Advances in human oxytocin measurement: challenges and proposed solutions.

Oxytocin, a neuropeptide known for its role in reproduction and socioemotional processes, may hold promise as a therapeutic agent in treating social impairments in patient populations. However, research has yet to uncover precisely how to manipulate this system for clinical benefit. Moreover, inconsistent use of standardized and validated oxytocin measurement methodologies-including the design and study of hormone secretion and biochemical assays-present unresolved challenges. Human studies measuring peripheral (i.e., in plasma, saliva, or urine) or central (i.e., in cerebrospinal fluid) oxytocin concentrations have involved very diverse methods, including the use of different assay techniques, further compounding this problem. In the present review, we describe the scientific value in measuring human endogenous oxytocin concentrations, common issues in biochemical analysis and study design that researchers face when doing so, and our recommendations for improving studies using valid and reliable methodologies.

First voided volume: A novel approach to characterize nocturia.

AIMS: Nocturnal polyuria syndrome (NPS) denotes nocturnal polyuria (NP) in the absence of identifiable contributory factors. The trajectory of nocturnal urine production (NUP; typically expressed as ml/hour) may be useful in delineating between NP patients with versus without NPS, but changes in absolute urine volume, the directly measured substrate for behavioral and pharmacologic interventions targeting nocturnal urine production, have not been well characterized. This study compares the ratio of the first nocturnal voided volume (FNVV) to the nocturnal average voided volume (NAVV) in patients with versus without NPS. METHODS: Secondary analysis of 24-h voiding diaries from male patients greater than or equal to 18 years of age with two or more nocturnal voids and NP using two different criteria for NP: NUP greater than or equal to 90 ml/h and nocturnal polyuria index (NPi) greater than or equal to 0.33. Patients with diabetes insipidus and CPAP-adherent obstructive sleep apnea (OSA) were excluded. Patients were divided into 2 groups: secondary NP (OSA, congestive heart failure, and chronic kidney disease) and NPS (absence of edema, diuretic use, and the aforementioned comorbidities). FNVV was defined as the volume of urine accompanying the first nocturic episode. NAVV was defined as nocturnal urine volume/(number of nocturnal voids + 1). The nocturnal urine trajectory ratio (NUTR) was defined as FNVV/NAVV. RESULTS: At NUP greater than or equal to 90 ml/h, NUTR was significantly greater in patients with (n = 73) versus without (n = 28) NPS (1.10 [0.89-1.33] vs. 0.91 [0.55-1.15], p = .012). At NPi greater than or equal to 0.33, NUTR was likewise significantly greater in patients with (n = 92) versus without (n = 32) NPS (1.09 [0.90-1.33] vs. 0.91 [0.57-1.17], p = .010). CONCLUSIONS: The volume of urine produced in the early hours of sleep is central to identification of NPS in patients with nocturia.

Identifying men with global polyuria on a nocturnal-only voiding diary.

AIMS: Nocturnal polyuria (NP) and global polyuria (GP) are not mutually exclusive. However, by rate, the common criteria for GP (40 mL/kg/24 hours [117 mL/kg/hour in a 70-kg individual] or 3000 mL/24 hours [125 mL/h]) are more stringent than those for NP (90 mL/hour during the sleep period or NP index [NPi; nocturnal volume/24-hour volume] > 0.33 [no minimum rate]). It remains unclear whether total nocturnal urine volume (NUV) may reliably delineate between NP patients with and without comorbid GP. METHODS: A clinical database of men with lower urinary tract symptoms was searched for voiding diaries completed by patients reporting greater than or equal to 1 nocturnal void(s). Four separate analyses were performed using all combinations of the two NP and two GP criteria listed above. For each analysis, patients were included if they met the criteria for NP, and then stratified by presence or absence of GP (ie, NP + GP vs isolated NP). RESULTS: Median NUV was greater among patients with NP + GP for all criteria combinations. Sensitivities greater than or equal to 80%/90%/100% for NP + GP were observed at 1275/1230/1085 mL for {NPi > 0.33 + 24-hour volume > 3000 mL}; 1075/1035/1035 mL for {NPi > 0.33 + 24-hour volume > 40 mL/kg}; 900/745/630 mL for {NUP > 90 mL/hour + 24-hour volume > 3000 mL}; and 1074/1035/990 mL for {NUP > 90 mL/hour + 24-hour volume > 40 mL/kg}. CONCLUSIONS: An inordinate NUV among men with NP is fairly sensitive for comorbid GP. In the appropriate clinical setting, nocturnal-only diaries may suffice in the evaluation and follow-up of patients with NP, so long as outlying nocturnal volumes prompt a 24-hour diary/urine collection.

THE EFFECTS OF HYPONATREMIA ON BONE DENSITY AND FRACTURES: A SYSTEMATIC REVIEW AND META-ANALYSIS.

Objective: Hyponatremia decreases bone mineral density and is a major risk factor for fragility fractures. Objectives of our systematic review and meta-analysis were to analyze the overall effects of hyponatremia on bone fractures, osteoporosis, and mortality. Methods: We extracted data from Medline, Cochrane Central, and EMBASE 1960-2017 and conference abstracts from 2007-2017. We included studies with data on serum sodium, fractures, bone density, or diagnoses of osteoporosis. Studies were independently reviewed by two authors and assessed for bias using the Newcastle-Ottawa scale. Random effect models meta-analysis was used when at least three studies reported the same outcome measures. We reported summary odds ratios (ORs) and 95% confidence intervals (CIs). Results: We included 26 studies for qualitative analysis. Fifteen studies were included in the meta-analysis to evaluate the effects of hyponatremia on fractures, four studies for bone mineral density changes, and six for mortality. Hyponatremia increased the odds of fractures at all sites (summary OR, 2.34 [95% CI, 1.86, 2.96]. There was an increase in the odds of osteoporosis (summary OR, 2.67 [95% CI, 2.07, 3.43]). Mortality risk among the included studies remained high (summary OR, 1.31 [95% CI, 1.16, 1.47]). Conclusion: Our meta-analysis confirms a statistically significant association of hyponatremia with bone fractures and osteoporosis along with higher mortality. Long-term prospective studies evaluating the impact of correcting hyponatremia on bone health, fractures, and mortality are required. Abbreviations: AVP = arginine vasopressin; CI = confidence interval; CKD = chronic kidney disease; OR = odds ratio; SIADH = syndrome of inappropriate antidiuretic hormone.

Aging-related impairment of urine-concentrating mechanisms correlates with dysregulation of adrenocortical angiotensin type 1 receptors in male Fischer rats.

To investigate age-associated impairments in fluid homeostasis, 4-mo (young) and 32-mo (old) Fischer 344/BN male rats were studied before and after a dietary sodium load. Transferring young rats from a low-sodium (LS) to a high-sodium (HS) diet increased water intake and urine volume by 1.9- and 3.0-fold, respectively, while urine osmolality and plasma aldosterone decreased by 33 and 98%. Concomitantly, adrenocortical angiotensin type 1 receptor (AT1R) density decreased by 35%, and AT1bR mRNA decreased by 39%; no changes were observed in AT1aR mRNA. In contrast, the increase in water intake (1.4-fold) was lower in the old rats, and there was no effect of the HS diet on urine volume or urine osmolality. AT1R densities were 29% less in the old rats before transferring to the HS diet, and AT1R densities were not reduced as rapidly in response to a HS diet compared with the young animals. After 6 days on the HS diet, plasma potassium was lowered by 26% in the old rats, whereas no change was detected in the young rats. Furthermore, while plasma aldosterone was substantially decreased after 2 days on the HS diet in both young and old rats, plasma aldosterone was significantly lower in the old compared with the young animals after 2 wk on the LS diet. These findings suggest that aging attenuates the responsiveness of the adrenocortical AT1R to a sodium load through impaired regulation of AT1bR mRNA, and that this dysregulation contributes to the defects in water and electrolyte homeostasis observed in aging.

Tolvaptan and Neurocognitive Function in Mild to Moderate Chronic Hyponatremia: A Randomized Trial (INSIGHT).

BACKGROUND: This trial assessed the effect of tolvaptan on cognition, gait, and postural stability in adult patients with mild to moderate asymptomatic hyponatremia. STUDY DESIGN: Phase 3b, multicenter, randomized, double-blind, placebo-controlled, parallel-group pilot study. SETTING & PARTICIPANTS: 57 men and women 50 years or older with chronic asymptomatic euvolemic or hypervolemic hyponatremia (serum sodium concentration >120-<135 mEq/L) at 16 sites. INTERVENTION: Patients were randomly assigned 1:1 to receive tolvaptan or matching placebo beginning at a dose of 15mg/d, with titration to 30 or 60mg/d based on change in serum sodium concentration and tolerance. OUTCOMES: Primary: change from baseline in the neurocognitive composite score of speed domains. Secondary: changes from baseline in individual neurocognitive domain scores, overall neurocognitive composite score, gait and postural stability test results, and serum sodium concentrations. RESULTS: Mean serum sodium concentration increased from 129 to 136 mEq/L in the tolvaptan group and from 130 to 132 mEq/L in the placebo group (P<0.001). There was no difference in overall neurocognitive composite scores of speed domains between groups, except for the psychomotor speed domain, which was statistically improved following hyponatremia correction with tolvaptan (treatment effect, 0.27; 95% CI, 0.04-0.51; P=0.03). LIMITATIONS: There were some imbalances between treatment groups in baseline neurocognitive function scores and some baseline test results were near normal, leaving little opportunity for improvement. Formal sample size calculations were not performed because this was a pilot study. The study population was small (n=57) and treatment was of short duration (3 weeks). The primary end point of the study was not significant; thus, subgroup analyses are subject to errors of multiplicity and should be regarded as hypothesis generating. CONCLUSIONS: Tolvaptan was effective in reversing chronic hyponatremia, and this correlated with improvements in results of a variety of neurocognition tests, particularly rapid motor movements, which tended to reverse following return to a low baseline serum sodium concentration after treatment withdrawal.

Current treatment practice and outcomes. Report of the hyponatremia registry.

Current management practices for hyponatremia (HN) are incompletely understood. The HN Registry has recorded diagnostic measures, utilization, efficacy, and outcomes of therapy for eu- or hypervolemic HN. To better understand current practices, we analyzed data from 3087 adjudicated adult patients in the registry with serum sodium concentration of 130 mEq/l or less from 225 sites in the United States and European Union. Common initial monotherapy treatments were fluid restriction (35%), administration of isotonic (15%) or hypertonic saline (2%), and tolvaptan (5%); 17% received no active agent. Median (interquartile range) mEq/l serum sodium increases during the first day were as follows: no treatment, 1.0 (0.0-4.0); fluid restriction, 2.0 (0.0-4.0); isotonic saline, 3.0 (0.0-5.0); hypertonic saline, 5.0 (1.0-9.0); and tolvaptan, 4.0 (2.0-9.0). Adjusting for initial serum sodium concentration with logistic regression, the relative likelihoods for correction by 5 mEq/l or more (referent, fluid restriction) were 1.60 for hypertonic saline and 2.55 for tolvaptan. At discharge, serum sodium concentration was under 135 mEq/l in 78% of patients and 130 mEq/l or less in 49%. Overly rapid correction occurred in 7.9%. Thus, initial HN treatment often uses maneuvers of limited efficacy. Despite an association with poor outcomes and availability of effective therapy, most patients with HN are discharged from hospital still hyponatremic. Studies to assess short- and long-term benefits of correction of HN with effective therapies are needed.

Melanocortin signaling in the brainstem influences vagal outflow to the stomach.

Activation of melanocortin 4 receptors (MC4-Rs) in brain nuclei associated with food intake profoundly influences consummatory behavior. Of these nuclei, the dorsal motor vagal nucleus (DMV), which has a dense concentration of MC4-Rs, is an important regulator of gastric tone and motility. Hence, the present study sought to examine the role of MC4-Rs in this nucleus on these activities. Using an in vivo approach, MC4-R agonists, melanotan-II (MT-II) or α-melanocyte stimulating hormone (α-MSH), were unilaterally microinjected into the DMV of rats, and their effects were noted on gastric activity. MT-II decreased phasic contractions, whereas α-MSH increased their amplitude. Both effects were blocked by the MC4-R antagonist SHU9119 or by ipsilateral vagotomy. Microinjection of the agonists (MT-II and α-MSH) into the overlying nucleus of the solitary tract (NTS), an important component of "vago-vagal" gastric circuitry, decreased phasic contractions. In addition, α-MSH reduced gastric tone and mean arterial blood pressure. To study the underlying mechanisms of the effect of MC4-R stimulation on gastric activity, electrophysiological recordings were made from labeled DMV antrum neurons in rat pups and MC4-R(-/-) mice. Bath application of MT-II or α-MSH significantly reduced spontaneous action potentials (but not in MC4-R(-/-) mice). However, in low-calcium ACSF, MT-II decreased neuronal firing, whereas α-MSH increased it. These effects mirror those of our in vivo DMV studies. Altogether, our novel findings show that activation of MC4-Rs in the brainstem, particularly in the medial NTS by the endogenous peptide α-MSH, modulates gastric activity, which may have physiological relevance for food intake and gastric function.

Sodium homeostasis and bone.

PURPOSE OF REVIEW: Sodium balance is primarily regulated through the renin-angiotensin-aldosterone system. Extracellular fluid (ECF) sodium concentrations ([Na]) reflect the overall body sodium content, but are also influenced by the osmoregulatory system, which is regulated by the posterior pituitary hormone arginine vasopressin (AVP). Consequently, changes in total body sodium content are not always accurately reflected by the ECF [Na]. This review summarizes the growing evidence base suggesting that skeletal bone, which is rich in sodium, may play a key role in overall body sodium homeostasis. RECENT FINDINGS: Hyponatremia, even when relatively mild, leads to increased morbidity and mortality in diverse clinical scenarios. In particular, hyponatremia has been shown to increase gait instability, falls, and fracture risk. It now appears likely that at least part of the fracture risk is because of the adverse effects of hyponatremia on bone density and quality. The mechanisms through which this occurs are not yet completely understood, but prominently involve increased bone osteoclast formation and activity. An additional direct effect of AVP on bone remodeling has also been recently suggested. SUMMARY: Recent evidence expands upon the previously accepted concepts of body sodium homeostasis and suggests that sodium balance can be augmented by inputs from skeletal bone, which acts as a sodium-rich reservoir that can be deployed during times of sodium deficiency. However, this evolutionarily adaptive mechanism to maintain sodium homeostasis during times of environmental sodium deprivation also has adverse consequences by negatively impacting bone quality and increasing fracture risk.

Characterization of the effects of the vasopressin V2 receptor on sweating, fluid balance, and performance during exercise.

A regulatory effect of arginine vasopressin (AVP) on sweat water conservation has been hypothesized but not definitively evaluated. AVP-mediated insertion of sweat and salivary gland aquaporin-5 (AQP5) water channels through activation of the vasopressin type 2 receptor (V2R) remains an attractive, yet unexplored, mechanism that could result in a more concentrated sweat with resultant decreased water loss. Ten runners participated in a double-blind randomized control treadmill trial under three separate pharmacological conditions: a placebo, V2R agonist (0.2 mg desmopressin), or V2R antagonist (30 mg tolvaptan). After a familiarization trial, runners ran for 60 min at 60% of peak speed followed by a performance trial to volitional exhaustion. Outcome variables were collected at three exercise time points: baseline, after the steady-state run, and after the performance run. Body weight losses were <2% across all three trials. Significant pharmacological condition effects were noted for urine osmolality [F = 84.98; P < 0.0001] and urine sodium concentration ([Na(+)]) [F = 38.9; P < 0.0001], which verified both pharmacological activation and inhibition of the V2R at the kidney collecting duct. Plasma osmolality and [Na(+)] demonstrated significant exercise (F = 26.0 and F = 11.1; P < 0.0001) and condition (F = 5.1 and F = 3.8; P < 0.05) effects (osmolality and [Na(+)], respectively). No significant exercise or condition effects were noted for either sweat or salivary [Na(+)]. Significant exercise effects were noted for plasma [AVP] (F = 22.3; P < 0.0001), peak core temperature (F = 103.3; P < 0.0001), percent body weight change (F = 6.3; P = 0.02), plasma volume change (F = 21.8; P < 0.0001), and thirst rating (F = 78.2; P < 0.0001). Performance time was not altered between conditions (P = 0.80). In summary, AVP acting at V2R does not appear to regulate water losses from body fluids other than renal excretion during exercise.

Renal physiology of nocturia.

Renal function, diurnal fluctuations in arginine vasopressin (AVP) secretion, sex, and advanced age affect urine formation and may contribute to nocturia. Renal effects of AVP are mediated by AVP V2 receptors in the kidney collecting duct. Changes in AVP concentration have the greatest relative effects on urine volume when AVP levels are low; therefore small changes can have a large effect on renal water excretion. AVP is the major regulator of water excretion by the kidneys, and AVP levels have been shown to affect nocturnal voiding. Results of several studies show that patients with nocturia had no significant variation in plasma AVP, whereas patients without nocturia had significant diurnal variation in plasma AVP. The V2 receptor gene is located on the X chromosome, which has important sex-specific consequences. For example, mutations in the V2 gene can cause nephrogenic diabetes insipidus, predominantly in men. Age-related changes in water metabolism are associated with overall body composition, kidney, and brain. Older people generally experience decreased extracellular fluid and plasma volume, which leads to increased adverse consequences from net body water gain or loss. Renal function declines with age, and the ability to concentrate urine and conserve sodium is reduced in the elderly. Thirst perception is also decreased in the elderly, who, compared with younger people, tend to hypersecrete AVP in response to higher plasma osmolality, possibly resulting in hyponatremia. These aspects of renal physiology should be considered when antidiuretic drugs are prescribed for the treatment of nocturia.

The need for salt: does a relationship exist between cystic fibrosis and exercise-associated hyponatremia?

Salt replacement is often recommended to prevent exercise-associated hyponatremia (EAH) despite a lack of evidence to support such practice. Exercise-associated hyponatremia is known to be a complex process resulting from the interplay of hydration, arginine vasopressin, and sodium balance. Although evidence suggests overhydration is the dominant pathophysiologic factor in most cases, the contributions of sweat sodium losses remain unclear. A theoretical genetic mechanism producing exuberant sweat sodium loss in athletes is the presence of cystic fibrosis (CF) gene. Individuals with CF develop hypovolemic hyponatremia by sodium loss via sweat through a defective chloride ion transport channel, the CF transmembrane conductance regulator (CFTR). Elevated sweat sodium concentrations in CF single heterozygotes suggest that athletes developing EAH may be CFTR carriers. We targeted the 2010 and 2011 Western States Endurance Run ultramarathon, an event where athletes with EAH regularly present in a hypovolemic state, for a cohort maximizing the potential to document such a relationship. A total of 798 runners started the 2010 (n = 423) and 2011 (n = 375) races. Of the 638 finishers, 373 were screened for EAH by blood draw, 60 (16%) were found to have EAH, and 31 (alpha = 0.05 for n = 9) reported their CF result from a saliva-based genetic testing kit. Neither the 31 EAH-positive athletes nor the 25 EAH-negative comparison cohort athletes tested positive for a CF mutation. This null relationship suggests that CFTR mutations are not associated with the development of EAH and that salt supplementation is unnecessary for such a reason.

Age-Associated Abnormalities of Water Homeostasis.

Deficits in renal function, thirst, and responses to osmotic and volume stimulation have been repeatedly demonstrated in older populations. The lessons learned over the past six decades serve to emphasize the fragile nature of water balance characteristic of aging. Older individuals are at increased risk for disturbances of water homeostasis due to both intrinsic disease and iatrogenic causes. These disturbances have real-life clinical implications in terms of neurocognitive effects, falls, hospital readmission and need for long-term care, incidence of bone fracture, osteoporosis, and mortality.

Hormones and Aging: An Endocrine Society Scientific Statement.

Multiple changes occur across various endocrine systems as an individual ages. The understanding of the factors that cause age-related changes and how they should be managed clinically is evolving. This statement reviews the current state of research in the growth hormone, adrenal, ovarian, testicular, and thyroid axes, as well as in osteoporosis, vitamin D deficiency, type 2 diabetes, and water metabolism, with a specific focus on older individuals. Each section describes the natural history and observational data in older individuals, available therapies, clinical trial data on efficacy and safety in older individuals, key points, and scientific gaps. The goal of this statement is to inform future research that refines prevention and treatment strategies in age-associated endocrine conditions, with the goal of improving the health of older individuals.

Treatment Guidelines for Hyponatremia: Stay the Course.

International guidelines designed to minimize the risk of complications that can occur when correcting severe hyponatremia have been widely accepted for a decade. On the basis of the results of a recent large retrospective study of patients hospitalized with hyponatremia, it has been suggested that hyponatremia guidelines have gone too far in limiting the rate of rise of the serum sodium concentration; the need for therapeutic caution and frequent monitoring of the serum sodium concentration has been questioned. These assertions are reminiscent of a controversy that began many years ago. After reviewing the history of that controversy, the evidence supporting the guidelines, and the validity of data challenging them, we conclude that current safeguards should not be abandoned. To do so would be akin to discarding your umbrella because you remained dry in a rainstorm. The authors of this review, who represent 20 medical centers in nine countries, have all contributed significantly to the literature on the subject. We urge clinicians to continue to treat severe hyponatremia cautiously and to wait for better evidence before adopting less stringent therapeutic limits.

Osteoclast response to low extracellular sodium and the mechanism of hyponatremia-induced bone loss.

Our recent animal and human studies revealed that chronic hyponatremia is a previously unrecognized cause of osteoporosis that is associated with increased osteoclast numbers in a rat model of the human disease of the syndrome of inappropriate antidiuretic hormone secretion (SIADH). We used cellular and molecular approaches to demonstrate that sustained low extracellular sodium ion concentrations ([Na(+)]) directly stimulate osteoclastogenesis and resorptive activity and to explore the mechanisms underlying this effect. Assays on murine preosteoclastic RAW 264.7 cells and on primary bone marrow monocytes both indicated that lowering the medium [Na(+)] dose-dependently increased osteoclast formation and resorptive activity. Low [Na(+)], rather than low osmolality, triggered these effects. Chronic reduction of [Na(+)] dose-dependently decreased intracellular calcium without depleting endoplasmic reticulum calcium stores. Moreover, we found that reduction of [Na(+)] dose-dependently decreased cellular uptake of radiolabeled ascorbic acid, and reduction of ascorbic acid in the culture medium mimicked the osteoclastogenic effect of low [Na(+)]. We also detected downstream effects of reduced ascorbic acid uptake, namely evidence of hyponatremia-induced oxidative stress. This was manifested by increased intracellular free oxygen radical accumulation and proportional changes in protein expression and phosphorylation, as indicated by Western blot analysis from cellular extracts and by increased serum 8-hydroxy-2'-deoxyguanosine levels in vivo in rats. Our results therefore reveal novel sodium signaling mechanisms in osteoclasts that may serve to mobilize sodium from bone stores during prolonged hyponatremia, thereby leading to a resorptive osteoporosis in patients with SIADH.

Development of an experimental model to study the pathophysiology of cerebral salt wasting following subarachnoid hemorrhage.

Hyponatremia is frequent following cranial -neurosurgery or acute brain injury like subarachnoid hemorrhage (SAH), and increases mortality by 30%. The patho-physiology is not understood nor does a causal therapy exist. Since clinical trials are potentially dangerous in this very ill population, we examined whether an established rat model allows studying cerebral salt wasting (CSW) following SAH. The daily urine sodium excretion as well as plasma sodium, osmolality and antidiuretic hormone (ADH) levels were measured for 10 days. Following the injection of 300 µl of blood into the great cistern (SAH(severe)), natriuresis peaked twice (days 1 and 3-5, p < 0.05) resulting in a plasma sodium nadir (day 1 - 133.9 mmol/L, day 5 - 132.6 mmol/L), while following the injection of 300 µL saline (ICP(control)), natriuresis occurred delayed on days 4-5 (p < 0.05). Following double SAH (200 µL twice, 24 h apart), a natriuresis on day 4 resulted in a hyponatremia (131.7 mmol/L, p = 0.025). Neither SAH(mild) (100 µL), the injection of hemolyzed blood (100 µL) or hypertonic saline (200 µL) replicated the effect. The immediate release of ADH (32.23 ± 34.87 pg/mL) following SAH(severe) normalized over the next few days. We conclude that first, the rat model of SAH is suitable for studying CSW, second the increase in intracranial pressure generates the delayed hyponatremia, and third, the ADH release does not mediate natriuresis.