Biomedical subjects

G L Dohm

Publications and source records attributed to G L Dohm.

At least 55 records · Page 3Linked to original sources

PubMed1995

Liver glucokinase: decreased activity in patients with type II diabetes.

Because of the demonstration of a genetic linkage between glucokinase and Type II diabetes, and the central role of glucokinase on glucose metabolism, we studied glucokinase activity in the liver of patients with and without Type II diabetes. Glucokinase activity was decreased by about 50% in obese subjects with diabetes (n = 12) compared with (p < 0.01) lean controls (n = 9) and (p < 0.05) obese controls (n = 10). There was no difference between lean and obese controls. Fifty percent of subjects with diabetes had lower liver glucokinase activity than the lowest value of the controls. These data further support the important role that glucokinase plays in the pathogenesis of Type II diabetes.

Adult↗

PubMed1995

Skeletal muscle fiber composition is related to adiposity and in vitro glucose transport rate in humans.

The purpose of this study was to determine if a relationship exists among skeletal muscle fiber composition, adiposity, and in vitro muscle glucose transport rate in humans. Rectus abdominus muscle was obtained during elective abdominal surgery from nonobese control (n = 12), obese (n = 12), and obese non-insulin-dependent diabetes mellitus (NIDDM) patients (n = 10). The obese NIDDM group had a significantly lower percentage of type I muscle fibers (32.2 +/- 1.9%) than the obese group (40.4 +/- 2.7%), and both obese groups were significantly lower than the control group (50.0 +/- 2.6%). Insulin-stimulated glucose transport, determined on 28 subjects, was significantly lower in both the obese (3.83 +/- 0.48 nmol.min-1.mg-1) and NIDDM (3.93 +/- 1.0 nmol.min-1.mg-1) groups vs. the control group (7.35 +/- 1.50 nmol.min-1.mg-1). Body mass index (BMI) was inversely correlated to percent type I fibers (r = -0.50, P < 0.01) and to the insulin-stimulated glucose transport rate (r = -0.53, P < 0.01). The percentage of type I muscle fibers was related to the insulin-stimulated glucose transport rate (r = 0.57, P < 0.01), although this relationship was not significant after adjusting for BMI. Although these data do not support an independent relationship between fiber type and insulin action in obesity, a reduced skeletal muscle type I fiber population may be one component of a multifactorial process involved in the development of insulin resistance.

Adipose Tissue↗

PubMed1995

Hindlimb perfusion induces GLUT-1 and immediate early gene expression in skeletal muscle.

The purpose of the present study was to test the suitability of the rat hindlimb perfusion technique for studying the acute regulation of the GLUT-1 and GLUT-4 glucose transporter genes in adult skeletal muscle. To further examine the stability of the technique, we also monitored the transcription rate and mRNA content of selected immediate early genes. Nuclei and total RNA were isolated from red and white hindlimb muscle from perfused (2 h) and nonperfused control animals. Although GLUT-4 transcription and mRNA content remained stable, perfusion elicited a marked 3.5-fold increase in GLUT-1 mRNA in red and 2.2-fold increase in white skeletal muscle in the absence of any detectable change in transcription. In contrast to both GLUT-1 and GLUT-4, transcription originating from the c-fos and c-myc immediate early genes increased from 2.0- to 2.7-fold with perfusion in both red and white skeletal muscle, whereas transcription of the beta-actin gene decreased by 40-60%. Both c-fos and c-myc mRNA levels also increased with perfusion, whereas beta-actin mRNA remained unchanged. These findings clearly demonstrate that the current method of performing the hindlimb perfusion technique rapidly and dramatically alters the regulation of selected genes in skeletal muscle.

Animals↗

PubMed1995

Differential effect of maturation on insulin- vs. contraction-stimulated glucose transport in Zucker rats.

Insulin-stimulated glucose transport has been shown to decline during maturation in lean rats. To determine whether this maturation-induced decrease occurred in the muscle of obese rats and whether the contraction-stimulated pathway for glucose transport was similarly affected, glucose transport rates were measured in insulin- and electrically stimulated skeletal muscle during hindlimb perfusion of 10- and 29-wk-old lean and obese male Zucker rats. Glucose transporter (GLUT-4) protein was also measured. Insulin-stimulated glucose transport rates were significantly decreased (36-56%) in 29-wk compared with 10-wk-old lean rats. There was no maturation-related decrease in GLUT-4. Insulin-mediated glucose transport was unaltered by maturation in skeletal muscle of obese rats. Differential effects of maturation on lean and obese rats caused the effect of obesity on maximally insulin-stimulated glucose transport to be much greater in 10- than 29-wk-old animals. Maturation had no effect on contraction-stimulated glucose transport rates in either lean or obese animals. The combined effect of maximal insulin plus contraction was not altered with maturity in lean animals but was significantly increased in 29- compared with 10-wk-old obese rats. Absence of a change in GLUT-4 content together with uncompromised contraction-stimulated glucose transport suggests that the maturation-induced decrease in insulin-stimulated glucose transport in lean rats is due to a defect in the insulin signaling pathway.

Aging↗

PubMed1995

Seven days of exercise increase GLUT-4 protein content in human skeletal muscle.

Insulin-responsive glucose transporter (GLUT-4) content increases by 1.8-fold in skeletal muscle with 14 wk of exercise training [Houmard et al. Am. J. Physiol. 264 (Endocrinol. Metab. 27): E896-E901, 1993]. The purpose of this study was to determine whether more short-term training (7 days) increases GLUT-4 protein content in human skeletal muscle. Seven sedentary men [25.0 +/- 1.1 (SE) yr, 44.1 +/- 2.2 ml.kg-1.min-1 maximal O2 uptake, 14.9 +/- 2.1% body fat] were examined before and after 7 days of cycle ergometer training (1 h/day, 76 +/- 2% maximal heart rate). Needle biopsy samples from the vastus lateralis were used to determine GLUT-4 protein content. Muscle GLUT-4 increased (P < 0.05) by an average of 2.8 +/- 0.5-fold with 7 days of training. GLUT-4 content in skeletal muscle thus increases substantially with short-term exercise training.

Blotting, Western↗

PubMed1995

Insulin receptor phosphorylation, insulin receptor substrate-1 phosphorylation, and phosphatidylinositol 3-kinase activity are decreased in intact skeletal muscle strips from obese subjects.

To determine whether the impaired insulin-stimulated glucose uptake in obese individuals is associated with altered insulin receptor signaling, we measured both glucose uptake and early steps in the insulin action pathway in intact strips of human skeletal muscle. Biopsies of rectus abdominus muscle were taken from eight obese and eight control subjects undergoing elective surgery (body mass index 52.9 +/- 3.6 vs 25.7 +/- 0.9). Insulin-stimulated 2-deoxyglucose uptake was 53% lower in muscle strips from obese subjects. Additional muscle strips were incubated in the basal state or with 10(-7) M insulin for 2, 15, or 30 min. In the lean subjects, tyrosine phosphorylation of the insulin receptor and insulin receptor substrate-1 (IRS-1), measured by immunoblotting with anti-phosphotyrosine antibodies, was significantly increased by insulin at all time points. In the skeletal muscle from the obese subjects, insulin was less effective in stimulating tyrosine phosphorylation (maximum receptor and IRS-1 phosphorylation decreased by 35 and 38%, respectively). Insulin stimulation of IRS-1 immunoprecipitable phosphatidylinositol 3-kinase (PI 3-kinase) activity also was markedly lower in obese subjects compared with controls (10- vs 35-fold above basal, respectively). In addition, the obese subjects had a lower abundance of the insulin receptor, IRS-1, and the p85 subunit of PI 3-kinase (55, 54, and 64% of nonobese, respectively). We conclude that impaired insulin-stimulated glucose uptake in skeletal muscle from severely obese subjects is accompanied by a deficiency in insulin receptor signaling, which may contribute to decreased insulin action.

Adult↗

PubMed1995

Skeletal muscle GLUT4 protein concentration and aging in humans.

The insulin resistance of aging has been attributed to a postreceptor defect in skeletal muscle. The present study examined whether a reduction in the concentration of the insulin-stimulated glucose transporter (GLUT4) in skeletal muscle was associated with advancing age in men (n = 55) and women (n = 29). Insulin sensitivity (minimal model) was negatively associated (P < 0.001) with age (range, 18-80 years) in men (r = -0.44) and women (r = -0.58). GLUT4 protein concentration in the vastus lateralis was also negatively associated (P < 0.05) with age (men, r = -0.28; women, r = -0.51). There was no relation (P > 0.15) between GLUT4 content in the gastrocnemius and age. GLUT4 concentration in the vastus lateralis was positively associated (P < 0.01) with insulin sensitivity in both sexes (r = 0.42); this relationship persisted in the men after adjusting for overall adiposity, regional adiposity, and cardiorespiratory fitness. These findings suggest that a decrement in GLUT4 protein concentration in skeletal muscle may at least partially contribute to the insulin resistance of aging in humans.

Adipose Tissue↗

PubMed1995

Okadaic acid, vanadate, and phenylarsine oxide stimulate 2-deoxyglucose transport in insulin-resistant human skeletal muscle.

In response to insulin, several proteins are phosphorylated on tyrosine and on serine/threonine residues. Decreased phosphorylation of signaling peptides by a defective insulin receptor kinase may be a cause of insulin resistance. Accordingly, inhibition of the appropriate phosphatases might increase the phosphorylation state of these signaling peptides and thereby elicit increased glucose transport. The purpose of this study was to examine the effect of the serine/threonine phosphatase inhibitor okadaic acid and the tyrosine phosphatase inhibitors phenylarsine oxide and vanadate on 2-deoxyglucose transport in insulin-resistant human skeletal muscle. All three phosphatase inhibitors stimulated 2-deoxyglucose transport in insulin-resistant skeletal muscle. These data suggest that these compounds have bypassed a defect in at least one of the signaling pathways leading to glucose transport. Furthermore, maximal transport rates induced by the simultaneous presence of insulin and phosphatase inhibitor in insulin-resistant muscle were equal to insulin-stimulated rates in lean control subjects. However, both vanadate alone and vanadate plus insulin stimulated 2-deoxyglucose transport significantly more in insulin-sensitive tissue than in insulin-resistant tissue. These results demonstrate that although vanadate is able to stimulate glucose transport in insulin-resistant muscle, it is not able to normalize transport to the same rate achieved in insulin-sensitive muscle.

Adult↗

PubMed1995

Hypoxia stimulates glucose transport in insulin-resistant human skeletal muscle.

Insulin and muscle contraction stimulate glucose transport into muscle cells by separate signaling pathways, and hypoxia has been shown to operate via the contraction signaling pathway. To elucidate the mechanism of insulin resistance in human skeletal muscle, strips of rectus abdominis muscle from lean (body mass index [BMI] < 25), obese (BMI > 30), and obese non-insulin-dependent diabetes mellitus (NIDDM) (BMI > 30) patients were incubated under basal and insulin-, hypoxia-, and hypoxia + insulin-stimulated conditions. Insulin significantly stimulated 2-deoxyglucose transport approximately twofold in muscle from lean (P < 0.05) patients, but not in muscle from obese or obese NIDDM patients. Furthermore, maximally insulin-stimulated transport rates in muscle from obese and diabetic patients were significantly lower than rates in muscle from lean patients (P < 0.05). Hypoxia significantly stimulated glucose transport in muscle from lean and obese patients. There were no significant differences in hypoxia-stimulated glucose transport rates among lean, obese, and obese NIDDM groups. Hypoxia + insulin significantly stimulated glucose transport in lean, obese, and diabetic muscle. The results of the present study suggest that the glucose transport effector system is intact in diabetic human muscle when stimulated by hypoxia.

Adult↗

PubMed1994

Stimulation of glucose uptake by insulin-like growth factor II in human muscle is not mediated by the insulin-like growth factor II/mannose 6-phosphate receptor.

Although the growth-promoting effects of insulin-like growth factor II (IGF-II) have been intensively studied, the acute actions of this hormone on glucose metabolism have been less well evaluated, especially in skeletal muscle of humans. We and other groups have shown that IGFs reduce glycaemic levels in humans and stimulate glucose uptake in rat muscle. The purpose of the present study was to evaluate the effect of IGF-II on glucose transport in muscle of normal and obese patients with and without non-insulin-dependent diabetes mellitus (NIDDM), as well as to identify the receptor responsible for this action. 2-Deoxyglucose transport was determined in vitro using a muscle-fibre strip preparation. IGF-II were investigated in biopsy material of rectus abdominus muscle taken from lean and obese patients and obese patients with NIDDM at the time of surgery. In the lean group, IGF-II (100 nM) stimulated glucose transport 2.1-fold, which was slightly less than stimulation by insulin (2.8-fold) at the same concentration. Binding of IGF-II was approx. 25% of that of insulin at 1 nM concentrations of both hormones. Obesity with or without NIDDM significantly reduced IGF-II-stimulated glucose uptake compared with the lean group. In order to explore which receptor mediated the IGF-II effect, we compared glucose uptake induced by IGF-II and two IGF-II analogues: [Leu27]IGF-II, with high affinity for the IGF-II/Man 6-P receptor but markedly reduced affinity for the IGF-I and insulin receptors, and [Arg54,Arg55]IGF-II was similar to that of IGF-II, whereas [Leu27]IGF-II had a very diminished effect. Results show that IGF-II is capable of stimulating muscle glucose uptake in lean but not in obese subjects and this effect seems not to be mediated via an IGF-II/Man 6-P receptor.

Adult↗

PubMed1994

Transcriptional regulation of muscle fatty acid-binding protein.

Heart fatty acid-binding protein (H-FABP) is present in a wide variety of tissues but is found in the highest concentration in cardiac and red skeletal muscle. It has been proposed that the expression of H-FABP correlates directly with the fatty acid-oxidative capacity of the tissue. In the present study, the expression of H-FABP was measured in red and white skeletal muscle under two conditions in which fatty acid utilization is known to be increased: streptozotocin-induced diabetes and fasting. Protein concentration, mRNA concentration and transcription rate were measured under both conditions. The level of both protein and mRNA increased approximately 2-fold under each condition. The transcription rate was higher in red skeletal muscle than in white muscle, was increased 2-fold during fasting, but was unchanged by streptozotocin-induced diabetes. In addition to supporting the hypothesis that H-FABP is induced during conditions of increased fatty acid utilization, these findings demonstrate that the regulation of H-FABP expression may or may not be at the level of transcription depending on the stimulus.

Animals↗

PubMed1994

Glucose transporter localization in rat skeletal muscle. Autoradiographic study using ATB-[2-3H]BMPA photolabel.

Surface glucose transporters of intact muscles were photolabeled with the membrane impermeant ATB-[2-3H]BMPA reagent and localized by autoradiography. We found sparse labeling of the glucose transporters by ATB-[2-3H]BMPA on the sarcolemmal membrane around the muscle fiber. The majority of label was on the interior of the muscle fiber, at a discrete site which matched the distribution of AI junctions and which was presumed to be on the exterior surface of T-tubules. The amount of photolabel on the T-tubule was increased in response to insulin and was blocked by cytochalasin B. These results support the concept that glucose transport may occur predominantly across the T-tubule membrane under basal and insulin-stimulated conditions.

Affinity Labels↗

PubMed1994

Glucose metabolism in incubated human muscle: effect of obesity and non-insulin-dependent diabetes mellitus.

Skeletal muscle contributes significantly to reduced insulin-stimulated glucose disposal in patients with obesity and non-insulin-dependent (type II) diabetes mellitus (NIDDM). The biochemical basis for insulin resistance is not known but may involve reduced glucose transport and/or a defect in intracellular pathways for glucose disposal. To address this question, we measured basal and insulin-stimulated glucose oxidation, glycogen formation, and nonoxidative glycolysis (lactate and amino acid release) in an incubated muscle preparation from nonobese and morbidly obese patients with and without NIDDM. Pathways of glucose disposal were also determined in muscle of obese NIDDM patients incubated under hyperglycemic (20 mmol/L) conditions, which increases glucose uptake by mass action. Under basal conditions (no insulin present) there were no significant differences in glycogen formation or glucose oxidation between nonobese control, obese nondiabetic, or obese diabetics. Lactate release was significantly higher in obese controls compared to nonobese controls in the basal state at 5 mmol/L glucose (10.2 +/- 2.8 v 24.7 +/- 3.5 nmol/min/g, P < .05). Under maximal insulin-stimulated conditions, rates of glycogen formation, glucose oxidation, and nonoxidized glycolysis increased 1.9-, 2.3-, and 2.2-fold over basal (P < .05) in nonobese controls. By contrast, insulin was ineffective at stimulating significant increases in any metabolic pathway of glucose disposal in muscle of obese or obese NIDDM patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

Effect of moderate obesity on glucose transport in human muscle.

We have shown that maximally stimulated glucose transport is reduced in in vitro incubated muscle of morbidly obese subjects. To investigate the possibility that a "threshold" of obesity exists, above which glucose transport is significantly decreased, hormone (insulin, IGF-I, or IGF-II) stimulation of glucose transport was correlated with body mass index using muscle biopsies from a group of 30 lean to obese females with BMI ranging from 16 to 40. There was a significant negative relationship between stimulation for glucose transport and BMI (R = 0.765). These data suggest there is no obesity threshold for insulin resistance in skeletal muscle but a continuous decline in glucose transport below a BMI of approximately 30 kg/m2, after which insulin and the IGFs no longer stimulate glucose transport.

3-O-Methylglucose↗

PubMed1993

Transcriptional regulation of the gene for glucose transporter GLUT4 in skeletal muscle. Effects of diabetes and fasting.

GLUT4 glucose transporter protein and mRNA levels in rat skeletal muscle are decreased with streptozotocin (STZ)-induced diabetes and increased by fasting, indicating that GLUT4 expression may be regulated at the pretranslational level. The purpose of the present study was to determine whether GLUT4 is subject to transcriptional regulation in skeletal muscle under the altered metabolic conditions of diabetes and fasting. Nuclei were isolated from red and white portions of the quadriceps and gastrocnemius/plantaris muscles of control, 7-day STZ-diabetic, and 3-day fasted rats. STZ-induced diabetes resulted in a 35% reduction in GLUT4 transcription in red skeletal muscle and thus accounted for a major portion of the corresponding 50% reduction in GLUT4 mRNA observed in red skeletal muscle. STZ-induced diabetes had no significant effect on GLUT4 transcription or mRNA in white skeletal muscle. Fasting, however, significantly increased both GLUT4 transcription (2.2-fold) and mRNA (2.9-fold) in white skeletal muscle with no change detected for either parameter in red skeletal muscle. The nearly 2-fold higher steady-state GLUT4 mRNA in red versus white skeletal muscle of control rats was not associated with any difference in basal transcription. These findings demonstrate that expression of the GLUT4 glucose transporter protein in skeletal muscle is subject to regulation in vivo at the level of transcription of the GLUT4 gene. In addition, GLUT4 transcription is regulated in a fiber type-specific manner in response to the metabolic challenges elicited by STZ-induced diabetes and fasting.

Animals↗

PubMed1993

Contractile activity restores insulin responsiveness in skeletal muscle of obese Zucker rats.

Both insulin and contraction stimulate glucose transport in skeletal muscle. Insulin-stimulated glucose transport is decreased in obese humans and rats. The aims of this study were (1) to determine if contraction-stimulated glucose transport was also compromised in skeletal muscle of genetically obese insulin-resistant Zucker rats, and (2) to determine whether the additive effects of insulin and contraction previously observed in muscle from lean subjects were evident in muscle from the obese animals. To measure glucose transport, hindlimbs from lean and obese Zucker rats were perfused under basal, insulin-stimulated (0.1 microM), contraction-stimulated (electrical stimulation of the sciatic nerve) and combined insulin-(+)contraction-stimulated conditions. One hindlimb was stimulated to contract while the contralateral leg served as an unstimulated control. 2-Deoxyglucose transport rates were measured in the white gastrocnemius, red gastrocnemius and extensor digitorum longus muscles. As expected, the insulin-stimulated glucose transport rate in each of the three muscles was significantly slower (P < 0.05) in obese rats when compared with lean animals. When expressed as fold stimulation over basal, there was no significant difference in contraction-induced muscle glucose transport rates between lean and obese animals. Insulin-(+)contraction-stimulation was additive in skeletal muscle of lean animals, but synergistic in skeletal muscle of obese animals. Prior contraction increased insulin responsiveness of glucose transport 2-5-fold in the obese rats, but had no effect on insulin responsiveness in the lean controls. This contraction-induced improvement in insulin responsiveness could be of clinical importance to obese subjects as a way to improve insulin-stimulated glucose uptake in resistant skeletal muscle.

Animals↗

PubMed1993

Role of transverse tubules in insulin stimulated muscle glucose transport.

Although the strongest evidence for recruitment of glucose transporters in response to insulin comes from studies with adipocytes, studies in muscle seem in general to confirm that glucose transporters are also translocated to the cell membrane in muscle in response to insulin. However, the observation that transverse tubule (T-tubule) membranes contain approximately five times more glucose transporter than sarcolemma raised a question as to where glucose transport occurs in muscle. The T-tubule membrane system is continuous with the surface sarcolemma and is a tubule system in which extracellular fluid is in proximity with the interior of the muscle fiber. The purpose of this Prospects article is to evaluate the possibility that the T-tubule membrane may represent a major site of glucose transport in skeletal muscle. Using immunocytochemical techniques we have located GLUT4 glucose transporters on the T-tubule membrane and in vesicles near T-tubules. Since T-tubules form channels into the interior of the muscle fiber, glucose could diffuse or be moved by some peristaltic-like pumping action into the transverse tubules and then be transported across the membrane deep into the interior of the muscle fiber. This mode of transport directly into the interior of the cell would be advantageous over transport across the sarcolemma and subsequent diffusion around the myofibrils to reach the interior of the muscle. Thus, in addition to the role of the T-tubule in ion fluxes and contraction, this unique membrane system can also provide a pathway for the delivery of substrates into the center of the muscle cell where many glycolytic enzymes and glycogen deposits are located.

Animals↗

PubMed1993

Increased muscle glucose uptake in response to chronic glyburide treatment is not related to changes in glucose transporter (GLUT4) protein.

1. The mechanism of action of glyburide (a sulfonylurea) on muscle has been investigated by measuring glucose uptake and glucose transporter (GLUT4) protein levels after chronic glyburide treatment. 2. A dietary induced insulin resistant rat model (4 wk of high-fat, high-sucrose feeding) was given glyburide (2 mg/kg/day) for 10 days and glucose uptake was measured in a perfused hindquarter preparation. 3. Protein levels of the GLUT4 glucose transporter were determined by Western analysis. 4. After 7 days of treatment, rats fed glyburide had lower blood glucose concentrations 2 hr (72 +/- 5 vs 103 +/- 12 mg/dl) and 24 hr (97 +/- 7 vs 123 +/- 7 mg/dl) after glyburide administration with no difference in serum insulin levels compared to vehicle treated animals. 5. Glucose uptake was approx doubled in basal state (0 insulin) in response to glyburide (2.8 +/- 0.4 vs 1.7 +/- 0.2 mumol/g per hr). 6. Maximal insulin (100 nM) stimulated glucose uptake tended to be higher in the glyburide treated group, but did not reach statistical significance (8.0 +/- 0.7 vs 7.0 +/- 0.6 mumol/g per hr). 7. Western analysis revealed no significant effect of glyburide on the GLUT4 protein level in skeletal muscle. 8. These results suggest that glyburide alters glucose uptake through some mechanism other than alterations in the level of the GLUT4 glucose transporter protein.

Animals↗