This investigation was undertaken to clarify the in vitro effect of the various stimulations, such as exercise (E), insulin (I) direct electrical stimulation (EST) and the combinations of the above, on the glucose incorporation intro glycogen molecules (glycogen synthesis) of the normal slow (soleus) and fast twitch (plantaris) muscles, and the different responses of slow and fast twitch muscles to persistent overloads causing compensatory muscle hypertrophy. In resting state, slow twitch muscle has greater capacity for glycogen synthesis than fast twitch muscle, and responses of different muscle to various stimuli were differ as follows: In slow twitch muscle, the glycogen synthesis was increased by insulin, and electrical stimulation but not increased by exercise; exercise increased insulin sensitivity and the effect of electrical stimulation. Whereas the glycogen synthesis in fast twitch muscle was increased only by the stimuli combined with E and EST, and E, I, and EST. As the result of removal of synergistic muscle, both muscles were hypertrophied, and the degree of hypertrophy in response to persistent overload was higher in fast twitch muscle (182%) than slow twitch muscle (151%). In hypertrophied muscles, glycogen synthesis of soleus in any groups was lower than that of the control, but similar in plantaris. In conclusions, there were marked heterogeneity in different muscle fiber in the effects of exercise and insulin addition and electrical stimulation on muscle glycogen synthesis, and fast twitch muscle may be adapted more easily to that kind of persistent overload than slow twitch muscle.
Electric Stimulation ; Glucose* ; Glycogen* ; Hypertrophy ; In Vitro Techniques* ; Insulin ; Insulin Resistance ; Muscles* ; Population Characteristics

No abstract available.
Animals ; Insulin Resistance ; Insulin ; Rats

The effect of exercise on plasma insulin, free fatty acid, and glucose uptake and glycogen concentration in soleus, and intravenous glucose tolerance of streptozotocin treated, diabetic Sprague-Dawley rats were studied. Diabetic-trained animals were subjected to a regular program of treadmill running for 4 weeks. Seventy-two hours after the last training session, basal and insulin-stimulated glucose uptake was studied in incubated strips (about 20 mg) of soleus muscle in vitro. Glucose tolerance was measured with intravenous infusion of 0.5 g glucose/kg body weight. In diabetic rats, training was associated with increase glucose uptake in basal and maximal insulin concentrations, decreased fasting glucose concentrations, and increased muscle glycogen levels, but there were no changes in glucose tolerance curve and plasma insulin concentrations. These results suggest that regular running program for 4 weeks improve responsiveness of insulin on soleus muscle, but fails to cause improvement of impaired intravenous glucose tolerance in mild degree streptozotocin induced diabetic rats.
Animals ; Body Weight ; Exercise* ; Fasting ; Glucose Tolerance Test* ; Glucose* ; Glycogen ; In Vitro Techniques ; Infusions, Intravenous ; Insulin ; Muscle, Skeletal ; Plasma ; Rats* ; Rats, Sprague-Dawley ; Running ; Streptozocin*

The influence of normal late pregnancy on insulin action and insulin secretion was studied in the Sprague-Dawley female rats. On 20th day after mating, intravenous glucose tolerance test(IVGTI) was performed in non pregnant control and pregnant rats. As results of IVGTT, glucose disappearance rate was not significantly different in both groups, but secretory response of insulin was significantly(p<0.05) increased in pregnant rat. And the ratio of insulin/ .glucose was significantly higher in pregnant rats, which means existence of insulin resistance. These insulin resistance was overcomed by increased secretory response of pancreatic insulin. Insulinogenic index( A insulin/glucose - 5 min) was highly significantly (r=0.62, p<0.01) correlated with progesterone concentration. Glycogen level and amounts of "C-glucose incorporated into glycogen after IVGTT were significantly(p<0. 05) decreased in the liver, but were not changed significantly in soleus. Glycogen synthase activity of soleus and liver was not differ significantly in the both groups. Insulin binding at varying concentrations of insulin to crude membrane of pregnant liver was not significantly different from control. In conclusions, although these pregnant rats were normal glucose tolerance due to increased secretory response of insulin, that was correlated with progesterone concentration, pregnant rat had insulin resistance. The mechanisms of insulin resistance were not related to defect of insulin binding phase and glycogen synthase, but suggest pre-receptor and/or postreceptor phase.
Animals ; Female ; Glucose ; Glucose Tolerance Test ; Glycogen ; Glycogen Synthase ; Humans ; Insulin Resistance* ; Insulin* ; Liver ; Membranes ; Pregnancy ; Progesterone ; Rats* ; Rats, Sprague-Dawley ; Receptor, Insulin

Insulin resistance is a prominent feature of diabetic state and has heterogeneous nature. However, the pathogenetic sequence of events leading to the emergence of the defect in insulin action remains controversial. It is well-known that prolonged hyperglycemia and hyperinsulinemia are one of the causes of development of insulin resistance, but both hyperglycemia and hyperinsulinemia stimulate glucose uptake in peripheral tissue. Therefore, it is hypothesized that insulin resistance may be generated by a kind of protective mechanism preventing cellular hypertrophy. In this study, to evaluate whether the acutely increased glucose uptake inhibits further glucose transport stimulated by insulin, insulin sensitivity was measured after preloaded glucose infusion for 2 hours at various conditions in rats. And also, to evaluate the mechanism of decreased insulin sensitivity, insulin receptor binding affinity and glucose transporter 4 (GLUT4) protein of plasma membrane of gastrocnemius muscle were assayed after hyperinsulinemic euglycemic clamp studies. Experimental animals were divided into five groups according to conditions of preloaded glucose infusion: group I, basal insulin (14+/-1.9 micronU/ml) and basal glucose (75+/-0.7 mg/dl), by normal saline infusion; group II, normal insulin (33+/-3.8 micronU/ml) and hyperglycemia (207+/-6.3 mg/dl), by somatostatin and glucose infusion; group III, hyperinsulinemia (134+/-34.8 micronU/ml) and hyperglycemia (204+/-4.6 mg/dl), by glucose infusion; IV, supramaximal insulin (100+/-2.2 mg/dl), by insulin and glucose infusion; group V, supramaximal insulin(4813+/-687.9 micronU/ml) and hyperglycemia (233+/-3.1 mg/dl), by insulin and glucose infusion. Insulin sensitivity was assessed with hyperinsulinemic euglycemic clamp technique. The amounts of preloaded glucose infusion(gm/kg) were 1.88+/-0.151 in group II, 2.69+/-0.239 in group III, 3.54+/-0.198 in groupIV, and 4.32+/-0.621 in group V. Disappearance rates of glucose (Rd, mg/kg/min) at steady state of hyperinsulinemic euglycemic clamp studies were 16.9+/-3.88 in group I, 13.5+/-1.05 in group II, 11.2+/-1.17 in group III, 13.2+/-2.05 in group IV, and 10.4+/-1.01 in group V. A negative correlation was observed between amount of preloaded glucose and Rd )r=-0.701, p<0.001) when all studies were combined. Insulin receptor binding affinity and content of GLUT4 were not significantly different in all experimental groups. These results suggest that increased glucose uptake may inhibit further glucose transport and lead to decreased insulin sensitivity.
Animals

The effect of persistant mild hyperglycemic hyperinsulinemia on the development of the insulin resistance in rats was studied in vivo. Also, the characteristics of the insulin resistance compared with the insulin resistance of STZ diabetic rats. Persistant mild hyperglycemic hyperinsulinemic rat model was produced by ingestion of glucose polymer for 8 days. The glucose disappearance and infusion rate was measured by hyperinsulinemic euglycemic clamp to"Imique at steady state of blood glucose and insulin levels. The clamped level of blood glucose was 100 mg/dl, and the clamped levels of insulin were 70 pU/ml (physiologic condition) and 3000 pU/ml (supramaximal condition). Hepatic glucose producticon rate was calculated using measured data. And the glycogen synthetic capacity of skeletal muscle(soleus) and liver was measured after 2 hours of hyperinsulinemic euglycemic clamp study. The glucose disappearance and glucose infusion rate in glucose polymer group was decreased in the both physiological and supramaximal insulin level compared to the rate of the normal control group. The rate of STZ diabetic group wase lowest at supramaximal insulin level among two another experimental groups. The hepatic glucose production rate of glucose polymer group was decreased compared to normal control but increased in STZ diabetic group.
Animals ; Blood Glucose ; Eating ; Glucans ; Glucose ; Glucose Clamp Technique ; Glycogen ; Hyperinsulinism* ; Insulin Resistance* ; Insulin* ; Liver ; Models, Animal ; Rats*

The effects of insulin and exercise on glucose uptake of skeletal muscle were investigated in soleus muscle isolated from low dose streptozotocin induced diabetic rat in vitro. Glucose uptake was assessed by measuring ³H-methylglucose uptake in vitro. Basal glucose uptake in diabetes was reduced by approximately one-third of the control value (5.6±0.73µMol/g/20min. in diabetes versus 8.4±0.77 in control, P<0.01). There was also a significant decrease (P<0.01) in glucose uptake of diabetes at physiologic insulin concentration (200 µIU/ml) by 40% (6.1±1.20 versus 10.0±0.81). Furthermore, maximal insulin (20000 µIU/ml)-stimulated glucose uptake was 36% lower in diabetes as compared with control (7.3±1.29 versus 11.4±1.29, P<0.01). In contrast, exercise (1.0 km/hr, treadmill running for 45 min.) effect on glucose uptake was so dramatic in diabetes that glucose uptake at basal state was 8.+1.09 and insulin stimulated-glucose uptake were 10.2±1.47 and 11.9±1.64, in 200 and 20000 µIU/ml added insulin, respectively. These results suggest that insulin insensitivity develops in skeletal muscle after 2 weeks of streptozotocin-induced diabetes, but these insensitivity was recovered significantly by single session of running exercise.
Animals ; Glucose* ; In Vitro Techniques ; Insulin* ; Muscle, Skeletal* ; Rats* ; Running ; Streptozocin

In the present study the effect of exercise on the conversion rate of ingested glucose to glycogen in the different types of hindlimb skeletal muscles in Sprague-Dawley male rats was studied. The amounts of synthetized glycogen from ingested glucose of fast-twitch white (WV), fast-twitch red (RV), mixed type of fast-twitch white and red (EDL), and slow-twitch (SOL) muscles were determined at 30 and 90 min. after ingestion of 25% glucose solution which contained 14C-glucose(2 ml(luCi)/100gm B.W.) in control and exercise loaded rats. The result was summarized as follows: The about 55% at 30 min. and 70% at 90 min. after glucose ingestion were absorbed from gastrointestinal tract. This result shows no effects of exercise on absorption rate from gastrointestinal tract. The amount of synthetized glycogen of SOL from ingested glucose at 30 and 90 min. after glucose ingestion were highest, whether WV were lowest in hindlimb skeletal muscles in control and exercise loaded rats. In the exercise loaded rats, the amounts of synthetized glycogen of SOL, RV, and EDL at 90 min. after glucose ingestion was much higher than control rats, but not different in WV between exercise-loaded and control rats. At 30 min. after glucose ingestion, only SOL of exercise loaded rats was higher than control rats. In the control rat, the synthesis of glycogen was almost completed during initial 30 minutes. On the other hand, in the exercise loaded rat, except WV was opposite result of control rats, i.e., amounts of synthetized glycogen were major during late period. The amount of synthetized glycogen of liver at 30 and 90 min. after glucose ingestion in exercise loaded rats was higher than control rats. The rate of glycogen synthesis in control and exercise loaded rats were higher between 30-90 minute than initial 30 minutes.
Absorption ; Animals ; Eating ; Gastrointestinal Tract ; Glucose* ; Glycogen* ; Hand ; Hindlimb* ; Humans ; Liver ; Male ; Muscle, Skeletal* ; Muscles ; Rats* ; Rats, Sprague-Dawley

This study observed the changes of the glycogen content in extensor digitorum and soleus by electrical stimulation on the sciatic nerve with various frequencies, and the result were compared with those of treadmill running exercise. The results are summarized as follows ; The glycogen content of extensor digitorum longus was greater than that of the soleus in the normal group, and the reducing amount of glycogen content of extensor digitorum longus was greater than that of the soleus by overnight fasting. As the frepuency of electrical stimulation was increased by 2, 5 and 10Hz., the glycogen content of the extensor digitorum longus was slightly reduced or changed minimally. As the loading period of clectrical stimulation was increased to 30 and 90minutes, the glycogen content of extensor digitorum longus was much reduced from early stage, and that of the soleus was the same tendency as the frepuency increased. The glycogen content of the extensor digitorum longus was proportionally reduced by treadmill running excercise, and that of the soleus was much reduced from the early stage. In summary, based on the experimental evidence of this investigation, it showed the different physio-chemical responses of th fast and slow twitch muscle fibers by electrical stimulation, and also not the equal responses of muscle fibers by electrical stimulation and treadmill running exercise.
Animals ; Electric Stimulation ; Fasting ; Glycogen ; Muscles ; Rats ; Running ; Sciatic Nerve

BACKGROUND: It is doubtful that aging causes deteriorated glucose metabolism and insulin resistance of skeletal muscle. Some researchers had different results about it. So we have studied the mechanism responsible for the abnormal glucose tolerance associated with aging in rapidly growing and matured rats. MATERIALS AND METHODS: Animals were used S.D. rats. Growing rats were 7 weeks old (BW: 160-190 gm) and matured rats were 28 weeks old (BW: 420-525 gm). RESULTS: Fasting blood glucose and plasma insulin levels were significantly elevated in matured rat compared with growing rats. And during oral glucose tolerance test the glucose level was also significantly elevated in matured rats. These results confirmed an insulin resistant state of aging. Insulin levels at 30 minutes of oral glucose tolerance test was significantly elevated in growing rat. But at 120 minutes it was maintained at higher level in matured rats than in growing rats. It suggested the possibility of increased insulin secretion by initial stimulation of beta-cells in growing rats, and increased secretion and decreased catabolic rate of insulin in matured rats. Glucose uptake rate of soleus muscle in matured rats was lower than that of growing rats, but the difference was not statistically significant. The dose(insulin)- responsive (glucose uptake) curve of soleus muscle was only slightly deviated to the right side. CONCLUSION: Glucose metabolism of rat skeletal muscle was worsened by aging. The data of glucose uptake experiments suggested the possibility of insulin resistance of skeletal muscle in matured rats, but the mechanism of insulin resistance of skeletal muscle need further studies.
Aging ; Animals ; Blood Glucose ; Fasting ; Glucose Tolerance Test ; Glucose* ; Insulin ; Insulin Resistance ; Metabolism* ; Muscle, Skeletal* ; Plasma ; Rats*