Estrogen effects on osmotic regulation of AVP and fluid balance

Hormonal changes during menopause and the impact on fluid regulation

Reproductive surgeries leave women more susceptible to postoperative hypervolemic hyponatremia because during this period women can retain water at an accelerated pace and much faster than they do sodium. This review proposes that estrogen and progestogen exposure play an important role in the increased risk of hyponatremia in menopausal women. Estrogen and progesterone exposure have important effects on both body fluid regulation and cardiovascular function and both of these reproductive hormones impact blood pressure responses to sodium loads. This article provides information on the effects of female reproductive hormones and hormone therapy (HT) on fluid regulation and cardiovascular function during menopause. Thirst- and fluid-regulating hormones respond to both osmotic and volume stimuli. Aging women maintain thirst sensitivity to osmotic stimuli but lose some thirst sensitivity to changes in central body fluid volume. Thus, older adults are more at risk of dehydration because they may replenish fluids at a slower rate. Estrogen therapy increases osmotic sensitivity for mechanisms to retain body water so may help menopausal women control body fluids and avoid dehydration. Some progestogens can mitigate estradiol effects on water and sodium retention through competition with aldosterone for the mineralocorticoid receptor and attenuating aldosterone-mediated sodium retention in the distal tubule. However, some progestogens can increase cardiovascular risks. Appropriate balance of these hormones within HT is important to avoid the negative consequences of body fluid and sodium retention, including edema and hypertension.

Running longer, running stronger: a brief review of endurance exercise and oestrogen

Athletic performance in endurance exercise is determined by an interplay among many physiological factors. Body fluid regulation, influenced by both hormonal and osmotic stimuli, is particularly important for maximising performance in endurance sports, as dehydration markedly decreases endurance. Oestrogen has a broad range of effects on the regulation of body fluid balance, as well as on aerobic capacity, metabolism, and other factors that impact endurance exercise performance, yet the role of oestrogen in endurance exercise performance has not been thoroughly examined. This review discusses the effects of oestrogen on compensatory hormonal and behavioural responses to dehydration, such as renin-angiotensin-aldosterone system activation and thirst, that restore body fluid balance and thereby affect exercise performance. Oestrogen-mediated effects and their potential consequences for endurance performance are also evaluated in the context of thermoregulation and aerobic capacity, as well as substrate utilisation during exercise. In addressing the role of oestrogen in endurance exercise, this review will examine human and animal models of endurance exercise and discuss similarities, differences, and limitations. Our aim is to integrate research from neuroscience, physiology, and exercise science to advance understanding of how oestrogen may impact exercise. Such understanding will have particularly important implications for female endurance athletes experiencing the hormonal fluctuations that occur during the reproductive cycle.

Should there be sex-specific criteria for the diagnosis and treatment of heart failure?

All-cause mortality from cardiovascular disease is declining in the USA. However, there remains a significant difference in risk factors for disease and in mortality between men and women. For example, prevalence and outcomes for heart failure with preserved ejection fraction differ between men and women. The reasons for these differences are multifactorial, but reflect, in part, an incomplete understanding of sex differences in the etiology of cardiovascular diseases and a failure to account for sex differences in pre-clinical studies including those designed to develop new diagnostic and treatment modalities. This review focuses on the underlying physiology of these sex differences and provides evidence that inclusion of female animals in pre-clinical studies of heart failure and in development of imaging modalities to assess cardiac function might provide new information from which one could develop sex-specific diagnostic criteria and approaches to treatment.

Blood pressure and water regulation: understanding sex hormone effects within and between men and women

Cardiovascular disease remains the leading cause of death for both men and women. Hypertension is less prevalent in young women compared with young men, but menopausal women are at greater risk for hypertension compared with men of similar age. Despite these risks, women do not consistently receive first line treatment for the early stages of hypertension, and the greater morbidity in menopause reflects this neglect. This review focuses on ovarian hormone effects on the cardiovascular and water regulatory systems that are associated with blood pressure control in women. The study of ovarian hormones within young women is complex because these hormones fluctuate across the menstrual cycle, and these fluctuations can complicate conclusions regarding sex differences. To better isolate the effects of oestrogen and progesterone on the cardiovascular and water regulation systems, we developed a model to transiently suppress reproductive function followed by controlled hormone administration. Sex differences in autonomic regulation of blood pressure appear related to ovarian hormone exposure, and these hormonal differences contribute to sex differences in hypertension and orthostatic tolerance. Oestrogen and progesterone exposure are also associated with plasma volume expansion, and a leftward shift in the osmotic operating point for body fluid regulation. In young, healthy women, the shift in osmoregulation appears to have only a minor effect on overall body water balance. Our overarching conclusion is that ovarian hormone exposure is the important underlying factor contributing to differences in blood pressure and water regulation between women and men, and within women throughout the lifespan.

Body composition and hydration status changes in male and female open-water swimmers during an ultra-endurance event

Body mass changes during ultra-endurance performances have been described for running, cycling and for swimming in a heated pool. The present field study of 20 male and 11 female open-water swimmers investigated the changes in body composition and hydration status during an ultra-endurance event. Body mass, both estimated fat mass and skeletal muscle mass, haematocrit, plasma sodium concentration ([Na+]) and urine specific gravity were determined. Energy intake, energy expenditure and fluid intake were estimated. Males experienced significant reductions in body mass (-0.5 %) and skeletal muscle mass (-1.1 %) (P < 0.05) during the race compared to females who showed no significant changes with regard to these variables (P > 0.05). Changes in percent body fat, fat mass, and fat-free mass were heterogeneous and did not reach statistical significance (P > 0.05) between gender groups. Fluid intake relative to plasma volume was higher in females than in males during the ultra-endurance event. Compared to males, females' average increase in haematocrit was 3.3 percentage points (pp) higher, urine specific gravity decrease 0.1 pp smaller, and plasma [Na+] 1.3 pp higher. The observed patterns of fluid intake, changes in plasma volume, urine specific gravity, and plasma [Na+] suggest that, particularly in females, a combination of fluid shift from blood vessels to interstitial tissue, facilitated by skeletal muscle damage, as well as exercise-associated hyponatremia had occurred. To summarise, changes in body composition and hydration status are different in male compared to female open-water ultra-endurance swimmers.

Gender difference in antidiuretic response to desmopressin

Increased age and female gender are well-known risk factors for the development of desmopressin-induced hyponatremia. However, little focus has been on exploring gender differences in the antidiuretic response to desmopressin. Based on an exploratory analysis from three clinical trials, we report a significant gender difference in the effects of desmopressin on nocturnal urine volume that could not be explained by pharmacokinetic differences. Mean desmopressin concentration profiles were tested for covariates, and age and gender were not statistically significant and only weight was significant for log(C(max)) (P = 0.0183) and borderline significant for log(AUC) (P = 0.0571). The decrease in nocturnal urine volume in nocturia patients treated with desmopressin over 28 days was significantly larger for women at the lower desmopressin melt doses of 10 and 25 μg than for men. The ED(50) for men was modeled to be 43.2 μg and 16.1 μg for women, with the ED(50) men/women estimated to be 2.7 (1.3-8.1 95% CI), corresponding to significantly higher sensitivity to desmopressin in women. An increasing incidence of hyponatremia with increasing dose was found, and at the highest dose level of 100 μg decreases in serum sodium were approximately twofold greater in women over 50 yr of age than in men. A new dose recommendation stratified by gender is suggested in the treatment of nocturia: for men, 50- to 100-μg melt is an efficacious and safe dose, while for women a dose of 25 μg melt is recommended as efficacious with no observed incidences of hyponatremia. Areas for further research are proposed to uncover pathophysiological mechanism(s) behind these gender differences.

Influence of increased plasma osmolality on sympathetic outflow during apnea

Animal models have shown that peripheral chemoreceptors alter their firing patterns in response to changes in plasma osmolality, which, in turn, may modulate sympathetic outflow. The purpose of this study was to test the hypothesis that increases in plasma osmolality augment muscle sympathetic nerve activity (MSNA) responses to chemoreceptor activation. MSNA was recorded from the peroneal nerve (microneurography) during a 23-min intravenous hypertonic saline infusion (3% NaCl; HSI). Chemoreceptor activation was elicited by voluntary end-expiratory apnea. MSNA responses to end-expiratory apnea were calculated as the absolute increase from the preceding baseline period. Plasma osmolality significantly increased from pre- to post-HSI (284 ± 1 to 290 ± 1 mOsm/kg H(2)O; P < 0.01). There was a significant overall effect of osmolality on sympathetic activity (P < 0.01). Duration of the voluntary end-expiratory apnea was not different after HSI (pre = 40 ± 5 s; post = 41 ± 4 s). MSNA responses to end-expiratory apnea were not different after HSI, expressed as an absolute change in burst frequency (n = 11; pre = 8 ± 2; post = 11 ± 1 burst/min) and as a percent increase in total activity (pre = 51 ± 4% AU; post = 53 ± 4% AU). A second group of subjects (n = 8) participated in 23-min volume/time-control intravenous isotonic saline infusions (0.9% NaCl). Isotonic saline volume-control infusions yielded no change in plasma osmolality or MSNA at rest. Furthermore, MSNA responses to apnea following isotonic saline infusion were not different. In summary, elevated plasma osmolality increased MSNA at rest and during apnea, but contrary to the hypothesis, MSNA responsiveness to apnea was not augmented. Therefore, this study does not support a neural interaction between plasma osmolality and chemoreceptor stimulation.

The neurosteroid 3alphaDIOL modulates place preference when infused in the basolateral amygdala according to sex

Three different behavioral tasks were used to study the role of the neurosteroid 5alpha -androstane-3alpha, 17beta-diol (3alphaDIOL) in affective components of behavior when infused into the basolateral amygdala (BLA) of both sexes. Female rats were ovariectomized; half received implants containing estradiol benzoate (OVX-EB), whereas the other half received empty implants (OVX). Male rats were gonadally intact. No differences were noted in male behavior according to the conditioned place preference (CPP) test, the modified Vogel conflict test (VCT), or the elevated plus maze (EPM) upon infusion of 3alphaDIOL. In contrast, 3alphaDIOL modulated CPP and VCT performance among female rats. Therefore, the authors propose that 3alphaDIOL modulates affect through the BLA via a sex-specific mechanism.

Sex hormone effects on body fluid and sodium regulation in women with and without exercise-associated hyponatremia

We hypothesized that exercise-associated hyponatremia (EAH) is a function of excess sodium loss combined with high water intake in women at risk for dysnatremias during endurance exercise. We further hypothesized that estradiol and progesterone exposure increases fluid retention and sodium loss during exercise in women at risk for EAH. For 16 days we suppressed estrogens and progesterone with a gonadotropin-releasing hormone antagonist (GnRH ant) in seven women with (Hypo) and nine women without (no Hypo) a history of hyponatremia; we added 17β-estradiol (0.2 mg/day patches) for days 4–16 (E2) and progesterone (200 mg/day) for days 13–16 (E2-P4). Under each hormone condition, subjects cycled in 35°C at 65% peak oxygen consumption (V̇o2peak) for 60 min, then at 55–60% V̇o2peak for 120 min. Subjects drank 8 ml/kg of water (and replenished urine volume) every 30 min over the final 120 min of exercise. S[Na+] fell by 4.3, 3.9, and 3.1 meq/l ( P < 0.05) with drinking during GnRH ant, E2, and E2-P4 in Hypo, with little fall in no Hypo. Under all conditions, combined urine and sweat sodium loss were similar between Hypo [−85.6 (SD 36.2), −86.4 (SD 39.2), and −112.0 (SD 30.0) meq] and no Hypo [−98.0 (SD 54.8), −80.9 (SD 57.6), and −105.1 (SD 46.4) meq, for GnRH, E2, and E2-P4], as was mass balance of electrolytes (EMB) for Hypo [−104.8 (SD 32.8), −103.6 (SD 42.1), and −132.8 (SD 34.9) meq] compared with no Hypo [−128.8 (SD 57.2), −113.5 (SD 61.1), and −143.4 (SD 49.6) meq for GnRH, E2, and E2-P4]. Mass balance of water [VMB, for Hypo, 0.42 (SD 0.10), 0.62 (SD 0.25), and −0.11 (SD 0.11) liter] compared with no Hypo [0.01 (SD 0.15), 0.03 (SD 17), and −0.16 (SD 0.13) liter for GnRH, E2, and E2-P4, P < 0.05] indicates water retention was the primary contributor to the lower S[Na+] in Hypo women.

Differential effects of estradiol on drinking by ovariectomized rats in response to hypertonic NaCl or isoproterenol: Implications for hyper- vs. hypo-osmotic stimuli for water intake

We examined the effects of estradiol on behavioral responses to osmotic challenges in ovariectomized (OVX) rats to test the hypothesis that estradiol enhances sensitivity to gradual changes in plasma osmolality (pOsm) in stimulating water intake. Despite comparably elevated pOsm after a slow infusion of 2 M NaCl, the latency to begin water intake was significantly less in estradiol-treated OVX rats compared to that in oil vehicle-treated rats. Other groups of OVX rats were injected with isoproterenol, which increases circulating angiotensin II. These rats then were given 0.15 M NaCl to drink instead of water, to prevent decreased pOsm associated with water ingestion. Isoproterenol stimulated 0.15 M NaCl intake by both groups; however, estradiol-treated rats consumed less 0.15 M NaCl than did oil-treated rats, findings that are similar to those reported when estradiol-treated rats consumed water. The estradiol enhancement of sensitivity to increased, but not to decreased, pOsm suggests that estradiol has directionally-specific effects on osmoregulatory drinking. Moreover, the estradiol attenuation of 0.15 M NaCl intake after isoproterenol suggests that estradiol effects on osmoregulatory drinking are independent of those on volume regulatory drinking.

The influence of high and low levels of estrogen on diurnal urine regulation in young women

BACKGROUND

Sex hormones have a pronounced effect on arginine vasopressin (AVP), and therefore on the diurnal water homeostasis. Low and high levels of plasma-estradiol as seen in the follicular phase of the menstrual cycle may therefore alter the diurnal regulation of urine production. Furthermore the structural resemblance of oxytocin to vasopressin has led to speculations about the possible antidiuretic properties of oxytocin under normal physiological conditions. To elucidate the influence of high and low p-estradiol on the regulation of the diurnal urine production, 15 normal menstruating women (21-33 y) underwent two circadian in-patient investigations, both situated in follicular phase.

METHODS

Admitting the participants solely in the follicular phase resulted in high and low plasma-estradiol whereas plasma-progesterone was similar. Urine and blood samples were taken at predetermined time points to determine plasma AVP, plasma oxytocin, plasma aldosterone, plasma natriuretic peptide (ANP), urinary solute excretions, and urinary excretions of prostaglandin E2 (PGE-2) and aquaporin-2 (AQP-2). Blood pressure was measured every hour.

RESULTS

Plasma AVP, plasma aldosterone and plasma ANP were unaffected by the different levels of estradiol. All had marked circadian variations whereas oxytocin did not display any circadian rhythm. High estradiol resulted in lower p-osmolality and p-sodium reflecting the downward resetting of the osmoreceptors. Oxytocin did not correlate with either diuresis or urine osmolality. The diurnal urine production was similar in the two groups as were urine osmolality, excretion of PGE-2 and AQP-2. AQP-2 does not have a circadian rhythm and is not significantly correlated to either AVP or oxytocin under normal physiological conditions.

CONCLUSION

High and low level of estradiol has no influence on the circadian rhythm of AVP or the subsequent urine production. High p-estradiol resets the osmoreceptors for AVP release. Furthermore it appears that oxytocin under normal physiological conditions do not contribute to the overall antidiuretic effect.

Neonatal growth and breast cancer risk in adulthood

Birth size of a woman has been positively associated with her breast cancer risk, particularly before menopause, but no study has investigated neonatal growth in relation to this risk. We conducted a case-control study nested within a population-based cohort of women, born in Sweden between 1901 and 1961, covering all 405 breast cancer patients and 1081 age- and hospital-matched controls, who were born after newborn charts became available. Compared to neonates who lost <200 g after birth and grew at a rate <25 g day(-1) after reaching postnatal weight nadir (ie, the minimum, before starting to regain weight), those who either lost >/=200 g after birth or grew >/=25 g day(-1) after nadir, or both, were at an approximately 50% increased breast cancer risk. The excess risk was striking and statistically significant among women below 50 years of age, but was not evident among older women. Immediate postnatal weight loss (an indicator of water loss, likely to reflect water retention associated with pregnancy hormones) as well as neonatal weight gain rate after the nadir (known to reflect growth hormone levels) was significantly positively associated with premenopausal breast cancer risk.

Sex hormone effects on body fluid regulation

In young women, estradiol and progesterone primarily control reproduction, but they also affect fluid regulation. Estradiol lowers the operating point for osmoregulation of arginine vasopressin and thirst and increases plasma volume. Although total body water and sodium content are only mildly affected, data presented in this article suggest that reproductive hormones alter homeostatic set points for body fluid and tonicity.

Endogenous and exogenous female sex hormones and renal electrolyte handling: effects of an acute sodium load on plasma volume at rest

This study was conducted to investigate effects of an acute sodium load on resting plasma volume (PV) and renal mechanisms across the menstrual cycle of endurance-trained women with natural (NAT) or oral contraceptive pill (OCP) controlled cycles. Twelve women were assigned to one of two groups, according to their usage status: 1) OCP [ n = 6, 29 yr (SD 6), 59.4 kg (SD 3.2)], or 2) NAT [ n = 6, 24 yr (SD 5), 61.3 kg (SD 3.6)]. The sodium load was administered as a concentrated sodium chloride/citrate beverage (164 mmol Na+/l, 253 mosmol/kgH2O, 10 ml/kg body mass) during the last high-hormone week of the OCP cycle (OCPhigh) or late luteal phase of the NAT cycle (NAThigh) and during the low-hormone sugar pill week of OCP (OCPlow) or early follicular phase of the NAT cycle (NATlow). The beverage (∼628 ml) was ingested in seven portions across 60 min. Over the next 4 h, PV expanded more in the low-hormone phase for both groups (time-averaged change): OCPlow 6.1% (SD 1.1) and NATlow 5.4% (SD 1.2) vs. OCPhigh 3.9% (SD 0.9) and NAThigh 3.5% (SD 0.8) ( P = 0.02). The arginine vasopressin increased less in the low-hormone phase [1.63 (SD 0.2) and 1.30 pg/ml (SD 0.2) vs. 1.82 (SD 0.3) and 1.57 pg/ml (SD 0.5), P = 0.0001], as did plasma aldosterone concentration (∼64% lower, P = 0.0001). Thus PV increased more and renal hormone sensitivity was decreased in the low-hormone menstrual phase following sodium/fluid ingestion, irrespective of OCP usage.

Effects on body weight and body composition of a low-dose oral estroprogestin containing ethinyl estradiol 20 microg plus levonorgestrel 100 microg

Weight gain is a common problem reported by users of estroprogestins (EPs) and is a frequent reason for EP discontinuation, even if this problem is not confirmed in several clinical studies. We studied the impact of a EP containing ethinyl estradiol (EE) 20 microg plus levonorgestrel (LNG) 100 microg on body weight (BW) and body composition in 47 treated women and 31 women as controls. Also, we studied the effect of this association on metabolic parameters (glycemia, lipid profile). EE20/LNG100 had no significant impact on body weight, body composition (fat mass, fat-free mass, total body water, intracellular water, extracellular water) or metabolic profile in comparison with no treatment. Thus, the use of EE20/LNG100 showed no impact on metabolic parameters, body weight and body composition. This could be important not only for the safety profile of this combination, but also in increasing patient compliance.

Preexercise sodium loading aids fluid balance and endurance for women exercising in the heat

This study was conducted during the high-hormone phase of both natural and oral contraceptive pill (OCP)-mediated menstrual cycles to determine whether preexercise ingestion of a concentrated sodium beverage would increase plasma volume (PV), reduce physiological strain, and aid endurance of moderately trained women cycling in warm conditions. Thirteen trained cyclists [peak O2 uptake 52 ml·kg−1·min−1 (SD 2), age 26 yr (SD 6), weight 60.8 kg (SD 5)] who were oral contraceptive users ( n = 6) or not ( n = 7) completed this double-blind, crossover experiment. Cyclists ingested a concentrated-sodium (High Na+: 164 mmol Na+/l) or low-sodium (Low Na+: 10 mmol Na+/l) beverage (10 ml/kg) before cycling to exhaustion at 70% Peak O2 uptake in warm conditions (32°C, 50% relative humidity, air velocity 4.5 m/s). Beverage (∼628 ml) was ingested in seven portions across 60 min beginning 105 min before exercise, with no additional fluid given until the end of the trial. Trials were separated by one to two menstrual cycles. High Na+ increased PV (calculated from hematocrit and hemoglobin concentration) before exercise, whereas Low Na+ did not [−4.4 (SD 1.1) vs. −1.9% (SD 1.3); 95% confidence interval: for the difference 5.20, 6.92; P < 0.0001], and it involved greater time to exhaustion [98.8 (SD 25.6) vs. 78.7 (SD 24.6) min; 95% confidence interval: 13.3, 26.8; P < 0.0001]. Core temperature rose more quickly with Low Na+ [1.6°C/h (SD 0.2)] than High Na+ [1.2°C/h (SD 0.2); P = 0.04]. Plasma [AVP], [Na+] concentration, and osmolality, and urine volume, [Na+], and osmolality decreased with sodium loading ( P < 0.05) independent of pill usage. Thus preexercise ingestion of a concentrated sodium beverage increased PV, reduced thermoregulatory strain, and increased exercise capacity for women in the high-hormone phase of natural and oral contraceptive pill-mediated menstrual cycles, in warm conditions.

Influence of plasma osmolality on baroreflex control of sympathetic activity

The purpose of this study was to determine if plasma osmolality alters baroreflex control of sympathetic activity when controlling for a change in intravascular volume; we hypothesized that baroreflex control of sympathetic activity would be greater during a hyperosmotic stimulus compared with an isoosmotic stimulus when intravascular volume expansion was matched. Seven healthy subjects (25 +/- 2 yr) completed two intravenous infusions: a hypertonic saline infusion (HSI; 3% NaCl) and, on a separate occasion, an isotonic saline infusion (ISO; 0.9% NaCl), both at a rate of 0.15 ml x kg(-1) x min(-1). To isolate the effect of osmolality, comparisons between HSI and ISO conditions were retrospectively matched based on hematocrit; therefore, baroreflex control of sympathetic outflow was determined at 20 min of a HSI and 40 min of an ISO. Muscle sympathetic outflow (MSNA) was directly measured using the technique of peroneal microneurography; osmolality and blood pressure (Finometer) were assessed. The baroreflex control of sympathetic outflow was estimated by calculating the slope of the relationship between MSNA and diastolic blood pressure during controlled breathing. Plasma osmolality was greater during the HSI compared with the ISO (HSI: 292 +/- 0.9 mosmol/kg and ISO: 289 +/- 0.8 mosmol/kg, P < 0.05). Hematocrits were matched (HSI: 39.1 +/- 1% and ISO: 39.1 +/- 1%, P > 0.40); thus, we were successful in isolating osmolality. The baroreflex control of sympathetic outflow was greater during the HSI compared with the ISO (HSI: -8.3 +/- 1.2 arbitrary units x beat(-1) x mmHg(-1) vs. ISO: -4.0 +/- 0.8 arbitrary units x beat(-1) x mmHg(-1), P = 0.01). In conclusion, when controlling for intravascular volume, increased plasma osmolality enhances baroreflex control of sympathetic activity in humans.

Exogenous oestradiol and progesterone administration does not cause oedema in healthy young women

OBJECTIVE

Oedema is an increase in the extravascular component of extracellular fluid volume (ECFV). Fluid movement across the ECF is controlled by hydrostatic and oncotic pressures, which are influenced by oestradiol and progesterone. Thus we hypothesized that oestradiol decreases, while combined oestradiol + progesterone increases, protein and fluid movement out of the vasculature.

SUBJECTS

Subjects were eight healthy women (22 +/- 2 years).

DESIGN

Oestrogens and progesterone were suppressed with a gonadotropin-releasing hormone antagonist for 16 days; oestradiol (2 x 0.1 mg/day patches) was added for days 5-16 (E(2)) and progesterone (200 mg/day) was added for days 13-16 (E(2)-P(4)).

MEASUREMENTS

We estimated intravascular (plasma) volume (PV), transcapillary albumin escape rate (TER(alb)), and Starling forces (hydrostatic pressures of plasma and interstitium, plasma colloid pressure, capillary filtration coefficient) in the forearm on days 2 (GnRH antagonist), 9 (E(2)) and 16 (E(2)-P(4)).

RESULTS

In E(2), P([E2]) increased from 85 +/- 26 to 984 +/- 136 pmol/ml (P < 0.05), with no change in P([P4]). In E(2)-P(4), P([E2]) increased to 775 +/- 195 pmol/ml and P([P4]) increased from 6.4 +/- 3.2 to 43.8 +/- 16.2 nmol/l, P < 0.05). TER(alb) was lower during E(2) (5.1 +/- 0.9) and E(2)-P(4) (5.0 +/- 1.1) compared to GnRH antagonist (5.8 +/- 0.9%/h, P < 0.05). Plasma volume was unchanged by E(2), and showed a trend (P = 0.07) for an increase during E(2)-P(4) (48.2 +/- 2.9, 49.0 +/- 3.0 and 53.9 +/- 3.5 ml/kg for GnRH antagonist, E(2), E(2)-P(4), respectively). Starling forces were unaffected by hormone treatments. Plasma renin activity and serum aldosterone concentration increased during E(2)-P(4).

CONCLUSIONS

Neither E(2) nor E(2)-P(4) altered TER(alb) sufficiently to impact Starling forces indicating neither E(2) nor P(4) administration at these levels would likely cause oedema.

Patterns of Ecstasy-Associated Hyponatremia in California

STUDY OBJECTIVE

We describe the clinical characteristics of patients with ecstasy- (3,4-methylenedioxymethamphetamine [MDMA]) associated hyponatremia (serum sodium level <130 mmol/L) reported to the California Poison Control System during a 5-year period and determine whether a sex difference exists among patients with ecstasy-associated hyponatremia and hyponatremia-associated adverse outcomes.

METHODS

We performed a retrospective review of cases involving ecstasy intoxication reported to the California Poison Control System and recorded in its computerized database from January 1, 2000, through October 9, 2005. We excluded cases that did not involve MDMA exposure or in which there were no symptoms or were minimal effects only. Confirmation of exposure to MDMA was based on history of use and, when available, urine toxicology testing results positive for MDMA or amphetamine derivatives. Hyponatremia was defined as a measured serum sodium level less than 130 mmol/L.

RESULTS

A total of 1,436 cases potentially involving ecstasy were reported to the California Poison Control System during the 5-year study period, of which 891 were excluded according to the criteria described above. Of the 545 cases that met inclusion criteria, 296 (54.3%) were women and 249 (45.7%) were men. There were 188 cases (34.5%) with a documented serum sodium level, of which 73 (38.8%) reported hyponatremia (Na <130 mmol/L). Of the 73 subjects with hyponatremia, 55 (75.3%) were women and 18 (24.7%) men; of the 115 nonhyponatremic subjects, 50 (43.5%) were women and 65 (56.5%) were men. Among patients with a documented serum sodium level, female sex was associated with increased odds of hyponatremia (odds ratio [OR] 4.0; 95% confidence interval [CI] 2.1 to 7.6). Among women, those with hyponatremia demonstrated increased odds of coma (OR 3.9; 95% CI 1.2 to 12.9), whereas among men, no increased odds of hyponatremia-associated coma were observed (OR 0.8; 95% CI 0.15 to 4.0).

CONCLUSION

Female sex was associated with increased odds of hyponatremia and increased odds of hyponatremia-associated coma among persons with ecstasy intoxication and a documented serum sodium level reported to the California Poison Control System from 2000 to 2005. Multiple potential confounders, including spectrum bias, incomplete laboratory data, and individual differences in study subject characteristics, prevent determination of causality about sex differences in the incidence of ecstasy-associated hyponatremia and its complications.

Sympathetic neural responses to increased osmolality in humans

The purpose of this study was to examine the relationship between osmolality and efferent sympathetic outflow in humans. We hypothesized that increased plasma osmolality would be associated with increases in directly measured sympathetic outflow. Muscle sympathetic outflow was successfully recorded in eight healthy subjects during a 60-min intravenous hypertonic saline infusion (HSI; 3% NaCl) on one day and during a 60-min intravenous isotonic saline (ISO) infusion (0.9% NaCl) on a different day. The HSI provides an osmotic and volume stimulus, whereas the ISO infusion provides a volume-only stimulus. Muscle sympathetic nerve activity was quantified using the technique of peroneal microneurography. Plasma osmolality increased during the HSI but not during the ISO infusion (ANOVA, P < 0.05). Sympathetic outflow differed between the trials (ANOVA, P < 0.05); during the HSI burst, frequency initially increased from 14.6 +/- 2.5 to 18.1 +/- 1.9 bursts/min; during the ISO infusion, burst frequency initially declined from 14.7 +/- 2.5 to 12.0 +/- 2.1 bursts/min. Plasma norepinephrine concentration was greater at the end of the HSI compared with the end of the ISO infusion (HSI: 297 +/- 64 vs. ISO: 202 +/- 49 pg/ml; ANOVA, P < 0.05). We conclude that HSI-induced increases in plasma osmolality are associated with increases in sympathetic activity in humans.

Gender specificity of programmed plasma hypertonicity and hemoconcentration in adult offspring of water-restricted rat dams

OBJECTIVE

We studied the impact of maternal water-restriction during rat pregnancy on newborn plasma composition, and determined the persistence of plasma composition alterations in adult offspring.

METHODS

Maternal dams were water-restricted from 10 days of pregnancy until term (21 days) and throughout lactation to increase plasma sodium levels by approximately 6 mEq/L. At 21 days of age, offspring were weaned, and subsequently maintained on ad libitum food and water until 12 weeks of age. Daily water and food intake was monitored. Blood samples and organs were collected from 1-day- and 12-week-old offspring. Hematocrit, plasma osmolality, sodium, and arginine vasopressin (AVP) levels were analyzed. Because water-restriction led to concomitant reduction in maternal food intake (ie, dehydration anorexia), henceforth these dams and their offspring are referred to as "water-deprived/food-reduced" rats.

RESULTS

Water-deprived/food-reduced dams had significantly increased plasma sodium levels, reduced food intake, and lower body weight gain during pregnancy and lactation as compared to control dams. One-day-old newborns of water-deprived/food-reduced dams weighed 17% less and had increased plasma sodium levels, osmolality, and hematocrit. At 12 weeks of age, males exhibited 11% and females 19% reduction in body weight from controls. Notably, male offspring of water-deprived/food-reduced dams showed significantly elevated plasma sodium levels, osmolality, and hematocrit. Additionally, males demonstrated reduced adrenal growth and decreased water intake. Conversely, the female offspring had similar plasma osmolality with decreased sodium levels, though a persistently elevated hematocrit. No differences were evident in plasma AVP levels.

CONCLUSIONS

Maternal water deprivation/food reduction is associated with increased newborn plasma osmolality and sodium levels and long-term physiologic changes in the offspring. The gender-specificity of programmed hyperosmolality, though not hemoconcentration, implicates differing pathways/mechanisms for these phenotypic alterations. The contributions of pregnancy hypertonicity versus nutrient restriction in the mechanism for programmed offspring phenotype remain to be elucidated.

Physiological adaptation in early human pregnancy: adaptation to balance maternal-fetal demands

After conception, the corpus luteum, placenta, and developing embryo release hormones, growth factors, and other substances into the maternal circulation. These substances trigger a cascade of events that transform the functioning of the maternal cardiovascular, respiratory, and renal systems, which in turn alter the physicochemical determinants of [H+]. Following implantation, maternal adaptations fulfill 4 important functions that support fetal growth. Increased availability of substrates and precursors for fetal-placental metabolism and hormone production is mediated by increases in dietary intake, as well as endocrine changes that increase the availability of glucose and low-density lipoprotein (LDL) cholesterol. Transport capacity is enhanced by increases in cardiac output, facilitating the transport of substrates and precursors to the placenta, and fetal waste products to maternal organs for disposal. Maternal-fetal exchange is regulated by the placenta after 10-12 weeks gestation, but it may occur through histiotrophic mechanisms before this time. Disposal of additional waste products (heat, carbon dioxide, and metabolic byproducts) occurs through peripheral vasodilation and increases in skin blood flow, ventilation, and renal filtration. The maternal physiological adaptations described above must meet the combined demands of maternal exercise and fetal growth. More research is needed to formulate evidence-based guidelines for healthy physical activity in early pregnancy.Key words: maternal adaptation, first trimester, exercise, fetal growth and development, hormones.

Blood pressure and hemodynamic responses to an acute sodium load in humans

The purpose of this study was to investigate the acute blood pressure (BP) and hemodynamic effects of sodium chloride (3% intravenous solution). Although many studies link a change in dietary sodium to a change in BP, few consider the effects of sodium concentration in the blood on BP. We hypothesized that an intravenous sodium load would increase BP, and we quantified alterations in cardiac output (Qc) and peripheral vascular resistance (PVR). Thirteen subjects (age 27 +/- 2 yr) underwent a 60-min 3% saline infusion (0.15 ml.kg(-1).min(-1)). BP was assessed on a beat-to-beat basis with a Finometer, Qc was assessed via the CO(2) rebreathing technique, and PVR was derived. Serum sodium and osmolality increased, and hematocrit declined during the infusion (ANOVA, P < 0.01). Mean arterial pressure (MAP) increased continuously during the infusion from 81.8 +/- 3.4 to 91.6 +/- 3.6 mmHg (ANOVA, P < 0.01). BP responsiveness to sodium was expressed as the slope of the serum sodium-MAP relationship and averaged 1.75 +/- 0.34 mmHg.mmol(-1).l(-1). BP responsiveness to the volume change was expressed as the slope of the hematocrit-MAP relationship and averaged -2.2 +/- 0.35 mmHg/%. The early change in MAP was mediated by an increase in Qc and the late change by an increase in PVR (P < 0.05), corresponding to a 30% increase in plasma norepinephrine. In conclusion, an acute infusion of hypertonic saline was effective in increasing BP, and both sodium and volume appear to be involved in this increase; acute BP responsiveness to serum sodium can be quantified using a MAP-sodium plot.

Progesterone increases plasma volume independent of estradiol

Adequate plasma volume (PV) and extracellular fluid (ECF) volume are essential for blood pressure and fluid regulation. We tested the hypotheses that combined progesterone (P4)-estrogen (E2) administration would increase ECF volume with proportional increases in PV, but that P4would have little independent effect on either PV or ECF volume. We further hypothesized that this P4-E2-induced fluid expansion would be a function of renin-angiotensin-aldosterone system stimulation. We suppressed P4and E2with a gonadotropin-releasing hormone (GnRH) antagonist in eight women (25 ± 2 yr) for 16 days; P4(200 mg/day) was added for days 5–16 (P4) and 17β-estradiol (2 × 0.1 mg/day patches) for days 13–16 (P4-E2). On days 2 (GnRH antagonist), 9 (P4), and 16 (P4-E2), we estimated ECF and PV. To determine the rate of protein and thus water movement across the ECF, we also measured transcapillary escape rate of albumin. In P4, [Formula: see text] increased from 2.5 ± 1.3 to 12.0 ± 2.8 ng/ml ( P < 0.05) with no change in [Formula: see text] (21.5 ± 9.4 to 8.6 ± 2.0 pg/ml). In P4-E2, plasma concentration of P4remained elevated (11.3 ± 2.7 ng/ml) and plasma concentration of E2increased to 254.1 ± 52.7 pg/ml ( P < 0.05). PV increased during P4(46.6 ± 2.5 ml/kg) and P4-E2(48.4 ± 3.9 ml/kg) compared with GnRH antagonist (43.3 ± 3.2 ml/kg; P < 0.05), as did ECF (206 ± 19, 244 ± 25, and 239 ± 27 ml/kg for GnRH antagonist, P4, and P4-E2, respectively; P < 0.05). Transcapillary escape rate of albumin was lowest during P4-E2(5.8 ± 1.3, 3.5 ± 1.7, and 2.2 ± 0.4%/h for GnRH antagonist, P4, and P4-E2, respectively; P < 0.05). Serum aldosterone increased during P4and P4-E2compared with GnRH antagonist (79 ± 17, 127 ± 13, and 171 ± 25 pg/ml for GnRH antagonist, P4, and P4-E2, respectively; P < 0.05), but plasma renin activity and plasma concentration of ANG II were only increased by P4-E2. This study is the first to isolate P4effects on ECF; however, the mechanisms for the ECF and PV expansion have not been clearly defined.

Physiologic considerations for exercise performance in women

Women exhibit several anatomic and physiologic characteristics that distinguish their responses to exercise from those of men. Women are smaller than men, have less muscle mass, and more fat mass for a given body size. Blood volume, stroke volume, and cardiac output are all lower in women than in men. These and other factors contribute to lower maximal aerobic power (even for similar training status) in women. The reproductive hormones, estrogen and progesterone, can influence ventilation, substrate metabolism, and thermoregulation during exercise. Women have a greater tendency for EIAH, which can limit VO2max as well as submaximal exercise performance at higher intensities. Women tend to use a greater percentage of fats during exercise, but also rely on CHOs. Thermoregulatory control is altered significantly over the course of the menstrual cycle by fluctuations in circulating levels of progesterone and estrogen. It is important for women to include regular exercise in their daily routines, particularly because regular physical activity has been implicated in the prevention of osteoporosis, breast cancer, heart disease, and depression.

Effects of estrogen and progesterone administration on extracellular fluid

To determine the effect of estrogen and progesterone on plasma volume (PV) and extracellur fluid volume (ECFV), we suppressed endogenous estrogen and progesterone by using the gonadotropin-releasing hormone (GnRH) antagonist ganirelix acetate in seven healthy women (22 ± 1 yr). Subjects were administered GnRH antagonist for 16 days. Beginning on day 5 of GnRH antagonist administration, subjects were administered estrogen (E2) for 11 days, and beginning on day 12 of GnRH antagonist administration, subjects added progesterone (E2-P4) for 4 days. On days 2, 9, and 16 of GnRH antagonist administration, we estimated ECFV (inulin washout), transcapillary escape rate of albumin (TERalb), and PV (Evans blue dye). Plasma E2concentration increased from 17.9 ± 4.5 (GnRH antagonist) to 195.9 ± 60.1 (E2, P < 0.05) to 245.6 ± 62.9 pg/ml (E2-P4, P < 0.05). Compared with GnRH antagonist (1.3 ± 0.5 ng/ml), plasma P4concentration was unchanged during E2(0.9 ± 0.3 ng/ml) and increased to 9.4 ± 3.1 ng/ml during E2-P4( P < 0.05). Both E2(44.1 ± 3.1 ml/kg) and E2-P4(47.7 ± 2.8 ml/kg) increased PV compared with GnRH antagonist (42.8 ± 1.3 ml/kg, P < 0.05). Within-subjects TERalbwas a strong negative predictor of PV (mean r = 0.92 ± 0.03, P < 0.05), and TERalbwas lowest during E2-P4(5.7 ± 0.5, 4.1.0 ± 1.1, and 2.8 ± 0.9%/h, P < 0.05, for GnRH antagonist, E2, and E2-P4, respectively). ECFV was reduced during E2(227 ± 31 ml/kg, P < 0.05) compared with both GnRH antagonist (291 ± 37 ml/kg) and E2-P4(283 ± 19 ml/kg). Thus the percentage of extracellular fluid in the plasma compartment increased to 21.0% ( P < 0.05) during E2compared with GnRH antagonist (16.1%) and E2-P4(17.2%) admistration. Thus E2increased PV via actions on the capillary endothelium to lower TERalband favor intravascular water retention, whereas during E2-P4PV increased via the combined responses of ECFV expansion and lower TERalb.

Oestrogen effects on urine concentrating response in young women

Oestrogen lowers the plasma osmotic threshold for arginine vasopressin (AVP) release but without commensurate changes in renal concentrating response, suggesting oestrogen (OE2) may lower renal sensitivity to AVP. Ten women (23 +/- 1 years) received a gonadotropin releasing hormone analogue (GnRHa), leuprolide acetate, to suppress OE2 for 35 days, and then added OE2 (two patches each delivering 0.1 mg day-1) on days 32-35. On days 28 and 35 we tested blood and renal water and sodium (Na+) regulation during stepwise 60 min AVP infusions (10, 35, 100, 150 and 200 microu (kg body weight)-1 Pitressin). Plasma OE2 concentration increased from 19 +/- 4 to 152 +/- 3 pg ml(-1) and plasma progesterone concentration was unchanged (1.0 +/- 0.4 and 0.7 +/- 0.1 ng ml(-1)) for GnRHa and OE2 administration, respectively. Standard log plots of plasma AVP concentration ([AVP]P) vs. urine osmolality (OsmU) were fitted to a sigmoidal curve, and EC50 was determined by non-linear regression curve fitting of concentration-response data. OsmU rose exponentially during AVP infusions, but hormone treatments did not affect EC50 (3.3 +/- 0.07 and 3.1 +/- 0.6 pg ml(-1), for GnRHa and OE2, respectively). However, the urine osmolality increase was greater within the physiological range (approximately 2.5-3.4 pg ml(-1) [AVP]P) during OE2 treatment. Throughout most of the AVP infusion, the rate of clearance of AVP from plasma (PCRAVP) was increased during OE2 (45.5 ml (kg body weight)(-1) min(-1)) compared to GnRHa administration (33.1 ml (kg body weight)(-1) min(-1); mean for the 100-200 microu (kg body weight)(-1) infusion rates). The rate of renal free water clearance (CH2O) was similar between hormone treatments. Sodium excretion fell during OE2 administration due to greater distal tubular sodium reabsorption. Despite more rapid PCRAVP, renal concentrating response to graded AVP infusions was unaffected by oestrogen treatment suggesting oestrogen does not affect overall renal sensitivity to AVP. However, OE2 may increase renal fluid retention within a physiological range of AVP.