Circadian variations in plasma renin activity, catecholamines and aldosterone during exercise in women

The relationship between hemoglobin and [Formula: see text]: A systematic review and meta-analysis

OBJECTIVE

There is widespread agreement about the key role of hemoglobin for oxygen transport. Both observational and interventional studies have examined the relationship between hemoglobin levels and maximal oxygen uptake ([Formula: see text]) in humans. However, there exists considerable variability in the scientific literature regarding the potential relationship between hemoglobin and [Formula: see text]. Thus, we aimed to provide a comprehensive analysis of the diverse literature and examine the relationship between hemoglobin levels (hemoglobin concentration and mass) and [Formula: see text] (absolute and relative [Formula: see text]) among both observational and interventional studies.

METHODS

A systematic search was performed on December 6th, 2021. The study procedures and reporting of findings followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Article selection and data abstraction were performed in duplicate by two independent reviewers. Primary outcomes were hemoglobin levels and [Formula: see text] values (absolute and relative). For observational studies, meta-regression models were performed to examine the relationship between hemoglobin levels and [Formula: see text] values. For interventional studies, meta-analysis models were performed to determine the change in [Formula: see text] values (standard paired difference) associated with interventions designed to modify hemoglobin levels or [Formula: see text]. Meta-regression models were then performed to determine the relationship between a change in hemoglobin levels and the change in [Formula: see text] values.

RESULTS

Data from 384 studies (226 observational studies and 158 interventional studies) were examined. For observational data, there was a positive association between absolute [Formula: see text] and hemoglobin levels (hemoglobin concentration, hemoglobin mass, and hematocrit (P<0.001 for all)). Prespecified subgroup analyses demonstrated no apparent sex-related differences among these relationships. For interventional data, there was a positive association between the change of absolute [Formula: see text] (standard paired difference) and the change in hemoglobin levels (hemoglobin concentration (P<0.0001) and hemoglobin mass (P = 0.006)).

CONCLUSION

These findings suggest that [Formula: see text] values are closely associated with hemoglobin levels among both observational and interventional studies. Although our findings suggest a lack of sex differences in these relationships, there were limited studies incorporating females or stratifying results by biological sex.

HPA axis activity across the menstrual cycle - a systematic review and meta-analysis of longitudinal studies

Differential HPA axis function has been proposed to underlie sex-differences in mental disorders; however, the impact of fluctuating sex hormones across the menstrual cycle on HPA axis activity is still unclear. This meta-analysis investigated basal cortisol concentrations as a marker for HPA axis activity across the menstrual cycle. Through a systematic literature search of five databases, 121 longitudinal studies were included, summarizing data of 2641 healthy, cycling participants between the ages of 18 and 45. The meta-analysis showed higher cortisol concentrations in the follicular vs. luteal phase (d_SMC = 0.12, p =.004, [0.04 - 0.20]). Comparisons between more precise cycle phases were mostly insignificant, aside from higher concentrations in the menstrual vs. premenstrual phase (d_SMC = 0.17, [0.02 - 0.33], p =.03). In all included studies, nine samples used established cortisol parameters to indicate HPA axis function, specifically diurnal profiles (k = 4) and the cortisol awakening response (CAR) (k = 5). Therefore, the meta-analysis highlights the need for more rigorous investigation of HPA axis activity and menstrual cycle phase.

The Effects of Physical Exercise on Saliva Composition: A Comprehensive Review

Saliva consists of organic and inorganic constituents. During exercise, analysis of the saliva can provide valuable information regarding training stress, adaptation and exercise performance. The objective of the present article was to review the effect of physical exercise on saliva composition. The shift in the composition of the saliva, during and after a workout, reflects the benefits of exercise, its potential risks and the capability of the saliva to serve as a health indicator. The type and the frequency of training, the physical condition and the athletes’ general health influence the hormones, immunoglobulins and saliva enzymes. The correlation between saliva and physical exercise has to be further investigated and the available knowledge to be applied for the benefit of the athletes during sports activities.

Sex differences in the physiological responses to exercise-induced dehydration: consequences and mechanisms

Physiological strain during exercise is increased by mild dehydration (∼1%-3% body mass loss). This response may be sex-dependent, but there are no direct comparative data in this regard. This review aimed to develop a framework for future research by exploring the potential impact of sex on thermoregulatory and cardiac strain associated with exercise-induced dehydration. Sex-based comparisons were achieved by comparing trends from studies that implemented similar experimental protocols but recruited males and females separately. This revealed a higher core temperature (T_c) in response to exercise-induced dehydration in both sexes; however, it seemingly occurred at a lower percent body mass loss in females. Although less clear, similar trends existed for cardiac strain. The average female may have a lower body water volume per body mass compared with males, and therefore the same percent body mass loss between the sexes may represent a larger portion of total body water in females potentially posing a greater physiological strain. In addition, the rate at which T_c increases at exercise onset might be faster in females and induce a greater thermoregulatory challenge earlier into exercise. The T_c response at exercise onset is associated with lower sweating rates in females, which is commonly attributed to sex differences in metabolic heat production. However, a reduced sweat gland sensitivity to stimuli, lower fluid output per sweat gland, and sex hormones promoting fluid retention in females may also contribute. In conclusion, the limited evidence suggests that sex-based differences exist in thermoregulatory and cardiac strain associated with exercise-induced dehydration, and this warrants future investigations.

Renin Activity in Heart Failure with Reduced Systolic Function-New Insights

Regardless of the cause, symptomatic heart failure (HF) with reduced ejection fraction (rEF) is characterized by pathological activation of the renin–angiotensin–aldosterone system (RAAS) with sodium retention and extracellular fluid expansion (edema). Here, we review the role of active renin, a crucial, upstream enzymatic regulator of the RAAS, as a prognostic and diagnostic plasma biomarker of heart failure with reduced ejection fraction (HFrEF) progression; we also discuss its potential as a pharmacological bio-target in HF therapy. Clinical and experimental studies indicate that plasma renin activity is elevated with symptomatic HFrEF with edema in patients, as well as in companion animals and experimental models of HF. Plasma renin activity levels are also reported to be elevated in patients and animals with rEF before the development of symptomatic HF. Modulation of renin activity in experimental HF significantly reduces edema formation and the progression of systolic dysfunction and improves survival. Thus, specific assessment and targeting of elevated renin activity may enhance diagnostic and therapeutic precision to improve outcomes in appropriate patients with HFrEF.

Endocrine responses after a single bout of moderate aerobic exercise in healthy adult humans

Exercise is a stress stimulus for the human organism affecting the homeostatic mechanisms of the body, depending on the type, duration, intensity and frequency of exercise. The aim of this study was to determine the effects of a moderate aerobic exercise bout on the Hypothalamo-Pituitary-Adrenal (HPA) axis acute hormonal responses in healthy adult humans. Twelve healthy male and female volunteers (age: 30.6 ± 4.4 years), performed a single bout of a 30-minute aerobic exercise at 70% of VO2max on a treadmill, following standard diet. Blood samples were collected before (t0), at the end of the exercise bout (t30), and 30 min after the completion of exercise (t60). Serum adrenocorticotropic hormone (ACTH), cortisol (COR), aldosterone (ALDO) and renin (REN) were measured. One-way ANOVA was used for statistics. ACTH and COR decreased after exercise, reaching significance (p < 0.01) 30 min after the completion of the exercise bout. ALDO increased at the end of exercise and remained elevated 30 min after its completion. REN significantly increased at the end of exercise (p < 0.05) and remained elevated. The exercise regimen used in this study had beneficial effects on the stress axis, suggesting that specific exercise protocols can be characterised by mild physiological stress-inducing effects hence be prescribed for special diseased populations.

Diurnal Rhythm of Muscular Strength Depends on Temporal Specificity of Self-Resistance Training

The study investigated the effect of the time-of-day at which maximal isometric voluntary co-contraction (MIVCC) training is conducted on the adaptation and diurnal variation of maximal and explosive force production. Twenty active men underwent a 6-week (3 times per week) MIVCC training of the right elbow joint. The participants were randomly assigned to a morning training group (MTG, 07:00-08:00 hours) and evening training group (ETG, 17:00-18:00 hours). The maximal voluntary force (MVF) and maximal rate of force development (MRFD) during isometric elbow flexion (MVFF and MRFD(F)) and extension (MVF(E) and MRFD(E)) were recorded before (T0) and after (T1) training in the morning and evening. At T0, MVF and MRFD were higher in the evening compared with those in the morning for the MTG and ETG (p ≤ 0.05). At T1, MVFF and MVFE increased in the morning and evening for both groups (p < 0.001). The MRFD(F) and MRFD(E) increased only if training and test session were scheduled at the same time. The relative increase of MVF was greater at the specific time of training for the MTG (12 and 17.6% in MVF(F) and MVF(E), respectively) and ETG (9.8 and 13.4% in MVF(F) and MVF(E), respectively). The diurnal variations in MVF and MRF(D) during flexion and extension disappeared in the MTG and persisted in the ETG. Maximal isometric voluntary co-contraction training enhanced muscle strength whatever the time-of-day at which the training was scheduled without alteration of explosive force. In contrast, to optimize the muscle strength, our results suggested that morning training may be accompanied by the greatest muscle strength gain and blunted muscle strength variation observed between the morning and evening.

The Differential Hormonal Milieu of Morning versus Evening May Have an Impact on Muscle Hypertrophic Potential

Substantial gains in muscle strength and hypertrophy are clearly associated with the routine performance of resistance training. What is less evident is the optimal timing of the resistance training stimulus to elicit these significant functional and structural skeletal muscle changes. Therefore, this investigation determined the impact of a single bout of resistance training performed either in the morning or evening upon acute anabolic signalling (insulin-like growth factor-binding protein-3 (IGFBP-3), myogenic index and differentiation) and catabolic processes (cortisol). Twenty-four male participants (age 21.4±1.9yrs, mass 83.7±13.7kg) with no sustained resistance training experience were allocated to a resistance exercise group (REP). Sixteen of the 24 participants were randomly selected to perform an additional non-exercising control group (CP) protocol. REP performed two bouts of resistance exercise (80% 1RM) in the morning (AM: 0800 hrs) and evening (PM: 1800 hrs), with the sessions separated by a minimum of 72 hours. Venous blood was collected immediately prior to, and 5 min after, each resistance exercise and control sessions. Serum cortisol and IGFBP-3 levels, myogenic index, myotube width, were determined at each sampling period. All data are reported as mean ± SEM, statistical significance was set at P≤0.05. As expected a significant reduction in evening cortisol concentration was observed at pre (AM: 98.4±10.5, PM: 49.8±4.4 ng/ml, P<0.001) and post (AM: 98.0±9.0, PM: 52.7±6.0 ng/ml, P<0.001) exercise. Interestingly, individual cortisol differences pre vs post exercise indicate a time-of-day effect (AM difference: -2±2.6%, PM difference: 14.0±6.7%, P = 0.03). A time-of-day related elevation in serum IGFBP-3 (AM: 3274.9 ± 345.2, PM: 3605.1 ± 367.5, p = 0.032) was also evident. Pre exercise myogenic index (AM: 8.0±0.6%, PM: 16.8±1.1%) and myotube width (AM: 48.0±3.0, PM: 71.6±1.9 μm) were significantly elevated (P<0.001) in the evening. Post exercise myogenic index was greater AM (11.5±1.6%) compared with PM (4.6±0.9%). No difference was observed in myotube width (AM: 48.5±1.5, PM: 47.8±1.8 μm) (P>0.05). Timing of resistance training regimen in the evening appears to augment some markers of hypertrophic potential, with elevated IGFBP-3, suppressed cortisol and a superior cellular environment. Further investigation, to further elucidate the time course of peak anabolic signalling in morning vs evening training conditions, are timely.

Effect of aerobic exercise on premenstrual symptoms, haematological and hormonal parameters in young women

The objective of this study was to investigate the effect of aerobic exercise on premenstrual symptoms, haematological and hormonal parameters in young women. A total of 30 participants aged 16-20 years and complaining of premenstrual syndrome (PMS) were randomly assigned into two groups: a control group received vitamin B6 and Ca supplements once daily and a study group received the same medical treatment and participated in treadmill training three times per week for 3 months. A premenstrual syndrome questionnaire (MSQ), complete blood picture and hormone assays were performed for the assessment of all participants at the start and after the end of the treatment course. The study group showed a significant decrease in all post-treatment subscale symptoms, scores and total score. Haemoglobin, haematocrit, red cell count and platelet count were significantly increased, while mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC) and white blood cell count showed no significant differences. There was also a significant decrease in prolactin, oestradiol and progesterone levels. In conclusion, aerobic exercise increases haemoglobin, haematocrit, red cell count and platelet count, and decreases levels of prolactin, oestradiol and progesterone, resulting in improvement of fatigue, impaired concentration, confusion and most premenstrual symptoms.

The effect of strength training at the same time of the day on the diurnal fluctuations of muscular anaerobic performances

The aim of this study was to examine the effects of training at the same time of the day on the diurnal variations of anaerobic performances to provide some recommendations to adjust training hours with the time of the day of competitive events. Thirty participants underwent 8 weeks of lower-extremity progressive resistance training performed 3 times per week designed to promote muscular strength and power. These subjects were randomly assigned to a morning training group (MTG, 07:00-08:00 hours, n = 10), an evening training group (ETG, 17:00-18:00 hours, n = 10), and a control group (CG, completed all tests but did not train, n = 10). Performance in the squat jump, the countermovement jump, the Wingate and 1 repetition maximum (1RM) during leg extension, leg curl, and squat tests was recorded just before and 2 weeks after an 8-week course of regular training. For all the subjects, the morning and evening tests were scheduled at the same time of the day as for the morning and evening training sessions. Before training, the results indicated a significant increase in performance from morning to evening tests (ca. 2.84-17.55% for all tests) for all groups. After training, the diurnal variations in anaerobic performances were blunted in the MTG. In fact, there was no significant difference in muscular power or strength between morning and evening tests. However, these intradaily variations in anaerobic performances persisted in the ETG and CG. From a practical point of view, adaptation to strength training is greater at the time of the day at which training was scheduled than at other times.

Circadian Variation in Stroke Onset: Identical Temporal Pattern in Ischemic and Hemorrhagic Events

Stroke is the culmination of a heterogeneous group of cerebrovascular diseases that is manifested as ischemia or hemorrhage of one or more blood vessels of the brain. The occurrence of many acute cardiovascular events--such as myocardial infarction, sudden cardiac death, pulmonary embolism, critical limb ischemia, and aortic aneurysm rupture--exhibits prominent 24 h patterning, with a major morning peak and secondary early evening peak. The incidence of stroke exhibits the same 24 h pattern. Although ischemic and hemorrhagic strokes are different entities and are characterized by different pathophysiological mechanisms, they share an identical double-peak 24 h pattern. A constellation of endogenous circadian rhythms and exogenous cyclic factors are involved. The staging of the circadian rhythms in vascular tone, coagulative balance, and blood pressure plus temporal patterns in posture, physical activity, emotional stress, and medication effects play central and/or triggering roles. Features of the circadian rhythm of blood pressure, in terms of their chronic and acute effects on cerebral vessels, and of coagulation are especially important. Clinical medicine has been most concerned with the prevention of stroke in the morning, when population-based studies show it is of greatest risk during the 24 h; however, improved protection of at-risk patients against stroke in the early evening, the second most vulnerable time of cerebrovascular accidents, has received relatively little attention thus far.

The combined effect of time of day and menstrual cycle on lactate threshold

PURPOSE

This study examined the isolated and combined effects of time of day and menstrual cycle phase on the determination of the lactate threshold (Tlac) and blood lactate concentration.

METHODS

Eleven endurance-trained female athletes (mean age 32.4+/- 6.9 yr) were tested at 06:00 and 18:00 h and at two phases of the menstrual cycle, the midfollicular phase and the midluteal phase. Capillary blood (25 muL) was obtained from the tip of the toe at rest, and during the last 30 s of a continuous, multistage, 3-min incremental protocol on the Concept II rowing ergometer. To determine Tlac, a curve-fitting procedure (Dmax method), a visual method (Tlac-vis), and the fixed blood lactate concentration of 4.0 mmol.L (Tlac-4 mM) were used. Ventilatory threshold (Tvent) was also determined.

RESULTS

In the midluteal phase of the menstrual cycle, Tlac-4 mM occurred at a significantly higher exercise intensity, heart rate, and oxygen consumption than it did in the midfollicular phase. Blood lactate concentration at Tvent and at Tlac using the Dmax method was significantly lower in the midluteal phase. No significant interaction effects (menstrual cycle x time of day) were observed for any of the methods used to determine Tlac or for values of blood lactate concentration at rest and at maximum.

CONCLUSION

These findings suggest that, when using fixed values of blood lactate in physiologic assessment, consideration should be given to the menstrual cycle phase in which the test is carried out.

Circadian rhythms in blood lactate concentration during incremental ergometer rowing

This study examined whether circadian rhythms affect lactate threshold (Th(lac)) during rowing exercise. Eleven male, endurance-trained athletes [mean (SD) age 29.5 (6.1) years] rowed at 0200, 0600, 1000, 1400, 1800 and 2200 hours under the same experimental conditions. Capillary blood (25 microl) was obtained from the tip of the toe during the last 30 s of a continuous, multi-stage, 3-min, incremental protocol on the Concept II ergometer. To determine Th(lac), a curve-fitting procedure (the D(max) method), a visual method (Th(lac-vis)) and the fixed blood lactate concentration of 4.0 mmol l(-1) (Th(lac-4 mM)) were used. Circadian rhythms were apparent for oxygen consumption and heart rate at Th(lac) using the D(max) method (P=0.02 and P=0.04 respectively), with the acrophases at 2139 hours and 2032 hours respectively coinciding in phase with that of core body temperature. The conclusion is that tests should be completed at the same time of day at which the athlete usually trains, to ensure precision of Th(lac) determination, especially when the D(max )method is used to determine Th(lac).

Effects of human pregnancy on fluid regulation responses to short-term exercise

This study tested the hypothesis that human pregnancy alters fluid and electrolyte regulation responses to acute short-term exercise. Responses of 22 healthy pregnant women (PG; gestational age, 37.0 +/- 0.2 wk) and 17 nonpregnant controls (CG) were compared at rest and during cycling at 70 and 110% of the ventilatory threshold (VT). At rest, ANG II concentration was significantly (P < 0.05) higher in PG vs. CG, whereas plasma osmolality and concentrations of AVP, sodium, and potassium were significantly lower. Atrial natriuretic peptide concentration at rest was similar between groups. ANG II and AVP concentrations increased significantly from rest to 110% VT in CG only, whereas increases in atrial natriuretic peptide concentration were similar between groups. Increases in osmolality, and total protein and albumin concentrations from rest to both work rates were similar between the two groups. PG and CG exhibited similar shifts in fluid during acute short-term exercise, but the increases in ANG II and AVP were absent and attenuated, respectively, during pregnancy. This was attributed to the significantly augmented fluid volume state already present at rest in late gestation.

Lifestyle, stress and cortisol response: Review II : Lifestyle

To prevent lifestyle related diseases, it is important to modify lifestyle behavior. The control of mental stress level and prevention of mental stress-related diseases have become one of the most important problems in Japan. To check mental stress level objectively during the early stage of stress-related diseases and determine appropriate coping methods, it is necessary to design a useful index for mental stress. Cortisol is a steroid hormone secreted by the adrenal cortex. This is an essential hormone to human survival, and plays a key role in adaptation to stress. In another review, we concluded that cortisol appears to be an adequate index for mental stress.However, lifestyle factors such as alcohol drinking, smoking, lack of exercise etc., are strongly associated with mental stress. Thus, in this review, we focus on the relationship between cortisol and lifestyle.The present findings suggested that lifestyle factors; smoking, alcohol drinking, exercise, sleep and nutrition are strongly associated with cortisol levels, and it may be impossible to determine whether alterations in cortisol levels are due to mental stress.It was suggested that those lifestyle effects on not only mental stress itself but also cortisol levels should be considered, when assessing mental stress by cortisol levels.

Effects of oral contraceptives on body fluid regulation

To test the hypothesis that estrogen reduces the operating point for osmoregulation of arginine vasopressin (AVP), thirst, and body water balance, we studied nine women (25 +/- 1 yr) during 150 min of dehydrating exercise followed by 180 min of ad libitum rehydration. Subjects were tested six different times, during the early-follicular (twice) and midluteal (twice) menstrual phases and after 4 wk of combined [estradiol-norethindrone (progestin), OC E + P] and 4 wk of norethindrone (progestin only, OC P) oral contraceptive administration, in a randomized crossover design. Basal plasma osmolality (P(osm)) was lower in the luteal phase (281 +/- 1 mosmol/kgH(2)O, combined means, P < 0.05), OC E + P (281 +/- 1 mosmol/kgH(2)O, P < 0.05), and OC P (282 +/- 1 mosmol/kgH(2)O, P < 0. 05) than in the follicular phase (286 +/- 1 mosmol/kgH(2)O, combined means). High plasma estradiol concentration lowered the P(osm) threshold for AVP release during the luteal phase and during OC E + P [x-intercepts, 282 +/- 2, 278 +/- 2, 276 +/- 2, and 280 +/- 2 mosmol/kgH(2)O, for follicular, luteal (combined means), OC E + P, and OC P, respectively; P < 0.05, luteal phase and OC E + P vs. follicular phase] during exercise dehydration, and 17beta-estradiol administration lowered the P(osm) threshold for thirst stimulation [x-intercepts, 280 +/- 2, 279 +/- 2, 276 +/- 2, and 280 +/- 2 mosmol/kgH(2)O for follicular, luteal, OC E + P, and OC P, respectively; P < 0.05, OC E + P vs. follicular phase], without affecting body fluid balance. When plasma 17beta-estradiol concentration was high, P(osm) was low throughout rest, exercise, and rehydration, but plasma arginine vasopressin concentration, thirst, and body fluid retention were unchanged, indicating a lowering of the osmotic operating point for body fluid regulation.

Physiological variability of fluid-regulation hormones in young women

We tested the physiological reliability of plasma renin activity (PRA) and plasma concentrations of arginine vasopressin (P[AVP]), aldosterone (P[ALD]), and atrial natriuretic peptide (P[ANP]) in the early follicular phase and midluteal phases over the course of two menstrual cycles (n = 9 women, ages 25 +/- 1 yr). The reliability (Cronbach's alpha >/=0.80) of these hormones within a given phase of the cycle was tested 1) at rest, 2) after 2.5 h of dehydrating exercise, and 3) during a rehydration period. The mean hormone concentrations were similar within both the early follicular and midluteal phase tests; and the mean concentrations of P[ALD] and PRA for the three test conditions were significantly greater during the midluteal compared with the early follicular phase. Although Cronbach's alpha for resting and recovery P[ANP] were high (0.80 and 0.87, respectively), the resting and rehydration values for P[AVP], P[ALD], and PRA were variable between trials for the follicular (alpha from 0.49 to 0.55) and the luteal phase (alpha from 0.25 to 0. 66). Physiological reliability was better after dehydration for P[AVP] and PRA but remained low for P[ALD]. Although resting and recovery P[AVP], P[ALD], and PRA were not consistent within a given menstrual phase, the differences in the concentrations of these hormones between the different menstrual phases far exceeded the variability within the phases, indicating that the low within-phase reliability does not prevent the detection of menstrual phase-related differences in these hormonal variables.

Effects of the menstrual cycle on excess postexercise oxygen consumption in healthy young women

The effects of the menstrual cycle on excess postexercise oxygen consumption (EPOC) were studied in seven healthy young women aged 18 to 20 years. EPOC, resting metabolic rate (RMR), and energy expenditure during exercise (EEDE) in the fasting state were measured in the follicular and luteal phases. On the experimental days, subjects exercised for 60 minutes on a bicycle ergometer at an intensity of 60% maximal oxygen consumption (VO2max) followed by rest for 6 hours. The EPOC and RMR were significantly higher (P < .05) and the postexercise respiratory exchange ratio (RER) was significantly lower (P < .05) in the luteal phase versus the follicular phase, whereas differences in the EEDE and basal and exercise RER were negligible in both phases. Fat oxidation during the experimental period was significantly greater in the luteal phase (P < .05). These results suggest that exercise in the luteal phase results in greater postexercise energy expenditure and fat utilization than in the follicular phase.

Fluid balance and renal response following dehydrating exercise in well-trained men and women

We examined the recovery of plasma volume, plasma osmolality, renal water and sodium handling and fluid-regulating hormones to dehydrating exercise in well-trained women and compared them to men. Ten male and eight female athletes cycled at anaerobic threshold at an ambient temperature of 32 degrees C until dehydration by 3% of their body mass (mb). After exercise, they drank water equal to 1% mb and rested for 240 min. Plasma renin activity (PRA), serum aldosterone [ALDO]s, plasma arginine vasopressin [AVP]pl, norepinephrine concentrations and plasma osmolality (Osmpl) were determined at baseline, end of exercise, 30, 60, 120 and 240 min postexercise. Urine was collected at baseline, end of exercise, 60, 120 and 240 min postexercise. Renal free water and sodium handling were assessed. The recovery of OSMpl and plasma volume occurred within the first 60 min of recovery and at similar rates between the groups. However, women had lower PRA at the end of exercise (P = 0.05), an earlier recovery of [ALDO]s, and a slower [AVP]pl recovery. Overall fluid balance was similar between the men and women, as were the early recovery of renal free water clearance (CH2O). During the last 120 min of recovery CH2O was more negative (greater water reabsorption) and fractional sodium excretion was increased in the women compared to the men. Despite small differences in sodium and water reabsorption following dehydration, it appears from other study that recovery from dehydrating exercise in well-trained men and women is remarkably similar.

Influence of time of day on psychological responses to exercise. A review

Circadian rhythms have been documented for various physiological variables, such as body temperature, heart rate, blood pressure, cortisol, adrenaline (epinephrine) and noradrenaline (norepinephrine) under resting, as well as exercise conditions. The extent to which psychological variables, such as perception of effort, mood states and anxiety, are subject to circadian rhythms at rest and during exercise, is not as well understood. Body temperature follows a circadian rhythm in which temperature is highest in the evening and lowest in the early morning. Exercise heart rate follows a similar rhythm, but peaks a little earlier. The findings for exercise blood pressure are not consistent. Performance of physical activity is generally improved in the afternoon or evening, compared with morning. Cortisol levels follow a circadian rhythm in which cortisol peaks in the morning and decreases throughout the rest of the day, at rest and during exercise. Plasma catecholamines show a rhythm at rest, but the findings during exercise are inconsistent. Research on circadian rhythms of perceived exertion and mood states are equivocal and the limited research on anxiety suggests that the anxiolytic response to exercise is not influenced by time of day.

Circadian rhythms of renal hemodynamics in unanesthetized, unrestrained rats

Catheters were placed in the jugular vein and femoral artery of male Sprague-Dawley rats and connected to a specially designed perfusor for continuous constant infusion of 0.9% NaCl and a syringe to perform simultaneous and intermittent blood collections. This permitted continuous 24-h study of renal hemodynamics, estimated by inulin (Cin) and p-amino-hippuric acid (CPAH) clearances; Cin represents glomerular filtration rate and CPAH renal plasma flow. Animals were individually housed in metabolism cages in a controlled environment with light/dark 12:12 h. Urine was collected every 4 h (12:00, 16:00, 20:00, 24:00, 04:00, and 08:00) and blood sampled at the midpoint of urine collection periods. Urine and plasma sodium, potassium, inulin, and PAH were spectrophotometrically assessed. During continuous infusion of isotonic saline, Cin exhibited circadian changes with large decrease between 12:00 and 20:00 h (0.9 +/- 0.2 ml/min) and acrophase at 00:30 h. Rhythmicity in CPAH was similar with the minimum between 16:00 and 20:00 h (2.5 +/- 0.3 ml/min) and peak between 00:00 and 04:00 h (acrophase at 00:25 h). Water and electrolyte excretion were also circadian rhythmic with a similar nighttime enhancement and daytime minimum. Such circadian changes persisted during continuous 0.9% NaCl infusion for several consecutive days. The unanesthetized, unrestrained rat model enables investigations in renal chronopharmacology and chronotoxicology.

Plasma catecholamine responses during a personalized physical stress as a dynamic characterization of essential hypertension

High performance liquid chromatography (HPLC) with electrochemical detection proves to be a reliable method for determination of plasma catecholamines (CA) to assess the possible role of the sympathetic nervous system (SNS) in essential hypertension (EH). The present investigation in a group of 15 normotensive (N) and 13 stable EH patients, homogeneous for age and duration of hypertension, was carried out without treatment in the supine position, up-right position and during a personalized bicycle exercise. Mean blood pressure, mean heart rate, plasma renin activity and plasma aldosterone were also evaluated at the various exertion phases. Norepinephrine (NE) and epinephrine (E) showed a progressive increase in N and in EH patients, reaching the highest values at maximum effort. However, EH patients showed higher E plasma levels than N before maximum effort. Dopamine (DA) reached the highest values in N at maximum effort and in EH patients at recovery time. These findings allow us to foresee the possibility of a better characterization of the SNS role in EH.