Patricia Ruell

The influence of menstrual cycle phase on skeletal muscle contractile characteristics in humans

1 The influence of the different phases of the menstrual cycle on skeletal muscle contractile characteristics was studied in 19 regularly menstruating women. Muscle function was measured when (i) oestrogen and progesterone concentrations were low (menstruation), (ii) oestrogen was elevated and progesterone was low (late follicular phase), and (iii) oestrogen and progesterone were both elevated (luteal phase). 2 Maximal isometric quadriceps strength, fatiguability and electrically stimulated contractile properties were measured. Isokinetic knee flexion and extension strength and fatiguability were also assessed as well as handgrip strength. Menstrual cycle phases were confirmed through measurement of oestrogen, progesterone, follicle stimulating hormone and luteinising hormone. 3 No significant changes were found in any of the muscle function parameters throughout the menstrual cycle (n = 15). The muscle function measurements showed no significant correlations with any of the female reproductive hormone concentrations. 4 These results suggest that the fluctuations in female reproductive hormone concentrations throughout the menstrual cycle do not affect muscle contractile characteristics.

Noninvasive assessment of hepatic lipid composition: advancing understanding and management of fatty liver disorders

Nonalcoholic fatty liver is frequently observed in obese individuals, yet the factors that predict its development and progression to liver disease are poorly understood. We proposed that proton magnetic resonance spectroscopy (1H‐MRS) might allow noninvasive assessment of hepatic lipid composition. Lipid saturation (SI) and polyunsaturation (PUI) indices measured by 1H‐MRS were in agreement with those expected in oils of known composition. Hepatic triglyceride concentration (HTGC) and composition were then measured in healthy lean (LEAN) men, obese men with normal HTGC (OB), and obese men with hepatic steatosis (OB+HS). The effect of marked changes in dietary fat consumption on hepatic lipids were also compared in lean men after 67 hours of a normal mixed (NM) diet versus a low‐carbohydrate, high‐saturated‐fat (LCHF) diet. SI was significantly higher in OB+HS (0.970 ± 0.004) and OB (0.944 ± 0.008) versus LEAN (0.818 ± 0.025) (P < 0.01 for both). PUI was significantly lower in OB+HS (0.003 ± 0.001) and OB (0.022 ± 0.005) versus LEAN (0.120 ± 0.021) (P < 0.01), and significantly lower in OB+HS versus OB (P < 0.05). LCHF diet did not alter HTGC, SI, or PUI (P > 0.05). The 1H‐MRS method provides for rapid, qualitative assessment of lipid composition. Application of this technique in the liver produces results that are consistent with biopsy‐based approaches demonstrating that relative hepatic lipid saturation increases and polyunsaturation decreases with obesity. Obesity‐related hepatic steatosis is characterized by further depletion of polyunsaturated hepatic lipids. Conclusion: This readily available and noninvasive approach should promote further study into interactions between hepatic and whole‐body lipid metabolism and help to elucidate the pathogenesis of disorders characterized by lipid accumulation within the liver. (HEPATOLOGY 2008.)

Sarcoplasmic reticulum function and muscle contractile character following fatiguing exercise in humans

1 This study examined the alterations in calcium release, calcium uptake and calcium ATPase activity of skeletal muscle sarcoplasmic reticulum in response to a bout of intense dynamic knee extensor exercise, and the relationship between these changes and alterations in muscle contractile characteristics in the human quadriceps. 2 In biopsy samples taken from the vastus lateralis, sarcoplasmic reticulum calcium release and calcium uptake were significantly depressed (P < 0.01 and 0.05, respectively) immediately following the exercise with no alteration in the sarcoplasmic reticulum Ca2+‐ATPase activity. 3 A 33 % reduction in the maximum voluntary isometric torque was found following the exercise, with reduced torques from electrically evoked isometric contractions at low frequencies of stimulation (10 and 20 Hz) but not at higher frequencies (50 and 100 Hz). 4 The depressed calcium release was correlated (P < 0.05) with a decreased ratio of torques generated at 20:50 Hz, indicating an involvement in low frequency fatigue; however, no correlations between the muscle relaxation times or rates of change of torque and calcium uptake were observed.

Sprint Training Increases Muscle Oxidative Metabolism During High-Intensity Exercise in Patients With Type 1 Diabetes

OBJECTIVE—To investigate sprint-training effects on muscle metabolism during exercise in subjects with (type 1 diabetic group) and without (control group) type 1 diabetes. RESEARCH DESIGN AND METHODS—Eight subjects with type 1 diabetes and seven control subjects, matched for age, BMI, and maximum oxygen uptake (V̇o2peak), undertook 7 weeks of sprint training. Pretraining, subjects cycled to exhaustion at 130% V̇o2peak. Posttraining subjects performed an identical test. Vastus lateralis biopsies at rest and immediately after exercise were assayed for metabolites, high-energy phosphates, and enzymes. Arterialized venous blood drawn at rest and after exercise was analyzed for lactate and [H+]. Respiratory measures were obtained on separate days during identical tests and during submaximal tests before and after training. RESULTS—Pretraining, maximal resting activities of hexokinase, citrate synthase, and pyruvate dehydrogenase did not differ between groups. Muscle lactate accumulation with exercise was higher in type 1 diabetic than nondiabetic subjects and corresponded to indexes of glycemia (A1C, fasting plasma glucose); however, glycogenolytic and glycolytic rates were similar. Posttraining, at rest, hexokinase activity increased in type 1 diabetic subjects; in both groups, citrate synthase activity increased and pyruvate dehydrogenase activity decreased; during submaximal exercise, fat oxidation was higher; and during intense exercise, peak ventilation and carbon dioxide output, plasma lactate and [H+], muscle lactate, glycogenolytic and glycolytic rates, and ATP degradation were lower in both groups. CONCLUSIONS—High-intensity exercise training was well tolerated, reduced metabolic destabilization (of lactate, H+, glycogenolysis/glycolysis, and ATP) during intense exercise, and enhanced muscle oxidative metabolism in young adults with type 1 diabetes. The latter may have clinically important health benefits.

Effect of temperature and duration of hyperthermia on HSP72 induction in rat tissues.

The aim of the present study was to determine whether heat shock protein 72 (HSP72) is induced in a heated rat model at rectal temperatures below 42 °C.Rats were divided into a control group and six groups (n=6) heated to different rectal temperatures: 39 °C for 1 h (39), 40.0 °C for either 15 min (40S) or 1 h (40L), 41.0 °C for either 15 min (41S) or 1 h (41L) and 42.0 °C for 15 min (42). Tissues were sampled 4 h after heating.Following 1 h at 40.0 °C, HSP72 was significantly elevated in heart (p < 0.005), but not in gut or liver tissue. In all three tissues, HSP72 was significantly elevated under the conditions 41L and 42 compared to control tissue (p < 0.005). Marked differences were found in the amount of HSP72 induced in different tissues in response to the same heat stress. Duration of heating was important in modulating HSP72 induction, with a significantly greater induction of HSP72 following 1 h compared to 15 min at 41 °C in all three tissues (p < 0.02). A correlation was found between thermal load and HSP72 content in liver, heart (both p < 0.01) and gut (p < 0.001) for the rats heated to 41 and 42 °C. These data show that HSP72 is induced at temperatures below 42 °C, with striking differences between tissues. (Mol Cell Biochem 267: 187–194, 2004)

Ultrastructural changes and sarcoplasmic reticulum Ca2+ regulation in red vastus muscle following eccentric exercise in the rat

This study examined the effects of a bout of low‐intensity, prolonged downhill exercise on sarcoplasmic reticulum (SR) Ca2+‐ATPase activity, Ca2+ uptake and release in rat red vastus muscle. Ionophore stimulation was determined to assess vesicle integrity by measuring the ratio of Ca2+‐ATPase activities in the presence and absence of A23187. Observations of the muscle ultrastructure were made to evaluate muscle damage at the level of the myofibrils and SR. Adult male Sprague–Dawley rats (weight, 395 ± 5.9 g) were either assigned as non‐exercise controls or subjected to 90 min of downhill treadmill exercise (–16 deg; 15 m min−1), and then killed immediately, 4, 24, 48, 72 or 144 h after exercise (n= 7). Calcium uptake was significantly lower (P < 0.05) compared with control values (19.25 ± 1.38 nmol min−1 (mg protein)−1), by 29 and 36% immediately and 4 h postexercise, respectively, and remained depressed (P < 0.05) 24 h postexercise. Calcium release was also significantly lower (P < 0.05) compared with control values (31.06 ± 2.36 nmol min−1 (mg protein)−1), by 37 and 39% immediately and 4 h postexercise, respectively, and remained depressed (P < 0.05) 24 h postexercise. Ca2+‐ATPase activity measured with ionophore was 31% lower (P < 0.05) 4 h postexercise, and remained lower (P < 0.05) 24 h postexercise. The ratio of Ca2+‐ATPase activities in the presence and absence of A23187 was not significantly changed after exercise, indicating that membrane integrity was not altered by the exercise. Focal dilatations of the SR were observed immediately and 4 h following exercise, implying that SR may be susceptible to damage in the localized regions of overstretched sarcomeres. The results demonstrate that a bout of low‐intensity, prolonged downhill exercise results in a long‐lasting depression of SR function that is not fully restored after 2 days of recovery, which may underlie some functional impairments induced by eccentric exercise.

Effects of type 1 diabetes, sprint training and sex on skeletal muscle sarcoplasmic reticulum Ca2+ uptake and Ca2+-ATPase activity.

Skeletal muscle calcium resequestration and performance is increased in male rats with induced diabetes; and whilst muscle calcium resequestration is important during exercise, it has not been investigated in human diabetes or compared between sexes. We show that Ca2+‐ATPase activity and Ca2+ uptake are higher among people with type 1 diabetes (T1D) compared with matched non‐diabetic controls (CON), but that performance during intense exercise was similar; Ca2+‐ATPase activity and Ca2+ uptake are also higher among men than women. We show that Ca2+‐ATPase activity is reduced during intense exercise in men but not women, and is reduced by high‐intensity exercise training (HIET) in T1D and CON. Fatigue is commonly reported by people with diabetes, but our data show that muscle calcium resequestration and performance during intense exercise and after HIET is not impaired in T1D, and hence other physiological or psychological mechanisms for fatigue in diabetes must be sought. Sex influences muscle calcium regulation.

High-glycaemic index and -glycaemic load meals increase the availability of tryptophan in healthy volunteers

The purpose of the present study was to determine the influence of the glycaemic index (GI) and glycaemic load (GL) on the ratio of tryptophan (TRP) relative to other large neutral amino acids (LNAA). Ten healthy men (age 22·9 (sd 3·4) years; BMI 23·5 (sd 1·6) kg/m2) underwent standard GI testing, and later consumed each of a mixed-macronutrient (1915 kJ; 66·5 % carbohydrate (CHO), 17 % protein and 16·5 % fat) high-GI (MHGI), an isoenergetic, mixed-macronutrient low-GI (MLGI) and a CHO-only (3212 kJ; 90 % CHO, 8 % protein, 2 % fat) high-GI (CHGI) meal on separate days. The GI, GL and insulin index values (e.g. area under the curve) were largest after the CHGI meal (117, 200, 158), followed by the MHGI (79, 59, 82) and MLGI (51, 38, 56) meals, respectively (all values were significantly different, P < 0·05). After the MHGI and MLGI meals but not after the CHGI meal, TRP was elevated at 120 and 180 min (P < 0·05). After the CHGI, LNAA was lower compared with the MLGI (P < 0·05); also the rate of decline in LNAA was higher after CHGI compared with MHGI and MLGI (both comparisons P < 0·05). The percentage increase from baseline in TRP:LNAA after CHGI (23 %) was only marginally higher than after the MHGI meal (17 %; P = 0·38), but it was threefold and nearly significantly greater than MLGI (8 %; P = 0·05). The present study demonstrates that the postprandial rise in TRP:LNAA was increased by additional CHO ingestion and higher GI. Therefore, the meal GL appears to be an important factor influencing the postprandial TRP:LNAA concentration.

Chronic erythropoietin treatment improves diet-induced glucose intolerance in rats

Erythropoietin (EPO) ameliorates glucose metabolism through mechanisms not fully understood. In this study, we investigated the effect of EPO on glucose metabolism and insulin signaling in skeletal muscle. A 2-week EPO treatment of rats fed with a high-fat diet (HFD) improved fasting glucose levels and glucose tolerance, without altering total body weight or retroperitoneal fat mass. Concomitantly, EPO partially rescued insulin-stimulated AKT activation, reduced markers of oxidative stress, and restored heat-shock protein 72 expression in soleus muscles from HFD-fed rats. Incubation of skeletal muscle cell cultures with EPO failed to induce AKT phosphorylation and had no effect on glucose uptake or glycogen synthesis. We found that the EPO receptor gene was expressed in myotubes, but was undetectable in soleus. Together, our results indicate that EPO treatment improves glucose tolerance but does not directly activate the phosphorylation of AKT in muscle cells. We propose that the reduced systemic inflammation or oxidative stress that we observed after treatment with EPO could contribute to the improvement of whole-body glucose metabolism.

The effect of ice-slushy consumption on plasma vasoactive intestinal peptide during prolonged exercise in the heat

The aim of this study was to determine the effect of exercise in the heat on thermoregulatory responses and plasma vasoactive intestinal peptide concentration (VIP) and whether it is modulated by ice-slushy consumption. Ten male participants cycled at 62% V̇O2max for 90min in 32°C and 40% relative humidity. A thermoneutral (37°C) or ice-slushy (-1°C) sports drink was given at 3.5mlkg(-1) body mass every 15min during exercise. VIP and rectal temperature increased during exercise (mean±standard deviation: 4.6±4.4pmolL(-1), P=0.005; and 1.3±0.4°C, P<0.001 respectively) and were moderately associated (r=0.35, P=0.008). While rectal temperature and VIP were not different between trials, ice-slushy significantly reduced heat storage (P=0.010) and skin temperature (time×trial interaction P=0.038). It appears that VIP does not provide the signal linking cold beverage ingestion and lower skin temperature in the heat.