Diverse effects of Glut 4 ablation on glucose uptake and glycogen synthesis in red and white skeletal muscle

The ability of muscles from Glut 4-null mice to take up and metabolize glucose has been studied in the isolated white EDL and red soleus muscles. In EDL muscles from male or female Glut 4-null mice, basal deoxyglucose uptake was lower than in control muscles and was not stimulated by insulin. In parallel, glycogen synthesis and content were decreased. Soleus muscles from male Glut 4-null mice took up twice more deoxyglucose in the absence of insulin than control muscles, but did not respond to insulin. In females, soleus deoxyglucose uptake measured in the absence of hormone was similar in Glut 4-null mice and in control mice. This uptake was stimulated twofold in Glut 4-null mice and threefold in control mice. Basal glycogen synthesis was increased by 4- and 2.2-fold in male and female null mice, respectively, compared to controls, and insulin had no or small (20% stimulation over basal) effect. These results indicate that while EDL muscles behaved as expected, soleus muscles were able to take up a large amount of glucose in the absence (males) or the presence of insulin (females). Whether this is due to a change in Glut 1 intrinsic activity or targeting and/or to the appearance of another glucose transporter remains to be determined.     

The role of glucose 6-phosphate in the control of glycogen synthase

Elevated blood glucose concentrations result in increased intracellular levels of glucose 6-phosphate in liver, skeletal muscle, and adipose tissue. In liver, blood glucose concentrations are the main factor in control of the synthesis of glycogen; insulin has only a potentiating effect. In skeletal muscle and adipocytes, glucose alone has little effect on the activity of glycogen synthase, the limiting enzyme in glycogen synthesis. However, insulin released as a result of elevated blood glucose stimulates the translocation of specific glucose transporters to the cell membrane, increases the uptake of glucose, and causes the covalent, dephosphorylation-mediated activation of glycogen synthase. We present evidence that elevated intracellular contents of glucose 6-phosphate provoke the activation of glycogen synthase in liver, muscle, and adipose tissue. In addition, glucose 6-phosphate may inhibit the phosphorylation of glycogen synthase by cyclic AMP-stimulated protein kinase. We show that the stimulated glucose uptake and phosphorylation appear to play a major role in the control by insulin of the enzymes involved in glycogen synthesis.     

A high-fat diet influences insulin-stimulated posttransport muscle glucose metabolism in rats

Because of a failure to detect significant quantities of intracellular glucose, it has been generally accepted that transport rather than phosphorylation is the rate-limiting process of muscle glucose metabolism under most (but not all) physiological conditions. Here, we have measured tissue free levels of the glucose analog 2-deoxy-D-glucose (2DG) in red quadriceps muscle of rats fed a high-fat diet (59% of energy from fat) for 3 weeks, to identify the barrier to insulin-stimulated glucose uptake previously seen in such animals. Measurements were performed on pentobarbital-anesthetized rats following exogenous infusion of radiolabeled 2DG. A glucose clamp was used to maintain plasma insulin at high physiological levels (approximately 120 mU/L). Three other treatment groups representing normal insulin action (chow-fed), extreme glucose uptake (maximal insulin stimulation + hyperglycemia), and insulin resistance with elevated free intracellular glucose (epinephrine infusion) were also studied for comparison. In chow-fed animals, no muscle free 2DG was detected, confirming transport as the rate-limiting process. In fat-fed animals, a significant elevation in muscle free 2DG was observed (P < .01 v chow-fed controls). The elevation was similar in magnitude to that in epinephrine-infused rats, and implied a limitation of insulin action at a posttransport step. This result was confirmed with a more complex modeling analysis. We conclude that posttransport steps influence insulin-stimulated in vivo muscle glucose metabolism in long-term high-fat-fed rats.     

Fasting does not impair insulin-stimulated glucose uptake but alters intracellular glucose metabolism in conscious rats

Effects of 24-h and 48-h fasting on maximal insulin-stimulated whole-body and muscle glucose uptake, glycogen synthesis, and glycolysis were studied in conscious rats by combining the glucose clamp technique with tracer methods. Fasting decreased body weight and basal plasma glucose, plasma insulin, hepatic glucose output, and glucose clearance (P < 0.05 for all). However, maximal insulin-stimulated whole-body glucose uptake, normalized to body weight, was almost identical in fed, 24-h fasted, and 48-h fasted rats (191 +/- 8, 185 +/- 14, and 182 +/- 5 mumol.kg-1.min-1, respectively; P > 0.7). Similarly, rates of insulin-stimulated glucose uptake by four different skeletal muscles, estimated by the 2-deoxyglucose injection technique, were not different among the three groups. In contrast to glucose uptake, insulin-stimulated whole-body glycolysis was decreased significantly after fasting (36% after 48 h fasting; P < 0.05), whereas insulin-stimulated whole-body glycogen synthesis was increased (44% after 48 h fasting; P < 0.05). In fed rats, glycolysis was the major pathway for glucose metabolism during hyperinsulinemia, accounting for 60 +/- 5% of glucose uptake. This fraction was decreased significantly by fasting (P < 0.01), so that after a 48-h fast, glycolysis accounted for only 40 +/- 3% of insulin-stimulated glucose uptake and glycogen synthesis became predominant pathway, accounting for 60 +/- 3% of whole-body glucose utilization. Whole-body patterns of glucose metabolism during hyperinsulinemia were paralleled by glucose metabolism in individual muscles.(ABSTRACT TRUNCATED AT 250 WORDS)     

Troglitazone action is independent of adipose tissue

We have investigated the antidiabetic action of troglitazone in aP2/DTA mice, whose white and brown fat was virtually eliminated by fat-specific expression of diphtheria toxin A chain. aP2/DTA mice had markedly suppressed serum leptin levels and were hyperphagic, but did not gain excess weight. aP2/DTA mice fed a control diet were hyperlipidemic, hyperglycemic, and had hyperinsulinemia indicative of insulin-resistant diabetes. Treatment with troglitazone alleviated the hyperglycemia, normalized the tolerance to intraperitoneally injected glucose, and significantly decreased elevated insulin levels. Troglitazone also markedly decreased the serum levels of cholesterol, triglycerides, and free fatty acids both in wild-type and aP2/DTA mice. The decrease in serum triglycerides in aP2/DTA mice was due to a marked reduction in VLDL- and LDL-associated triglyceride. In skeletal muscle, triglyceride levels were decreased in aP2/DTA mice compared with controls, but glycogen levels were increased. Troglitazone treatment decreased skeletal muscle, but not hepatic triglyceride and increased hepatic and muscle glycogen content in wild-type mice. Troglitazone decreased muscle glycogen content in aP2/DTA mice without affecting muscle triglyceride levels. The levels of peroxisomal proliferator-activated receptor gamma mRNA in liver increased slightly in aP2/DTA mice and were not changed by troglitazone treatment. The results demonstrate that insulin resistance and diabetes can occur in animals without significant adipose deposits. Furthermore, troglitazone can alter glucose and lipid metabolism independent of its effects on adipose tissue.     

Androgyny of physique in female track and field athletes

Long term feeding of a sucrose rich diet to rats is accompanied by a decreased glucose assimilation rate, despite high plasma insulin levels. Hyperinsulinism is at least partially based on a relative obesity, with increased amounts of abdominal- and retroperitoneal fat tissue, but unchanged total body weight compared to starch fed controls. The secretory pattern of insulin release was studied following glucose, arginine, fructose and sulfonylurea administration in the isolated perfused pancreas of sucrose and isocaloric starch fed rats. In addition, isolated islets of Langerhans were used to demonstrate the effects of glucose on insulin secretion and the incorporation of H-3 leucine into the proinsulin and insulin fraction of islet proteins. Following 11 mM glucose, the dynamics of insulin release in the isolated perfused pancreas of sucrose fed rats is characterized by a markedly elevated, late plateau-like response, usually seen only at higher glucose concentrations. Hyperinsulinism, as compared to starch fed controls, can also be demonstrated following arginine and the sulfonylurea HB-419, whereas fructose has no effect in the presence of low glucose concentrations. During incubation of the pancreatic islets, the hyperinsulinism in sucrose-, compared to starch fed rats, is more pronounced at 11 mM glucose than at 5.5 mM glucose. The incorporation of H-3 leucine into the proinsulin-insulin fraction of islet proteins in sucrose compared to starch fed rats, however, is significantly greater with glucose 5.5 mM than at high glucose level. In sucrose fed rats, secretion and biosynthesis of insulin thus appear to be elevated but closely linked only at physiological glucose concentration.     

The conserved amino-terminal domain of hSRP1 alpha is essential for nuclear protein import

Transgenic mice that overexpressed IGFBP-1 are hyperinsulinemic in the first week of life and gradually develop fasting hyperglycemia. In adult transgenic mice, the hypoglycemic response to IGF-I but not insulin or des (1-3) IGF-I was attenuated (P < 0.05) compared with wild-type mice. Furthermore, in isolated adipocytes from transgenic mice, the stimulatory effect of IGF-I but not insulin on 2-deoxy-[3H]-glucose uptake was reduced (P < 0.02). In contrast, in isolated soleus muscle, the effects of both IGF-I and insulin on 2-deoxy-3H-glucose uptake and on [3H]-glucose incorporation into glycogen were significantly reduced compared to wild-type mice. The decline in specific activity of the 2-deoxy-3H-glucose, a measure of glucose appearance in the circulation, was more marked in transgenic animals (P < 0.05). In addition, tissue uptake of glucose was significantly higher in diaphragm, heart, intestine, liver, soleus muscle, and adipose tissue from fasting transgenic mice. Plasma concentrations of alanine, lysine, and methionine were also elevated in transgenic mice. These data suggest that overexpression of IGFBP-1 attenuates the hypoglycemic effect of endogenous IGF-I, which is initially compensated for by enhanced pancreatic insulin production. However, in adult mice pancreatic insulin content is reduced, insulin resistance is demonstrable in skeletal muscle and fasting hyperglycemia develops.     

Early metabolic adaptations of rabbit fast-twitch muscle to chronic low-frequency stimulation

To investigate early adaptive responses to chronic low-frequency stimulation (CLFS), rabbit tibialis anterior (TA) muscles were continuously stimulated at 10 Hz for 8 days, allowed to rest for 1 h, and then subjected to a 15-min fatigue test at 10-Hz stimulation. The contralateral TA muscles which had not been exposed to CLFS, served as controls during the fatigue test. Compared to the controls, the initial tension output of the 8-day prestimulated muscles was reduced by 25%. However, these muscles maintained higher tensions during the fatigue test than the controls. Citrate synthase activity, an indicator of aerobic-oxidative capacity, was only slightly elevated (40%) in the 8-day stimulated muscles. Unlike the controls, the prestimulated muscles failed to produce potentiation during the fatigue test. Control muscles responded to the fatigue test with pronounced reductions in contents of adenosine 5'-triphosphate (ATP), phosphocreatine (PCr), and glycogen, as well as with large increases in contents of inosine monophosphate (IMP), inorganic phosphate (Pi), creatine (Cr), and lactate. Under the same conditions contents of ATP, PCr, Cr, glycogen, lactate, Pi, and IMP were unaltered in the 8-day prestimulated muscles. These findings demonstrated that CLFS for 8 days elicited pronounced alterations in energy metabolism and contractile properties. These adaptive changes occurred prior to fibre type transitions and substantial increases in aerobic-oxidative potential.     

Mechanisms of liver and muscle insulin resistance induced by chronic high-fat feeding

To elucidate cellular mechanisms of insulin resistance induced by excess dietary fat, we studied conscious chronically high-fat-fed (HFF) and control chow diet-fed rats during euglycemic-hyperinsulinemic (560 pmol/l plasma insulin) clamps. Compared with chow diet feeding, fat feeding significantly impaired insulin action (reduced whole body glucose disposal rate, reduced skeletal muscle glucose metabolism, and decreased insulin suppressibility of hepatic glucose production [HGP]). In HFF rats, hyperinsulinemia significantly suppressed circulating free fatty acids but not the intracellular availability of fatty acid in skeletal muscle (long chain fatty acyl-CoA esters remained at 230% above control levels). In HFF animals, acute blockade of beta-oxidation using etomoxir increased insulin-stimulated muscle glucose uptake, via a selective increase in the component directed to glycolysis, but did not reverse the defect in net glycogen synthesis or glycogen synthase. In clamp HFF animals, etomoxir did not significantly alter the reduced ability of insulin to suppress HGP, but induced substantial depletion of hepatic glycogen content. This implied that gluconeogenesis was reduced by inhibition of hepatic fatty acid oxidation and that an alternative mechanism was involved in the elevated HGP in HFF rats. Evidence was then obtained suggesting that this involves a reduction in hepatic glucokinase (GK) activity and an inability of insulin to acutely lower glucose-6-phosphatase (G-6-Pase) activity. Overall, a 76% increase in the activity ratio G-6-Pase/GK was observed, which would favor net hepatic glucose release and elevated HGP in HFF rats. Thus in the insulin-resistant HFF rat 1) acute hyperinsulinemia fails to quench elevated muscle and liver lipid availability, 2) elevated lipid oxidation opposes insulin stimulation of muscle glucose oxidation (perhaps via the glucose-fatty acid cycle) and suppression of hepatic gluconeogenesis, and 3) mechanisms of impaired insulin-stimulated glucose storage and HGP suppressibility are not dependent on concomitant lipid oxidation; in the case of HGP we provide evidence for pivotal involvement of G-6-Pase and GK in the regulation of HGP by insulin, independent of the glucose source.     

Acute and chronic effects of leptin on glucose utilization in lean mice

Experiments described here show that in vivo glucose uptake is impaired in mice given 30 micrograms leptin by intraperitoneal injection 2 hours before an oral glucose tolerance test (GTT). When mice were infused for 7 days with 10 micrograms/day leptin, the 4-fold increase in circulating leptin caused a transient hypophagia, a sustained weight loss and significantly inhibited insulin release in response to an oral GTT. Adipocytes from these mice were not insulin responsive whereas insulin-stimulated muscle and liver glycogen synthesis were increased. In contrast, leptin added to 2 hour in vitro incubations had an insulin-like effect on muscle glucose utilization and augmented insulin stimulation of adipocyte lipid synthesis. Thus, normal mice treated chronically with leptin develop tissue specific changes in insulin sensitivity and compensate for inhibition of glucose-stimulated insulin release. The contrasting response to acute leptin exposure suggests these changes are not a direct effect of the protein.     

Obese gene expression: reduction by fasting and stimulation by insulin and glucose in lean mice, and persistent elevation in acquired (diet-induced) and genetic (yellow agouti) obesity

Mutations in the obese (ob) gene lead to obesity. This gene has been recently cloned, but the factors regulating its expression have not been elucidated. To address the regulation of the ob gene with regard to body weight and nutritional factors, Northern blot analysis was used to assess ob mRNA in adipose tissue from mice [lean, obese due to diet, or genetically (yellow agouti) obese] under different nutritional conditions. ob mRNA was elevated in both forms of obesity, compared to lean controls, correlated with elevations in plasma insulin and body weight, but not plasma glucose. In lean C57BL/6J mice, but not in mice with diet-induced obesity, ob mRNA decreased after a 48-hr fast. Similarly, in lean C57BL/6J controls, but not in obese yellow mice, i.p. glucose injection significantly increased ob mRNA. For up to 30 min after glucose injection, ob mRNA in lean mice significantly correlated with plasma glucose, but not with plasma insulin. In a separate study with only lean mice, ob mRNA was inhibited >90% by fasting, and elevated approximately 2-fold 30 min after i.p. injection of either glucose or insulin. These results suggest that in lean animals glucose and insulin enhance ob gene expression. In contrast to our results in lean mice, in obese animals ob mRNA is elevated and relatively insensitive to nutritional state, possibly due to chronic exposure to elevated plasma insulin and/or glucose.     

Effects of antihypertensive drugs on blood pressure and metabolic alterations in the fructose-induced hypertensive rat

Fructose feeding induces a moderate increase in blood pressure (BP) levels in normal rats, which is associated with insulin resistance, hyperinsulinemia, and hypertriglyceridemia. Increased vascular resistances in skeletal muscle have been proposed to contribute to BP elevation and insulin resistance in this animal model. To further explore the mechanisms underlying the fructose-induced hypertension in rats, the effects of quinapril and diltiazem on BP, renal function, plasma levels of glucose, insulin, and triglycerides, and insulin resistance were studied. Male Sprague-Dawley rats were fed for 4 weeks with diets containing 60% fructose or 60% starch and received quinapril or diltiazem in the drinking water. Fructose-fed rats showed higher BP and plasma levels of insulin and triglycerides when compared to controls. Treatments with quinapril or diltiazem prevented BP elevation and reduced elevated plasma insulin levels in fructose-fed rats. Plasma glucose and insulin levels were higher (P < .05) in fructose-fed rats than in controls at 15, 30, and 60 min after oral glucose load. Treatments with either quinapril or diltiazem prevented the exaggerated plasma insulin and glucose levels in response to oral glucose load in fructose-fed rats. In summary, both quinapril and diltiazem were able to prevent BP elevation levels in the fructose-fed rat, and reduced the exaggerated response to an oral glucose tolerance test in these animals.     

Decreased basal, noninsulin-stimulated glucose uptake and metabolism by skeletal soleus muscle isolated from obese-hyperglycemic (ob/ob) mice

Insulin resistance of diaphragms of ob/ob mice has been repeatedly demonstrated previously both in vitro and in vivo. In the present study, transport and metabolism of glucose with and without insulin stimulation were compared in a skeletal muscle more likely than diaphragm or heart to be representative of the overall striated muscle mass, i.e. isolated soleus muscle. Compared with soleus muscle from lean controls, unstimulated lactate release in the presence of exogenous glucose was depressed from 16.2 to 12.3 nmol/60 min per mg wet wt in soleus from ob/ob mutants; glycolysis was decreased from 6.6 to 3.7 and [14C]glucose oxidation to 14CO2 from 0.90 to 0.33 nmol glucose/60 min per mg wet wt. Uptake of 2-deoxyglucose (2-DOG), both with and without insulin, was very much less for soleus from ob/ob than from lean mice, at 2-DOG concentrations ranging from 0.1 to 10 mM, and in mice of 6-15 wk. When 2-DOG concentration was 1 mM, its basal uptake was 0.53 nmol/30 min per mg wet wt for soleus of ob/ob as against 0.96 for soleus of lean mice. The absolute increment due to 1 mU/ml insulin was 0.49 in muscle of ob/ob as against 1.21 in that of lean mice. When the resistance to insulin action was decreased by pretreatment in vivo by either streptozotocin injection or fasting, the decreased basal 2-DOG uptake of subsequently isolated soleus muscle was not improved. Inhibition of endogenous oxidation of fatty acids by 2-bromostearate, while greatly increasing 14CO2 production from [14C]glucose, did not affect basal [5-3H]glucose metabolism or 2-DOG uptake. It is suggested that transport and/or phosphorylation of glucose under basal, unstimulated conditions are depressed in soleus muscle of ob/ob mice, whether or not resistance to insulin and hyperinsulinemia are also present. Although the origin of the decreased basal glucose uptake remains unknown it might be related to a similar decrease in basal glucose uptake by ventromedial hypothalamic cells, an event presumably resulting in a tendency to hyperphagia. Decreased basal glucose uptake by soleus muscle of ob/ob mice might explain the hyperglycemia, and hence partly the hyperinsulinemia and excessive fat deposition of those animals.     

Characterization of cellular defects of insulin action in type 2 (non-insulin-dependent) diabetes mellitus

Seven non-insulin-dependent diabetes mellitus (NIDDM) patients participated in three clamp studies performed with [3-3H]- and [U-14C]glucose and indirect calorimetry: study I, euglycemic (5.2 +/- 0.1 mM) insulin (269 +/- 39 pM) clamp; study II, hyperglycemic (14.9 +/- 1.2 mM) insulin (259 +/- 19 pM) clamp; study III, euglycemic (5.5 +/- 0.3 mM) hyperinsulinemic (1650 +/- 529 pM) clamp. Seven control subjects received a euglycemic (5.1 +/- 0.2 mM) insulin (258 +/- 24 pM) clamp. Glycolysis and glucose oxidation were quantitated from the rate of appearance of 3H2O and 14CO2; glycogen synthesis was calculated as the difference between body glucose disposal and glycolysis. In study I, glucose uptake was decreased by 54% in NIDDM vs. controls. Glycolysis, glycogen synthesis, and glucose oxidation were reduced in NIDDM patients (P < 0.05-0.001). Nonoxidative glycolysis and lipid oxidation were higher. In studies II and III, glucose uptake in NIDDM was equal to controls (40.7 +/- 2.1 and 40.7 +/- 1.7 mumol/min.kg fat-free mass, respectively). In study II, glycolysis, but not glucose oxidation, was normal (P < 0.01 vs. controls). Nonoxidative glycolysis remained higher (P < 0.05). Glycogen deposition increased (P < 0.05 vs. study I), and lipid oxidation remained higher (P < 0.01). In study III, hyperinsulinemia normalized glycogen formation, glycolysis, and lipid oxidation but did not normalize the elevated nonoxidative glycolysis or the decreased glucose oxidation. Lipid oxidation and glycolysis (r = -0.65; P < 0.01), and glucose oxidation (r = -0.75; P < 0.01) were inversely correlated. In conclusion, in NIDDM: (a) insulin resistance involves glycolysis, glycogen synthesis, and glucose oxidation; (b) hyperglycemia and hyperinsulinemia can normalize total body glucose uptake; (c) marked hyperinsulinemia normalizes glycogen synthesis and total flux through glycolysis, but does not restore a normal distribution between oxidation and nonoxidative glycolysis; (d) hyperglycemia cannot overcome the defects in glucose oxidation and nonoxidative glycolysis; (e) lipid oxidation is elevated and is suppressed only with hyperinsulinemia.     

The effect of chromium III on the intravenous glucose tolerance of rats given diets of different protein values

The effect of chromium administration on glucose utilization was investigated in 32 rats fed either high or low protein diet. In rats fed a low protein diet of NDpE% 4.3 the glucose removal rate increased significantly following the administration of chromium. However, the administration of chromium has no effect on the glucose removal rate in rats fed high protein diet of NDpE% 10.1. The glucose removal rate of rats kept on a diet of high protein value free from chromium was significantly higher than those kept on a low protein diet. Chromium deficiency did not appear to be the only responsible cause for the impaired glucose tolerance in animals fed low protein diet. It could be concluded that both chromium supplementation and protein ingestion promote insulin secretion.     

Interaction between BTBR and C57BL/6J genomes produces an insulin resistance syndrome in (BTBR x C57BL/6J) F1 mice

Insulin resistance is a common syndrome that often precedes the development of noninsulin-dependent diabetes mellitus (NIDDM). Both diet and genetic factors are associated with insulin resistance. BTBR and C57BL/6J (B6) mice have normal insulin responsiveness and normal fasting plasma insulin levels. However, a cross between these two strains yielded male offspring with severe insulin resistance. Surprisingly, on a basal diet (6.5% fat), the insulin resistance was not associated with fasting hyperinsulinemia. However, a 15% fat diet produced significant hyperinsulinemia in the male mice (twofold at 10 weeks; P < .05). At 10 weeks of age, visceral fat contributed approximately 4.3% of the total body weight in the males versus 1.8% in females. In the males, levels of plasma triacylglycerol and total cholesterol increased 40% and 30%, respectively, compared to females. Plasma free fatty acid concentrations were unchanged. Oral glucose tolerance tests revealed significant levels of hyperglycemia and hyperinsulinemia 15 to 90 minutes after oral glucose administration in the male mice. This was particularly dramatic in males on a 15% fat diet. Glucose transport was examined in skeletal muscles in (BTBR x B6)F1 mice. In the nonhyperinsulinemic animals (females), insulin stimulated 2-deoxyglucose transport 3.5-fold in the soleus and 2.8-fold in the extensor digitorum longus muscles. By contrast, glucose transport was not stimulated in the hyperinsulinemic male mice. Hypoxia stimulates glucose transport through an insulin-independent mechanism. This is known to involve the translocation of GLUT4 from an intracellular pool to the plasma membrane. In the insulin-resistant male mice, hypoxia induced glucose transport as effectively as it did in the insulin-responsive mice. Thus, defective glucose transport in the (BTBR x B6)F1 mice is specific for insulin-stimulated glucose transport. This is similar to what has been observed in muscles taken from obese NIDDM patients. These animals represent an excellent genetic model for studying insulin resistance and investigating the transition from insulin resistance in the absence of hyperinsulinemia to insulin resistance with hyperinsulinemia.     

Effect of creatine phosphate on the contractile activity in acutely failing rat heart

The hypothesis was tested that infusion of a solution containing creatine phosphate (CP) into rats with acutely failing hearts would enhance recovery of cardiac function. The acutely failing heart was produced by constricting the ascending aorta. This overload produced failure in approximately 25 min. At the point of failure the constriction was removed and solutions containing sterile physiological saline (PSS), PSS and CP, PSS and creatine, or PSS and creatine plus phosphate were infused. Cardiac function was assessed from systolic and diastolic blood pressure, +/- dp/dt, heart rate, and cardiac work. Ca2+ uptake by isolated sarcoplasmic reticulum and the concentrations of selected blood and tissue metabolites were measured. Normal cardiac function was restored in the PSS-CP infused rats whereas all other treatments did not restore cardiac function. Adenosine triphosphate and CP had declined in the myocardium of the failing hearts while lactate was elevated. The concentrations of these metabolites were normal in the PSS-CP infused animals. The glycogen concentration in the myocardium was reduced following the constriction. Ca2+ uptake by isolated sarcoplasmic reticulum was depressed in the failed hearts but normal in the hearts of CP-infused animals. These results demonstrate that the infusion of CP into animals with failing hearts can be effective in restoring cardiac function.     

Decreased insulin action on muscle glucose transport after eccentric contractions in rats

We have recently shown that eccentric contractions (Ecc) of rat calf muscles cause muscle damage and decreased glycogen and glucose transporter GLUT-4 protein content in the white (WG) and red gastrocnemius (RG) but not in the soleus (S) (S. Asp, S. Kristiansen, and E. A. Richter. J. Appl. Physiol. 79: 1338-1345, 1995). To study whether these changes affect insulin action, hindlimbs were perfused at three different insulin concentrations (0, 200, and 20,000 microU/ml) 2 days after one-legged eccentric contractions of the calf muscles. Compared with control, basal glucose transport was slightly higher (P < 0.05) in Ecc-WG and -RG, whereas it was lower (P < 0.05) at both submaximal and maximal insulin concentrations in the Ecc-WG and at maximal concentrations in the Ecc-RG. In the Ecc-S, the glucose transport was unchanged in hindquarters perfused in the absence or presence of a submaximal stimulating concentration of insulin, whereas it was slightly (P < 0.05) higher during maximal insulin stimulation compared with control S. At the end of perfusion the glycogen concentrations were lower in both Ecc-gastrocnemius muscles compared with control muscles at all insulin concentrations. Fractional velocity of glycogen synthase increased similarly with increasing insulin concentrations in Ecc- and control WG and RG. We conclude that insulin action on glucose transport but not glycogen synthase activity is impaired in perfused muscle exposed to prior eccentric contractions.     

Anti-obesity and anti-diabetic effects of CL 316,243, a highly specific beta 3-adrenoceptor agonist, in yellow KK mice

The anti-obesity and anti-diabetic effects of CL 316,243, a highly specific beta 3-adrenoceptor agonist (beta 1: beta 2: beta 3 = 0:1:100,000), were evaluated in obese diabetic yellow KK mice and C57Bl control mice. The study compound was fed through a gastric tube at a rate of 0.1 mg/kg/day for 2 weeks. The following parameters were compared in the treated and control animals given distilled water: brown adipose tissue thermogenesis, resting metabolic rate, insulin receptors in adipocytes, and blood glucose and serum insulin levels during a glucose overloading test. CL 316,243 significantly increased brown adipose tissue thermogenesis and resting metabolic rate in both yellow KK mice and C57Bl controls. The amount of white adipose tissue decreased, although food intake was not affected. The effects contributed to the mitigation of obesity in yellow KK mice. CL 316,243 also increased the concentration of insulin receptors and decreased the levels of serum insulin and blood glucose during the glucose overloading test in yellow KK mice. These observations suggest that CL 316,243 possesses anti-obesity and anti-diabetic effects and consequently may be useful for treating obesity as well as non-insulin-dependent diabetes mellitus in obese persons, without causing excessive side effects.     

Long-term normalization of GLUT 4 protein content in skeletal muscle of streptozotocin-diabetic Lewis rats after islet transplantation

Islet transplantation under the kidney capsule of STZ-diabetic Lewis rats was able to maintain near-normoglycemia over a period of 6 months. Fasting insulin in these animals was higher compared to controls but did not increase after feeding. Plasma glucose following an OGTT at 2 months was only slightly impaired, and after 6 months was more severely impaired in the Tx rats. An IVGTT 6 months after Tx confirmed impaired glucose tolerance and showed a loss of first phase insulin release. GLUT 4 protein content in skeletal muscle was completely restored in Tx animals. In conclusion, long-term near-normoglycemia after syngeneic islet transplantation under the kidney capsule of STZ-diabetic Lewis rats is associated with complete normalization of skeletal muscle GLUT 4 protein content, even in the presence of abnormal glucose tolerance and impaired insulin secretion.