Differential diagnosis of polyuric/polydipsic syndromes with the aid of urinary vasopressin measurement in adults

Diagnosis and Management of Pineal Germinoma: From Eye to Brain

Pineal germinomas can be very complex in terms of presentation, diagnosis, and management. This review attempts to simplify this complexity in an organized manner, addressing the anatomic relationships that provide the basis for the uniqueness of pineal germinoma. Ocular findings and signs and symptoms of elevated intracranial pressure are the keys to suspecting the diagnosis and obtaining the necessary imaging and cerebrospinal fluid studies. Other symptoms can suggest spread beyond the pineal region. Surgery may only be needed to obtain tissue for a definitive diagnosis, as germinoma is highly responsive to chemotherapy and focused radiation therapy. Hydrocephalus, usually related to tumor obstruction of the cerebral aqueduct, may also need to be addressed. Outcome for pineal germinoma is usually excellent, but relapse can occur and may require additional intervention. These issues are detailed in this review.

Factors affecting the drinking behavior of black howler monkeys (Alouatta pigra)

Water is essential for animals, and is particularly critical for thermoregulation. Animals obtain water from three main sources, free water, water contained in food, and water produced in the body during metabolism. Howler monkeys (Alouatta spp.) spend a small proportion of their time drinking water and some populations have not been observed drinking, suggesting they obtain most of their water requirements in food or by metabolism. However, when howler monkeys have been observed drinking there is evidence suggesting the drinking is associated with low precipitation, temperature, and fruit consumption, and high mature leaf consumption, although it remains unclear which factors determine drinking by this genus. In this study we tested the hypothesis that drinking by howler monkeys results from increased hydration requirements in drier climates and from lower consumption of foods rich in water (e.g., new leaves, fruit). We tested this hypothesis by comparative analysis of 14 groups of Yucatán black howler monkeys (A. pigra) living under different climatic conditions. From April 2005 to November 2008 we collected a total of 3,747.2 focal observation hours of the feeding and drinking behavior of 60 individuals, with data on ambient temperature and rainfall. Individuals spent more time drinking when they lived in habitats with higher maximum temperature and when they consumed more mature leaves. For this species, therefore, drinking seems to be linked to heat stress and a low availability of water in ingested food.

Preliminary Experience with Low-dose Desmopressin Treatment and Urinary Arginine Vasopressin Concentration as a Response Predictor for Patients with Nocturia with Nocturnal Polyuria

OBJECTIVES

To assess whether urinary arginine vasopressin (AVP) concentrations adjusted for urinary creatinine (Cr) can predict responsiveness to low-dose desmopressin for nocturia with nocturnal polyuria (NP).

METHODS

Nine NP patients aged 64-84 years with ≥ 2 nocturnal voids received 2.5 µg of intranasal desmopressin for 4 weeks and were evaluated for its effectiveness. Prior to treatment, urinary AVP/Cr concentrations at first morning void and serum sodium and plasma natriuretic peptide (BNP) concentrations were measured, and all patients underwent 5% hypertonic saline infusion.

RESULTS

Six responders to 2.5 µg desmopressin had average decreases in nocturnal frequency from 3.2 to 1.8 voids nightly and in nocturnal diuresis by 40%, without clinically significant adverse events. Non-responders remained unaffected even with dose escalation to 5.0 µg desmopressin. For responders, urinary AVP/Cr concentrations were less than 14 pg/mg · Cr, which is lower than in non-responders. Within a physiological range of plasma osmolality, plasma AVP release in response to 5% hypertonic saline infusion was less in responders than in non-responders. Blood pressure measurements and BNP concentrations were unchanged.

CONCLUSIONS

Urinary AVP/Cr at first morning void may have potential clinical value as a predictor for responsiveness to low-dose desmopressin in nocturia with NP.

Arginine vasopressin-dependent and AVP-independent mechanisms of renal fluid absorption during thirsting despite glucocorticoid-mediated vasopressin suppression

OBJECTIVE

Glucocorticoids seem to modify the release and effects of plasma arginine vasopressin (pAVP). However, underlying processes are not well understood. This study aimed to evaluate the mechanism of the modulating effects of glucocorticoids on pAVP and renal water reabsorption.

DESIGN

Fluid deprivation tests were performed without (d0) and after one (d1) and five days (d5) of oral prednisolone (Pred) pretreatment in a dosage relevant to drug therapy (30 mg/day).

PATIENTS

Twelve healthy male volunteers participated in this trial.

MEASUREMENTS

Plasma and urinary osmolality, pAVP, renin, aldosterone, plasma atrial natriuretic peptide (ANP) as well as urinary secretion of aquaporin-2 (AQP2) and prostaglandin E(2) (PGE2) were analysed.

RESULTS

An appropriate rise in pAVP was observable during thirsting (P < 0.001), which was absent after Pred pretreatment. However, the plasma and urinary osmolality after Pred treatment did not differ when compared with the basal thirsting test. Unchanged urinary AQP2 excretion suggests AVP-independent mechanisms of renal fluid reabsorption. Plasma renin concentration as well as ANP was substantially increased after Pred intake at d1 and d5 (both P < 0.05), which may mediate such AVP-independent mechanisms. Urinary PGE2 secretion was not influenced by Pred pretreatment, making a PGE2-mediated effect on renal AQP2 translocation and water permeability unlikely. Increased efficacy of exogenous desmopressin at d1 and d5 indicates also a relative increase in AVP sensitivity of the tubular cells after Pred intake.

CONCLUSIONS

The here presented data are compatible with an increased AVP sensitivity and a partially AVP-independent regulation of AQP2 translocation and renal fluid reabsorption during glucocorticoid treatment.

[Central diabetes insipidus: diagnostic difficulties]

Central diabetes insipidus is rare in children. Characteristic features include polyuria and polydipsia due to arginine vasopressin deficiency. The differential diagnosis of polyuric states may be difficult. Etiologic diagnosis of central diabetes insipidus may be an equally difficult task.

OBJECTIVE

To specify the difficulties encountered in the diagnosis of central diabetes insipidus and to point out features of the etiologic work-up and of long-term follow-up of children with idiopathic central diabetes insipidus.

METHODS

A retrospective study of 12 children admitted with a polyuria/polydipsia syndrome to the pediatric - consultation and emergency unit of the children's hospital of Tunis between 1988 and 2005. Children with acquired nephrogenic central diabetes insipidus were excluded. Fourteen-hour fluid restriction test and/or desmopressin test were used without plasma vasopressin measurement.

RESULTS

Eight patients were classified as having central diabetes insipidus, which was severe in seven children and partial in one girl. One patient was classified as having primary polydipsia. The diagnosis remains unclear in three patients. The etiological work-up in eight patients with central diabetes insipidus enabled the identification of Langerhan's-cell histiocytosis in two patients and neurosurgical trauma in one. The cause was considered idiopathic in five patients. The median follow-up of the five patients with idiopathic central diabetes insipidus was five years two months plus or minus six years seven months (range five months, 14.5 years). During this follow-up, neither brain magnetic resonance imaging scans findings nor anterior pituitary function have changed.

CONCLUSION

Fluid restriction and desmopressin tests did not enable an accurate distinction between partial diabetes insipidus and primary polydipsia. Regular surveillance is warranted in patients with idiopathic central diabetes insipidus to identify potential etiologies.

Effect of exogenous glucocorticoid on osmotically stimulated antidiuretic hormone secretion and on water reabsorption in man

OBJECTIVE

Glucocorticoids exert tonic suppression of antidiuretic hormone (ADH) secretion. Hypocortisolism in secondary adrenocortical insufficiency can result in a clinical picture similar to the syndrome of inappropriate ADH secretion. On the other hand, in vitro and in vivo results provide evidence for ADH suppression in states of hypercortisolism. To test the hypothesis that ADH suppression is of relevance during glucocorticoid therapy, we investigated the influence of prednisolone on the osmotic stimulation of ADH.

DESIGN AND METHODS

Seven healthy men were subjected to water deprivation tests with the measurement of plasma ADH (pADH) and osmolality (posmol) before and after glucocorticoid treatment (5 days 30 mg prednisolone per day).

RESULTS

Before glucocorticoid treatment, the volunteers showed a normal test with an adequate increase of pADH (basal 0.54 +/- 0.2 to 1.9 +/- 0.72 pg/ml (mean +/- S.D.)) in relation to posmol(basal 283.3 +/- 8.5 to 293.7 +/- 6 mosmol/kg). After prednisolone intake, pADH was attenuated (<0.4 pg/ml) in spite of an increase of posmol from 289.3 +/- 3.6 to 297.0 +/- 5.5 mosmol/kg. However, urine osmolar concentration increased normally during water deprivation after prednisolone. Urinary cAMP excretion increased during water deprivation without glucocorticoid treatment from 3.56 +/- 0.55 to 6.07 +/- 0.76 micro mol/l, reflecting the increased pADH levels. The rise in cAMP excretion was completely blunted by prednisolone treatment.

CONCLUSIONS

We speculate that there may be an ADH-independent stimulation of the formation or function of aquaporin-2 channels by prednisolone and/or a direct osmotic stimulation of water reabsorption independent of ADH and glucocorticoid control.

Diabetes insipidus

Water balance is precisely regulated by vasopressin, thirst and the kidneys; plasma osmolality is maintained within a narrow range, despite large variations in normal water intake and loss. Disruption of these finely balanced mechanisms is common, however, and can be precipitated by various disease states. Diabetes insipidus is a disease process with several underlying pathogenic mechanisms--all ultimately resulting in excretion of large volumes of dilute urine. This review will discuss the pathophysiology, diagnosis and treatment of diabetes insipidus, with emphasis on disorders of osmoregulation following neurosurgery of the pituitary and hypothalamus.

Urinary oxytocin as a non-invasive biomarker for neurohypophyseal hormone secretion

The objective was to characterize the urinary oxytocin (OT) system with the goal of using it as a biomarker for neurohypophyseal peptide secretion. We studied urinary OT secretion in mice under three conditions: (1) in OT gene deletion mice (OT -/-) which lack the ability to produce the peptide; (2) after arterial vascular infusion of OT and (3) after physiological stimulation with consumption of 2% sodium chloride. OT was measured by radioimmunoassay (RIA) and Surface-Enhanced Laser Desorption Ionization Time of Flight Mass Spectroscopy (SELDI TOF MS). In OT -/- mice (n=25), urinary OT levels were not detectable, while in OT +/+ mice (n=23) levels were 250.2+/-35.3 pg/ml. To evaluate blood/urine transfer, mice with chronic carotid arterial catheters were infused with saline or OT (5 or 20 pmol/min). Peak urine OT levels were 89+/-11.5 and 844+/-181 ng/ml in the low and high OT groups, respectively. Proteomic evaluation showed MS peaks, corresponding to OT ( approximately 1009 Da) and a related peptide ( approximately 1030 Da) with highest levels in mice infused with OT. Salt loading (5 days of 2% NaCl as drinking water) increased plasma osmolality (3.3%), increased plasma and urinary vasopressin (AVP), but caused no changes in OT. Thus, using non-invasive urine samples, we document that urinary OT and AVP can be used to monitor changes in peptide secretion. Urinary OT and AVP, as well as other urinary peptides, may provide a viable biomarker for peptide secretion and may be useful in clinical studies.

Congenital nephrogenic diabetes insipidus presented with bilateral hydronephrosis: genetic analysis of V2R gene mutations

Most cases of hydronephrosis are caused by urinary tract obstruction. However, excessive polyuric syndrome rarely gives rise to non-obstructive hydronephrosis, megaureter, and a distended bladder. The authors report here on two cases of congenital nephrogenic diabetes insipidus (NDI) with severe bilateral hydronephrosis and megaureter. It is Interesting that the patients were symptomless except for their polyuria, and they both presented with bilateral hydronephrosis. Fluid deprivation testing revealed the presence of AVP resistant NDI. Gene analysis for these patients showed the AVP receptor 2 (V2R) missense mutations (Q225X and S126F), which have previously been reported on in other studies. We made the diagnosis of NDI by using a physiologic test, and we confirmed it by mutation analysis of the V2R gene.

Pulsatile secretion pattern of vasopressin under basal conditions, after water deprivation, and during osmotic stimulation in dogs

Measurement of plasma osmolality (Posm) and plasma vasopressin (VP) concentration in response to hypertonicity is regarded as the gold standard for the assessment of VP release in polyuric conditions. Yet the interpretation of the VP curve as a function of Posm may be hampered by the occurrence of VP pulses. To determine whether VP is secreted in a pulsatile fashion in the dog and whether stimulation of VP release changes the secretion pattern of VP, we measured VP at 2-min intervals for 2 h under basal conditions, after 12 h of water deprivation, and during osmotic stimulation with hypertonic saline (20%) in eight healthy dogs. Vasopressin was secreted in a pulsatile fashion with a wide variation in number of VP pulses, VP pulse duration, and VP pulse amplitude and height. After water deprivation, total and basal VP secretion, the number of significant VP pulses, as well as the pulse characteristics did not differ from the basal situation. During osmotic stimulation, there was a large increase in both basal and pulsatile VP secretion, and the number of VP pulses and VP pulse height and amplitude were significantly increased. The VP pulse amplitude correlated significantly with the basal plasma VP concentration during osmotic stimulation. It is concluded that VP is secreted in a pulsatile manner in healthy dogs. The basal and pulsatile VP secretion increases during osmoreceptor-mediated stimulation. The VP pulses may occur to the magnitude that they may be interpreted as erratic bursts, when occurring in the hypertonic saline infusion test.

Renal expression of sodium transporters and aquaporin-2 in hypothyroid rats

Hypothyroidism is associated with significant abnormalities in the renal handling of salt and water. To address the involvement of tubular transport proteins in these abnormalities, rats were rendered pharmacologically hypothyroid and the abundance of major tubular transport proteins was assessed by immunoblot and immunohistochemistry. Hypothyroidism resulted in a marked reduction in kidney size and creatinine clearance along with decreased or unchanged total kidney abundance of the transport proteins. Whereas the proximal tubular type 3 Na/H exchanger (NHE3) and type 2 Na-phosphate cotransporter (NaPi2) stood out by their disproportionately reduced abundance, the bumetanide-sensitive type 2 Na-K-2Cl cotransporter (NKCC2) and aquaporin-2 (AQP2) were unaltered in their total kidney abundance despite a markedly lower kidney mass. The latter proteins in fact showed enhanced immunostaining. Decreased NHE3 and NaPi2 expression was most likely due to a combination of triiodo-l-thyronine (T(3)) deficiency along with a reduced glomerular filtration rate. The increased abundance of NKCC2 and AQP2 may have been caused by an increased action of vasopressin since urinary excretion of this hormone was elevated. On the other hand, the thiazide-sensitive Na-Cl cotransporter; the alpha-, beta-, and gamma-subunits of the amiloride-sensitive epithelial Na channel; and the alpha(1)-subunit of Na-K-ATPase showed a moderate decrease in total kidney abundance that was largely proportional to the smaller kidney mass. Although the observed expression of transporters was associated with a balanced renal sodium handling, altered transporter abundance may become functionally relevant if the hypothyroid kidney is challenged by an additional destabilization of the milieu interieur that has previously been shown to result in an inadequate natriuresis and clinical symptoms.