No effect of menstrual cycle phase on glycerol or palmitate kinetics during 90 min of moderate exercise.

The systemic flux of glycerol and palmitate [a representative nonesterified free fatty acid (NEFA)] was assessed in three different phases of the menstrual cycle at rest and during moderate-intensity exercise. It was hypothesized that circulating glycerol and NEFA turnover would be greatest in the midfollicular (MF) phase of the menstrual cycle, when estrogen is elevated but progesterone low, followed by the midluteal phase (ML; high estrogen and progesterone), and lowest in the early follicular (EF) phase of the menstrual cycle (low estrogen and progesterone). Subjects included moderately active, eumenorrheic, healthy women. Testing occurred after 3 days of diet control and after an overnight fast (12-13 h). Resting and exercise (50% maximal oxygen uptake, 90 min) measurements of tracer-determined glycerol and palmitate kinetics were made. There was a significant increase in both glycerol and palmitate turnover from rest to exercise in all phases of the menstrual cycle (P<0.0001). No significant differences, however, were observed between cycle phases in the systemic flux of glycerol or palmitate, at rest or during exercise. Maximal peripheral lipolysis during exercise, as represented by glycerol rate of appearance at 90 min, equaled 8.45+/-0.96, 8.35+/-1.12, and 7.71+/-0.96 micromol.kg-1.min-1 in the EF, MF, and ML phases, respectively. Circulating free fatty acid utilization also peaked at 90 min of exercise, as indicated by the palmitate rate of disappearance (3.31+/-0.35, 3.17+/-0.39, and 3.47+/-0.26 micromol.kg-1.min-1) in the EF, MF, and ML phases, respectively. In conclusion, systemic rates of glycerol and NEFA turnover (as represented by palmitate flux) were not significantly affected by the cyclic fluctuations in estrogen and progesterone that occur throughout the normal menstrual cycle, either at rest or during 90 min of moderate exercise.     

Resting and exercise ventilatory chemosensitivity across the menstrual cycle

We hypothesized that resting and exercise ventilatory chemosensitivity would be augmented in women when estrogen and progesterone levels are highest during the luteal phase of the menstrual cycle. Healthy, young females (n = 10; age = 23 ± 5 yrs) were assessed across one complete cycle: during early follicular (EF), late follicular (LF), early luteal, and mid-luteal (ML) phases. We measured urinary conjugates of estrogen and progesterone daily. To compare values of ventilatory chemosensitivity and day-to-day variability of measures between sexes, males (n = 10; age = 26 ± 7 yrs) were assessed on 5 nonconsecutive days during a 1-mo period. Resting ventilation was measured and hypoxic chemosensitivity assessed using an isocapnic hypoxic ventilatory response (iHVR) test. The hypercapnic ventilatory response was assessed using the Read rebreathing protocol and modified rebreathing tests. Participants completed submaximal cycle exercise in normoxia and hypoxia. We observed a significant effect of menstrual-cycle phase on resting minute ventilation, which was elevated in the ML phase relative to the EF and LF phases. Compared with males, resting end-tidal CO(2) was reduced in females during the EF and ML phases but not in the LF phase. We found that iHVR was unaffected by menstrual-cycle phase and was not different between males and females. The sensitivity to chemical stimuli was unaffected by menstrual-cycle phase, meaning that any hormone-mediated effect is of insufficient magnitude to exceed the inherent variation in these chemosensitivity measures. The ventilatory recruitment threshold for CO(2) was generally lower in women, which is suggestive of a hormonally related lowering of the ventilatory recruitment threshold. We detected no effect of menstrual-cycle phase on submaximal exercise ventilation and found that the ventilatory response to normoxic and hypoxic exercise was quantitatively similar between males and females. This suggests that feed-forward and feed-back influences during exercise over-ride the effects of naturally occurring changes in sex hormones.     

Women at altitude: carbohydrate utilization during exercise at 4,300 m.

To evaluate the hypothesis that exposure to high altitude would reduce blood glucose and total carbohydrate utilization relative to sea level (SL), 16 young women were studied over four 12-day periods: at 50% of peak O(2) consumption in different menstrual cycle phases (SL-50), at 65% of peak O(2) consumption at SL (SL-65), and at 4,300 m (HA). After 10 days in each condition, blood glucose rate of disappearance (R(d)) and respiratory exchange ratio were measured at rest and during 45 min of exercise. Glucose R(d) during exercise at HA (4.71 +/- 0.30 mg. kg(-1). min(-1)) was not different from SL exercise at the same absolute intensity (SL-50 = 5.03 mg. kg(-1). min(-1)) but was lower at the same relative intensity (SL-65 = 6.22 mg. kg(-1). min(-1), P < 0.01). There were no differences, however, when glucose R(d) was corrected for energy expended (kcal/min) during exercise. Respiratory exchange ratios followed the same pattern, except carbohydrate oxidation remained lower (-23.2%, P < 0.01) at HA than at SL when corrected for energy expended. In women, unlike in men, carbohydrate utilization decreased at HA. Relative abundance of estrogen and progesterone in women may partially explain the sex differences in fuel utilization at HA, but subtle differences between menstrual cycle phases at SL had no physiologically relevant effects.     

Influence of menstrual cycle and oral contraceptives on tolerance to uncompensable heat stress

In this study we examined the influence of menstrual cycle phase and oral contraceptive use on thermoregulation and tolerance during uncompensable heat stress. Eighteen women (18-35 years), who differed only with respect to oral contraceptive use (n = 9) or non-use (n = 9), performed light intermittent exercise at 40 degrees C and 30% relative humidity while wearing nuclear, biological and chemical protective clothing. Their responses were compared during the early follicular (EF, days 2-5) and mid-luteal (ML, days 19-22) phases of the menstrual cycle. Since oral contraceptives are presumed to inhibit ovulation, a quasi-early follicular (q-EF) and quasi-mid-luteal (q-ML) phase was assumed for the users. Estradiol and progesterone measurements verified that all subjects were tested during the desired phases of the menstrual cycle. Results demonstrated that rectal temperature (Tre) was elevated in ML compared with EF among the non-users at the beginning and throughout the heat-stress trial. For the users, Tre was higher in q-ML compared with q-EF at the beginning, and for 75 min of the heat-stress exposure. Tolerance times were significantly longer during EF [128.1 (13.4) min, mean (SD)] compared with ML [107.4 (8.6) min] for the nonusers, indicating that these women are at a thermoregulatory advantage during the EF phase of their menstrual cycle. For the users, tolerance times were similar in both the q-EF [113.0 (5.8) min] and q-ML [116.8 (11.2) min] phases and did not differ from those of the non-users. It was concluded that oral contraceptive use had little or no influence on tolerance to uncompensable heat stress, whereas tolerance was increased during EF for non-users of oral contraceptives.     

Vestibulosympathetic reflex during the early follicular and midluteal phases of the menstrual cycle

Evidence suggests that both the arterial baroreflex and vestibulosympathetic reflex contribute to blood pressure regulation, and both autonomic reflexes integrate centrally in the medulla cardiovascular center. A previous report indicated increased sympathetic baroreflex sensitivity during the midluteal (ML) phase of the menstrual cycle compared with the early follicular (EF) phase. On the basis of this finding, we hypothesize an augmented vestibulosympathetic reflex during the ML phase of the menstrual cycle. Muscle sympathetic nerve activity (MSNA), mean arterial pressure (MAP), and heart rate responses to head-down rotation (HDR) were measured in 10 healthy females during the EF and ML phases of the menstrual cycle. Plasma estradiol (Delta72 +/- 13 pg/ml, P < 0.01) and progesterone (Delta8 +/- 2 ng/ml, P < 0.01) were significantly greater during the ML phase compared with the EF phase. The menstrual cycle did not alter resting MSNA, MAP, and heart rate (EF: 13 +/- 3 bursts/min, 80 +/- 2 mmHg, 65 +/- 2 beats/min vs. ML: 14 +/- 3 bursts/min, 81 +/- 3 mmHg, 64 +/- 3 beats/min). During the EF phase, HDR increased MSNA (Delta3 +/- 1 bursts/min, P < 0.02) but did not change MAP or heart rate (Delta0 +/- 1 mmHg and Delta1 +/- 1 beats/min). During the ML phase, HDR increased both MSNA and MAP (Delta4 +/- 1 bursts/min and Delta3 +/- 1 mmHg, P < 0.04) with no change in heart rate (Delta0 +/- 1 beats/min). MSNA and heart rate responses to HDR were not different between the EF and ML phases, but MAP responses to HDR were augmented during the ML phase (P < 0.03). Our results demonstrate that the menstrual cycle does not influence the vestibulosympathetic reflex but appears to alter MAP responses to HDR during the ML phase.     

Menstrual cycle phase and sex influence muscle glycogen utilization and glucose turnover during moderate-intensity endurance exercise

Numerous studies from our and other laboratories have shown that women have a lower respiratory exchange ratio (RER) during exercise than equally trained men, indicating a greater reliance on fat oxidation. Differences in estrogen concentration between men and women likely play a role in this sex difference. Differing estrogen and progesterone concentrations during the follicular (FP) and luteal (LP) phases of the female menstrual cycle suggest that fuel use may also vary between phases. The purpose of the current study was to determine the effect of menstrual cycle phase and sex upon glucose turnover and muscle glycogen utilization during endurance exercise. Healthy, recreationally active young women (n = 13) and men (n = 11) underwent a primed constant infusion of [6,6-2H]glucose with muscle biopsies taken before and after a 90-min cycling bout at 65% peak O2 consumption. LP women had lower glucose rate of appearance (Ra, P = 0.03), rate of disappearance (Rd, P = 0.03), and metabolic clearance rate (MCR, P = 0.04) at 90 min of exercise and lower proglycogen (P = 0.04), macroglycogen (P = 0.04), and total glycogen (P = 0.02) utilization during exercise compared with FP women. Men had a higher RER (P = 0.02), glucose Ra (P = 0.03), Rd (P = 0.03), and MCR (P = 0.01) during exercise compared with FP women, and men had a higher RER at 75 and 90 min of exercise (P = 0.04), glucose Ra (P = 0.01), Rd (P = 0.01), and MCR (P = 0.001) and a greater PG utilization (P = 0.05) compared with LP women. We conclude that sex, and to a lesser extent menstrual cycle, influence glucose turnover and glycogen utilization during moderate-intensity endurance exercise.     

Menstrual cycle and sex affect hemodynamic responses to combined orthostatic and heat stress

Women have decreased orthostatic tolerance compared with men, and anecdotal evidence suggests women are more susceptible to orthostatic intolerance in warm environments. Because estrogen and progesterone affect numerous physiological variables that may alter orthostatic tolerance, the purpose of our study was to compare orthostatic tolerance across the menstrual cycle phases in women during combined orthostatic and heat stress and to compare these data with those of men. Eight normally menstruating women and eight males (22 +/- 4.0 and 23 +/- 3.5 yr, respectively) completed the protocol. Women were studied during their early follicular (EF), ovulatory (OV), and midluteal (ML) phases. Men were studied twice within 2-4 wk. Heart rate, cardiac output, blood pressure, core temperature (T(c)), and cutaneous vascular conductance (CVC) were measured during three head-up tilt tests, consisting of two tilts in the thermoneutral condition and one tilt after a 0.5 degrees C rise in T(c). There was no difference in orthostatic tolerance across the menstrual cycle phases, despite higher CVC in the ML phase after heating (EF, 42.3 +/- 4.8; OV, 40.1 +/- 3.7; ML, 57.5 +/- 4.5; P < 0.05). Orthostatic tolerance in the heat was greater in men than women (P < 0.05). These data suggest that although many physiological variables associated with blood pressure regulation fluctuate during the menstrual cycle, orthostatic tolerance in the heat remains unchanged. Additionally, our data support a clear sex difference in orthostatic tolerance and extend upon previous data to show that the sex difference in the heat is not attributable to fluctuating hormone profiles during the menstrual cycle.     

Glucose kinetics and substrate oxidation during exercise in the follicular and luteal phases.

The purpose of this investigation was to determine whether plasma glucose kinetics and substrate oxidation during exercise are dependent on the phase of the menstrual cycle. Once during the follicular (F) and luteal (L) phases, moderately trained subjects [peak O(2) uptake (V(O(2))) = 48.2 +/- 1.1 ml. min(-1). kg(-1); n = 6] cycled for 25 min at approximately 70% of the V(O(2)) at their respective lactate threshold (70%LT), followed immediately by 25 min at 90%LT. Rates of plasma glucose appearance (R(a)) and disappearance (R(d)) were determined with a primed constant infusion of [6,6-(2)H]glucose, and total carbohydrate (CHO) and fat oxidation were determined with indirect calorimetry. At rest and during exercise at 70%LT, there were no differences in glucose R(a) or R(d) between phases. CHO and fat oxidation were not different between phases at 70%LT. At 90%LT, glucose R(a) (28.8 +/- 4.8 vs. 33.7 +/- 4.5 micromol. min(-1). kg(-1); P < 0.05) and R(d) (28.4 +/- 4.8 vs. 34.0 +/- 4.1 micromol. min(-1). kg(-1); P < 0.05) were lower during the L phase. In addition, at 90%LT, CHO oxidation was lower during the L compared with the F phase (82.0 +/- 12.3 vs. 93.8 +/- 9.7 micromol. min(-1) .kg(-1); P < 0.05). Conversely, total fat oxidation was greater during the L phase at 90%LT (7.46 +/- 1.01 vs. 6.05 +/- 0.89 micromol. min(-1). kg(-1); P < 0.05). Plasma lactate concentration was also lower during the L phase at 90%LT concentrations (2.48 +/- 0.41 vs. 3.08 +/- 0.39 mmol/l; P < 0.05). The lower CHO utilization during the L phase was associated with an elevated resting estradiol (P < 0.05). These results indicate that plasma glucose kinetics and CHO oxidation during moderate-intensity exercise are lower during the L compared with the F phase in women. These differences may have been due to differences in circulating estradiol.     

Conditioning exercise decreases premenstrual symptoms. A prospective controlled three month trial

Conditioning exercise decreased premenstrual symptoms during 3 months of a prospective controlled training study. Eight women with normal ovulatory menstrual cycles began a running exercise training programme while completing intensity-graded questionnaires concerning molimina. Six sedentary control women followed the same protocol for 3 months but did not exercise. Oral basal temperatures evaluated by mean temperature analysis were obtained for all cycles. Exercise distance and time, average exercise heart rate, basal and maximal heart rate and body weights were recorded prospectively and evaluated during the control (0) and 3rd month of the study. Mid-luteal phase progesterone and estrogen levels were sampled during the analyzed cycles for the exercise group. Molimina did not change over 3 months time in the control group. The exercise group, after increasing distance run to 51.0 +/- 18.1 km/cycle at 3 months, showed decreases in overall molimina (scores on a 9-point scale) 6.5 +/- 1.8 to 3.5 +/- 0.9, p less than 0.01). Breast symptoms decreased from 8.3 +/- 0.7, p less than 0.005. Fluid symptoms also decreased from 7.3 +/- 1.8 to 5.5 +/- 0.9, p less than 0.025. Menstrual cycle intervals, luteal lengths, body weights and mid-luteal estrogen and progesterone levels were normal and unchanged. Moderate exercise training without major weight, hormonal or menstrual cycle alteration significantly decreased premenstrual symptoms.     

Menstrual cycle phase dissociation of blood glucose homeostasis during exercise

The purpose of this investigation was to evaluate the effects of 24-h carbohydrate-poor diet on metabolic and hormonal responses induced by prolonged exercise in both follicular (FP) and luteal (LP) phases of the menstrual cycle. At mid-FP and at mid-LP, seven eumenorrheic young women [means +/- SE; chronological age, 21.1 +/- 0.6 yr; O2 uptake (VO2) peak, 43.7 +/- 2.0 ml X kg-1 X min-1; body fat, 19.2 +/- 2.0%] were subjected to a 90-min bicycle exercise period at an intensity representing 63% of their measured VO2 peak. Venous blood samples obtained before and during exercise were analyzed for levels of substrates (glucose, lactate, free fatty acids, glycerol) and hormones (luteinizing hormone, progesterone, estradiol, insulin, glucagon, cortisol, catecholamines). Contrary to FP, a significant (P less than 0.01) decrease in blood glucose concentration was observed after 70 and 90 min of exercise during LP. Significant phase differences were also observed for blood lactate (highest in FP), cortisol (highest in LP), and progesterone (highest in LP). Although not significantly different, tendencies for menstrual phase dissociations were noticed for some of the other measured variables. Hence, a menstrual phase dissociation in circulating glucose level, unmasked by a prolonged exercise performed after a 24-h carbohydrate-poor diet, suggests to the authors a specific metabolic involvement for gonadotrophic and/or gonadal hormones.     

Fatty acid reesterification but not oxidation is increased by oral contraceptive use in women.

We evaluated the hypothesis that fatty acid reesterification would be increased during rest and exercise in the midluteal menstrual cycle phase and during oral contraceptive use, when ovarian hormone concentrations are high, compared with the early follicular phase. Subjects were eight moderately active, weight-stable, eumenorrheic women (24.8 +/- 1.2 yr, peak oxygen consumption = 42.0 +/- 2.3 ml.kg(-1).min(-1)) who had not taken oral contraceptives for at least 6 mo. Plasma free fatty acid (FFA) kinetics were assessed in the 3-h postprandial state by continuous infusion of [1-(13)C]palmitate and [1,1,2,3,3-(2)H]glycerol during 90 min of rest and 60 min of exercise at 45% and 65% peak oxygen consumption in the early follicular and midluteal menstrual cycle phases and during the inactive- and high-dose phases following 4 mo of oral contraceptive use. Plasma FFA rates of appearance, disappearance, and oxidation increased significantly from rest to exercise with no differences noted between menstrual cycle or oral contraceptive phases or exercise intensities. Compared with either menstrual cycle phase, oral contraceptive use resulted in an increase in plasma-derived fatty acid reesterification and a decrease in the proportion of plasma FFA rate of disappearance that was oxidized at rest and during exercise. Endogenous and exogenous synthetic ovarian hormones do not exert a measurable influence on plasma FFA turnover or oxidation at rest or during moderate-intensity exercise in the 3-h postprandial state when carbohydrate use predominates. The increase in whole body lipolytic rate during exercise noted previously with oral contraceptive use is not matched by an increase in fatty acid oxidation and results in an increase in reesterification. Synthetic ovarian hormones contained in oral contraceptives increase lipolytic rate, but fatty acid oxidation during exercise is determined by exercise intensity and its metabolic and endocrine consequences.     

Regulation of exercise carbohydrate metabolism by estrogen and progesterone in women

To assess the roles of endogenous estrogen (E2) and progesterone (P4) in regulating exercise carbohydrate use, we used pharmacological suppression and replacement to create three distinct hormonal environments: baseline (B), with E2 and P4 low; estrogen only (E), with E2 high and P4 low; and estrogen/progesterone (E + P), with E2 and P4 high. Blood glucose uptake (R(d)), total carbohydrate oxidation (CHO(ox)), and estimated muscle glycogen utilization (EMGU) were assessed during 60 min of submaximal exercise by use of stable isotope dilution and indirect calorimetry in eight eumenorrheic women. Compared with B (1.26 +/- 0.04 g/min) and E + P (1.27 +/- 0.04 g/min), CHO(ox) was lower with E (1.05 +/- 0.02 g/min). Glucose R(d) tended to be lower with E and E + P relative to B. EMGU was 25% lower with E than with B or E + P. Plasma free fatty acids (FFA) were inversely related to EMGU (r(2) = 0.49). The data suggest that estrogen lowers CHO(ox) by reducing EMGU and glucose R(d). Progesterone increases EMGU but not glucose R(d). The opposing actions of E(2) and P(4) on EMGU may be mediated by their impact on FFA availability or vice versa.     

Substrate turnover and oxidation during moderate-intensity exercise following acute plasma volume expansion.

In previous work using prolonged, light cycle exercise, we were unable to demonstrate an effect of acute plasma volume (PV) expansion on glucose kinetics or substrate oxidation, despite a decline in whole-body lipolysis (Phillips et al., 1997). However, PV is known to decrease arterial O2 content. The purpose of this study was to examine whether substrate turnover and oxidation would be altered with heavier exercise where the challenge to O2 delivery is increased. Eight untrained males (VO2max = 3.52 +/- 0.12 l/min) twice performed 90 min of cycle ergometry at 62 % VO2peak, both prior to (CON) and following induced plasma volume expansion (Dextran [6 %] or Pentaspan [10 %]) (6.7 ml/kg) (PVX). Glucose and glycerol kinetics were determined with primed constant infusions of [6.6-(2)H2] glucose and [(2)H5] glycerol, respectively. PVX resulted in a 15.8 +/- 2.2 % increase (p < 0.05) in PV. Glucose and glycerol appearance (Ra) and utilization (Rd), although increasing progressively (p < 0.05) with exercise, were not different between conditions. Similarly, no differences in substrate oxidation, either fat or carbohydrate, were observed between the two conditions. Prolonged exercise resulted in an increase (p < 0.05) in plasma glucagon and a decrease (p < 0.05) in plasma insulin during both conditions. With PVX, the exercise-induced increase in glucagon was diminished (p < 0.05). We conclude that impairment in O2 content mediated by an elevated PV does not alter glucose, and glycerol kinetics or substrate oxidation even at moderate exercise intensity.     

Predominance of distal skin temperature changes at sleep onset across menstrual and circadian phases

Menstrual cycle-associated changes in reproductive hormones affect body temperature in women. We aimed to characterize the interaction between the menstrual, circadian, and scheduled sleep-wake cycles on body temperature regulation. Eight females entered the laboratory during the midfollicular (MF) and midluteal (ML) phases of their menstrual cycle for an ultradian sleep-wake cycle procedure, consisting of 36 cycles of 60-minute wake episodes alternating with 60-minute nap opportunities, in constant bed-rest conditions. Core body temperature (CBT) and distal skin temperature (DT) were recorded and used to calculate a distal-core gradient (DCG). Melatonin, sleep, and subjective sleepiness were also recorded. The circadian variation of DT and DCG was not affected by menstrual phase. DT and DCG showed rapid, large nap episode-dependent increases, whereas CBT showed slower, smaller nap episode-dependent decreases. DCG values were significantly reduced for most of the wake episode in an overall 60-minute wake/60-minute nap cycle during ML compared to MF, but these differences were eliminated at the wake-to-nap lights-out transition. Nap episode-dependent decreases in CBT were further modulated as a function of both circadian and menstrual factors, with nap episode-dependent deceases occurring more prominently during the late afternoon/evening in ML, whereas nap episode-dependent DT and DCG increases were not significantly affected by menstrual phase but only circadian phase. Circadian rhythms of melatonin secretion, DT, and DCG were significantly phase-advanced relative to CBT and sleep propensity rhythms. This study explored how the thermoregulatory system is influenced by an interaction between circadian phase and vigilance state and how this is further modulated by the menstrual cycle. Current results agree with the thermophysiological cascade model of sleep and indicate that despite increased CBT during ML, heat loss mechanisms are maintained at a similar level during nap episodes, which may allow for comparable circadian sleep propensity rhythms between menstrual phases.     

Heart-type fatty acid-binding protein reciprocally regulates glucose and fatty acid utilization during exercise

The role of heart-type cytosolic fatty acid-binding protein (H-FABP) in mediating whole body and muscle-specific long-chain fatty acid (LCFA) and glucose utilization was examined using exercise as a phenotyping tool. Catheters were chronically implanted in a carotid artery and jugular vein of wild-type (WT, n = 8), heterozygous (H-FABP(+/-), n = 8), and null (H-FABP(-/-), n = 7) chow-fed C57BL/6J mice, and mice were allowed to recover for 7 days. After a 5-h fast, conscious, unrestrained mice were studied during 30 min of treadmill exercise (0.6 mph). A bolus of [(125)I]-15-(p-iodophenyl)-3-R,S-methylpentadecanoic acid and 2-deoxy-[(3)H]glucose was administered to obtain rates of whole body metabolic clearance (MCR) and indexes of muscle LCFA (R(f)) and glucose (R(g)) utilization. Fasting, nonesterified fatty acids (mM) were elevated in H-FABP(-/-) mice (2.2 +/- 0.9 vs. 1.3 +/- 0.1 and 1.3 +/- 0.2 for WT and H-FABP(+/-)). During exercise, blood glucose (mM) increased in WT (11.7 +/- 0.8) and H-FABP(+/-) (12.6 +/- 0.9) mice, whereas H-FABP(-/-) mice developed overt hypoglycemia (4.8 +/- 0.8). Examination of tissue-specific and whole body glucose and LCFA utilization demonstrated a dependency on H-FABP with exercise in all tissues examined. Reductions in H-FABP led to decreasing exercise-stimulated R(f) and increasing R(g) with the most pronounced effects in heart and soleus muscle. Similar results were seen for MCR with decreasing LCFA and increasing glucose clearance with declining levels of H-FABP. These results show that, in vivo, H-FABP has reciprocal effects on glucose and LCFA utilization and whole body fuel homeostasis when metabolic demands are elevated by exercise.     

Substrate utilization during exercise in formerly morbidly obese women.

The purpose of this study was to compare substrate utilization during fasting and submaximal exercise in morbidly obese women after weight loss (WL) with that in weight-matched controls (C). WL were studied in the weight-stable condition approximately 24 mo after gastric bypass surgery. Energy intake (self-reported) and expenditure ((2)H(2)(18)O) were also compared. The respiratory exchange ratio during exercise at the same absolute (15 W) workload was significantly (P < or = 0.05) elevated in WL vs. C (0.90 +/- 0.02 vs. 0.83 +/- 0.03); this was reflected as lower fat utilization in WL (29.7 +/- 4.8 vs. 53.2 +/- 9.7% of energy from fat). Respiratory exchange ratio during exercise at the same relative (65% of maximal O(2) uptake) intensity was also significantly (P < 0.05) elevated in WL (0.96 +/- 0.01 vs. 0.89 +/- 0.02), and fat use was concomitantly depressed (12.4 +/- 3.0 vs. 34.3 +/- 9.9% of energy from fat). Resting substrate utilization, daily energy expenditure, and self-reported relative macronutrient intake did not differ between groups. These data suggest that lipid oxidation is depressed during physical activity in WL. This defect may, at least in part, contribute to a propensity for the development of morbid obesity.     

The effects of ovarian hormones on glucose and fatty acid oxidation during exercise in female ovariectomized rats

The effects of ovarian hormones on glucose and fatty acid oxidation during exercise were investigated in adult female ovariectomized rats. Rats subdivided into 3 groups received intraperitoneal injections of hormones or sesame oil for 8 days. Estrogen (E) treated rats received 17-beta estradiol in daily doses of 2 micrograms. Estrogen and progesterone treated rats (EP) received 17-beta estradiol in daily doses of 2 micrograms and 2 mg, respectively. Control rats (S) received sesame oil alone. After an overnight fast, rats ran at the speed of 25 m.min-1 for 60 min. [U-14C]glucose or [1-14C]palmitate was injected into rats at 5 min of exercise and before 10 min of exercise, respectively. Expired 14CO2 was collected using bottomless chamber on a treadmill belt. No significant differences were found in mean blood glucose, lactate and plasma free fatty acid concentrations after the exercise. Until the end of the exercise 34.7 +/- 2.6 (E, n = 5), 40.8 +/- 2.9 (EP, n = 5) and 43.7 +/- 3.5% (S, n = 6) (mean +/- SE) of 14C which was injected as 14C-glucose was recovered as 14CO2. During 60 min of the exercise 27.5 +/- 1.0 (E, n = 7), 19.8 +/- 2.7 (EP, n = 6) and 25.0 +/- 1.9% (S, n = 6) of 14C which was injected as 14C-palmitate was recovered as 14CO2. A significant difference was found in this rate between E and EP (P less than 0.05). It was concluded that estrogen treatment stimulated fatty acid oxidation compared with the estrogen plus progesterone treatment and tended to inhibit glucose oxidation during prolonged exercise.     

Oxidation of nonplasma fatty acids during exercise is increased in women with abdominal obesity.

We evaluated plasma fatty acid availability and plasma and whole body fatty acid oxidation during exercise in five lean and five abdominally obese women (body mass index = 21 +/- 1 vs. 38 +/- 1 kg/m(2)), who were matched on aerobic fitness, to test the hypothesis that obesity alters the relative contribution of plasma and nonplasma fatty acids to total energy production during exercise. Subjects exercised on a recumbent cycle ergometer for 90 min at 54% of their peak oxygen consumption. Stable isotope tracer methods ([(13)C]palmitate) were used to measure fatty acid rate of appearance in plasma and the rate of plasma fatty acid oxidation, and indirect calorimetry was used to measure whole body substrate oxidation. During exercise, palmitate rate of appearance increased progressively and was similar in obese and lean groups between 60 and 90 min of exercise [3.9 +/- 0.4 vs. 4.0 +/- 0.3 micromol. kg fat free mass (FFM)(-1). min(-1)]. The rate of plasma fatty acid oxidation was also similar in obese and lean subjects (12.8 +/- 1.7 vs. 14.5 +/- 1.8 micromol. kg FFM(-1). min(-1); P = not significant). However, whole body fatty acid oxidation during exercise was 25% greater in obese than in lean subjects (21.9 +/- 1.2 vs. 17.5 +/- 1.6 micromol. kg FFM(-1). min(-1); P < 0.05). These results demonstrate that, although plasma fatty acid availability and oxidation are similar during exercise in lean and obese women, women with abdominal obesity use more fat as a fuel by oxidizing more nonplasma fatty acids.     

Effects of menstrual cycle and oral contraceptive use on calf venous compliance

Numerous studies have shown that the female sex hormones estrogen and progesterone have multiple effects on the vasculature. Thus our goal was to investigate the effects of estrogen and progesterone on calf venous compliance by looking for cyclic changes during the early follicular, ovulatory, and midluteal phases of the menstrual cycle and during high and low hormone phases of oral contraceptive use. Additionally, we wanted to compare the venous compliance of normally menstruating women, oral contraceptive users, and men. We studied eight normally menstruating women (23 +/- 1 yr of age) during the early follicular, ovulatory, and midluteal phases of the menstrual cycle. Nine triphasic oral contraceptive users (21 +/- 1 yr of age) were studied during weeks of high and low hormone concentrations. Eight men (23 +/- 1 yr of age) were studied twice within 2-4 wk. With the use of venous occlusion plethysmography with mercury in-Silastic strain gauges, lower limb venous compliance was measured by inflating a venous collection cuff that was placed on the thigh to 60 mmHg for 8 min and then reducing the pressure to 0 mmHg at a rate of 1 mmHg/s. Venous compliance was calculated as the derivative of the pressure-volume curves. There were no differences between early follicular, ovulatory, and midluteal phases of the menstrual cycle or between high and low hormone phases of oral contraceptive use (P > 0.05). Male venous compliance was significantly greater than in normally menstruating women (P < 0.001) and oral contraceptive users (P < 0.002). These data support a sex difference but also suggest that venous compliance does not change with menstrual cycle phase or during the course of oral contraceptive use.     

Glucose kinetics and exercise performance during phases of the menstrual cycle: effect of glucose ingestion

To study the effect of menstrual cycle phase and carbohydrate ingestion on glucose kinetics and exercise performance, eight healthy, moderately trained, eumenorrheic women cycled at 70% of peak O(2) consumption for 2 h and then performed a 4 kJ/kg body wt time trial. A control (C) and a glucose ingestion (G) trial were completed during the follicular (F) and luteal (L) phases of the menstrual cycle. Plasma substrate concentrations were similar before the commencement of exercise. Glucose rates of appearance and disappearance were higher (P < 0.05) during the 2nd h of exercise in FC than in LC. The percent contribution of carbohydrate to total energy expenditure was greater in FC than in LC, and subjects performed better (13%, P < 0.05) in FC. Performance improved (19% and 26% in FG and LG compared with FC and LC, respectively, P < 0.05) with the ingestion of glucose throughout exercise. These data demonstrate that substrate metabolism and exercise performance are influenced by the menstrual cycle phase, but ingestion of glucose minimizes these effects.