,578 +/- 133 vs. 1,147 +/- 86 microM (P < 0.01); hepatic loads, 56 +/- 3 vs. 32 +/- 4 mumol.kg-1.min-1 (P < 0.01); and net hepatic uptakes, 14.1 +/- 1.4 vs. 5.6 +/- 0.4 mumol.kg-1.min-1 (P < 0.01). The rate of net hepatic glycogen synthesis was 7.5 +/- 1.9 (PoAA) vs. 10.7 +/- 2.3 (NoAA) mumol.kg-1.min-1 (P = 0.1). In a net sense, intraportal gluconeogenic amino acid delivery directed glucose carbon away from the liver. Despite this, net hepatic carbon uptake was equivalent in the presence and absence of amino acid infusion.

Amino Acids↗

PubMed1998

Menhaden oil prevents but does not reverse sucrose-induced insulin resistance in rats.

Although fish oil supplementation may prevent the onset of diet-induced insulin resistance in rats, it appears to worsen glycemic control in humans with existing insulin resistance. In the present study, the euglycemic, hyperinsulinemic (4x basal) clamp technique with [3-3H]glucose and 2-deoxy-[1-14C]glucose was used to directly compare the ability of fish oil to prevent and reverse sucrose-induced insulin resistance. In study 1 (prevention study), male Wistar rats were fed a purified high-starch diet (68% of total energy), high-sucrose diet (68% of total energy), or high-sucrose diet in which 6% of the fat content was replaced by menhaden oil for 5 wk. In study 2 (reversal study), animals were fed the high-starch or high-sucrose diets for 5 wk and then the sucrose animals were assigned to one of the following groups for an additional 5 wk: high starch, high sucrose, or high sucrose with 6% menhaden oil. Rats fed the high-starch diet for 10 wk served as controls. In study 3 (2nd reversal study), animals followed a similar diet protocol as in study 2; however, the reversal period was extended to 15 wk. In study 1, the presence of the fish oil in the high-sucrose diet prevented the development of insulin resistance. Glucose infusion rates (GIR, mg.kg-1.min-1) were 17.0 +/- 0.9 in starch, 10.6 +/- 1.7 in sucrose, and 15.1 +/- 1.5 in sucrose with fish oil animals. However, in study 2, this same diet was unable to reverse sucrose-induced insulin resistance (GIR, 16.7 +/- 1.4 in starch, 7.1 +/- 1.5 in sucrose, and 4.8 +/- 0.9 in sucrose with fish oil animals). Sucrose-induced insulin resistance was reversed in rats that were switched back to the starch diet (GIR, 18.6 +/- 3.0). Results from study 3 were similar to those observed in study 2. In summary, fish oil was effective in preventing diet-induced insulin resistance but not able to reverse it. A preexisting insulin-resistant environment interferes with the positive effects of menhaden oil on insulin action.

Animals↗

PubMed1998

Fuel metabolism in men and women during and after long-duration exercise.

This study aimed to determine gender-based differences in fuel metabolism in response to long-duration exercise. Fuel oxidation and the metabolic response to exercise were compared in men (n = 14) and women (n = 13) during 2 h (40% of maximal O2 uptake) of cycling and 2 h of postexercise recovery. In addition, subjects completed a separate control day on which no exercise was performed. Fuel oxidation was measured using indirect calorimetry, and blood samples were drawn for the determination of circulating substrate and hormone levels. During exercise, women derived proportionally more of the total energy expended from fat oxidation (50.9 +/- 1.8 and 43. 7 +/- 2.1% for women and men, respectively, P < 0.02), whereas men derived proportionally more energy from carbohydrate oxidation (53.1 +/- 2.1 and 45.7 +/- 1.8% for men and women, respectively, P < 0.01). These gender-based differences were not observed before exercise, after exercise, or on the control day. Epinephrine (P < 0.007) and norepinephrine (P < 0.0009) levels were significantly greater during exercise in men than in women (peak epinephrine concentrations: 208 +/- 36 and 121 +/- 15 pg/ml in men and women, respectively; peak norepinephrine concentrations: 924 +/- 125 and 659 +/- 68 pg/ml in men and women, respectively). As circulating glycerol levels were not different between the two groups, this suggests that women may be more sensitive to the lipolytic action of the catecholamines. In conclusion, these data support the view that different priorities are placed on lipid and carbohydrate oxidation during exercise in men and women and that these gender-based differences extend to the catecholamine response to exercise.

Adult↗

PubMed1998

Adipose tissue-derived tumor necrosis factor activity correlates with fat cell size but not insulin action in aging rats.

Adipose tissue-derived tumor necrosis factor (AT-TNF) protein and messenger RNA (mRNA) has been shown to correlate with insulin resistance in some studies. However, in a study using different aged Fischer 344 rats, AT-TNF activity correlated more strongly with cell size than with fasting plasma insulin. The present study was undertaken to more carefully examine the relationship among AT-TNF, adipose cell size, and insulin action using more precise measures of insulin action. Basal and hyperinsulinemic, euglycemic clamps were performed in male Sprague Dawley rats at four different ages (8, 13, 21, and 61 weeks old). [3-(3)H]glucose and 2-deoxy-D-[1-(14)C]glucose were used to assess glucose kinetics and tissue-specific glucose uptake. Because TNF activity represents the summation of TNF synthesis, secretion, and the amount of soluble inhibitors present, TNF activity was measured using a bioassay, in addition to measuring TNF protein and mRNA levels. AT-TNF activity increased significantly with age, as did the glucose infusion rate, a measure of whole body insulin resistance. However, AT-TNF activity did not correlate with any parameter of insulin action measured during the hyperinsulinemic, euglycemic clamps. In epididymal fat, AT-TNF activity correlated with: glucose infusion rate: r = -0.50, P = 0.17; rate of appearance: r = -0.19, P = 0.35; rate of disappearance: r = 0.08, P = 0.69. As was noted before, AT-TNF activity correlated well with fat cell size (r = 0.76, P < 0.001 in epididymal fat; r = 0.58, P = 0.007 in SUB fat). These data suggest that although AT-TNF activity and insulin resistance increase with age, the two are not functionally related. These data do not eliminate the potential role of nonadipose TNF in the regulation of insulin action.

Adipocytes↗