Skeletal Muscle Of Diabetic Rats Research Articles

Dynamics of microvascular oxygen pressure during rest-contraction transition in skeletal muscle of diabetic rats.

Type I diabetes reduces dramatically the capacity of skeletal muscle to receive oxygen (QO(2)). In control (C; n = 6) and streptozotocin-induced diabetic (D: n = 6, plasma glucose = 25.3 +/- 3.9 mmol/l and C: 8.3 +/- 0.5 mmol/l) rats, phosphorescence quenching was used to test the hypothesis that, in D rats, the decline in microvascular PO(2) [Pm(O(2)), which reflects the dynamic balance between O(2) utilization (VO(2)) and QO(2)] of the spinotrapezius muscle after the onset of electrical stimulation (1 Hz) would be faster compared with that of C rats. Pm(O(2)) data were fit with a one or two exponential process (contingent on the presence of an undershoot) with independent time delays using least-squares regression analysis. In D rats, Pm(O(2)) at rest was lower (C: 31.2 +/- 3.2 mmHg; D: 24.3 +/- 1.3 mmHg, P < 0.05) and at the onset of contractions decreased after a shorter delay (C: 13.5 +/- 1.8 s; D: 7.6 +/- 2.1 s, P < 0.05) and with a reduced mean response time (C: 31.4 +/- 3.3 s; D: 23.9 +/- 3.1 s, P < 0.05). Pm(O(2)) exhibited a marked undershoot of the end-stimulation response in D muscles (D: 3.3 +/- 1.1 mmHg, P < 0.05), which was absent in C muscles. These results indicate an altered VO(2)-to-QO(2) matching across the rest-exercise transition in muscles of D rats.

Calsequestrin expression and calcium binding is increased in streptozotocin-induced diabetic rat skeletal muscle though not in cardiac muscle

Altered mechanisms of Ca2+ transport may underlie the contractile dysfunctions that have been frequently reported to occur in diabetic cardiac and skeletal muscle tissues. Calsequestrin, a high-capacity Ca2+-binding protein, is involved in the regulation of the excitation-contraction-relaxation cycle of both skeletal and cardiac muscle fibres. We have investigated the expression of calsequestrin and Ca2+ binding in cardiac and skeletal muscle from streptozotocin-induced diabetic rat. Immunoblotting of microsomal membranes from normal and streptozotocin-induced diabetic muscle revealed no significant changes in heart, but an increase in the relative abundance of calsequestrin and calsequestrin-like proteins in skeletal muscle. In analogy, the overall Ca2+-binding capacity of sarcoplasmic reticulum vesicles from diabetic skeletal muscle was drastically increased. The expression of fast muscle marker proteins was not affected, indicating that no relevant fibre transformation occurred in streptozotocin-treated rat muscles. The up-regulation of the high-capacity Ca2+-binding element calsequestrin might represent a compensatory mechanism of diabetic skeletal muscle. An increased Ca2+-buffering capacity of the sarcoplasmic reticulum lumen might counteract elevated cytosolic Ca2+ levels in diabetes thereby preventing Ca2+-dependent myo-necrosis.

Orally administered leucine enhances protein synthesis in skeletal muscle of diabetic rats in the absence of increases in 4E-BP1 or S6K1 phosphorylation.

In this study, food-deprived (18 h) control rats and rats with alloxan-induced diabetes were orally administered saline or the amino acid leucine to assess whether it regulates protein synthesis independently of a change in serum insulin concentrations. Immediately after leucine administration, diabetic rats were infused with insulin (0.0, 4.0, or 20 pmol small middle dot min(-1) small middle dot kg(-1)) for 1 h to examine the role of the hormone in the protein synthetic response to leucine. In control rats, leucine stimulated protein synthesis by 58% and increased phosphorylation of the translational repressor, eukaryotic initiation factor (eIF) 4E-binding protein (BP)-1, 4E-BP1, fivefold. Consequently, association of the mRNA cap-binding protein eukaryotic initiation factor (eIF)4E with 4E-BP1 was reduced to 50% of control values, and eIF4G*eIF4E complex assembly was increased 80%. Furthermore, leucine increased the phosphorylation of the 70-kDa ribosomal protein S6 (rp S6) and the ribosomal protein S6 kinase (S6K1). Diabetes attenuated protein synthesis compared with control rats. Nonetheless, in diabetic rats, leucine increased protein synthesis by 53% without concomitant changes in the phosphorylation of 4E-BP1 or S6K1. Skeletal muscle protein synthesis was stimulated in diabetic rats infused with insulin, but rates of synthesis remained less than values in nondiabetic controls that were administered leucine. Phosphorylation of 4E-BP1 and S6K1 was increased in diabetic rats infused with insulin in a dose-dependent manner, and the response was enhanced by leucine. The results suggest that leucine enhances protein synthesis in skeletal muscle through both insulin-dependent and -independent mechanisms. The insulin-dependent mechanism is associated with increased phosphorylation of 4E-BP1 and S6K1. In contrast, the insulin-independent effect on protein synthesis is mediated by an unknown mechanism.

Exercise training increases the activity of pyruvate dehydrogenase complex in skeletal muscle of diabetic rats.

The effects of diabetes and exercise training on the activity of pyruvate dehydrogenase (PDH) complex in skeletal muscle were examined in rats. Male Sprague-Dawley rats were divided into four groups as follows: non-diabetic sedentary, non-diabetic trained, diabetic sedentary, and diabetic trained groups. Diabetic rats were prepared by a bolus injection of intravenous streptozotocin (50 mg/kg body weight). Exercise training was performed by having rats run on a treadmill at a speed of 25 m/min for 45 min/day, 6 days/wk for 4 wks. Exercise training decreased serum concentrations of glucose and non-esterified fatty acid in diabetic rats. GLUT4 content in skeletal muscle in sedentary rats was significantly decreased by diabetes; however, exercise training significantly increased the GLUT4 content in diabetic rats. The total and actual activities and the proportion of actual activity of the PDH complex were decreased in diabetic sedentary rats. Exercise training did not affect the total activity of the PDH complex in non-diabetic rats, whereas it increased the total activity in diabetic rats to the same level as that in non-diabetic rats. In diabetic rats, exercise training tended to increase the proportion of actual activity of the PDH complex from 2.7 +/- 0.4% to 4.7 +/- 0.8%, although the proportion of actual activity in non-diabetic rats was decreased by exercise training. The present study suggests that exercise training may improve glucose metabolism in the skeletal muscle of streptozotocin-induced diabetic rats probably through the mechanisms of increasing both GLUT4 content and the activity of the PDH complex.

Gene therapy for diabetic rats by electroporational transfer of naked plasmid with human pre-pro-insulin gene into skeletal muscle

A naked plasmid with human pre-pro-insulin gene was transferred into skeletal muscle of diabetic rats by electric pulses and gene expression was detected. Blood glucose concentration was decreased from 24 mmol l−1 to 8.5 mmol l−1. Circulating insulin-like protein was increased significantly to 15–20 μU ml−1, while that of the control group injected with the empty vector remained at less than 10 μU ml−1. The low blood glucose concentration lasted for more than two months. These studies indicate that electroporational transfer of plasmid with human pre-pro-insulin gene into skeletal muscle could be a potential method of gene therapy for human diabetes mellitus.

Vanadium increases GLUT4 in diabetic rat skeletal muscle.

The effect of vanadium in lowering blood glucose in diabetic animals is well established; however, the exact mechanism of action of vanadium still eludes us. There are several reports from in vitro studies indicating that vanadium increases enzyme activity in insulin signalling pathways; however, these findings have not been duplicated in vivo. Glucose transporters (GLUT) have a major role to play in any glucoregulatory effects. Insulin dependent GLUT4 is a major glucose transporter present in skeletal muscle, adipocytes and heart. In the present study we found that the plasma glucose in streptozotocin (STZ) diabetic animals was restored to normal following treatment with a single dose of BMOV, an organic vanadium compound, given by oral gavage (0.6 mmol/kg), similar to the response with chronic BMOV treatment. The response to BMOV by oral gavage was rapid and the animals were normoglycemic within 24 h of treatment and still demonstrated a significant effect even after 72 h. Using a specific antibody against GLUT4 we found an overall reduction in the GLUT4 in the total membrane fraction in skeletal muscle of diabetic animals. However, with a single dose of BMOV the GLUT4 level was restored to normal. This is the first report that establishes a direct effect of vanadium on the regulation of GLUT4 expression in diabetic animals in vivo, and may at least partially explain the glucoregulatory effects of vanadium.

The content of glycogen phosphorylase and glycogen in preparations of sarcoplasmic reticulum-glycogenolytic complex is enhanced in diabetic rat skeletal muscle

We have examined the effect of diabetes and pharmacological insulin treatment on the content of glycogen phosphorylase and glycogen associated with the sarcoplasmic reticulum-glycogenolytic complex from rat skeletal muscle. Diabetes was induced in rats by streptozotocin injection. Enzymatic activities were measured using spectrophotometric methods. Glycogen phosphorylase was determined measuring the pyridoxal-5' -phosphate content and using polyacrylamide gel electrophoresis. Glycogen content was measured by enzymatic and the phenol sulfuric methods. The content of glycogen phosphorylase associated with the sarcoplasmic reticulum glycogenolytic complex gradually arises after diabetes induction. The content of glycogen phosphorylase was restored to a control value by pharmacological insulin treatment. In addition, the content of glycogen in preparations of sarcoplasmic reticulum-glycogenolytic complex of diabetic animals was also increased, whereas the content of glycogen in total muscle of diabetic rats was similar to that of the control rats. The absolute and relative amount of glycogen associated with sarcoplasmic reticulum seemed to increase in diabetic animals. These effects on the compartmentalisation of glycogen were suppressed by insulin treatment. Additionally, the rate of conversion of glycogen phosphorylase b to a, an index of the phosphorylase kinase activity, was 50 % lower in diabetic rats, increasing the dephosphorylated form of glycogen phosphorylase and, as a consequence, its association with sarcoplasmic reticulum membranes. These results suggest that under diabetic conditions, both glycogen phosphorylase and a small percentage of muscle glycogen are relocalized in the sarcoplasmic reticulum-glycogenolytic complex.

Immunization against IGF-I prevents increases in protein synthesis in diabetic rats after resistance exercise.

These studies examined whether passive immunization against insulin-like growth factor I (IGF-I) would prevent increases in rates of protein synthesis in skeletal muscle of diabetic rats after resistance exercise. Male Sprague-Dawley rats were pancreatectomized and randomly assigned to either an exercise or a sedentary group. Animals in each of these groups received either an IGF-I antibody or a nonspecific IgG from a subcutaneous osmotic pump. Exercise did not change plasma or gastrocnemius IGF-I concentrations in nondiabetic rats. However, plasma and muscle IGF-I concentrations were higher in IgG-treated diabetic rats that exercised compared with respective sedentary groups (P < 0.05). Passively immunized diabetic rats did not exhibit the same exercise-induced increase in IGF-I concentrations. In nondiabetic rats, protein synthesis rates were higher after exercise in both control and immunized groups. In diabetic rats, exercise increased protein synthesis in the IgG-treated animals but not in those treated with IGF-I antibody. There was also a significant positive correlation between both plasma and gastrocnemius IGF-I concentrations and rates of protein synthesis in diabetic (P < 0.01), but not nondiabetic, rats. These results suggest that IGF-I is compensatory for insulin in hypoinsulinemic rats by facilitating an anabolic response after acute resistance exercise.

The Ubiquitin-Proteasome Proteolytic Pathway in Heart vs Skeletal Muscle: Effects of Acute Diabetes

The ubiquitin-proteasome system is thought to play a major role in normal muscle protein turnover and to contribute to diabetes-induced protein wasting in skeletal muscle. However, its importance in cardiac muscle is not clear. We measured heart muscle mRNA for ubiquitin and for the C2 and C8 proteasomal subunits, the amount of free ubiquitin and the proteasome chymotrypsin-like proteolytic activity in control and diabetic rats. Results were compared to those in skeletal muscle (rectus). Heart ubiquitin, C2 and C8 subunit mRNA and proteolytic activity were significantly greater than in skeletal muscle (P ≤ 0.05). This suggests that the ubiquitin proteasomal pathway may also be important for normal heart muscle turnover. Diabetes increased ubiquitin mRNA by ∼50% in heart (P < 0.03) and by ∼100% in skeletal muscle (P < 0.005). It remained high after 3 days of insulin treatment in both tissues. C2 and C8 subunit mRNA did not change with diabetes or insulin treatment. Diabetes did not change the amount of free ubiquitin or the proteasomal (lactacystin-inhibitable) chymotrypsin-like peptidase activity in heart or skeletal muscle. In conclusions, gene expression for several components of the ubiquitin-proteasome proteolytic pathway is significantly higher in cardiac than in skeletal muscle, as is the proteasome chymotrypsin-like peptidase activity. Diabetes increases the expression of ubiquitin but not C2 or C8 subunit mRNA, nor does it significantly alter the amount of free ubiquitin or the proteasome chymotrypsin-like peptidase activity. The rate-limiting step of enhanced protein degradation in diabetic rat heart and skeletal muscle may be located at ubiquitin conjugation and/or its binding to proteasome, not at the ubiquitin availability or the proteasome itself.

Inverse alterations of BCKA dehydrogenase activity in cardiac and skeletal muscles of diabetic rats.

Rat cardiac and skeletal muscles, which have been used as model tissues for studies of regulation of branched-chain alpha-keto acid (BCKA) oxidation, vary greatly in the activity state of their BCKA dehydrogenase. In the present experiment, we have investigated whether they also vary in response of their BCKA dehydrogenase to a metabolic alteration such as diabetes and, if so, to investigate the mechanism that underlies the difference. Diabetes was produced by depriving streptozotocin-treated rats of insulin administration for 96 h. The investigation of BCKA dehydrogenase in the skeletal muscle (gastrocnemius) showed that diabetes 1) increased its activity, 2) increased the protein and gene expressions of all of its subunits (E(1)alpha, E(1)beta, E(2)), 3) increased its activity state, 4) decreased the rate of its inactivation, and 5) decreased the protein expression of its associated kinase (BCKAD kinase) without affecting its gene expression. In sharp contrast, the investigation of BCKA dehydrogenase in the cardiac muscle showed that diabetes 1) decreased its activity, 2) had no effect on either protein or gene expression of any of its subunits, 3) decreased its activity state, 4) increased its rate of inactivation, and 5) increased both the protein and gene expressions of its associated kinase. In conclusion, our data suggest that, in diabetes, the protein expression of BCKAD kinase is downregulated posttranscriptionally in the skeletal muscle, whereas it is upregulated pretranslationally in the cardiac muscle, causing inverse alterations of BCKA dehydrogenase activity in these muscles.

Hypertrophy of skeletal muscle in diabetic rats in response to chronic resistance exercise.

This study had the following objectives: 1) to determine whether diabetic rats could increase muscle mass due to a physiological manipulation (chronic resistance exercise), 2) to determine whether exercise training status modifies the effect of the last bout of exercise on elevations in rates of protein synthesis, and 3) to determine whether chronic resistance exercise alters basal glycemia. Groups consisted of diabetic or nondiabetic rats that performed progressive resistance exercise for 8 wk, performed acute resistance exercise, or remained sedentary. Arterial plasma insulin in diabetic groups was reduced by about one-half (P < 0.05) compared with nondiabetic groups. Soleus and gastrocnemius-plantaris complex muscle wet weights were lower because of diabetes, but in response to chronic exercise these muscles hypertrophied in diabetic (0.028 +/- 0.003 vs. 0.032 +/- 0.0015 g/cm for sedentary vs. exercised soleus and 0.42 +/- 0.068 vs. 0.53 +/- 0.041 g/cm for sedentary vs. exercised gastrocnemius-plantaris, both P < 0.05) but not in nondiabetic (0.041 +/- 0.0026 vs. 0.042 +/- 0.003 g/cm for sedentary vs. exercised soleus and 0.72 +/- 0.015 vs. 0.69 +/- 0.013 g/cm for sedentary vs. exercised gastrocnemius-plantaris) rats when muscle weight was expressed relative to tibial length or body weight (data not shown). Another group of diabetic rats that lifted heavier weights showed muscle hypertrophy. Rates of protein synthesis were higher in red gastrocnemius in chronically exercised than in sedentary rats: 155 +/- 11 and 170 +/- 7 nmol phenylalanine incorporated x g muscle(-1) x h(-1) in exercised diabetic and nondiabetic rats vs. 110 +/- 14 and 143 +/- 7 nmol phenylalanine incorporated x g muscle(-1) x h(-1) in sedentary diabetic and nondiabetic rats. These elevations, however, were lower than in acutely exercised (but untrained) rats: 176 +/- 15 and 193 +/- 8 nmol phenylalanine incorporated x g muscle(-1) x h(-1) in diabetic and nondiabetic rats. Finally, chronic exercise training in diabetic rats was associated with reductions in basal glycemia, and such reductions did not occur in sedentary diabetic groups. These data demonstrate that, despite lower circulating insulin concentrations, diabetic rats can increase muscle mass in response to a physiological stimulus.

Selective impairment in GLUT4 translocation to transverse tubules in skeletal muscle of streptozotocin-induced diabetic rats.

We previously reported that insulin induces the translocation of GLUT4 to both the plasma membrane and the transverse tubules (T-tubules) in rat skeletal muscle (Am J Physiol 270:E667-E676, 1996). The aim of the present study was to investigate whether the insulin-resistant glucose utilization of skeletal muscle from streptozotocin (STZ)-induced diabetic rats is linked to an impaired translocation of GLUT4 to the plasma membrane, the T-tubules, or both surface compartments. Whole-body insulin-mediated glucose disposal, assessed during a hyperinsulinemic-euglycemic clamp, was reduced by 48% (P < 0.01) in diabetic rats as compared with controls. Subcellular membrane fractions enriched with plasma membranes, T-tubules, or GLUT4-enriched intracellular membranes were isolated from hindlimb muscles of control and insulin-stimulated rats, and GLUT4 content was measured by Western blot analysis. In the absence of insulin (unstimulated), GLUT4 content in muscle of diabetic rats was markedly lower (by approximately 40%) in both the T-tubules and the intracellular membrane fraction as compared with controls. In contrast, the transporter protein levels were similar in the plasma membrane fraction. In skeletal muscle of control animals, the hyperinsulinemic clamp induced GLUT4 translocation from the intracellular membrane pool to both the plasma membrane and the T-tubule-enriched fractions (approximately 2.2-fold to approximately 2.5-fold). Surprisingly, insulin increased plasma membrane GLUT4 content to comparable levels in control and diabetic rat skeletal muscle. However, insulin-mediated GLUT4 translocation to the T-tubules was significantly reduced in the same muscle. Whole-body insulin action was significantly correlated with GLUT4 protein levels in the T-tubules, but not with the transporter content in either plasma membranes or intracellular membranes. These results strongly suggest that peripheral resistance to insulin action on glucose disposal in STZ-induced diabetic rats is caused by a selective impairment of GLUT4 translocation to skeletal muscle T-tubules.

Brain-Derived Neurotrophic Factor mRNA Levels Are Up-Regulated in Hindlimb Skeletal Muscle of Diabetic Rats: Effect of Denervation

In a previous study the levels of brain-derived neurotrophic factor (BDNF) mRNA were shown to be elevated in skeletal muscle of the diabetic rat compared with age-matched control animals. It was proposed that diabetes-induced changes in nerve function may initiate changes in nerve/muscle contact akin to those following denervation of target skeletal muscle. In this study hindlimb skeletal muscles were denervated by sciatic nerve crush or transection and the effect on BDNF mRNA levels in control and diabetic rats was observed using Northern blotting. Contralateral to the side of nerve injury, the levels of BDNF mRNA in soleus muscle of diabetic rats were higher than in controls (three- to sevenfold), as has been seen previously in diabetic rats without any axotomy. Sciatic nerve crush or transection, of 1 week or of 3 weeks duration, lowered the levels of BDNF mRNA by 50% in ipsilateral soleus muscle of diabetic rats. BDNF mRNA levels in contralateral gastrocnemius muscle were not similarly raised in diabetic rats compared with controls and nerve injury had no effect. In control animals, ipsilaterally, the BDNF mRNA levels of soleus muscle were raised approximately twofold at 1 week and were lowered by approximately 50% at 3 weeks following nerve injury. Neurotrophin-3 mRNA levels were reduced approximately 50% in soleus muscle of diabetic rats compared with control rats, and nerve injury had no significant effect. The specific up-regulation of BDNF mRNA in soleus muscle of diabetic rats is discussed in terms of a proposed diabetes-induced ischemia within hindlimb skeletal muscle, with a protective role for BDNF in muscle and/or nerve being introduced.

Long-term normalization of GLUT-4 protein content in skeletal muscle of diabetic rats following islet transplantation.

Skeletal muscle GLUT-4 content is decreased in streptozotocin (STZ)-diabetic rats. This decrease is associated with impairment in glucose transport across the plasma membrane. In this study we investigated whether islet transplantation might normalize GLUT-4 content. Transplantation of syngeneic islets restored long-term near-normoglycemia in STZ-diabetic Lewis rats. Transplanted rats, followed up to 6 months, maintained slightly but significantly higher fasting and fed glucose levels when compared with age-matched normal controls. Although fasting insulin levels of transplanted rats were significantly higher than those of controls, insulin levels did not increase significantly with feeding. Plasma glucose levels following an oral glucose load (2 g/kg) were only slightly higher than in normal controls 2 months after transplantation, whereas after 6 months more severe glucose intolerance was detected. Transplanted rats completely lost the first-phase insulin release in response to i.v. glucose although they showed an increased second phase and preserved response to arginine. Six months after transplantation, endocrine beta cell mass of the grafts was similar to pretransplantation values. GLUT-4 protein content in skeletal muscle homogenates was reduced in untreated diabetic animals whereas it was completely restored by islet transplantation. In conclusion, achievement of long-term nearnormoglycemia after islet transplantation was associated with complete normalization of skeletal muscle GLUT-4 content in the diabetic animals, even in the presence of abnormal glucose tolerance and an altered pattern of insulin secretion.

Expression of the gene encoding glycogen phosphorylase is elevated in diabetic rat skeletal muscle and is regulated by insulin and cyclic AMP.

Glycogen phosphorylase regulates the breakdown of glycogen into glucose, but as previous studies have demonstrated, the control of glycogen metabolism becomes deregulated in diabetes mellitus. Messenger RNA levels encoding several different proteins are altered in skeletal muscle biopsies of patients with insulin-dependent and non-insulin-dependent diabetes. The possible alteration of expression of the gene encoding the skeletal muscle isoform of glycogen phosphorylase during diabetes has not previously been investigated. We examined the effect of streptozotocin-induced diabetes and insulin treatment on glycogen phosphorylase mRNA in rat skeletal muscle; glycogen phosphorylase mRNA levels were elevated in diabetic rat muscle tissue, but were partially suppressed in diabetic rat muscle following insulin treatment. To distinguish between the effects of insulin and counter-regulatory hormones on glycogen phosphorylase mRNA levels, we employed differentiating rat L6 myoblasts in culture. Insulin stimulated the accumulation of glycogen phosphorylase mRNA as determined by Northern blot analysis. Moreover, insulin and dibutyryl cAMP stimulated expression of a transiently transfected chloramphenicol acetyl transferase reporter gene under the control of the muscle glycogen phosphorylase promoter in differentiating myotubes in culture, suggesting that the effects of insulin and counter-regulatory hormones on glycogen phosphorylase mRNA are at the level of transcription. These results suggest that insulin and epinephrine may participate in the induction of the glycogen phosphorylase gene during myogenesis; moreover, activation of this gene in muscle tissue may be a contributing factor in impaired glycogen storage during uncontrolled diabetes.

Microcirculatory structure-function relationships in skeletal muscle of diabetic rats

Pages H1502–H1511: W. L. Sexton, D. C. Poole, and O. Mathieu-Costello. “Microcirculatory structure-function relationships in skeletal muscle of diabetic rats.” Page H1508: Figure 6 was inadvertently printed upside down and should appear as follows. (See PDF)

Microcirculatory structure-function relationships in skeletal muscle of diabetic rats.

The effects of streptozotocin-induced diabetes on microcirculatory structure-function relationships in skeletal muscle were studied in control (C) and diabetic (D; 65 mg/kg streptozotocin ip) rats 6-8 wk after injection. Capillary exchange capacity was determined from measurements of capillary filtration coefficient (CFC) and permeability-surface area product (PS) for 51Cr-labeled EDTA in maximally vasodilated (papaverine), isolated hindquarters of C (n = 9) and D (n = 12) rats. Capillary numerical density, length, surface area, capillary geometry, and muscle fiber cross-sectional area were determined using morphometric methods in perfusion-fixed plantaris muscles from a second series of C (n = 5) and D (n = 6) rats. Hindquarters of D rats (61 +/- 3 g) weighed less than C rats (90 +/- 3 g) because of marked muscle atrophy. Minimal total vascular resistance was lower in D rats (P < or = 0.05), indicating an increased flow capacity. CFC was not different in C and D rats (0.0282 +/- 0.0020 vs. 0.0330 +/- 0.0025 ml.min-1.mmHg-1 x 100 g-1, respectively). The relationship between PS and flow was depressed in D rats (P < or = 0.05) compared with C rats, which indicated a reduced capillary diffusing capacity. Plantaris muscle weight was 41% less in D rats (174 +/- 9 vs. 293 +/- 11 mg; P < or = 0.001). Morphometric analysis revealed that muscle fiber cross-sectional area was reduced 39% in D rats, which, despite a lower capillary-to-fiber ratio (1.59 +/- 0.04 vs. 2.12 +/- 0.13; P < or = 0.001), resulted in a 27% increase in capillary density in D rats. Capillary diameter was less in D rats (3.58 +/- 0.12 vs. 4.51 +/- 0.23 microns; P < or = 0.005). Total capillary surface area was reduced 42% in D rats; however, capillary surface area per muscle fiber volume was unchanged in D rats (231 +/- 34 vs. 237 +/- 16 cm-1). These data indicate that there is remodeling of the capillary bed in skeletal muscle of D rats, resulting in a reduction in total microvascular surface area. The reduction in capillary surface area is proportional to the degree of muscle atrophy in D rats such that functional microvascular surface area per tissue mass (e.g., CFC) is unchanged. The lower diffusing capacity (PS) in D rats suggests that either small solute permeability is reduced and/or there is greater perfusion heterogeneity in D rat skeletal muscle.

Microcirculatory structure-function relationships in skeletal muscle of diabetic rats

Pages H1502–H1511: W. L. Sexton, D. C. Poole, and O. Mathieu-Costello. “Microcirculatory structure-function relationships in skeletal muscle of diabetic rats.” Page H1508: Figure 6 was inadvertently printed upside down and should appear as follows. (See PDF)

Modification of the glyoxalase system in streptozotocin-induced diabetic rats: Effect of the aldose reductase inhibitor statil

The glyoxalase system was characterized in tissue (liver, skeletal muscle, kidney cortex and medulla, lens and sciatic nerve) and blood from streptozotocin-induced diabetic rats and normal controls. The effect of the aldose reductase inhibitor, Statil [3-(4-bromo-2-fluorobenzyl)-4-oxo-3 H-phthalazine-1-yl-acetic acid; ICI 128 436], was also investigated. Glyoxalase I and glyoxalase II activities were decreased in the liver and increased in skeletal muscle of diabetic rats and of Statil-treated diabetic rats, relative to normal controls. The concentration of non-protein sulphydryl (NPSH) was decreased in the liver and lens of diabetic rats, relative to normal controls; Statil prevented these effects. The concentrations of methylglyoxal in the kidney cortex and medulla, lens and blood were increased in diabetic rats, relative to normal controls. Statil prevented these increases except in the kidney cortex. The concentration of D-lactate was increased in the lens and blood of diabetic rats, relative to normal controls, which was partially prevented in blood but not in the lens by Statil. These data suggest that the glyoxalase system is modified in tissues and blood of streptozotocin-induced diabetic rats and some of the modifications may be prevented by Statil. The increased concentrations of methylglyoxal in the kidney, lens and blood, and the decreased concentration of NPSH in the lens may be related to the development of diabetic complications.

Insulin-induced activation of pyruvate dehydrogenase complex in skeletal muscle of diabetic rats

The pyruvate dehydrogenase (PDH) complex undergoes reversible phosphorylation catalyzed by a PDH kinase (inactivating) and a PDH phosphatase (activating). In skeletal muscle, a decreased proportion of active PDH (PDH a) complex limits glucose oxidation in insulin-deficient states. The time-course for reactivation of the PDH complex by insulin in skeletal muscle of diabetic rats is important to understanding the potential mode of the action of insulin in regulating glucose metabolism. A single injection of insulin (1 U/kg) completely reversed the effects of alloxan-diabetes on PDH a activity within 1 hour. The normalization of the effects of diabetes on PDH a activity by insulin was maintained for a minimum of 6 hours. The increase in PDH a activity occurred before an insulin-induced decrease in plasma free fatty acids levels, demonstrating a dissociation between the antilipolytic effects of insulin and its ability to activate the PDH complex. PDH kinase activity was not normalized to control values following a single injection of insulin. Therefore, acute (1 to 6 hours) insulin-mediated activation of the PDH complex does not result from a decrease in PDH kinase activity. However, longer-term insulin therapy (1 U/kg body weight; twice daily) restored both PDH a and PDH kinase activities. The results are consistent with the hypothesis that activation of the PDH complex immediately following insulin administration is not mediated by a decreased PDH kinase activity. However, with daily insulin therapy in diabetes, activation of the PDH complex results from decreased PDH kinase activity.