Puberty alters renal water handling

We investigated the influence of sex and puberty stage on circadian urine production and levels of antidiuretic hormone [arginine vasopressin (AVP)] in healthy children. Thirty-nine volunteers (9 prepuberty boys, 10 prepuberty girls, 10 midpuberty boys, and 10 midpuberty girls) were included. All participants underwent a 24-h circadian inpatient study under standardized conditions regarding Na(+) and fluid intake. Blood samples were drawn every 4 h for measurements of plasma AVP, serum 17-β-estradiol, and testosterone, and urine was fractionally collected for measurements of electrolytes, aquaporin (AQP)2, and PGE2. We found a marked nighttime decrease in diuresis (from 1.69 ± 0.08 to 0.86 ± 0.06 ml·kg(-1)·h(-1), P < 0.001) caused by a significant nighttime increase in solute-free water reabsorption (TcH2O; day-to-night ratio: 0.64 ± 0.07, P < 0.001) concurrent with a significant decrease in osmotic excretion (day-to-night ratio: 1.23 ± 0.06, P < 0.001). Plasma AVP expressed a circadian rhythm (P < 0.01) with a nighttime increase and peak levels at midnight (0.49 ± 0.05 pg/ml). The circadian plasma AVP rhythm was not influenced by sex (P = 0.56) or puberty stage (P = 0.73). There was significantly higher nighttime TcH2O in prepuberty children. This concurred with increased nighttime urinary AQP2 excretion in prepuberty children. Urinary PGE2 exhibited a circadian rhythm independent of sex or puberty stage. Levels of serum 17β-estradiol and testosterone were as expected for sex and puberty stage, and no effect on the AVP-AQP2-TcH2O axis was observed. This study found a circadian rhythm of plasma AVP independent of sex and puberty stage, although nighttime TcH2O was higher and AQP2 excretion was more pronounced in prepuberty children, suggesting higher prepuberty renal AVP sensitivity.

Melamine-related urinary stones in 195 infants and young children: clinical features within 2 years of follow-up

OBJECTIVE

To summarize the clinical features and follow-up, the effects of melamine-tainted milk powder (MMP) consumption on kidney and body growth in children who suffered from melamine-related urinary stones (MUS) 2 years earlier were checked.

MEASUREMENTS

Body height and weight, kidney and bladder morphology monitored by ultrasound, urinalysis and renal function were recorded. Plain abdominal radiography was performed for differential diagnosis. The first follow-up was carried out at 15 months and the second 2 years later for patients who showed any abnormality at the first follow-up. Two hundred age- and gender-matched cohorts were included.

RESULTS

All cases received conservative treatment in hospital. Fifteen months of follow-up was successfully carried out in 167 cases. 91 children had residual MUS at the time of discharge, 58 MUS disappeared completely, 25 dissolved partially, 1 increased in size, and 7 did not change. At 2 years of follow-up, the residual stones all disappeared except for 1 case; the patient who showed a delayed development with regard to height caught up at 24 months of follow-up.

CONCLUSIONS

Conservative treatment shows a high effectiveness in cases with residual MUS. Consumption of MMP with timely treatment did not demonstrate an evident impact on kidney and bladder although body height is slightly affected in a few cases.

Excess diuresis and natriuresis during acute sleep deprivation in healthy adults

The transition from wakefulness to sleep is associated with a pronounced decline in diuresis, a necessary physiological process that allows uninterrupted sleep. The aim of this study was to assess the effect of acute sleep deprivation (SD) on urine output and renal water, sodium, and solute handling in healthy young volunteers. Twenty young adults (10 male) were recruited for two 24-h studies under standardized dietary conditions. During one of the two admissions, subjects were deprived of sleep. Urine output, electrolyte excretions, and osmolar excretions were calculated. Activated renin, angiotensin II, aldosterone, arginine vasopressin, and atrial natriuretic peptide were measured in plasma, whereas prostaglandin E2 and melatonin were measured in urine. SD markedly increased the diuresis and led to excess renal sodium excretion. The effect was more pronounced in men who shared significantly higher diuresis levels during SD compared with women. Renal water handling and arginine vasopressin levels remained unaltered during SD, but the circadian rhythm of the hormones of the renin-angiotensin-aldosterone system was significantly affected. Urinary melatonin and prostaglandin E2 excretion levels were comparable between SD and baseline night. Hemodynamic changes were characterized by the attenuation of nocturnal blood pressure dipping and an increase in creatinine clearance. Acute deprivation of sleep induces natriuresis and osmotic diuresis, leading to excess nocturnal urine production, especially in men. Hemodynamic changes during SD may, through renal and hormonal processes, be responsible for these observations. Sleep architecture disturbances should be considered in clinical settings with nocturnal polyuria such as enuresis in children and nocturia in adults.

Age related nocturnal urine volume and maximum voided volume in healthy children: reappraisal of International Children's Continence Society definitions

PURPOSE

We determined normal, age related reference data regarding maximum voided volume and nocturnal urine production using the same methodology as in clinical practice.

MATERIALS AND METHODS

A total of 62 girls and 86 boys without enuresis (mean +/- SD age 9.64 +/- 2.63 years, range 3 to 15) completed 4 days (2 weekends) of frequency-volume charts and 14 days of home recording of nocturnal urine production. From these recordings maximum voided volume with and without first morning void was derived for each subject. Also, average nocturnal urine volume with and without nocturia was calculated. Percentiles were produced by dividing the population into 1-year age groups.

RESULTS

Based on 2,836 daytime voids and 1,977 overnight recordings, maximum voided volume and nocturnal urine volume showed a significant linear relationship with age but not with gender. Maximum voided volume with first morning void was significantly higher than without (403 +/- 137 ml vs 281 +/- 112 ml, p <0.0001) and the 50th percentile line of maximum voided volume with first morning void was 80 to 100 ml higher than Koff's formula (30 x [age + 1] ml). Conversely the 50th percentile of maximum voided volume without first morning void was almost identical to Koff's formula. Regarding nocturnal measurements, nocturia was noted on 128 nights (6.5%) and nocturnal urine volume on nights with nocturia was significantly higher than on nights without nocturia (365 +/- 160 ml vs 248 +/- 75 ml, respectively, p <0.0001). The 97.5th nocturnal urine volume percentile line of healthy children deviated markedly from the current International Children's Continence Society definition of nocturnal polyuria, especially at low and high ages.

CONCLUSIONS

We demonstrate clearly that the universally used formula 30 x (age + 1) ml is indeed valid for a population of healthy Danish children but only if the first morning void is disregarded. Furthermore, we question the validity of the current International Children's Continence Society formula for nocturnal polyuria (nocturnal urine volume greater than 130% of maximum voided volume for age), and instead we propose the formula, nocturnal urine volume greater than 20 x (age + 9) ml.

Unilateral ureteral obstruction alters expression of acid-base transporters in rat kidney

PURPOSE

Unilateral ureteral obstruction is a common clinical problem that is often associated with a urinary acidification defect caused by decreased net H(+) secretion and/or HCO(3)(-) reabsorption. To clarify the molecular mechanisms of these defects we examined expression levels of key acid-base transporters along the renal nephron segments and collecting duct.

MATERIALS AND METHODS

Wistar rats (Møllegard Breeding Centre, Eiby, Denmark) underwent 24-hour unilateral ureteral obstruction, unilateral ureteral obstruction release followed for 4 days or unilateral ureteral obstruction release followed for 4 days plus experimental acidosis induced by NH(4)Cl oral administration. After sacrifice kidneys were processed for immunoblotting and immunohistochemistry.

RESULTS

Semiquantitative immunoblotting revealed that unilateral ureteral obstruction caused significant mean +/- SE down-regulation of type 3 Na(+)/H(+) exchanger to 53% +/- 9%, electrogenic Na(+)/HCO(3)(-) cotransporter to 60% +/- 9%, type 1 bumetanide sensitive Na(+)-K(+)(NH(4)(+)) -2Cl(-) cotransporter to 64% +/- 7%, electroneutral Na(+)/HCO(3)(-) cotransporter to 43% +/- 4% and anion exchanger (pendrin) to 53% +/- 10% in the obstructed kidney, which was confirmed by immunohistochemistry. After release of unilateral ureteral obstruction down-regulation of these transporters persisted together with marked down-regulation of H(+)-adenosine triphosphatase in the obstructed kidney. In rats with unilateral ureteral obstruction release followed for 4 days with experimental acidosis induced by NH(4)Cl oral administration plasma pH and HCO(3)(-) were dramatically decreased in response to NH(4)Cl for 2 days compared with those in sham operated rats with acid loading, indicating a defect in H(+) excretion and HCO(3)(-) reabsorption after obstruction release. Expression of these transporters did not change in the contralateral nonobstructed kidney of rats with unilateral ureteral obstruction and unilateral ureteral obstruction release followed for 4 days.

CONCLUSIONS

The expression of renal acid-base transporters is markedly decreased in the obstructed kidney, which may be responsible for the contribution of impaired renal H(+) excretion and HCO(3)(-) reabsorption to the urinary acidification defect in response to unilateral ureteral obstruction.

Transcutaneous electrical nerve stimulation for refractory daytime urinary urge incontinence

PURPOSE

We studied the effect of transcutaneous electrical nerve stimulation in children with overactive bladder and treatment refractory daytime urinary incontinence.

MATERIALS AND METHODS

We recruited 27 children 5 to 14 years old with daytime urge incontinence refractory to timer assisted standard urotherapy and anticholinergics who had normal urinalysis, and unremarkable urinary tract ultrasound and physical examination. Study exclusion criteria were bladder underactivity, lower urinary tract obstruction, ongoing defecation disorders, lower urinary tract surgery and previous transcutaneous electrical nerve stimulation. After a 2-week run-in of standard urotherapy the children underwent natural fill ambulatory urodynamics to confirm detrusor overactivity. Subsequently they were randomly allocated to 4 weeks of 2 hours of daily active or placebo S2-S3 transcutaneous electrical nerve stimulation. The severity of incontinence and urgency, and 48-hour bladder diaries were recorded before randomization and during intervention week 4. Children withdrew from anticholinergics throughout the study period.

RESULTS

Two children were excluded from randomization due to urodynamic signs of lower urinary tract obstruction. After 4 weeks of intervention 8 children (61%) in the active group showed a significant decrease in incontinence severity but this occurred in only 2 (17%) in the sham treated group (p <0.05). The active group had a significantly greater decrease in daily incontinence episodes compared to the sham treated group (p <0.01). Transcutaneous electrical nerve stimulation did not alter maximal and average voided volumes.

CONCLUSIONS

Sacral transcutaneous electrical nerve stimulation seems superior to placebo for refractory daytime incontinence in children with overactive bladder. This effect does not seem to be a consequence of improved bladder reservoir function.

Age-dependent renal expression of acid-base transporters in neonatal ureter obstruction

Congenital obstructive nephropathy accounts for a major proportion of renal insufficiency in infancy and childhood. In an earlier investigation we demonstrated that bilateral complete ureteral obstruction (BUO) in rats is associated with inadequate urinary acidification [Am J Physiol Renal Physiol. 295(2):F497-506, 2008]. The aim of the study reported here was to determine whether this defect is also associated with unilateral ureteral obstruction (UUO), which is clinically more common than BUO. The time-course of the changes in protein expression levels of major renal acid-base transporters was examined at 7 and 14 weeks in rats with neonatally induced partial unilateral ureteral obstruction (PUUO), which was performed within the first 48 h of life. We observed that protein expression of the renal acid-base transporters NHE3, NBC1, NBCn1, pendrin and Na(+)-K(+)-ATPase was increased in both obstructed and non-obstructed kidneys 7 weeks after the induction of neonatal PUUO. This was confirmed by immunocytochemistry. In contrast, 14 weeks after the induction of PUUO, there was a significant downregulation of the renal acid-base transporters NBC1, NBCn1 and Na(+)-K(+)-ATPase in the obstructed kidneys. These time/age-dependent changes in protein expression were associated with parallel changes in renal function resulting in urine acidification in response to exogenous acid loading. In conclusion, these results show that downregulation of protein expression is a time/age-dependent response to PUUO, which could contribute to the decreased net acid excretion and development of metabolic acidosis in neonatal rats with PUUO.

Endoluminal pelvic perfusion with norepinephrine causes only minor systemic effects and diminishes the increase in pelvic pressure caused by perfusion

OBJECTIVE

To evaluate the effect of endoluminal norepinephrine (NE) on transport pressures of the normal upper urinary tract of the pig and on plasma levels of NE in relation to possible systemic effects.

MATERIAL AND METHODS

Six anaesthetized pigs weighing approximately 39 kg were studied. Transparenchymally, two 6-F catheters were introduced into the renal pelvis bilaterally to measure pressure and perfusion. Ultrasonic flow probes recorded renal arterial blood flow, and a transurethral 10-F catheter drained the bladder and monitored diuresis. In all six animals, the bilateral pelvic pressure response was examined at increasing perfusion rates (2, 4, 6, 8, 10 and 15 ml/min) and with increasing doses of NE (0, 5, 50 and 100 microg/ml). Arterial blood samples were analysed for NE, epinephrine and blood glucose. The systemic blood pressure, heart rate and electrocardiogram were registered.

RESULTS

At all the investigated concentrations, endoluminal NE significantly diminished the increase in pelvic pressure caused by pelvic perfusion at all flow rates. At the lowest concentration of NE, no significant increase in the plasma level of NE was observed and the blood pressure did not increase. During perfusion with 50 and 100 microg/ml NE, plasma levels of NE increased significantly from 487+/-398 to 1798+/-910 and 2961+/-2093 pg/ml, respectively. This was accompanied by significant rises in mean systolic blood pressure from a baseline value of 95+/-10 mmHg to 111+/-20 and 118+/-23 mmHg, respectively. Heart rate, renal arterial blood flow and plasma levels of epinephrine and glucose did not change.

CONCLUSIONS

Endoluminal NE diminished the increase in pelvic pressure caused by pelvic perfusion even at concentrations too low to cause significant changes in NE plasma levels or systemic effects. Very high NE concentrations in the perfusion fluid caused increased plasma levels and a modest but significant increase in blood pressure. Administration of endoluminal NE may be useful in upper urinary tract stone treatment and endoscopy.

Biomechanical properties of the anterior urethra of the male rabbitA study using impedance planimetry

OBJECTIVE

To evaluate the anterior urethra of the male rabbit regarding its luminal cross-sectional area (CSA), CSA distensibility, circumferential tension-strain relation, histology and the collagen content of the tissue. material and methods: Nineteen rabbits were examined with impedance planimetry by distending the urethra at the passage from the spongious to the bulbous part and 1 cm proximally in the bulbous part. Four weeks later, eight rabbits underwent a second examination. After the measurements the urethras were processed for either histology or determination of collagen content. The urethras from six additional rabbits served as controls for histology and collagen content.

RESULTS

The CSA and the CSA distensibility were smaller at the distal than the proximal distension site. At both sites the CSA distensibility was high at low luminal pressure loads and decreased with increasing pressure. The circumferential tension-strain plot displayed an exponential relation, with a steeper slope distally than proximally. Repeated biomechanical investigation revealed a significantly increased CSA and a decreased slope of the circumferential tension-strain relation at both distension sites. The biomechanical investigation induced abrasion of the epithelium, extravasation of erythrocytes and separation of the collagen fibres, suggesting oedema of the luminal part of the wall. After 4 weeks the epithelium had changed from transitional to stratified, squamous and often keratinized epithelium and the collagen beneath the epithelium formed a dense network instead of wavy lines as seen in the control urethras. The collagen content was larger at the distal than the proximal distension site. No change in collagen content could be demonstrated between the urethras investigated once or twice with impedance planimetry.

CONCLUSIONS

The non-linear pressure-CSA, pressure-CSA distensibility and circumferential tension-strain relations found at both distension sites demonstrate that the urethra yields readily at low pressures, thus facilitating flow. At higher pressure loads, the tissue becomes less distensible, a property that protects it against over-distension and damage. Impedance planimetry cannot be used to study before-and-after phenomena as the biomechanical investigation changed both the histology and the biomechanical properties of the rabbit urethra.

Clinical evaluation of a novel ultrasound-based bladder volume monitor

OBJECTIVE

Bladder volume monitors may be useful for surveillance of bladder volume and urine production in urologic patients. Therefore, we designed an ultrasonic bladder volume monitor and evaluated it in vitro using phantoms and in vivo in one male volunteer. The purpose of this study was to perform a more thorough in vivo evaluation of our monitor in urologic patients to investigate biological effects and variance over a wide range of bladder volumes.

MATERIAL AND METHODS

Thirty urologic patients of either gender were examined using the bladder volume monitor, which is based on seven phased array ultrasonic transducers arranged in a circular pattern to optimize detection of the bladder walls. The monitor was set up to record bladder volume every 30 s during two sequential cystometries with infusion rates of 30 and 60 ml/min. The measured volumes were analyzed using regression analysis to determine volume increments (slopes), offset volume (intercept) and correlation (Pearson's correlation coefficient).

RESULTS

In the male patients, the median correlation coefficient between the infused and measured volumes was 0.97 and the slope was 0.68 ml/ml, thus warranting a correction factor of approximately 1.47 with no general volume offset. In the female patients, small bladders were generally outside the field of view of the monitor. Consequently, the correlation coefficients and slopes were 0.834 (median) and 0.43 (mean), respectively, whereas volume offsets were generally negative.

CONCLUSIONS

For examinations in male patients, the performance of the bladder volume monitor was adequate. However, for examinations in female patients, a minor redesign of the transducer unit is necessary to insure proper operation.

Regional changes in renal cortical glucose, lactate and urea during acute unilateral ureteral obstruction

OBJECTIVE

Acute unilateral ureteral obstruction (UUO) leads to changes in kidney function and metabolism. Microdialysis offers the possibility of topical analysis of changes in kidney metabolism. We applied microdialysis to the porcine kidney and evaluated its impact on gross kidney function. Furthermore, we investigated regional variations in renal interstitial fluid (RIF) glucose, lactate and urea during acute UUO.

MATERIAL AND METHODS

Eight anesthetized pigs were used. Microdialysis probes were inserted in the upper, middle and lower thirds of the left renal cortex and perfused with Ringer's chloride at a rate of 0.3 microl/min. Dialysates were fractionated for 30-min periods. Bilateral intrapelvic pressure, urinary output, urinary osmolality, the excretion fractions of sodium and potassium, renal blood flow and the glomerular filtration rate were measured. Subsequently, left-sided graded ureteral obstruction was initiated, using the kidney's own urine production as a counter-pressure.

RESULTS

The application of three microdialysis probes did not have any impact on kidney function. Ureteral obstruction decreased RIF glucose in the upper and lower thirds of the kidney, but not in the middle third. RIF lactate did not change. Interstitial urea increased in all regions of the kidney, but most markedly in the upper and lower poles.

CONCLUSIONS

Microdialysis is of potential value for assessing the renal interstitial milieu under different pathophysiological conditions. Ureteral obstruction resulted in regional differences in cortical metabolites, predominantly affecting the upper and lower poles.

Effect of Bladder Volume, Gender and Body Position on the Shape and Position of the Urinary Bladder

OBJECTIVE

The optimal design of bladder volume-monitoring equipment, e.g. regarding transducer design and software algorithms, depends greatly on the shape and position of the bladder or on potential changes due to body position and bladder volume. The purpose of this study was to study the influence of body position, bladder volume and gender on the shape and position of the bladder.

MATERIAL AND METHODS

MRI scans of 11 young volunteers were performed during changes in posture. Images were recorded in the transverse and frontal planes and repeated four to six times through the bladder-filling cycle from empty to full. The position of the bladder midpoint was measured in the three planes. Moreover, to account for shape, the compactness of the cross-section of the bladder was calculated based on its perimeter and area. The effect of body position and gender was analyzed using repeated-measures ANOVA and the independent samples t-test, respectively.

RESULTS

No significant effect of body position on bladder position or shape was found. Gender was shown to have a significant impact on both the position and shape of the bladder: the female bladder was positioned more caudally and was less compact in the transverse plane than the male bladder. Furthermore, there was significant cranial-dorsal movement of the bladder during filling.

CONCLUSION

No significant changes in the position or shape of the bladder were observed during changes in body position in young subjects, regardless of bladder volume or gender. However, changes in both parameters were found due to bladder filling.

Twenty-four-hour ambulatory urodynamics in healthy young men

OBJECTIVE

To describe normal natural fill urodynamics in young men during normal and increased fluid intake.

MATERIAL AND METHODS

Thirty healthy males aged 21-32 years volunteered for an ambulatory urodynamic 24 h investigation with a suprapubic catheter. The recorded micturition data were: frequency (f), voided volume (VV), voiding time, maximal flow rate (Qmax) and time to Qmax. The number of sensed and not-sensed bladder contractions, duration and time in relation to voiding were also recorded. During the recording day subjects were randomized to normal (30 ml/kg body weight per day) or larger (60 ml/kg body weight per day) fluid intake.

RESULTS

As expected there was a larger urine production and an increased voiding frequency in the fluid-loaded group (p<0.0001). The detrusor pressure (Pdet) Qmax was significantly higher in the fluid-loaded group (73 cmH2O, range 57-94) than in the normal fluid intake group (60 cmH2O, range 45-86) (p=0.003). No other urodynamic data differed significantly between the two groups. When comparing the ambulatory urodynamic data with previously obtained home flowmetry recordings from the same volunteers differences were only found in voiding frequency. The majority of participants had detrusor contractions, felt and unfelt, during the filling phase. Three types of detrusor activity during voiding phase could be described: type 1, with one micturition contraction, type 2, with several small contractions before micturition, and type 3, with large prolonged contractions leading to micturition.

CONCLUSIONS

Ambulatory urodynamics in normal young men showed a large interindividual variation. Bladder contractions during filling were frequently recorded, and premicturition contractions were consistently found. The data found in this study were similar to previous home flow recordings in the same group.

Treatment outcome of day-time urinary incontinence in children

OBJECTIVE

To analyse retrospectively the efficacy of day-time incontinence treatment in a secondary referral centre and consider characteristics of responders to the different therapeutic interventions.

MATERIAL AND METHODS

All children treated for day-time urinary incontinence at the authors' clinics from 2000 to 2004 were included. Children with ongoing urinary tract infections were excluded. Before treatment, children filled out registrations of incontinence episodes and 48h frequency-volume charts. Faecal disorders were treated before urinary incontinence. All children were subjected to standard urotherapy and were secondarily recommended a timer-watch. If standard urotherapy had no effect, anticholinergics were added.

RESULTS

The study included 240 children with day-time urinary incontinence. Of these, 45 had faecal problems and 17% obtained urinary continence when these were successfully treated. In total, 126 (55%) became dry on standard urotherapy. Of the 60 children who had a timer-watch in addition to standard urotherapy, 70% became dry. Of the 62 children who had anticholinergics in addition to standard urotherapy, 81% became continent. Fifteen (6%) did not achieve continence and another 11 patients were lost to follow-up. Children who became dry solely on standard urotherapy had a significantly lower voiding frequency (p<0.05), larger voided volumes as a percentage of those expected for age (p<0.01) and fewer incontinence episodes per week (p<0.05) than children needing anticholinergics.

CONCLUSIONS

Most children achieve day-time continence solely on standard urotherapy. Children who need anticholinergics to achieve dryness seem to be those with more severe bladder reservoir function abnormalities and symptoms.

Long-term EGF treatment partially prevents reduction of renal blood flow in response to neonatally induced partial unilateral ureteral obstruction

BACKGROUND/AIMS

To investigate the effects of long-term epidermal growth factor (EGF) treatment on kidney growth, renal blood flow (RBF), AQP2 expression and urine output in newborn rats with partial unilateral ureteral obstruction (PUUO).

METHODS

PUUO (n = 29) and sham-operated control (CON) (n = 26) was created in 2-day-old rats. Fifteen PUUO and 14 CON rats were treated with EGF beginning from the second day after operation to 8 weeks of age. Total kidney volume (TKV) and RBF were measured by MRI at weeks 4 and 8, respectively. Urine volume and osmolality, plasma osmolality, and free water clearance were measured. Renal AQP2 expression was determined using semiquantitative immuno-blotting.

RESULTS

PUUO induced a severe hydronephrosis and RBF reduction in the obstructed kidney which was attenuated in EGF-treated rats. Body weight, urine output and free water clearance increased, osmolality and the osmolar clearance decreased significantly in EGF-treated rats, despite unchanged AQP2 levels.

CONCLUSIONS

Long-term EGF treatment attenuated the obstruction- induced RBF reduction. Body weight, urine output increased, and urine osmolality decreased in both control and PUUO rats treated with EGF. Solute-free water clearance increased in PUUO rats which seem to be independent of AQP2 expression.