How long does it take to deliver a baby by emergency Caesarean section?

This audit documented the current range of decision-to-delivery reaction times for 464 emergency Caesarean sections performed in maternity hospitals with differing levels of facilities, and examined the reasons for any perceived delay. The median (with 10th-90th percentile) times from when the decision was made to perform an emergency Caesarean section to the delivery of the child were: 69 (37-114), 54 (28-94) and 42 (17-86) minutes in Level 1, 2 and 3 maternity hospitals respectively when the indication for delivery was urgent. Less urgent emergency Caesarean sections took 70 (42-125), 66 (38-141) and 67 (35-164) minutes respectively. The main perceived reasons for delay in the delivery were staff unavailability in Level 1 hospitals, theatre access in Level 2 hospitals and anaesthetic complications in Level 3 hospitals. Therefore the decision-to-delivery reaction times in the majority of urgent emergency Caesarean sections are, in practice, much longer than the times commonly advocated and are influenced by the facilities and staff available.

Haematopoietic indicators of fetal metabolic acidosis

We aimed to study the haematopoietic response in normal and acidotic deliveries following vaginal and abdominal delivery and to compare this to the surrogate markers of perinatal acidosis. Blood gas analyses, complete blood pictures and erythropoietin assays were performed on umbilical or early neonatal blood samples. Placental sections were examined for the presence of nucleated red blood cells. Perinatal clinical risk factors and major neonatal outcomes were collected. The control population was 78 deliveries where the cord arterial pH was > 7.10. Controls born after labour were compared to those born prior to the onset of labour and to 14 acidotic infants born after labour. Nucleated red blood cells did not increase with labour in the control groups but were significantly higher (p < 0.05) in the acidotic group. Erythropoietin did not significantly change with either labour or acidosis. The predictive values from nucleated red blood cell counts were higher than those from low Apgar scores, atypical cardiotocograph traces, meconium-stained amniotic fluid, erythropoietin and the presence of nucleated red blood cells in placental sections. Nucleated red blood cell counts may be a useful surrogate marker of acidosis where blood gas analysis is unavailable. Further studies are required to examine the timing of the increase of erythropoiesis to help define the onset of the stimulus.

Reliability of a handgrip test for evaluating heart rate and pressor responses in multiple sclerosis

PURPOSE

The purpose of this study was to determine the test-retest reliability of an isometric handgrip exercise protocol designed to evaluate heart rate and arterial pressure responses in individuals with multiple sclerosis (MS). METHODS Three males and eleven females, aged 24 through 51, performed isometric handgrip contractions at 30% of maximal voluntary contraction (MVC) to the point of fatigue (defined as inability to maintain the target force for three consecutive seconds). During this exercise, rate of perceived exertion (RPE) was recorded every 30 s. Heart rate and beat-to-beat systolic, diastolic, and mean arterial pressures were recorded continuously throughout the duration of exercise. Surface EMG was monitored continuously via loudspeaker to provide feedback on extraneous muscular activity. Each subject performed three trials. A repeated measures ANOVA was used to calculate interclass reliability estimates for each dependent variable.

RESULTS

Reliability estimates for MVC and time to fatigue were 0.98 and 0.84, respectively. Reliability estimates for the following dependent variables at the point of fatigue were: RPE, 0.90; delta HR, 0.97; delta systolic pressure, 0.92; delta diastolic pressure, 0.87; and delta MAP, 0.88.

CONCLUSIONS

We conclude that this isometric handgrip protocol is a reliable method for evaluating heart rate and blood pressure responses in MS patient.

The effects of mountain bike suspension systems on energy expenditure, physical exertion, and time trial performance during mountain bicycling

The purpose of this 3-Phase study was to investigate the effects of suspension systems on muscular stress, energy expenditure, and time trial performance during mountain biking. Three suspension systems were tested, a rigid frame bike (RIG), a suspension fork bike (FS), and a front and rear suspension bike (FSR). Phase I and II consisted of cycling at 16.1 km.hr-1 over a flat, bumpy course for 63 min. Phase III consisted of ascending (ATT), descending (DTT), and cross country (XTT) time trials. Phase I assessed muscular stress by 24 h change in CK, Phase II assessed HR, VO2, VE, and Phase III assessed performance responses to the suspension systems. The 24 hr change in CK was greater for RIG than FS and FSR (+91.9 +/- 79.5 IU vs +8.6 +/- 17.5 IU and +9.7 +/- 21.8 IU). Mean HR was greater for RIG than FS and FSR (153.7 +/- 15.6 bpm vs 146.7 +/- 15.4 bpm, 146.3 +/- 16.2 bpm). Subjects rode significantly faster on FS than FSR and RIG during the XTT (30.9 +/- 2.0 min vs 32.3 +/- 3.6 min, 32.3 +/- 3.2 min). Subjects RPE was lower for FSR than FS and RIG, however, no differences were observed for VO2, VE, ATT, or DTT. Cyclists incurred less muscular stress, indicated by CK and HR, when riding the FS and FSR. Although the FS and FSR weigh from 0.7 to 2.2 kg more than RIG, no differences were observed for energy expenditure and that riding the FS in a XTT resulted in a faster finishing time than FSR or RIG.

Pressor response to isometric exercise in patients with multiple sclerosis

The purpose of this study was to determine whether patients with multiple sclerosis (MS) would show attenuated heart rate and/or pressor responses to isometric handgrip exercise. Patients with MS (30 males, 74 females, aged 23-61 yr) and control subjects (9 males, 16 females, aged 25-47 yr) performed isometric handgrip exercise at 30% of maximal voluntary contraction (MVC) to fatigue. Systolic, diastolic, and mean arterial pressure (MAP) increased linearly in both groups, but were significantly lower (P < 0.05) in patients with MS at 20%, 40%, 60%, 80%, and 100% of exercise duration. Mean change in MAP at fatigue was +47.9 mm Hg for controls and +28.2 mm Hg for patients with MS, with 18 patients with MS between -6 mm Hg and +15 mm Hg. Heart rate increased normally in patients with MS. To predict change in MAP at fatigue in patients with MS, stepwise regression analysis using six variables yielded an R2 of 0.26. These data suggest that in some patients MS lesions exist in areas of autonomic cardiovascular control that result in attenuated pressor responses to exercise. In 17% of patients tested, attenuation was profound. Data also suggest an abnormal dissociation between the heart rate and pressor response to static work in patients with MS.

Impact of aerobic training on fitness and quality of life in multiple sclerosis

Fifty-four multiple sclerosis (MS) patients were randomly assigned to exercise (EX) or nonexercise (NEX) groups. Before and after 15 weeks of aerobic training, aspects of fitness including maximal aerobic capacity (VO2max), isometric strength, body composition, and blood lipids were measured. Daily activities, mood, fatigue, and disease status were measured by the Profile of Mood States (POMS), Sickness Impact Profile (SIP), Fatigue Severity Scale (FSS), and neurological examination. Training consisted of 3 x 40-minute sessions per week of combined arm and leg ergometry. Expanded Disability Status Scale (EDSS) scores were unchanged, except for improved bowel and bladder function in the EX group. Compared with baseline, the EX group demonstrated significant increases in VO2max, upper and lower extremity strength, and significant decreases in skinfolds, triglyceride, and very-low-density lipoprotein (VLDL). For the EX group, POMS depression and anger scores were significantly reduced at weeks 5 and 10, and fatigue was reduced at week 10. The EX group improved significantly on all components of the physical dimension of the SIP and showed significant improvements for social interaction, emotional behavior, home management, total SIP score, and recreation and past times. No changes were observed for EX or NEX groups on the FSS. Exercise training resulted in improved fitness and had a positive impact on factors related to quality of life.

No effect of carbohydrate feeding on glycogen synthase in human muscle during exercise

The effect of carbohydrate (CHO) feedings on exercise-mediated changes in glycogen synthase fractional (GSF) activity has been investigated. Subjects cycled at approximately 70% of maximal oxygen uptake on two occasions: the first to fatigue (135 +/- 17 min; mean +/- SE) (control, CON), and the second at the same workload and duration as the first, but with the addition of frequent ingestion of CHO during exercise (0.27 g kg-1 body weight every 15 min). Biopsies were taken from the quadriceps femoris muscle before and immediately after exercise. Plasma glucose and insulin decreased during CON exercise, but remained elevated throughout CHO exercise (end of exercise: glucose = 4.4 +/- 0.2 mM CON vs. 5.8 +/- 0.2 CHO, P < 0.01; insulin = 9 +/- 1 uU ml-1 CON vs. 19 +/- 3 CHO, P < 0.05). Glycogen decreased to approximately 10% of the basal value during CON and to approximately 20% during CHO, and there was no significant difference in net glycogenolysis between treatments. GSF activity averaged 0.25 +/- 0.03 and 0.22 +/- 0.05 at rest, and increased to 0.51 +/- 0.08 and 0.48 +/- 0.09 after exercise in CON and CHO, respectively (P > 0.05 between treatments). It is concluded that under the present conditions CHO feedings do not alter the exercise-mediated changes in GSF activity. The increase in GSF during exercise is attributed at least in part to the decrease in muscle glycogen (which increases the suitability of GS as substrate for GS phosphatase).

Regulation of glycogen synthase in human muscle during isometric contraction and recovery

Six subjects performed isometric contraction (66% maximal force) to fatigue with the knee extensor muscles. Biopsies were taken from the quadriceps femoris muscle at rest, at fatigue and 1 min after termination of contraction. In three of the subjects recovery from contraction occurred in the presence of an intact circulation (non-occluded, NON) to the thigh, whereas in the other three the circulation during recovery was occluded (OCC). Glycogen synthase fractional activity (GSF) decreased in all subjects from (mean +/- SE) 0.53 +/- 0.06 at rest to 0.37 +/- 0.04 at fatigue (P < 0.001). In the OCC group GSF returned to the pre-exercise value within 1 min after termination of contraction (0.59 +/- 0.07 at rest vs. 0.57 +/- 0.04 at 1 min post-exercise), whereas in the NON group GSF increased to a higher extent (0.48 +/- 0.09 at rest vs. 0.70 +/- 0.06 at 1 min post-exercise). The increase in GSF during the 1-min recovery was almost three-fold higher in the NON group (0.15 +/- 0.02 vs. 0.38 +/- 0.03). Cyclic AMP-dependent protein kinase (cAMP-PK) (assayed at 0/100 microM and 0.2/100 microM cAMP) did not change at fatigue or during recovery in either group. Glycogen synthase phosphatase (GSP) increased at fatigue by approximately 30% (P < 0.05 vs. rest). It is concluded that isometric contraction mediated inactivation of GS (i.e. phosphorylation of GS) is due to activation of a protein kinase(s) but not cAMP-PK. The rapid activation of GS in the NON group demonstrates that a humoral factor(s), possibly insulin and/or oxygen, is responsible for this phenomenon.

Effect of low glycogen on glycogen synthase in human muscle during and after exercise

Subjects cycled at a work load calculated to elicit 75% of maximal oxygen uptake on two occasions: the first to fatigue (34.5 +/- 5.3 min; mean +/- SE), and the second at the same workload and for the same duration as the first. Biopsies were obtained from the quadriceps femoris muscle before and immediately after exercise, and 5 min post-exercise. Before the first experiment, muscle glycogen was lowered by a combination of exercise and diet, and before the second, experiment muscle glycogen was elevated. In the low glycogen condition (LG), muscle glycogen decreased from 169 +/- 15 mmol glucosyl units kg-1 dry wt at to rest to 13 +/- 6 after exercise. In the high glycogen condition (HG) glycogen decreased from 706 +/- 52 at rest to 405 +/- 68 after exercise. Glycogen synthase fractional activity (GSF) was always higher during the LG treatment. During exercise in the HG condition, those subjects who cycled for less than 35 min (n = 3) had GSF values in muscle which were lower than at rest, whereas those subjects who cycled for greater than 35 min (n = 4) had values which were similar to or higher than at rest. Thus the change in GSF in muscle during HG was positively related to the exercise duration (r = 0.94; y = 254-17x + 0.3x2; P less than 0.001) and negatively related to the glycogen content at the end of exercise (r = -0.82; y = 516-2x + 0.001x2; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of low glycogen on carbohydrate and energy metabolism in human muscle during exercise

The effect of preexercise muscle glycogen content on the metabolic responses to exercise has been investigated. Seven men cycled at a work load calculated to elicit 75% of maximal oxygen uptake [211 +/- 17 (SE) W] on two occasions: 1) to fatigue (37.2 +/- 5.3 min) and 2) at the same work load and for the same duration as the first. Biopsies were obtained from the quadriceps femoris muscle before and after exercise. Before the first experiment, muscle glycogen was lowered by exercise and diet, and before the second experiment, muscle glycogen was elevated. In the low-glycogen condition (LG), muscle glycogen decreased from 182 +/- 15 at rest to 7 +/- 4 mmol glucosyl units/kg dry wt at fatigue, while in the high-glycogen condition (HG), glycogen decreased from 725 +/- 31 at rest to 353 +/- 53 mmol glucosyl units/kg dry wt at the end of exercise. Hexose monophosphates were not increased after LG exercise but increased approximately fivefold after HG exercise. Lactate increased more during HG exercise (LG = 16 +/- 5, HG = 61 +/- 7 mmol/kg dry wt; P less than or equal to 0.001), whereas IMP increased more during LG (LG = 2.8 +/- 0.6, HG = 0.9 +/- 0.2 mmol/kg dry wt; P less than or equal to 0.05). The increases in the sum of tricarboxylic acid cycle intermediates (TCAI; citrate+malate+fumarate) and acetylcarnitine (which is in equilibrium with acetyl CoA) were significantly greater during HG exercise (P less than or equal to 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Fasting inhibits insulin-mediated glycolysis and anaplerosis in human skeletal muscle

Euglycemic (approximately 5.5 mM) hyperinsulinemic (60 mU.m-2.min-1) clamps were performed for 2 h after a 10-h fast and after a prolonged (72-h) fast. Biopsies were obtained from the quadriceps femoris muscle before and after each clamp. The rate of whole body glucose disposal was approximately 50% lower during the clamp after the 72-h fast (P less than or equal to 0.001). The increase in carbohydrate (CHO) oxidation (which is proportional to glycolysis) during the clamp after the 10-h fast (to 13.8 +/- 1.5 mumol.kg fat free mass-1.min-1) was completely abolished during the clamp after the 72-h fast (1.7 +/- 0.6; P less than or equal to 0.001). During the clamp after the 10-h fast, postphosphofructokinase (PFK) intermediates and malate in muscle increased, whereas glutamate decreased (P less than or equal to 0.05-0.001 vs. basal) and citrate did not change. During the clamp after the 72-h fast, there were no significant changes in post-PFK intermediates or glutamate (P greater than 0.05 vs. basal), but there was a decrease in citrate (P less than or equal to 0.01 vs. basal). Euglycemic hyperinsulinemia increased glycogen synthase fractional activity in muscle under both conditions but to a greater extent after the 72-h fast (P less than or equal to 0.01). It is concluded that insulin (after 10-h fast) increases glycolytic flux and the content of malate in muscle, which is probably due to increased anaplerosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Basal and insulin-mediated carbohydrate metabolism in human muscle deficient in phosphofructokinase 1

Biopsies were obtained from the quadriceps femoris muscle of two male patients deficient in phosphofructokinase (PFK) 1. In the basal state the patients had markedly higher contents of UDP-glucose (approximately 5-fold), hexose monophosphates (approximately 7- to 13-fold), inosine monophosphate (IMP) (approximately 15-fold), and fructose 2,6-bisphosphate (F-2,6-P2; approximately 6-fold) than controls. Fructose 1,6-bisphosphate was not detectable, and phosphocreatine was lower (33 and 54 mmol/kg dry wt) than in controls [72 +/- 4 (SD)]. Patients had normal fasting plasma glucose and insulin levels and basal glucose turnover rates and responded normally to a 75-g oral glucose challenge. Patients were also studied during euglycemic hyperinsulinemia (approximately 95 mg/dl; 40 and 400 mU.m-2.min-1). Whole body glucose disposal rates were normal during both insulin infusion rates. Biopsies taken after the 400 mU insulin infusion showed decreases in acetylcarnitine and citrate and increases in the fractional activity of glycogen synthase. It is suggested that the high basal levels of F-2,6-P2 are, at least partly, a consequence of the high levels of fructose 6-phosphate, which will stimulate flux through PFK-2 and inhibit fructose-2,6-bisphosphatase. The low phosphocreatine and high IMP contents indicate that carbohydrate availability is important for control of high-energy phosphate metabolism, even in the basal state. The insulin-mediated decreases in acetylcarnitine and citrate suggest an activation of the tricarboxylic acid cycle in skeletal muscle but an absence of the normal response to replenish these intermediates.

Carbohydrate supplementation attenuates IMP accumulation in human muscle during prolonged exercise

The effect of carbohydrate (CHO) ingestion on metabolic responses to exercise has been investigated. Subjects cycled at approximately 70% of maximal oxygen uptake to fatigue [135 +/- 17 (+/- SE) min] on the first occasion (control, CON) and at the same work load and duration on the second occasion but with addition of ingestion of CHO during the exercise. Biopsies were taken from the quadriceps femoris muscle before and after exercise. The sum of the hexose monophosphates (HMP), as well as lactate and alanine, in muscle was higher after CHO exercise (P less than or equal to 0.05, P less than or equal to 0.05, and P less than or equal to 0.01, respectively). Acetylcarnitine increased during exercise but was not significantly different between treatments after exercise (CON, 6.6 +/- 1.7; CHO, 10.0 +/- 1.2 mmol/kg dry wt; P = NS). The sum of the tricarboxylic acid cycle intermediates (TCAI; citrate + malate + fumarate) was increased during exercise and was higher after CHO exercise (2.34 +/- 0.32 vs. 1.68 +/- 0.17 mmol/kg dry wt; P less than or equal to 0.05). IMP was less than 0.1 mmol/kg dry wt at rest and increased to 0.77 +/- 0.26 (CON) and 0.29 +/- 0.11 mmol/kg dry wt (CHO) (P less than or equal to 0.05) during exercise. It was recently found that during prolonged exercise there is initially a rapid and large expansion of TCAI and glycogenolytic intermediates in human muscle followed by a continuous decline in TCAI and glycogenolytic intermediates [K. Sahlin, A. Katz, and S. Broberg. Am. J. Physiol. 259 (Cell Physiol. 28): C834-C841, 1990].(ABSTRACT TRUNCATED AT 250 WORDS)

Role of glycogen in control of glycolysis and IMP formation in human muscle during exercise

The effect of prior glycogen depletion on glycolysis [flux through phosphofructokinase (PFK)] and inosine monophosphate (IMP) formation in human skeletal muscle has been investigated. Eight subjects cycled at a work load calculated to elicit 95% of maximal O2 uptake on two occasions, the first to fatigue [5.5 +/- 0.3 (SE) min] and the second at the same workload and for the same duration as the first. Before the first experiment, muscle glycogen stores were lowered by a combination of exercise and diet. Before the second experiment, muscle glycogen stores were supercompensated. In the low-glycogen (LG) state muscle glycogen decreased from 201 +/- 31 mmol glucosyl units/kg dry wt at rest to 105 +/- 28 after exercise, and in the high-glycogen (HG) state from 583 +/- 40 to 460 +/- 49. The accumulation of fructose 6-phosphate (F-6-P; activator of PFK) during exercise was markedly attenuated in the LG state (P less than 0.01), whereas lactate accumulation in muscle was similar between treatments, suggesting that muscle pH was also similar. Glycolysis (estimated from glycogenolysis minus accumulation of hexose monophosphates) was not measurably different between treatments (LG = 88 +/- 17, HG = 106 +/- 43 mmol/kg dry wt; P greater than 0.05). IMP was significantly greater in the LG state after exercise (3.63 +/- 0.85 vs. 1.97 +/- 0.44 mmol/kg dry wt; P less than 0.05). It is concluded that decreased glycogen availability does not measurably alter the rate of muscle glycolysis during intense exercise. It is hypothesized that the attenuated increase in F-6-P in the LG state, which should theoretically decrease glycolysis, is compensated for by increases in free ADP and AMP (activators of PFK) at the enzymatic site during the contraction phase. The greater increase in IMP in the LG state is consistent with this hypothesis, since ADP and AMP are also activators of AMP deaminase.

Hyperglycemia induces accumulation of glucose in human skeletal muscle

The effect of hyperglycemia on whole body substrate utilization and the metabolic profile of skeletal muscle has been investigated. Eight glucose-tolerant men were infused with somatostatin (S) for 190 min. During the last 120 min of S infusion, glucose was infused to achieve a steady-state plasma level of 26 mmol/l. Biopsies were obtained from the quadriceps femoris muscle immediately before and 35 and 120 min after induction of hyperglycemia. Steady-state glucose disposal during hyperglycemia averaged (+/- SE) 33.8 +/- 3.2 mumol.kg fat-free mass-1.min-1, and approximately 70% of the glucose disposal was accounted for by skeletal muscle. Intracellular glucose increased from 0.9 +/- 0.2 mmol/kg dry wt during S to 9.5 +/- 2.5 during hyperglycemia (P less than 0.01). It was estimated that approximately 35% of the glucose taken up by muscle during 120 min of hyperglycemia was not phosphorylated. Muscle contents of alpha-D-glucose 1,6-diphosphate, D-glucose 6-phosphate, ATP, ADP, and AMP (both of which are based on the phosphocreatine-to-creatine ratio), which have been shown to inhibit hexokinase in vitro, did not change significantly during hyperglycemia, nor were there any significant changes in any of the other postphosphofructokinase intermediates, D-fructose 2,6-diphosphate, and citrate. Hyperglycemia did not alter the fractional activities of glycogen synthase or phosphorylase, nor total phosphorylase activity. However, hyperglycemia resulted in a 55% increase in glycogen synthase-specific activity (P less than 0.01). It is concluded that hyperglycemia results in a marked increase in muscle glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Epinephrine inhibits insulin-mediated glycogenesis but enhances glycolysis in human skeletal muscle

The effect of epinephrine (E) infusion on insulin-mediated glucose metabolism in humans has been studied. Eight glucose-tolerant men were studied on two separate occasions: 1) during 120 min of euglycemic hyperinsulinemia (UH, approximately 5 mM; 40 mU.m-2.min-1); and 2) during UH while E was infused (UHE, 0.05 microgram.kg-1.min-1). Biopsies were taken from the quadriceps femoris muscle before and after each clamp. Glucose disposal, correcting for endogenous glucose production, was 36 +/- 3 and 18 +/- 2 (SE) mumol.kg fat-free mass (FFM)-1.min-1 during the last 40 min of UH and UHE, respectively (P less than 0.001). Nonoxidative glucose disposal (presumably glycogenesis) averaged 23.0 +/- 3.0 and 4.0 +/- 1.1 (P less than 0.001), whereas carbohydrate oxidation (which is proportional to glycolysis) averaged 13.1 +/- 1.4 and 15.3 +/- 1.1 mumol.kg FFM-1.min-1 (P less than 0.05) during UH and UHE, respectively. UHE resulted in significantly higher contents of UDP-glucose, hexose monophosphates, postphosphofructokinase intermediates, and glucose 1,6-bisphosphate (G-1,6-P2) in muscle (P less than 0.05-0.001), but there were no significant differences in high-energy phosphates or fructose 2,6-bisphosphate (F-2,6-P2) between treatments. Fractional activities of phosphorylase increased (P less than 0.01), and glycogen synthase decreased (P less than 0.001) during UHE. It is concluded that E inhibits insulin-mediated glycogenesis because of an inactivation of glycogen synthase and an activation of glycogenolysis. E also appears to inhibit insulin-mediated glucose utilization, at least partly, because of an increase in G-6-phosphate (which inhibits hexokinase) and enhances glycolysis by G-1,6-P2-, fructose 6-phosphate-, and F-1,6-P2-mediated activation of PFK.

Epinephrine increases tricarboxylic acid cycle intermediates in human skeletal muscle

The effects of epinephrine (E) and insulin infusions on the contents of tricarboxylic acid cycle intermediates (TCAI), adenine nucleotides and their catabolites, and amino acids in skeletal muscle have been investigated. Eight men were studied on two separate occasions: 1) during 120 min of euglycemic hyperinsulinemia (UH, approximately 5 mM; 40 mU.m-2.min-1) and 2) during UH while E was infused (UHE, 0.05 microgram.kg-1.min-1). Biopsies were taken from the quadriceps femoris muscle before and after each clamp. The sum of citrate, malate, and fumarate in muscle did not change significantly during UH (P greater than 0.05) but doubled during UHE (P less than 0.001). There were no significant changes in any of the adenine nucleotides, their catabolites (including inosine monophosphate), or aspartate during UH and UHE (P greater than 0.05); nor were there any significant changes in pyruvate or alanine contents during UH (P greater than 0.05). On the other hand, there were significant increases in pyruvate and alanine contents during UHE (P less than 0.01 and 0.05, respectively), suggesting that there was increased production of 2-oxoglutarate (a TCAI) via the alanine aminotransferase (ALT) reaction. It is concluded that E infusion increases the contents of TCAI in human skeletal muscle, and it is likely that at least part of the increase is attributable to increased flux through the ALT reaction.

Failure of glutamate dehydrogenase system to predict oxygenation state of human skeletal muscle

In a recent study, the total tissue contents of glutamate (Glu), ammonium (NH+4), and 2-oxoglutarate (2-OG) were used to estimate changes in the mitochondrial redox state ([NAD+]/[NADH]) of contracting skeletal muscle with intact circulation [Am. J. Physiol. 253 (Cell Physiol. 22): C263-C268, 1987]. These metabolites participate in the glutamate dehydrogenase (GDH) reaction, which, based on a number of assumptions, theoretically enables calculation of the mitochondrial redox state as follows (brackets indicate concentrations): [NAD+]/[NADH] = ([NH+4] [2-OG])/[( Glu]Kapp), where Kapp is the apparent equilibrium constant for GDH. The purpose of this study was to determine whether changes in the total tissue contents of Glu, NH+4, and 2-OG could be used to predict a reduction of the mitochondrial redox state in anoxic skeletal muscle. Anoxia was induced in the quadriceps femoris muscle by 10 min of circulatory occlusion (low metabolic rate) and isometric contraction to fatigue (high metabolic rate). The mean (+/- SE) value for the metabolite ratio ([NH+4][2-OG]/[Glu]) at rest was 6 +/- 3 mmol/kg dry wt (x 10(-4]. No significant change occurred after circulatory occlusion (4 +/- 2 x 10(-4); P greater than 0.05), whereas an almost 60-fold increase was observed after isometric contraction (P less than 0.05). Because the muscle was anoxic under both conditions, a significant decrease in the metabolite ratio should have occurred. These data demonstrate that changes in total tissue contents of Glu, NH+4, and 2-OG cannot be used to estimate changes in the redox and oxygenation state of mitochondria in intact human skeletal muscle.