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R Bergeron

Publications and source records attributed to R Bergeron.

At least 19 recordsLinked to original sources
PubMed2005

Role of the glycine site of the N-methyl-D-aspartate receptor in synaptic plasticity induced by pairing.

In the hippocampal CA1 region of the rat, activity-dependent plasticity requires substantial postsynaptic depolarization and activation of the N-methyl-D-aspartate glutamate receptor subtype (NMDAR). Exogenous and endogenous compounds selectively modulate NMDAR function by acting at the glycine coagonist site. Here we investigate the modulatory role of the glycine site in the induction of bidirectional synaptic plasticity. Plasticity was induced by pairing low-frequency afferent pulses with different levels of postsynaptic depolarization in the absence and presence of glycine site compounds. We found strong dependence of glycine site agonist modulation on membrane voltage during induction. Thus, D-serine and glycine were more effective in enhancing long-term potentiation (LTP) during pairing of small depolarization (-60 or -50 mV) with subthreshold EPSCs than during pairing of stronger depolarization (-40 mV) with suprathreshold synaptic responses. The glycine site role in bidirectional synaptic plasticity was studied with the selective antagonist 7-chlorokynurenic acid. Blockade of the glycine site during the pairing reversed the direction of plasticity from LTP towards long-term depression. The magnitude of depression was dependent on antagonist concentration and the level of depolarization during the pairing. Thus, these experiments demonstrate the role of the glycine site in the induction of bidirectional synaptic plasticity.

Afferent Pathways↗
PubMed2004

Subthreshold contribution of N-methyl-d-aspartate receptors to long-term potentiation induced by low-frequency pairing in rat hippocampal CA1 pyramidal cells.

Long-term potentiation (LTP) is a use-dependent and persistent enhancement of synaptic strength. In the CA1 region of the hippocampus, LTP has Hebbian characteristics and requires precisely timed interaction between presynaptic firing and postsynaptic depolarization. Although depolarization is an absolute requirement for plasticity, it is still not clear whether the postsynaptic response during LTP induction should be subthreshold or suprathreshold for the generation of somatic action potential. Here, we use the whole-cell patch-clamp technique and different pairing protocols to examine systematically the postsynaptic induction requirements for LTP. We induce LTP by changes only in membrane potential while keeping the afferent stimulation constant and at minimal levels. This approach permits differentiation of two types of LTP: LTP induced with suprathreshold synaptic responses (LTP(AP)) and LTP induced with subthreshold excitatory postsynaptic current (EPSCs; LTP(EPSC)). We found that LTP(AP) (>40%) required pairing of depolarization (V(m)>or=-40 mV, for 40-60 s) with four to six (0.1 Hz) single synaptically initiated action potentials. LTP(EPSC) was of smaller magnitude (<30%) and required pairing of depolarization to -50 mV (60 s) with six subthreshold EPSCs. The N-methyl-d-aspartate receptor (NMDAR) antagonists aminophosphonovaleric acid and 7-chlorokynurenic acid consistently blocked LTP(EPSC) but were ineffective in preventing LTP(AP). Robust, NMDAR-independent LTP is obtained by stronger postsynaptic depolarization that converts the EPSCs to suprathreshold somatic action potentials. Purely NMDAR-dependent LTP is obtained by pairing mild somatic depolarization with subthreshold afferent pulses to the postsynaptic cell. Our results indicate that the degree of postsynaptic depolarization in the presence of single afferent pulses determines the type and magnitude of LTP.

Animals↗
PubMed2001

Chronic activation of AMP kinase results in NRF-1 activation and mitochondrial biogenesis.

The underlying mechanism by which skeletal muscle adapts to exercise training or chronic energy deprivation is largely unknown. To examine this question, rats were fed for 9 wk either with or without beta-guanadinopropionic acid (beta-GPA; 1% enriched diet), a creatine analog that is known to induce muscle adaptations similar to those induced by exercise training. Muscle phosphocreatine, ATP, and ATP/AMP ratios were all markedly decreased and led to the activation of AMP-activated protein kinase (AMPK) in the beta-GPA-fed rats compared with control rats. Under these conditions, nuclear respiratory factor-1 (NRF-1) binding activity, measured using a cDNA probe containing a sequence encoding for the promoter of delta-aminolevulinate (ALA) synthase, was increased by about eightfold in the muscle of beta-GPA-fed rats compared with the control group. Concomitantly, muscle ALA synthase mRNA and cytochrome c content were also increased. Mitochondrial density in both extensor digitorum longus and epitrochlearis from beta-GPA-fed rats was also increased by more than twofold compared with the control group. In conclusion, chronic phosphocreatine depletion during beta-GPA supplementation led to the activation of muscle AMPK that was associated with increased NRF-1 binding activity, increased cytochrome c content, and increased muscle mitochondrial density. Our data suggest that AMPK may play an important role in muscle adaptations to chronic energy stress and that it promotes mitochondrial biogenesis and expression of respiratory proteins through activation of NRF-1.

5-Aminolevulinate Synthetase↗
PubMed2001

Splanchnic blood flow and hepatic glucose production in exercising humans: role of renin-angiotensin system.

The study examined the implication of the renin-angiotensin system (RAS) in regulation of splanchnic blood flow and glucose production in exercising humans. Subjects cycled for 40 min at 50% maximal O(2) consumption (VO(2 max)) followed by 30 min at 70% VO(2 max) either with [angiotensin-converting enzyme (ACE) blockade] or without (control) administration of the ACE inhibitor enalapril (10 mg iv). Splanchnic blood flow was estimated by indocyanine green, and splanchnic substrate exchange was determined by the arteriohepatic venous difference. Exercise led to an approximately 20-fold increase (P < 0.001) in ANG II levels in the control group (5.4 +/- 1.0 to 102.0 +/- 25.1 pg/ml), whereas this response was blunted during ACE blockade (8.1 +/- 1.2 to 13.2 +/- 2.4 pg/ml) and in response to an orthostatic challenge performed postexercise. Apart from lactate and cortisol, which were higher in the ACE-blockade group vs. the control group, hormones, metabolites, VO(2), and RER followed the same pattern of changes in ACE-blockade and control groups during exercise. Splanchnic blood flow (at rest: 1.67 +/- 0.12, ACE blockade; 1.59 +/- 0.18 l/min, control) decreased during moderate exercise (0.78 +/- 0.07, ACE blockade; 0.74 +/- 0.14 l/min, control), whereas splanchnic glucose production (at rest: 0.50 +/- 0.06, ACE blockade; 0.68 +/- 0.10 mmol/min, control) increased during moderate exercise (1.97 +/- 0.29, ACE blockade; 1.91 +/- 0.41 mmol/min, control). Refuting a major role of the RAS for these responses, no differences in the pattern of change of splanchnic blood flow and splanchnic glucose production were observed during ACE blockade compared with controls. This study demonstrates that the normal increase in ANG II levels observed during prolonged exercise in humans does not play a major role in the regulation of splanchnic blood flow and glucose production.

Adrenocorticotropic Hormone↗
PubMed2001

Effect of 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside infusion on in vivo glucose and lipid metabolism in lean and obese Zucker rats.

Activation of AMP-activated protein kinase (AMPK) with 5-aminoimidazole-4-carboxamide-1-beta-D-ribofurano-side (AICAR) increases glucose transport in skeletal muscle via an insulin-independent pathway. To examine the effects of AMPK activation on skeletal muscle glucose transport activity and whole-body carbohydrate and lipid metabolism in an insulin-resistant rat model, awake obese Zuckerfa/fa rats (n = 26) and their lean (n = 23) littermates were infused for 90 min with AICAR, insulin, or saline. The insulin infusion rate (4 mU.kg(-1).min(-1)) was selected to match the glucose requirements during AICAR (bolus, 100 mg/kg; constant, 10 mg.kg(-1).min(-1)) isoglycemic clamps in the lean rats. The effects of these identical AICAR and insulin infusion rates were then examined in the obese Zucker rats. AICAR infusion increased muscle AMPK activity more than fivefold (P < 0.01 vs. control and insulin) in both lean and obese rats. Plasma triglycerides, fatty acid concentrations, and glycerol turnover, as assessed by [2-13C]glycerol, were all decreased in both lean and obese rats infused with AICAR (P < 0.05 vs. basal), whereas insulin had no effect on these parameters in the obese rats. Endogenous glucose production rates, measured by [U-13C]glucose, were suppressed by >50% during AICAR and insulin infusions in both lean and obese rats (P < 0.05 vs. basal). In lean rats, rates of whole-body glucose disposal increased by more than two-fold (P < 0.05 vs. basal) during both AICAR and insulin infusion; [3H]2-deoxy-D-glucose transport activity increased to a similar extent, by >2.2-fold (both P < 0.05 vs. control), in both soleus and red gastrocnemius muscles of lean rats infused with either AICAR or insulin. In the obese Zucker rats, neither AICAR nor insulin stimulated whole-body glucose disposal or soleus muscle glucose transport activity. However, AICAR increased glucose transport activity by approximately 2.4-fold (P < 0.05 vs. control) in the red gastrocnemius from obese rats, whereas insulin had no effect. In summary, acute infusion of AICAR in an insulin-resistant rat model activates skeletal muscle AMPK and increases glucose transport activity in red gastrocnemius muscle while suppressing endogenous glucose production and lipolysis. Because type 2 diabetes is characterized by diminished rates of insulin-stimulated glucose uptake as well as increased basal rates of endogenous glucose production and lipolysis, these results suggest that AICAR-related compounds may represent a new class of antidiabetic agents.

Adenylate Kinase↗
PubMed2001

[Collaboration between family physicians and home care professionals. Is it possible?].

OBJECTIVE: To describe perceptions of physicians and home care professionals working in local community service centres (CLSCs) with respect to collaboration on home care follow up, and to identify conditions likely to help or hinder cooperation. DESIGN: Descriptive study using individual and group interviews. SETTING: Areas served by three CLSCs in the Quebec city region. PARTICIPANTS: Forty-five general practitioners with large home care practices and coordinators and representatives of CLSC home care teams. MAIN OUTCOME MEASURES: Perceptions of physicians and home care professionals with respect to interprofessional cooperation on and barriers to home care follow up. RESULTS: Most participants thought that cooperation would be beneficial to complex case management and continuity of follow-up care. In practice, however, cooperation is hindered by differences in medical practice and home care team service delivery and in methods of remuneration, and lack of knowledge of the other field of practice. CONCLUSION: All participants recognized the importance of cooperation. This study did not reveal any real integration of medical and CLSC home care services. Efforts must be made to identify the strategies most conducive to improving interprofessional cooperation.

Canada↗
PubMed2001

[Palliative care: profile of medical practice in the Quebec city region].

OBJECTIVE: To describe the palliative care provided by physicians in the Quebec city region and to identify factors that affect its delivery. DESIGN: Mailed survey. SETTING: Quebec city region. PARTICIPANTS: General practitioners in active clinical practice. MAIN OUTCOME MEASURES: Physicians' personal and professional characteristics and their palliative care practice (volume of work, source of requests for follow-up care, place of delivery of care, resources used, difficulties, encountered). RESULTS: Of the 476 physicians (67%) who responded to our survey, 295 (62%) provided palliative care. Of these, 70% saw no more than two patients requiring palliative care per month, and 55% devoted no more than 2 hours per week to this aspect of patient care. Most (76%) provided palliative care in a variety of settings (private office, home, institution). Home care teams working out of local community health centres are the resource physicians drew upon most frequently (69%). The main difficulties encountered were a lack of clinical expertise, scheduling home care, and providing patients and families with emotional support. CONCLUSION: Most physicians in the Quebec city region provided palliative care occasionally. This care could be improved by removing various logistical and professional barriers.

Adult↗
PubMed2000

Feeding motivation and stereotypies in pregnant sows fed increasing levels of fibre and/or food.

Twenty-one multiparous sows were used in a Latin square design, from days 7 to 90 of gestation, to test the effect of fibre and food levels on feeding motivation and feeding-related stereotypies. Treatments were: VHF (very high-fibre, 29% ADF, 50% NDF, 4.5kg/day); HF (high-fibre, 23% ADF, 43% NDF, 3.5kg/day); C (control, 8% ADF, 20% NDF, 2.5kg/day); and control fed ad libitum (CAL). All diets except CAL provided a similar amount of major nutrients on a daily basis and were served in two meals. Each sow was subjected to each treatment for a 21-day period, at the end of which, behavioural observations were made. Two-hour observation periods starting at the afternoon food delivery revealed that sows spent more time eating on VHF and CAL (mean=21.2min) than on HF (13.2min) and C (7.6min) and more time on HF compared to C (p<0.01). When time spent eating was removed from total observation time, the percentage of remaining time spent in stereotypies was lower for VHF (median=17.9%) compared to C (median=49.8%), and lower for CAL (median=6.3%) compared to all other diets (p<0.01). During the period when lights were on (6.00-18.00h), 5min interval scans showed that VHF sows spent more time lying down and less time standing than C sows (p<0.05). Also, CAL sows spent more time lying down than sows on other treatments (p<0.01). During operant conditioning tests (OCT) performed before the afternoon meal and after the morning meal, less rewards were obtained by CAL sows (p<0.01), with no difference between other treatments. In conclusion, no reduction in feeding motivation of sows fed high-fibre diets could be measured by OCT, but very high levels of fibre were effective at reducing stereotypies and activity during the 2h post-feeding. However, these effects were not as marked as those observed with ad libitum feeding.

Journal Article↗
PubMed2000

Intramuscular glycogen and intramyocellular lipid utilization during prolonged exercise and recovery in man: a 13C and 1H nuclear magnetic resonance spectroscopy study.

Depletion of muscle glycogen is considered a limiting performance factor during prolonged exercise, whereas the role of the intramyocellular lipid (IMCL) pool is not yet fully understood. We examined 1) intramyocellular glycogen and lipid utilization during prolonged exercise, 2) resynthesis of muscle glycogen and lipids during recovery, and 3) changes in glycogen content between nonexercising and exercising muscles during recovery. Subjects ran on a treadmill at submaximal intensity until exhaustion. Glycogen concentrations were assessed in thigh, calf, and nonexercising forearm muscle, and IMCL content was measured in soleus muscle using magnetic resonance spectroscopy techniques. At the time of exhaustion, glycogen depletion was 2-fold greater in calf than in thigh muscles, but a significant amount of glycogen was left in both leg muscles. The glycogen concentration in nonexercising forearm muscle decreased during the initial 5 h of recovery to 73% of the baseline value. Duringthe exercise, the IMCL content decreased to 67% and subsequently during recovery increased to 83% of the baseline value. In summary, we found during prolonged running 1) significantly greater muscle glycogen utilization in the calf muscle group than in the thigh muscle group, 2) significant utilization of IMCL in the soleus muscle, and 3) a decrease in glycogen content in nonexercising muscle and an increase in glycogen content in recovering muscles during the postexercise phase. These latter data are consistent with the hypothesis that there is transfer of glycogen by the glucose-lactate and the glucose-->alanine cycle from the resting muscle (forearm) to recovering muscles (thigh and calf) after running exercise.

Blood Glucose↗
PubMed2000

[Delivery of home health care. Survey of the Quebec region].

OBJECTIVE: To describe the characteristics of home health care delivered by general practitioners and to identify the conditions that facilitate or hinder development of this practice. DESIGN: Mailed survey. SETTING: Quebec city region. PARTICIPANTS: General practitioners in private practice, family practice units, community health centres, or hospitals. MAIN OUTCOME MEASURES: A self-administered questionnaire was used to gather information on volume of home care provided, characteristics of clients and visits, methods of follow up, and factors that promoted or hindered home care. RESULTS: Of the 487 physicians surveyed, 58.1% (283) made housecalls to a clientele consisting mainly of elderly patients (87.6%): 42% saw fewer than five patients per week, and 31% spent 2 hours or less per week on housecalls. Close to two thirds (64%) devoted 15 to 30 minutes to these visits, and 90.2% said they used community health centres for assessment or home follow up of their patients. Difficulties with scheduling and methods of remuneration reportedly hampered development of this practice. CONCLUSION: Home care practice is widespread around Quebec city, but represents only a small portion of the clinical work of many GPs.

Delivery of Health Care↗
PubMed1999

Effect of adrenaline on glucose kinetics during exercise in adrenalectomised humans.

1. The role of adrenaline in regulating hepatic glucose production and muscle glucose uptake during exercise was examined in six adrenaline-deficient, bilaterally adrenalectomised humans. Six sex- and age-matched healthy individuals served as controls (CON). 2. Adrenalectomised subjects cycled for 45 min at 68 +/- 1 % maximum pulmonary O2 uptake (VO2,max), followed by 15 min at 84 +/- 2 % VO2, max without (-ADR) or with (+ADR) adrenaline infusion, which elevated plasma adrenaline levels (45 min, 4.49 +/- 0.69 nmol l-1; 60 min, 12.41 +/- 1.80 nmol l-1; means +/- s.e.m.). Glucose kinetics were measured using [3-3H]glucose. 3. Euglycaemia was maintained during exercise in CON and -ADR, whilst in +ADR plasma glucose was elevated. The exercise-induced increase in hepatic glucose production was similar in +ADR and -ADR; however, adrenaline infusion augmented the rise in hepatic glucose production early in exercise. Glucose uptake increased during exercise in +ADR and -ADR, but was lower and metabolic clearance rate was reduced in +ADR. 4. During exercise noradrenaline and glucagon concentrations increased, and insulin and cortisol concentrations decreased, but plasma levels were similar between trials. Adrenaline infusion suppressed growth hormone and elevated plasma free fatty acids, glycerol and lactate. Alanine and beta-hydroxybutyrate levels were similar between trials. 5. The results demonstrate that glucose homeostasis was maintained during exercise in adrenalectomised subjects. Adrenaline does not appear to play a major role in matching hepatic glucose production to the increase in glucose clearance. In contrast, adrenaline infusion results in a mismatch by simultaneously enhancing hepatic glucose production and inhibiting glucose clearance.

Adrenalectomy↗
PubMed1999

Which physicians make home visits and why? A survey.

BACKGROUND: Recent changes in the North American health care system and certain demographic factors have led to increases in home care services. Little information is available to identify the strategies that could facilitate this transformation in medical practice and ensure that such changes respond adequately to patients' needs. As a first step, the authors attempted to identify the major factors influencing physicians' home care practices in the Quebec City area. METHODS: A self-administered questionnaire was sent by mail to all 696 general practitioners working in the Quebec City area. The questionnaire was intended to gather information on physicians' personal and professional characteristics, as well as their home care practice (practice volume, characteristics of both clients and home visits, and methods of patient assessment and follow-up). RESULTS: A total of 487 physicians (70.0%) responded to the questionnaire, 283 (58.1%) of whom reported making home visits. Of these, 119 (42.0%) made fewer than 5 home visits per week, and 88 (31.1%) dedicated 3 hours or less each week to this activity. Physicians in private practice made more home visits than their counterparts in family medicine units and CLSCs (centres locaux des services communautaires [community centres for social and health services]) (mean 11.5 v. 5.8 visits per week), although the 2 groups reported spending about the same amount of time on this type of work (mean 5.6 v. 5.0 hours per week). The proportion of visits to patients in residential facilities or other private residences was greater for private practitioners than for physicians from family medicine units and CLSCs (29.7% v. 18.9% of visits), as were the proportions of visits made at the patient's request (28.0% v. 14.2% of visits) and resulting from an acute condition (21.4% v. 16.0% of visits). The proportion of physicians making home visits at the request of a CLSC was greater for those in family medicine units and CLSCs than for those in private practice (44.0% v. 11.3% of physicians), as was the proportion of physicians making home visits at the request of a colleague (18.0% v. 4.5%) or at the request of hospitals (30.0% v. 6.8%). Physicians in family medicine units and CLSCs did more follow-ups at a frequency of less than once per month than private practitioners (50.9% v. 37.1% of patients), and they treated a greater proportion of patients with cognitive disorders (17.2% v. 12.6% of patients) and palliative care needs (13.7% v. 8.6% of patients). Private practitioners made less use of CLSC resources to assess home patients or follow them. Male private practitioners made more home visits than their female counterparts (mean 12.8 v. 8.3 per week), although they spent an almost equal amount of time on this activity (mean 5.7 v. 5.2 hours per week). INTERPRETATION: These results suggest that practice patterns for home care vary according to the physician's practice setting and sex. Because of foreseeable increases in the numbers of patients needing home care, further research is required to evaluate how physicians' practices can be adapted to patients' needs in this area.

Attitude of Health Personnel↗
PubMed1999

Regulation of myocardial glucose uptake and transport during ischemia and energetic stress.

Myocardial glucose utilization increases in response to the energetic stress imposed on the heart by exercise, pressure overload, and myocardial ischemia. Recruitment of glucose transport proteins is the cellular mechanism by which the heart increases glucose transport for subsequent metabolism. Moderate regional ischemia leads to the translocation of both glucose transporters, GLUT4 and GLUT1, to the sarcolemma in vivo. Myocardial ischemia also stimulates 5'-adenosine monophosphate-activated protein kinase, which may be a fuel gauge in the heart and other tissues signaling the need to turn on energy-generating metabolic pathways. Pharmacologic stimulation of this kinase increases cardiac glucose uptake and transporter translocation, suggesting that it may play an important role in augmenting glucose entry in the setting of ischemic or energetic stress. Thus, recent work has provided insight into the cellular and molecular mechanisms responsible for glucose uptake during energetic stress, which may lead to new approaches to the treatment of patients with coronary artery disease.

Adenosine Monophosphate↗
PubMed1999

Effects of hepatic portal infusion of hypertonic saline on glucagon response to exercise.

The present study was conducted to evaluate the influence of a hepatic portal infusion of hypertonic saline on the metabolic and hormonal responses to exercise. Adrenodemedullated male rats were studied at rest or after 30 min of treadmill exercise (26 m/min, 0% grade). Three groups of rats were infused continuously at a rate of 52 microL/min with one of the following randomly assigned conditions: hypertonic 3.6% NaCl (P3.6% NaCl) or 1.8% NaCl (P1.8% NaCl) infused into the hepatic portal vein, and hypertonic 3.6% NaCl (J3.6% NaCl) infused into the jugular vein. One group of rats received no infusion (SHAM). The infusions of hypertonic NaCl into the portal or the jugular site resulted in a significant (p < 0.05) increase in peripheral concentration of Na+, Cl-, and osmolality at rest and after exercise. The antidiuretic hormone (ADH) concentration was significantly (p < 0.05) increased by the P3.6% NaCl and J3.6% NaCl infusions at rest and after exercise. Exercise caused a significant (p < 0.05). decrease in liver glycogen content, peripheral and portal plasma glycemia, and insulinemia regardless of the different types and sites of infusions. However, the peripheral glucagon response to exercise was significantly (p < 0.05) increased only when hypertonic saline (1.8 or 3.6%) was infused into the portal vein. Portal and peripheral lactate concentrations at rest and after exercise were significantly (p < 0.01) higher in P3.6% NaCl than in all other groups. It is concluded that a 30-min hypertonic saline infusion into the hepatic portal vein does not specifically influence the insulin response at rest and after exercise, but that glucagon response to exercise is increased by such an infusion.

Adrenal Medulla↗
PubMed1999

Pregnancy reduces brain sigma receptor function.

1. Sigma (sigma) receptors have recently been cloned, though their endogenous ligand(s) remain unidentified. However, some neuroactive steroids, such as progesterone, have a high affinity for these receptors. Some sigma ligands, such as DTG, (+)-pentazocine and DHEA, act as sigma 'agonists' by potentiating the neuronal response to NMDA. Others, such as haloperidol, NE-100 and progesterone, act as sigma 'antagonists' by reversing the potentiations induced by sigma 'agonists'. 2. We compared the effects of sigma 'agonists' in four series of female rats: in controls, at day 18 of pregnancy, at day 5 post-partum, and in ovariectomized rats following a 3-week treatment with a high dose of progesterone. 3. In pregnant rats and following a 3-week treatment with progesterone, 10 fold higher doses of DTG, (+)-pentazocine and DHEA were required to elicit a selective potentiation of the NMDA response comparable to that obtained in control females. Conversely, at day 5 post-partum and following the 3-week treatment with a progesterone and after a 5-day washout, the potentiation of the NMDA response induced by the sigma 'agonist' DTG was greater than in control females. 4. The present data suggest that endogenous progesterone acts as an 'antagonist' at sigma receptors. The resulting changes in the function of sigma receptors during pregnancy and post-partum may be implicated in emotional phenomena occurring during these periods.

Action Potentials↗
PubMed1999

Effects of physical exercise on liver ATP levels in fasted and phosphate-injected rats.

The purpose of the present study was to investigate the effects of exercise (30 min, 23 m/min, 0% grade) on the hepatic levels of ATP in fasted adrenodemedullated rats, with an intraperitoneal injection of sodium phosphate (Na (2) PO (4 ), 0.91 mM) or saline (NaCl). Sodium phosphate was injected to determine if the postulated decrease in liver ATP during exercise may be changed by providing an excess of phosphate. At the end of exercise, a piece of liver was rapidly freeze clamped and used for the enzymatic determination of ATP levels. Liver ATP, in saline-injected rats, was significantly (P < 0.05) decreased by fasting, compared to fed rats (&Xscr; +/- SE: 3. 21 +/- 0.2 vs 2.86+/- 0.2 micromol/g). Exercise in fasted rats decreased even more the ATP response in liver (2.58 +/- 0.14 micromol/g). Injection of Na (2) PO (4) did not significantly (P > 0. 05) alter the pattern of ATP response following these 3 conditions (3.35 +/- 0.14 vs 3.0 +/-0.12 vs 2.57 +/- 0.1 micromol/g), ATP levels being significantly (P <0.05) decreased by the fast and the exercise in the fasted state. Fasting and exercise resulted in a significant (P < 0.05) decrease in liver glycogen and plasma glucose concentrations and an increase in free fatty acid levels in both NaCl- and Na (2 )PO (4) -injected groups. In both injection conditions, beta-hydroxybutyrate and peripheral insulin concentrations were respectively, increased and decreased (P < 0.05) by fasting, while norepinephrine and portal glucagon were decreased (P > 0.05) following exercise. The main effect of the injection of Na ( 2) PO (4) was a stimulation (P < 0.05) of peripheral glucagon response following exercise. It is concluded that exercise results in a decrease in liver ATP levels even in fasted rats and that this decrease is not corrected by Na (2 )PO( 4) administration. The decreased liver ATP levels might be involved in the metabolic adaptations to exercise.

Adenosine Triphosphate↗
PubMed1999

Effect of AMPK activation on muscle glucose metabolism in conscious rats.

The effect of AMP-activated protein kinase (AMPK) activation on skeletal muscle glucose metabolism was examined in awake rats by infusing them with 5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside (AICAR; 40 mg/kg bolus and 7.5 mg. kg-1. min-1 constant infusion) along with a variable infusion of glucose (49.1 +/- 2.4 micromol. kg-1. min-1) to maintain euglycemia. Activation of AMPK by AICAR caused 2-deoxy-D-[1,2-3H]glucose (2-DG) uptake to increase more than twofold in the soleus and the lateral and medial gastrocnemius compared with saline infusion and occurred without phosphatidylinositol 3-kinase activation. Glucose uptake was also assessed in vitro by use of the epitrochlearis muscle incubated either with AICAR (0.5 mM) or insulin (20 mU/ml) or both in the presence or absence of wortmannin (1.0 microM). AICAR and insulin increased muscle 2-DG uptake rates by approximately 2- and 2.7-fold, respectively, compared with basal rates. Combining AICAR and insulin led to a fully additive effect on muscle glucose transport activity. Wortmannin inhibited insulin-stimulated glucose uptake. However, neither wortmannin nor 8-(p-sulfophenyl)-theophylline (10 microM), an adenosine receptor antagonist, inhibited the AICAR-induced activation of glucose uptake. Electrical stimulation led to an about threefold increase in glucose uptake over basal rates, whereas no additive effect was found when AICAR and contractions were combined. In conclusion, the activation of AMPK by AICAR increases skeletal muscle glucose transport activity both in vivo and in vitro. This cellular pathway may play an important role in exercise-induced increase in glucose transport activity.

AMP-Activated Protein Kinases↗