A. Leturque

Effect of anesthesia on glucose production and utilization in rats.

This study was undertaken to determine the effects of pentobarbital anesthesia (50 mg/kg ip) on glucose kinetics and individual tissue glucose utilization in vivo, in chronically catheterized rats. Glucose turnover studies were carried out using [3-3H]glucose as tracer. A transient hyperglycemia and an increased glucose production were observed 3 min after induction of anesthesia. However, 40 min after induction of anesthesia, glycemia returned to the level observed in awake animals, whereas glucose turnover was decreased by 30% as compared with unanesthetized rats. These results are discussed with regard to the variations observed in plasma insulin, glucagon, and catecholamine levels. Glucose utilization by individual tissues was studied by the 2-[1-3H]deoxyglucose technique. A four- to fivefold decrease in glucose utilization was observed in postural muscles (soleus and adductor longus), while in other nonpostural muscles (epitrochlearis, tibialis anterior, extensor digitorum longus, and diaphragm) and other tissues (white and brown adipose tissues) anesthesia did not modify the rate of glucose utilization. A decrease in glucose utilization was also observed in the brain.

Hyperlactatemia reduces muscle glucose uptake and GLUT-4 mRNA while increasing (E1α)PDH gene expression in rat

An increased basal plasma lactate concentration is present in many physiological and pathological conditions, including obesity and diabetes. We previously demonstrated that acute lactate infusion in rats produced a decrease in overall glucose uptake. The present study was carried out to further investigate the effect of lactate on glucose transport and utilization in skeletal muscle. In chronically catheterized rats, a 24-h sodium lactate or bicarbonate infusion was performed. To study glucose uptake in muscle, a bolus of 2-deoxy-[3H]glucose was injected in basal condition and during euglycemic-hyperinsulinemic clamp. Our results show that hyperlactatemia decreased glucose uptake in muscles (i.e., red quadriceps; P< 0.05). Moreover in red muscles, both GLUT-4 mRNA (-30% in red quadriceps and -60% in soleus; P < 0.025) and protein (-40% in red quadriceps; P < 0.05) were decreased, whereas the (E1α)pyruvate dehydrogenase (PDH) mRNA was increased (+40% in red quadriceps; P< 0.001) in lactate-infused animals. PDH protein was also increased (4-fold in red gastrocnemius and 2-fold in red quadriceps). These results indicate that chronic hyperlactatemia reduces glucose uptake by affecting the expression of genes involved in glucose metabolism in muscle, suggesting a role for lactate in the development of insulin resistance.

Glucose Metabolism in Pregnancy

Pregnancy is characterized by a number of maternal metabolic modifications in order to meet the energy requirements of the growing fetus. A progressive alteration of maternal glucose homeostasis develops throughout gestation and becomes maximal during the last trimester. A relative hypoglycemia is observed during the postabsorptive period despite an elevated plasma insulin concentration and an enhanced hepatic glucose production. In addition, the glucose utilization rate by peripheral maternal tissues is lowered in late gestation indicating that the mother supplies glucose to the fetus at the expense of her own tissues. Concomitantly, an insulin-resistant state develops in the mother to help sparing glucose for the pregnant uterus. It involves both glucose-producing (liver) and glucose-utilizing tissues. So far, the factor(s) responsible for the development of pregnancy-induced insulin resistance has not been identified although a number of circulating hormones are known to counteract insulin effects.

In Vivo Glucose Utilization in Rat Tissues During the Three Phases of Starvation

Three phases of starvation have been described from changes in protein and lipid utilization in birds and mammals. In the present study, tissue glucose utilization was measured in vivo during these three phases, using a 2-deoxy-[1-3H]glucose technique in the anesthetized rat. According to this technique, the term glucose utilization therefore refers to transport and phosphorylation of glucose in tissues, ie, whatever is the fate of glucose. Whole-body glucose turnover rate, which was determined by a continuous infusion of [3-3H]glucose, decreased by 40% during the first two days of starvation (phase 1); it did not change thereafter, neither in the protein-sparing phase 2 nor in phase 3, which is marked by an increase in net protein breakdown. Two days of starvation caused a marked decrease in the glucose utilization in skeletal muscles; this decrease was higher in oxidative muscles (65% in diaphragm, 66% in soleus) than in glycolytic muscles (31% in extensor digitorum longus, 34% in epitrochlearis). Glucose utilization also decreased in heart atria (75%), heart ventricles (93%), and white adipose tissue (54%); by contrast, there was a two-fold increase in glucose utilization in brown adipose tissue and no change in brain and skin. No variations were observed in glucose utilization in any of the tissues from phase 1 to phase 2. However, phase 3 was marked by a decrease in glucose utilization in extensor digitorum longus (45%), brown adipose tissue (76%), brain (29%), and skin (40%), whereas there was a 2.3- and 3.4-fold increase in glucose utilization in diaphragm and heart ventricles, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

AN UNUSUAL HIGH-KM HEXOKINASE IS EXPRESSED IN THE MHAT3F HEPATOMA CELL LINE

In most hepatoma cells, the high-K m GLUT2/glucokinase proteins are replaced by the ubiquitous low-K m GLUT1/hexokinase type I proteins. In the mhAT3F hepatoma cells, the stimulatory effect of glucose on gene expression and glycogen accumulation was not maximal at 5 mmol/liter glucose. This response to high glucose is observed in mhAT3F cells, where GLUT2 was expressed, but not glucokinase (assessed by Northern blotting and reverse transcription-polymerase chain reaction). A low-K m hexokinase activity (19.6 ± 3.8 milliunits/mg of protein) was present, but a high-K m (40 mmol/liter) hexokinase activity (13.9 ± 2.5 milliunits/mg) was also detected in mhAT3F cells. The high-K m hexokinase activity was dependent on both ATP (or PPi) and glucose in the assay and was recovered in a 10–50-kDa fraction after filtration. A 30-kDa protein was detected using an anti-glucokinase antibody and localized by confocal microscopy at the same sites as glucokinase in hepatocytes. In FAO cells, the high-K m hexokinase activity and 30-kDa protein were not found. We conclude that a high-K m hexokinase activity is present in mhAT3F cells. This might explain why the effects of glucose on gene expression were not maximal at a glucose concentration of 5 mmol/liter. A 30-kDa protein identified using an anti-glucokinase antibody may be responsible for this activity present in mhAT3F cells.

Effect of feeding a high-fat diet during pregnancy on glucose metabolism in the rat.

To alter glucose homeostasis in a period of great glucose demand, pregnant rats were submitted to a high-fat diet and compared to virgin rats. In virgin rats, blood glucose, ketone bodies, plasma insulin, and free fatty acids were not affected by the diet consumed. Glucose turnover measured in the postabsorptive period was slightly decreased in virgin rats fed a high-fat diet compared to rats fed a standard diet. Assuming that the glucose turnover rate is representative for the 24-hour average endogenous glucose production, in rats fed a standard diet the daily carbohydrate intake (9.2 +/- 0.7 g/d) exceeded the glucose turnover rate (4 +/- 0.2 g/d) and could meet the glucose requirement. In rats fed a high-fat diet the carbohydrate intake (2.7 +/- 0.2 g/d) was lower than the glucose turnover rate (3.8 +/- 0.2 g/d), which demonstrated the need for an active endogenous glucose production. Blood glucose, ketone bodies, plasma insulin, and free fatty acid concentrations followed the same patterns during pregnancy in rats fed a standard diet compared to rats fed a high-fat diet. The glucose turnover rate in the postabsorptive period was no more decreased by the high-fat diet in pregnant rats compared to virgin rats despite the greater glucose demand. In late pregnancy the glucose turnover rate was increased up to 70%.(ABSTRACT TRUNCATED AT 250 WORDS)