BACKGROUND: The regulation of glycemia is challenged in healthy men and women after exercise bouts of substantial energy expenditure. OBJECTIVE: We determined rates of glucose appearance (Ra), ...disappearance (Rd), and metabolic clearance (MCR) before, during, and after isoenergetic moderate and hard-intensity exercise. DESIGN: Ten men and 8 women received primed-continuous infusion of 6,6-²H₂glucose tracer to measure glucose kinetics. Participants were studied under 3 different conditions with diet unchanged between trials: 1) before, during, and 3 h after 90 min of exercise at 45% of peak oxygen consumption (VO₂peak; E45); 2) before, during, and 3 h after 60 min of exercise at 65% VO₂peak (E65), and 3) in a time-matched sedentary control trial. RESULTS: In men and women, Ra, Rd, and MCR increased above the control trial during exercise and were higher in E65 than in E45 (P < 0.05). Average Ra, Rd, and MCR remained elevated above the control over 3 h of postexercise recovery in men after exercise in E45 and E65 (P < 0.05), and blood glucose concentrations were depressed below the control during recovery (P < 0.05). Glucose concentrations were not depressed in women during 3 h of postexercise recovery, and in contrast with that in men, average Ra and Rd did not remain significantly elevated during postexercise recovery in women, although MCR did remain elevated in E65 (P < 0.05). CONCLUSIONS: After exercise bouts, women are better able to maintain glucose concentrations at sedentary control levels, thus not requiring the counter-regulation of glucose production that is seen in men and requiring less accentuation of lipid metabolism.
The mdx mouse is a model for Duchenne muscular dystrophy (DMD), a debilitating disease affecting striated muscle. It is established that the fatty acid (FA) composition of skeletal muscle ...phospholipid (PL) is altered in mdx mice, but it is not known if cardiac muscle is similarly affected by dystrophin-deficiency. We tested FA profiles in PL and triacylglycerol (TAG) in cardiac muscle of 12-week old mdx and control (con) mice. Of 22 different FA, similar to our previous finding for skeletal muscle, the most abundant FA in heart PL were palmitic, stearic,
cis
-vaccenic, linoleic, and docosahexaenoic acid, while for TAG the most abundant FA were palmitic, oleic,
cis
-vaccenic, and linoleic acid. In comparing mdx and con, no significant group differences were detected for any FA in PL or TAG. Thus, unlike skeletal muscle, FA composition in cardiac muscle PL is not different between mdx and con at the age studied. The results can be understood in the context of tissue-specific disease severity in mdx mice, as pathology is quite modest in cardiac compared with skeletal muscle.
Abstract only
We have previously shown that the content of triacylglycerol (TAG) in the liver transiently increases after a single bout of exercise in untrained mice, and this phenomenon has been ...observed in human subjects as well. This discovery depicted a new phenomenon in the metabolic exercise response. Here we propose the term “lipogenic flexibility” to describe this ability to rapidly alter hepatic TAG content in response to FFA supply. To explore lipogenic flexibility after exercise, we performed lipidomics analysis on liver samples obtained 3 hours after exercise and the following day. Female mice performed a single bout of continuous exercise (CE), high intensity interval exercise (HIIE), or no exercise (CON). The total concentration of hepatic TAG rose 3 hours after exercise (P < 0.05 for both CE and HIIE vs CON), but the total concentration of all other measured lipid classes remained unchanged after exercise (NSD). Hepatic TAG declined back to control levels by the day after exercise. We performed correlation analysis to test the association of TAG (an inert lipid depot) with lipotoxic lipid classes in the liver. Hepatic TAG was positively correlated with hepatic diacylglycerol (DAG) in CON (P < 0.05); however, during the hepatic TAG pool expansion after exercise, liver TAG and DAG were no longer significantly correlated with one another (NSD). Exhibiting lipogenic flexibility after exercise appears to break the equilibration between DAG and TAG, allowing fatty acids to be drawn toward the inert lipid pool (TAG) and away from the lipotoxic lipid pool (DAG). The results suggest that the TAG pool actively expands to buffer elevated FFA supply after exercise and may act to prevent lipotoxicity.
Support or Funding Information
This work was supported by the Faculty Research Grant Program of Rutgers University, the American Diabetes Association grant # 7‐13‐JF‐27‐BR to G Henderson, and the Purdue University College of Health and Human Sciences.
Protein metabolism adapts during caloric restriction (CR) to minimize protein loss, and it is unclear whether greater fat stores favorably affect this response. We sought to determine whether protein ...metabolism is related to degree of obesity and whether the response to CR is impacted by pre-CR adiposity level. Whole body protein metabolism was studied in 12 obese women over a wide range of BMI (30–53 kg/m2) as inpatients using 1-13Cleucine as a tracer following 5 days of a weight-maintaining diet and then after 30 days of CR (1,400 kcal deficit with maintained protein intake). When expressed as total rates, per body weight (BW) or per fat-free mass (FFM), leucine rate of appearance (Ra), and nonoxidative leucine disposal (NOLD) were significantly higher in the individuals with a greater degree of obesity (P < 0.05). Leucine oxidation (Rox) was also higher in more highly obese women when expressed as a total rate (P < 0.05) but not if expressed per BW or FFM. CR reduced BW, FFM, and fat mass (P < 0.001), and declines were relatively similar between individuals. CR reduced Ra (P < 0.001), NOLD (P < 0.01), and Rox (P < 0.05), and the relative decline was not affected by differences in fat mass. CR-induced declines were significant even when Ra and NOLD were normalized to BW or FFM. We conclude that fat mass, like FFM, is a key determinant of protein turnover. However, during CR, higher fat mass does not favorably alter the response of protein metabolism and does not mitigate the loss of FFM.
It is known that chronic endurance training leads to improvements in the lipoprotein profile, but less is known about changes that occur during postexercise recovery acutely. We analyzed triglyceride ...(TG), cholesterol classes and apolipoproteins in samples collected before, during and after individual moderate- and hard-intensity exercise sessions in men and women that were isoenergetic between intensities. Young healthy men (
n
= 9) and young healthy women (
n
= 9) were studied under three different conditions with diet unchanged between trials: (1) before, during and 3 h after 90 min of exercise at 45% VO
2
peak (E45); (2) before, during and 3 h after 60 min of exercise at 65% VO
2
peak (E65), and (3) in a time-matched sedentary control trial (C). At baseline, high-density lipoprotein cholesterol (HDL-C) was higher in women than men (
P
< 0.05). In men and in women, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), HDL-C, apolipoprotein A-I (apoA-I), apolipoprotein B (apoB), and LDL peak particle size were unaltered by exercise either during exertion or after 3 h of recovery. In women, but not in men, average plasma TG was significantly reduced below C at 3 h postexercise by approximately 15% in E45 and 25% in E65 (
P
< 0.05) with no significant difference between exercise intensities. In summary, plasma TG concentration rapidly declines following exercise in women, but not in men. These results demonstrate an important mechanism by which each individual exercise session may incrementally reduce the risk for cardiovascular disease (CVD) in women.
The effects of prolonged caloric restriction (CR) on protein kinetics in lean subjects has not been investigated previously. The purpose of this study was to test the hypotheses that 21 days of CR in ...lean subjects would 1) result in significant losses of lean mass despite a suppression in leucine turnover and oxidation and 2) negatively impact exercise performance. Nine young, normal-weight men 23 +/- 5 y, 78.6 +/- 5.7 kg, peak oxygen consumption (Vo2 peak) 45.2 +/- 7.3 ml.kg(-1).min(-1), mean +/- SD were underfed by 40% of the calories required to maintain body weight for 21 days and lost 3.8 +/- 0.3 kg body wt and 2.0 +/- 0.4 kg lean mass. Protein intake was kept at 1.2 g.kg(-1).day(-1). Leucine kinetics were measured using alpha-ketoisocaproic acid reciprocal pool model in the postabsorptive state during rest and 50 min of exercise (EX) at 50% of Vo2 peak). Body composition, basal metabolic rate (BMR), and exercise performance were measured throughout the intervention. At rest, leucine flux (approximately 131 micromol.kg(-1).h(-1)) and oxidation (R(ox); approximately 19 micromol.kg(-1).h(-1)) did not differ pre- and post-CR. During EX, leucine flux (129 +/- 6 vs. 121 +/- 6) and R(ox) (54 +/- 6 vs. 46 +/- 8) were lower after CR than they were pre-CR. Nitrogen balance was negative throughout the intervention ( approximately 3.0 g N/day), and BMR declined from 1,898 +/- 262 to 1,670 +/- 203 kcal/day. Aerobic performance (Vo2 peak, endurance cycling) was not impacted by CR, but arm flexion endurance decreased by 20%. In conclusion, 3 wk of caloric restriction reduced leucine flux and R(ox) during exercise in normal-weight young men. However, despite negative nitrogen balance and loss of lean mass, whole body exercise performance was well maintained in response to CR.
We describe the isotopic exchange of lactate and pyruvate after arm vein infusion of 3-(13)Clactate in men during rest and exercise. We tested the hypothesis that working muscle (limb net lactate and ...pyruvate exchange) is the source of the elevated systemic lactate-to-pyruvate concentration ratio (L/P) during exercise. We also hypothesized that the isotopic equilibration between lactate and pyruvate would decrease in arterial blood as glycolytic flux, as determined by relative exercise intensity, increased. Nine men were studied at rest and during exercise before and after 9 wk of endurance training. Although during exercise arterial pyruvate concentration decreased to below rest values (P < 0.05), pyruvate net release from working muscle was as large as lactate net release under all exercise conditions. Exogenous (arterial) lactate was the predominant origin of pyruvate released from working muscle. With no significant effect of exercise intensity or training, arterial isotopic equilibration (IE(pyruvate)/IE(lactate)).100%, where IE is isotopic enrichment decreased significantly (P < 0.05) from 60 +/- 3.1% at rest to an average value of 12 +/- 2.7% during exercise, and there were no changes in femoral venous isotopic equilibration. These data show that 1). the isotopic equilibration between lactate and pyruvate in arterial blood decreases significantly during exercise; 2). working muscle is not solely responsible for the decreased arterial isotopic equilibration or elevated arterial L/P occurring during exercise; 3). working muscle releases similar amounts of lactate and pyruvate, the predominant source of the latter being arterial lactate; 4). pyruvate clearance from blood occurs extensively outside of working muscle; and 5). working muscle also releases alanine, but alanine release is an order of magnitude smaller than lactate or pyruvate release. These results portray the complexity of metabolic integration among diverse tissue beds in vivo.
Epstein-Barr virus (EBV), a human herpesvirus, establishes a persistent asymptomatic infection of the circulating B-lymphocyte pool. The mechanism of virus persistence is not understood but, given ...the limited lifespan of most B cells in vivo, it seems most likely that EBV-infected cells must gain access to the long-lived memory B-cell pool. Here we show in an in vitro system that EBV, through expression of the full set of eight virus-coded 'latent' proteins, can protect human B cells from programmed cell death (apoptosis), the deletion mechanism which normally restricts entry into memory. We have found that EBV-positive Burkitt's lymphoma (BL) cell clones retaining the original tumour cell phenotype and expressing only one of the virus latent proteins, the nuclear antigen EBNA 1, are extremely sensitive to apoptosis; in this respect they resemble the tumour's normal cell of origin found in the germinal centres of lymphoid tissue. By contrast, isogenic BL cell clones which have activated expression of all eight EBV latent proteins are resistant to the induction of apoptosis. The EBV latent proteins should therefore be seen not just as activators of B-cell proliferation but, perhaps more importantly, as mediators of enhanced B-cell survival.
The effects of exercise on energy substrate metabolism persist into the postexercise recovery period. We sought to derive bicarbonate retention factors (k) to correct for carbon tracer oxidized, but ...retained from pulmonary excretion before, during, and after exercise. Ten men and nine women received a primed-continuous infusion of (13)Cbicarbonate (sodium salt) under three different conditions: 1) before, during, and 3 h after 90 min of exercise at 45% peak oxygen consumption (Vo(2peak)); 2) before, during, and 3 h after 60 min of exercise at 65% Vo(2peak); and 3) during a time-matched resting control trial, with breath samples collected for determination of (13)CO(2) excretion rates. Throughout the resting control trial, k was stable and averaged 0.83 in men and women. During exercise, average k in men was 0.93 at 45% Vo(2peak) and 0.94 at 65% Vo(2peak), and in women k was 0.91 at 45% Vo(2peak) and 0.92 at 65% Vo(2peak), with no significant differences between intensities or sexes. After exercise at 45% Vo(2peak), k returned rapidly to control values in men and women, but following exercise at 65% Vo(2peak), k was significantly less than control at 30 and 60 min postexercise in men (0.74 and 0.72, respectively, P < 0.05) and women (0.75 and 0.76, respectively, P < 0.05) with no significant postexercise differences between men and women. We conclude that bicarbonate/CO(2) retention is transiently increased in men and women for the first hour of postexercise recovery following endurance exercise bouts of hard but not moderate intensity.
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