Biomedical subjects

J Turinsky

Publications and source records attributed to J Turinsky.

At least 19 recordsLinked to original sources

PubMed1999

Akt kinases and 2-deoxyglucose uptake in rat skeletal muscles in vivo: study with insulin and exercise.

Activities of Akt1, Akt2, and Akt3 kinases and glucose uptake in hindlimb muscles of the rat in vivo were investigated. The rats were studied either after intravenous injection of 0.1 U of insulin or during exercise induced by stimulating calf muscles electrically at 1 contraction/s. Akt kinases were immunoprecipitated from supernatants of muscle homogenates. Glucose uptake by muscles in vivo was assessed by cellular accumulation of 2-deoxy-D-[1, 2-3H(N)]glucose. Administration of insulin resulted in rapid activation of Akt1 kinase, with peak activity observed 5 min after insulin injection. Soleus muscle, a slow-twitch muscle, and plantaris muscle, a fast-twitch muscle, differed in their content of Akt1 kinase and in their response to insulin. Soleus muscle exhibited a 105% higher abundance of Akt1 kinase, a 101% higher insulin-stimulated activity of Akt1 kinase, and 83% higher insulin-stimulated 2-deoxyglucose uptake compared with plantaris muscle. Additionally, insulin administration increased the activities of Akt1, Akt2, and Akt3 kinases in calf muscles and caused a sevenfold augmentation in 2-deoxyglucose uptake by these muscles. In contrast, the exercised calf muscles exhibited an increase in Akt1 kinase activity at 5, 15, and 25 min of exercise but no change in activities of Akt2 and Akt3 isoforms, and the 2-deoxyglucose uptake by calf muscles exercised for 25 min was 11-fold higher compared with muscles of resting rats. The data demonstrate that 1) there is a close, direct correlation between the magnitude of insulin-stimulated activity of Akt1 kinase and the level of glucose uptake in muscles with different fiber populations, 2) insulin activates three isoforms of Akt kinase in skeletal muscle, and 3) exercise in vivo is associated with activation of Akt1 but not Akt2 and Akt3 kinases in contracting muscles.

Animals↗

PubMed1998

Blood flow and glucose uptake in denervated, insulin-resistant muscles.

To investigate whether changes in blood flow contribute to the insulin resistance in denervated muscles, basal and insulin-stimulated 2-deoxy-D-glucose (2-DG) uptake in vivo and blood flow were measured in soleus (slow twitch), plantaris (fast twitch), and gastrocnemius (fast twitch) muscles at 1 and 3 days after a right hindlimb denervation in the rat. Muscles of the contralateral sham hindlimb served as an internal control. Sham plantaris and gastrocnemius muscles showed 32 and 60% lower basal 2-DG uptake, 46 and 66% lower insulin-stimulated 2-DG uptake, and 79 and 81% lower blood flow, respectively, compared with sham soleus muscle. At 1 day after denervation, soleus, plantaris, and gastrocnemius muscles exhibited an 80, 64, and 42% decrease in insulin-stimulated 2-DG uptake, respectively, in the presence of 63, 323, and 304% higher blood flow, respectively. At 3 days after denervation, soleus muscle showed a 60% decrease in basal 2-DG uptake, complete unresponsiveness to insulin, and an 86% decrease in blood flow. In contrast, the denervated plantaris and gastrocnemius muscles exhibited a 262 and 105% increase in basal 2-DG uptake, respectively, no change in insulin-stimulated 2-DG uptake, and no change in blood flow compared with corresponding contralateral sham muscles. The results demonstrate that muscle blood flow is influenced by muscle fiber population and time after denervation and that changes in blood flow do not contribute to the insulin resistance in the denervated muscles.

Animals↗

PubMed1998

Sphingomyelinase has an insulin-like effect on glucose transporter translocation in adipocytes.

Rat epididymal adipocytes were incubated with 0, 0.1, and 1 mU sphingomyelinase/ml for 30 or 60 min, and glucose uptake and GLUT-1 and GLUT-4 translocation were assessed. Adipocytes exposed to 1 mU sphingomyelinase/ml exhibited a 173% increase in glucose uptake. Sphingomyelinase had no effect on the abundance of GLUT-1 in the plasma membrane of adipocytes. In contrast, 1 mU sphingomyelinase/ml increased plasma membrane content of GLUT-4 by 120% and produced a simultaneous decrease in GLUT-4 abundance in the low-density microsomal fraction. Sphingomyelinase had no effect on tyrosine phosphorylation of either the insulin receptor beta-subunit or the insulin receptor substrate-1, a signaling molecule in the insulin signaling pathway. It is concluded that the incubation of adipocytes with sphingomyelinase results in insulin-like translocation of GLUT-4 to the plasma membrane and that this translocation does not occur via the activation of the initial components of the insulin signaling pathway.

Adipocytes↗

PubMed1998

Akt1 kinase and dynamics of insulin resistance in denervated muscles in vivo.

Basal and insulin-stimulated activity of Akt1 kinase and uptake of 2-deoxy-D-glucose (2-DG) were measured in soleus (slow-twitch) and plantaris (fast-twitch) muscles of rats at 1 and 3 days after sectioning the sciatic nerve in one hindlimb of the animals. At 1 day after surgery, the insulin-stimulated activity of Akt1 kinase in denervated soleus and plantaris muscles remained unchanged, but the insulin-stimulated 2-DG uptake by these muscles was reduced by 71 and 61%, respectively, compared with the corresponding muscles of the contralateral sham (control) hindlimb. At 3 days, the insulin-stimulated activity of Akt1 kinase in the denervated soleus and plantaris muscles was 86 and 71% lower, respectively, than in their sham counterparts. At this time point, the denervated soleus muscles showed no increase in 2-DG uptake in response to insulin. In contrast, the denervated plantaris muscle exhibited the same absolute level of insulin-stimulated 2-DG uptake as the sham plantaris muscle; however, the insulin-induced increment in 2-DG uptake was reduced by 60%, whereas basal 2-DG uptake was increased by 251% compared with the sham plantaris muscle. None of the denervated muscles showed a decrease in the abundance of Akt1 kinase. The results demonstrate that the causes of insulin resistance in denervated muscles are dependent on time after surgery. Initially, they involve only mechanisms downstream of Akt1 kinase (day 1), whereas at day 3 they also involve mechanisms upstream of, and including, Akt1 kinase.

Animals↗

PubMed1997

Phosphatidylinositol 3-kinase and dynamics of insulin resistance in denervated slow and fast muscles in vivo.

Regulation of glucose uptake by 1- and 3-day denervated soleus (slow-twitch) and plantaris (fast-twitch) muscles in vivo was investigated. One day after denervation, soleus and plantaris muscles exhibited 62 and 65% decreases in insulin-stimulated 2-deoxyglucose uptake, respectively, compared with corresponding control muscles. At this interval, denervated muscles showed no alterations in insulin receptor binding and activity, amount and activity of phosphatidylinositol 3-kinase, and amounts of GLUT-1 and GLUT-4. Three days after denervation, there was no increase in 2-deoxyglucose uptake in response to insulin in soleus muscle, whereas plantaris muscle exhibited a 158% increase in basal and an almost normal absolute increment in insulin-stimulated uptake. Despite these differences, denervated soleus and plantaris muscles exhibited comparable decreases in insulin-stimulated activities of the insulin receptor (approximately 40%) and phosphatidylinositol 3-kinase (approximately 50%) and a pronounced decrease in GLUT-4. An increase in GLUT-1 in plantaris, but not soleus, muscle 3 days after denervation is consistent with augmented basal 2-deoxyglucose uptake in plantaris muscle at this interval. These results demonstrate that, in denervated muscles, there is a clear dissociation between insulin-stimulated 2-deoxyglucose uptake and upstream events involved in insulin-stimulated glucose uptake.

Animals↗

PubMed1997

Growth hormone-induced insulin resistance: role of the insulin receptor, IRS-1, GLUT-1, and GLUT-4.

Treatment of rats with growth hormone (GH; 1 mg/kg sc) twice daily over 2.5 days did not alter fasting plasma glucose or glucose tolerance but increased fasting plasma insulin levels 65% and peak insulin response to a glucose load 35% over controls, indicating the development of insulin resistance. Studies on partially purified insulin receptors from soleus muscles showed that GH increased the abundance of insulin receptor beta-subunits by 48% as measured by immunoblotting. Despite this increase, GH abolished the increase in autophosphorylation of the insulin receptor beta-subunit in response to physiological hyperinsulinemia and diminished by 28% the response to supraphysiological hyperinsulinemia. Similarly, insulin-stimulated phosphorylation of insulin receptor substrate-1 (IRS-1) was decreased 25% by GH, but the abundance of IRS-1 was not affected. Studies on rats pretreated with streptozotocin suggested that the effects of GH are direct and not secondary to GH-induced hyperinsulinemia. GH decreased basal GLUT-1 abundance in the low-density microsome and plasma membrane fractions of epididymal adipocytes by 50 and 42%, respectively, but decreased basal GLUT-4 abundance only in the low-density microsome fraction by 24%. Despite these alterations, the abundance of both transporters in the plasma membrane fraction of adipocytes incubated with 0.1 U insulin/ml was not diminished by GH.

Adipocytes↗

PubMed1997

Effect of monensin on 2-deoxyglucose uptake, the insulin receptor and phosphatidylinositol 3-kinase activity in rat muscle.

Preincubation of rat soleus muscle with 1 and 10 microM monensin for 2 h increased the subsequent basal 2-deoxyglucose uptake by muscle 76 and 121% respectively. Under the same conditions, monensin decreased the insulin-stimulated (1 mU/ml) 2-deoxyglucose uptake by 29 and 37% respectively. The monensin-induced augmentation of basal 2-deoxyglucose uptake was inhibited 92% by cytochalasin B suggesting that the uptake is mediated by glucose transporters. Monensin did not increase the cellular accumulation of L-glucose in muscle indicating that it does not affect the cell membrane integrity. Neither the stimulatory effect of monensin on basal 2-deoxyglucose uptake nor the opposite, inhibitory action of monensin on the insulin-stimulated 2-deoxyglucose uptake were influenced by the removal of Ca2+ from the medium or by dantrolene, an inhibitor of Ca2+ release from the sarcoplasmic reticulum, suggesting that the actions of monensin are not mediated by calcium. Monensin had no effect on muscle ATP concentration. The monensin-induced augmentation of basal 2-deoxyglucose uptake was neither associated with stimulation of muscle phosphatidylinositol 3-kinase activity nor inhibited by wortmannin, demonstrating that the increase in basal 2-deoxyglucose uptake is not mediated by activation of phosphatidylinositol 3-kinase. The inhibition of insulin-stimulated 2-deoxyglucose uptake by monensin was associated with a 31% decrease in the abundance of insulin receptors in muscles, a 64% decrease in the insulin-induced autophosphorylation of the insulin receptor beta-subunit, and a 44% reduction of the insulin-stimulated phosphatidylinositol 3-kinase activity. Addition of monensin into the phosphatidylinositol 3-kinase reaction had no effect on the activity of the enzyme, demonstrating that the inhibition in monensin-treated muscles is indirect and occurs upstream of phosphatidylinositol 3-kinase. It is concluded that monensin has a dual effect on 2-deoxyglucose uptake by skeletal muscle: it stimulates basal uptake but inhibits the insulin-stimulated uptake. The primary cause of the latter, inhibitory effect of monensin is at the level of the insulin receptor.

Adenosine Triphosphate↗

PubMed1996

Sphingomyelinase stimulates 2-deoxyglucose uptake by skeletal muscle.

The effects of sphingomyelinase, phosphorylcholine, N-acetylsphingosine (C2-ceramide), N-hexanoylsphingosine (C6-ceramide) and sphingosine on basal and insulin-stimulated cellular accumulation of 2-deoxy-D-glucose in rat soleus muscles were investigated. Preincubation of muscles with sphingomyelinase (100 or 200 m-units/ml) for 1 or 2 h augmented basal 2-deoxyglucose uptake by 29-91%, and that at 0.1 and 1.0 m-unit of insulin/ml 32-82% and 19-25% respectively compared with control muscles studied at the same insulin concentrations. The sphingomyelinase-induced increase in basal and insulin-stimulated 2-deoxyglucose uptake was inhibited by 91% by 70 microM cytochalasin B, suggesting that it involves glucose transporters. Sphingomyelinase had no effect on the cellular accumulation of L-glucose, which is not transported by glucose transporters. The sphingomyelinase-induced increase in 2-deoxyglucose uptake could not be reproduced by preincubating the muscles with 50 microM phosphorylcholine, 50 microM C2-ceramide or 50 microM C6-ceramide. Preincubation of muscles with 50 microM sphingosine augmented basal 2-deoxyglucose transport by 32%, but reduced the response to 0.1 and 1.0 m-unit of insulin/ml by 17 and 27% respectively. The stimulatory effect of sphingomyelinase on basal and insulin-induced 2-deoxyglucose uptake was not influenced by either removal of Ca2+ from the incubation medium or dantrolene, an inhibitor of Ca2+ release from the sarcoplasmic reticulum. This demonstrates that Ca2+ does not mediate the action of sphingomyelinase on 2-deoxyglucose uptake. Sphingomyelinase also had no effect on basal and insulin-stimulated activities of insulin receptor tyrosine kinase and phosphatidylinositol 3-kinase. In addition, 1 and 5 microM wortmannin, an inhibitor of phosphatidylinositol 3-kinase, failed to inhibit the sphingomyelinase-induced increase in 2-deoxyglucose uptake. These results suggest that sphingomyelinase does not increase 2-deoxyglucose uptake by stimulating the insulin receptor or the initial steps of the insulin-transduction pathway. The data suggest the possibility that sphingomyelinase increases basal and insulin-stimulated 2-deoxyglucose uptake in skeletal muscle as the result of an unknown post-receptor effect.

Androstadienes↗

PubMed1995

Insulin-stimulated phosphatidylinositol 3-kinase activity and 2-deoxy-D-glucose uptake in rat skeletal muscles.

To date there is suggestive evidence that phosphatidylinositol 3-kinase participates in insulin-stimulated glucose transport. However, its involvement in skeletal muscle, a major site of insulin-stimulated glucose disposal, has not been addressed. Therefore, we tested the effects of wortmannin, a known inhibitor of phosphatidylinositol 3-kinase, on insulin-stimulated 2-deoxyglucose uptake by rat soleus muscle in vitro: Wortmannin (1 microM) reversibly inhibited insulin-induced 2-deoxyglucose uptake in soleus muscle by 44%. Inclusion of 5 microM wortmannin in the incubation medium completely abolished the insulin-induced increment in 2-deoxyglucose uptake. In conclusion, the insulin-signaling cascade linking insulin-receptor tyrosine kinase activation to glucose uptake in skeletal muscle.

Androstadienes↗

PubMed1992

Effect of sphingoid bases on basal and insulin-stimulated 2-deoxyglucose transport in skeletal muscle.

Incubation of rat soleus muscles with 50 microM sphingosine or 50 microM sphinganine augmented basal 2-deoxy-D-glucose (2DG) transport 32%, but reduced the response to 0.1 and 1.0 mU insulin/ml by 17 and 27%, respectively. When the muscles were incubated with 50 microM phytosphingosine, a 63-93% increase in basal 2DG transport was observed. However, this treatment had no effect on insulin-stimulated 2DG transport. The phytosphingosine-induced increase in basal 2-DG transport was inhibited 93 and 98% with 35 and 70 microM cytochalasin B, respectively, suggesting that it is mediated by glucose transporters. Cellular accumulation of L-glucose, which is not mediated by glucose transporters, was not affected by phytosphingosine. It is concluded that (a) both sphingosine and sphinganine increase basal 2DG transport in muscle but diminish insulin-stimulated transport, and (b) phytosphingosine stimulates basal 2DG transport in muscle by a mechanism involving glucose transporters.

Animals↗

PubMed1992

Modulation of prostaglandin E2 synthesis in rat skeletal muscle.

The effect of muscle denervation, inhibitors of protein synthesis, G proteins, and sphingolipids on prostaglandin E2 (PGE2) release by rat soleus muscle in vitro was investigated. To assess the effect of muscle denervation, the sciatic nerve in one hindlimb of rats was interrupted, and soleus muscles from the denervated hindlimb and the contralateral sham (control) hindlimb were excised 1-5 days after surgery. Compared with corresponding sham muscles, PGE2 release by denervated muscles was increased 56, 230, and 435% at 1, 3, and 5 days after denervation, respectively. Protein synthesis inhibitors cycloheximide (10 microM) and puromycin (10 microM) lowered PGE2 release by sham and denervated muscles 62-80%. The release of PGE2 by sham and denervated muscles was not altered by pertussis toxin (1 microgram/ml) but was inhibited 30-51% by AlF4-. Addition of 100 microM guanosine 5'-O-(3-thiotriphosphate) to saponin-permeabilized sham and denervated muscles had only a moderate, if any, stimulatory effect on PGE2 release. This effect was not counteracted by 1 mM guanosine 5'-O-(2-thiodiphosphate). Increasing muscle ceramide concentration by incubation with sphingomyelinase (100 mU/ml) increased PGE2 release by sham and denervated muscles 43 and 157%, respectively. Because degradation of ceramides yields sphingosine, the effect of sphingosine was also tested. Sphingosine (25 microM) increased PGE2 release by sham and denervated muscles 139 and 187%, respectively, without affecting muscle viability, as assessed by the release of lactate dehydrogenase. The data indicate that muscle denervation, treatment with sphingomyelinase, and sphingosine stimulate, whereas inhibitors of protein synthesis inhibit PGE2 synthesis by muscle.

Aluminum↗

PubMed1991

1,2-Diacylglycerol and ceramide levels in rat liver and skeletal muscle in vivo.

1,2-Diacylglycerol and ceramide levels were measured in liver and skeletal muscle of rats under the following four experimental conditions: 1) during rapid fetal growth in the second half of gestation and during postnatal aging, 2) during tissue anoxia lasting up to 10 min, 3) during fasting for up to 6 days, and 4) during stress induced by injection of endotoxin (lipopolysaccharide from Salmonella enteritidis). 1,2-Diacylglycerol and ceramide levels in fetal liver were 77 and 58% lower, respectively, than those of young rats after weaning. 1,2-Diacylglycerol and ceramide concentrations in liver of postnatal rats were not influenced by aging. Anoxia produced a 41-64% increase in liver 1,2-diacylglycerol levels and a 9-21% increase in liver ceramides. Fasting of adult rats for up to 6 days had no effect on 1,2-diacylglycerol and ceramide levels in liver. However, fasting increased skeletal muscle concentrations of 1,2-diacylglycerol and ceramides 88 and 44%, respectively. Injection of endotoxin had a biphasic effect on liver 1,2-diacylglycerol levels, causing a transient 52% increase at 1 h, followed by a 24-38% decrease below the control level at 17 h after endotoxin administration. Liver ceramide levels were increased 66, 52, and 27% at 1, 3, and 5 h after endotoxin, respectively, but did not differ from control at 17 h after injection. Endotoxin had no effect on muscle 1,2-diacylglycerol and ceramide concentrations at any interval.

Aging↗

PubMed1990

1,2-Diacylglycerol and ceramide levels in insulin-resistant tissues of the rat in vivo.

Phorbol esters have been reported to decrease sensitivity or responsiveness to insulin in cells in vitro. Since phorbol esters are analogues of endogenously produced 1,2-diacylglycerol, the present study investigated whether 1,2-diacylglycerol concentration is elevated in insulin-resistant tissues of the rat in vivo. Studies were done on 11-12-week-old genetically obese Zucker rats, which are insulin-resistant. Lean Zucker rats served as controls. Levels of 1,2-diacylglycerol in obese rats were increased 82% in liver, 136% in calf muscles, 72% in soleus muscle, a slow-twitch muscle, and 40% in plantaris muscle, a fast-twitch muscle. Ceramide levels in the same tissues were increased 26, 52, 69, and 13%, respectively. Studies were also done on normal, non-obese Sprague-Dawley rats 3 h, 1, 3, 8, and 15 days after interrupting the nerve supply to hindlimb muscles. We have previously shown that 3-17 days after denervation, soleus muscles are completely unresponsive to insulin and do not increase glucose uptake in response to insulin stimulation in vivo, whereas plantaris muscles show a normal glucose uptake when stimulated by insulin; however, the insulin-induced increment in glucose uptake is reduced 68% because it is superimposed on already elevated basal glucose uptake (Turinsky, J. (1987) Am. J. Physiol. 252, R531-R537). In the present study, the denervated soleus muscles exhibited a sustained increase of 23-56% in 1,2-diacylglycerol concentration between 3 h and 15 days after interruption of nerve supply. The denervated soleus muscles also showed 34 and 42% increases in ceramide concentration at 3 and 8 days after denervation, respectively. In contrast, no increases in 1,2-diacylglycerol concentration were observed in plantaris muscles at shorter intervals than 15 days after denervation. Ceramide concentrations in plantaris muscles were increased 43 and 75% at 8 and 15 days after denervation, respectively. These observations demonstrate that tissue insulin resistance is frequently associated with a long term increase in tissue 1,2-diacylglycerol concentration. This suggests the possibility that augmented 1,2-diacylglycerol levels contribute to the development of some types of tissue insulin resistance.

Animals↗

PubMed1990

1,2-Diacylglycerol and ceramide levels in rat skeletal muscle and liver in vivo. Studies with insulin, exercise, muscle denervation, and vasopressin.

Studies on BC3H-1 myocytes suggest that the insulin-induced increase in cellular diacylglycerol level mediates the insulin-stimulated glucose transport in these cells (Standaert, M. L., Farese, R. V., Cooper, D. R., and Pollet, R. J. (1988) J. Biol. Chem. 263, 8696-8705). The present study tested whether diacylglycerol could mediate the insulin-induced and exercise-induced increases in glucose uptake by rat skeletal muscle in vivo. Glucose uptake by calf muscles of the rat was assessed by measuring cellular 2-deoxyglucose uptake in vivo. Diacylglycerol and ceramides in muscles frozen in situ were assayed with diacylglycerol kinase. Intravenous injection of 0.1 unit of insulin/rat resulted in a 6-fold increase in muscle 2-deoxyglucose uptake during the subsequent 25-min period. In contrast, no statistically significant changes in muscle diacylglycerol or ceramide levels were observed at 2, 5, 10, and 25 min after insulin injection. When calf muscles of the hindlimb were exercised in vivo for 25 min by electrical stimulation inducing one contraction/s, 2-deoxyglucose uptake by muscles was increased 15-fold. However, no statistically significant changes in muscle diacylglycerol or ceramide content were observed at 5, 10, 15, and 25 min of exercise. Although the findings do not exclude the possibility of a compartmentalized increase in diacylglycerol level, the present data suggest that diacylglycerol is not a mediator of the insulin-induced or exercise-induced augmentation of glucose uptake by skeletal muscle in vivo. Since interruption of nerve supply to the muscles makes the muscles insulin resistant (Turinsky, J., (1987) Am. J. Physiol. 252, R531-R537), the effect of denervation on diacylglycerol and ceramide levels in calf muscles of the rat was also examined. The denervation resulted in 21, 51, and 117% increases in muscle diacylglycerol levels at 3, 16, and 32 days after denervation, respectively. No statistically significant changes in muscle ceramide levels were observed at any postdenervation interval. Finally, the measured lipids were studied in muscles and livers of rats infused with supraphysiological doses of vasopressin (86 pmol/min). In controls, diacylglycerol concentrations of the muscles and liver did not significantly differ, but the liver exhibited a 5-fold higher level of ceramides than the muscles. Infusion of vasopressin for 5 min did not have a statistically significant effect on diacylglycerol concentration of the liver but continuation of the same infusion for 10 min resulted in a 63% increase in liver diacylglycerol. The 10-min infusion had no effect on muscle diacylglycerol concentration or ceramide levels in any of the tissues studied.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

Free amino acids in muscle: effect of muscle fiber population and denervation.

One hindlimb of each rat was denervated by sectioning the sciatic nerve. Three days later, soleus, plantaris, and gastrocnemius muscles of the sham hindlimb and the contralateral denervated hindlimb were excised and analyzed for intracellular concentrations of 23 free amino acids and the dipeptides carnosine and anserine. Compared with the sham soleus (slow-twitch) muscle, the sham plantaris and gastrocnemius (fast-twitch) muscles showed 57-81% lower concentrations of histidine, glutamine, glutamate, aspartate, and serine and also 32-78% lower levels of taurine, citrulline, phosphoserine, and ornithine. On the other hand the fast-twitch muscles exhibited 31% higher concentrations of free glycine and alanine and 113-127% higher levels of carnosine and anserine than the soleus muscle. The denervation caused greater changes in soleus muscle than in the other two muscles. The denervation-induced changes in soleus muscle included 38-87% increases in concentrations of free valine, leucine, isoleucine, and glutamate associated with 21-56% decreases in the levels of glutamine, glycine, aspartate, serine, alanine, and citrulline. It is concluded that both muscle fiber population and muscle denervation have an independent effect on the intracellular concentrations of free amino acids in muscles.

Amino Acids↗

PubMed1987

Dynamics of insulin resistance in denervated slow and fast muscles in vivo.

Sciatic nerve in one hindlimb of rats was sectioned, and animals were investigated 3, 6, 9, and 24 h and 3, 8, and 17 days after surgery. Cellular uptakes of 2-deoxy-D-glucose (DG) and alpha-aminoisobutyric acid (AIB) by soleus, plantaris, and gastrocnemius muscles of the denervated and contralateral sham hindlimb were compared in vivo. Effects of insulin on DG and AIB uptakes by soleus and plantaris muscles, but not gastrocnemius muscles, were reduced 20-58% as early as 3-6 h after denervation. Three to 17 days after denervation, soleus muscle did not respond to insulin stimulation of DG uptake, whereas plantaris and gastrocnemius muscles responded, but the insulin-induced increment in DG uptake was reduced 24-68% compared with the sham muscles. In contrast, none of the denervated muscles increased AIB uptake in response to insulin stimulation 3-17 days after surgery. The levels of creatine phosphate and ATP in calf muscles frozen in situ 3 days after denervation were increased 7 and 9%, respectively, and those of ADP, AMP, glucose-6-phosphate, and lactate were unchanged compared with sham muscles. It is concluded that muscle denervation results in a rapid development of insulin resistance, the effect of denervation depends on muscle fiber population, and insulin resistance of denervated muscles is not due to a cellular energy deficit.

Aminoisobutyric Acids↗

PubMed1987

Glucose and amino acid uptake by exercising muscles in vivo: effect of insulin, fiber population, and denervation.

The first series of experiments was performed on control rats. The animals were injected iv with trace amounts of 2-deoxy-D-[1-14C]glucose [( 14C]DG) or alpha-[1-14C] aminoisobutyric acid with or without 0.1 U insulin/rat, and calf muscles of the right hindlimb were electrically stimulated to induce 1 contraction/sec. The exercise was discontinued 25 min after the injection, and cellular uptakes of DG or aminoisobutyric acid by soleus, plantaris, and gastrocnemius muscles in disintegrations per min/mg dry tissue weight were determined. The results of these experiments demonstrated that basal, insulin-induced, and exercise-induced uptakes of glucose and amino acids by muscles are dependent on muscle fiber population, and the stimulatory effects of exercise and insulin on soleus and plantaris muscles, but not gastrocnemius muscles, are synergistic rather than merely additive when both stimuli act together. The second series of experiments was performed in the same manner as the first series, except that the right hindlimb of each rat was denervated 3 days before the experiment. Cellular DG uptakes were determined in soleus, plantaris, and gastrocnemius muscles of the left (sham) hindlimb, which was always resting, and in corresponding muscles of the right (denervated) limb, which was either resting or exercising. In the resting state, the denervated soleus muscle had normal basal DG uptake, but, unlike sham soleus muscle, did not respond to insulin stimulation. Denervated plantaris and gastrocnemius muscles exhibited 264% and 150% elevations in basal glucose uptake, respectively, compared with corresponding sham muscles. The latter two denervated muscles did respond to insulin, but the hormone-induced increments in DG uptake were 68% and 45%, respectively, lower than in corresponding contralateral sham muscles. Under basal conditions, exercise had no effect on DG uptake by the denervated soleus muscle, but increased uptake by denervated plantaris and gastrocnemius muscles 207% and 778%, respectively. Stimulation of exercising denervated muscles with exogenous insulin did not increase DG uptake by any muscle above the level observed with exercise alone. The results show that manifestations of insulin resistance in denervated muscles depend on muscle fiber population; denervated muscles, which still retain some ability to respond to insulin, increase DG uptake during exercise, whereas such an increase is absent in denervated muscles completely unresponsive to insulin; and exercise does not improve or restore the ability of denervated muscles to respond to insulin.

Aminoisobutyric Acids↗

PubMed1986

Hepatic and skeletal muscle phospholipid metabolism in recovering burned rats.

Liver and soleus muscles of control animals and rats recovering from a single hindlimb scald were analyzed for diphosphatidyl glycerol, phosphatidyl ethanolamine, phosphatidyl choline, sphingomyelin, lysophosphatidyl choline, phosphatidyl inositol, and phosphatidyl serine. Liver of 4-hr postburn rats exhibited decreased contents of diphosphatidyl glycerol (-20%), phosphatidyl ethanolamine (-11%), and phosphatidyl choline (-7%). At 3 days after the burn, only an 11% decrease in hepatic phosphatidyl inositol was observed. Soleus muscle of the unburned limb of burned rats showed at 3 days postburn an 11% decrease in sphingomyelin content but the other measured phospholipids were at control level. In contrast, soleus muscle from the contralateral burned limb exhibited increased contents of sphingomyelin (+29%), lysophosphatidyl choline (+145%), and phosphatidyl serine (+27%) compared to control uninjured animals. It also showed a 25% higher phosphatidyl inositol level than the contralateral uninjured counterpart. It is concluded that recovery from a single hindlimb scald is associated with alterations in phospholipid metabolism in the liver and in the region of the wound. The local response to thermal injury may be mediated, in part, by stimulated activity of phospholipase A2.

Animals↗