The response of plasma arginine vasopressin to 14 h water deprivation in the elderly

Neuropeptides of the human magnocellular hypothalamus

Hypothalamic magnocellular nuclei with their large secretory neurons are unique and phylogenetically conserved brain structures involved in the continual regulation of important homeostatic and autonomous functions in vertebrate species. Both canonical and newly identified neuropeptides have a broad spectrum of physiological activity at the hypothalamic neuronal circuit level located within the supraoptic (SON) and paraventricular (PVN) nuclei. Magnocellular neurons express a variety of receptors for neuropeptides and neurotransmitters and therefore receive numerous excitatory and inhibitory inputs from important subcortical neural areas such as limbic and brainstem populations. These unique cells are also densely innervated by axons from other hypothalamic nuclei. The vast majority of neurochemical maps pertain to animal models, mainly the rodent hypothalamus, however accumulating preliminary anatomical structural studies have revealed the presence and distribution of several neuropeptides in the human magnocellular nuclei. This review presents a novel and comprehensive evidence based evaluation of neuropeptide expression in the human SON and PVN. Collectively this review aims to cast a new, medically oriented light on hypothalamic neuroanatomy and contribute to a better understanding of the mechanisms responsible for neuropeptide-related physiology and the nature of possible neuroendocrinal interactions between local regulatory pathways.

Clinical aspects of changes in water and sodium homeostasis in the elderly

The population of elderly individuals is increasing worldwide. With aging, various hormonal and kidney changes occur, both affecting water homeostasis. Aging is a risk factor for chronic kidney disease (CKD) and many features of CKD are reproduced in the aging kidney. Dehydration and hyperosmolarity can be triggered by diminished thirst perception in this population. Elderly with dementia are especially susceptible to abnormalities of their electrolyte and body water homeostasis and should be (re-)assessed for polypharmacy. Hypo- and hypernatremia can be life threatening and should be diagnosed and treated promptly, following current practice guidelines. In severe cases of acute symptomatic hyponatremia, a rapid bolus of 100 to 150 ml of intravenous 3% hypertonic saline is appropriate to avert catastrophic outcomes; for asymptomatic hyponatremia, a very gradual correction is preferred. In summary, the body sodium (Na+) balance is regulated by a complex interplay of environmental and individual factors. In this review, we attempt to provide an overview on this topic, including dehydration, hyponatremia, hypernatremia, age-related kidney changes, water and sodium balance, and age-related changes in the vasopressin and renin-angiotensin-aldosterone system.

Vasopressin, copeptin, and renal concentrating capacity in patients with autosomal dominant polycystic kidney disease without renal impairment

BACKGROUND AND OBJECTIVES

Autosomal dominant polycystic kidney disease (ADPKD) is the most prevalent hereditary renal disease, characterized by cyst formation in the kidneys leading to end stage kidney failure. It is clinically acknowledged that ADPKD patients have impaired urine concentrating capacity, but the mechanism behind this observation is unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Fifteen ADPKD patients (estimated GFR ≥60 ml/min per 1.73 m(2)) and 15 age- and sex-matched healthy controls underwent a standard prolonged water deprivation test in which urine and plasma osmolality, vasopressin, and copeptin were measured. The effect of a synthetic vasopressin analog (desmopressin) injected at the moment of maximal urine concentrating capacity was also studied.

RESULTS

After 14 hours of water deprivation, ADPKD patients tended to have higher plasma osmolality (P=0.07) and significantly higher vasopressin and copeptin levels (both P<0.05), whereas urine osmolality was similar in ADPKD patients and controls (710 versus 742 mOsmol/kg; P=0.61). Maximal urine concentrating capacity was lower in ADPKD patients (758 versus 915 mOsmol/kg in controls; P<0.001). At maximal urine concentrating capacity, plasma osmolality, vasopressin, and copeptin levels were significantly higher in ADPKD patients. The median increase in urine osmolality after desmopressin administration in ADPKD patients was less than in healthy controls.

CONCLUSIONS

Already early in their disease, ADPKD patients have impaired maximal urine concentrating capacity brought out upon dehydration, with no evidence of impaired hypothalamic response. To maintain fluid balance, vasopressin concentration increases, which is hypothesized to play a role in ADPKD disease progression.

Renal effects of long-term lithium therapy in the elderly: a cross-sectional study

OBJECTIVES

To determine the effect of long-term lithium therapy on glomerular filtration rate (GFR) and maximum renal concentrating capacity (Umax) in the elderly, to identify possible risk factors, to determine the clinical impact of a reduced Umax in this population and in case of polyuria to establish a diagnosis.

METHODS

This is a cross-sectional study with 48 outpatients of 65 years or over (mean 74.8 years), who were treated with lithium for more than 6 months (mean 9.2 years). The GFR was determined with the Cockcroft-Gault formula (GFR-CG) and the Umax was measured in a urine sample collected between 3 and 5 h after the patients received 40 microg desmopressin (DDAVP) intranasally.

RESULTS

No relation was found between duration of lithium treatment and GFR-CG, but there was a significant negative relation between duration of lithium treatment and Umax (B -0.73; CI: -1.249/-0.212); 73% of the patients had a moderate to severe concentrating defect. No other risk factors than duration of lithium therapy were identified. A reduced Umax caused polyuria (>2500 mL/24 h) in 33% but did not cause significant more thirst, incontinence or disturbed sleep.

CONCLUSIONS

In this geriatric population a negative relation was found between duration of lithium treatment and Umax. But a reduced Umax did not result in significant more clinical symptoms. In case of polyuria other mechanisms beside nephrogenic diabetes insipidus were found to play a role in this age group.

A Clinical Investigation of Nocturnal Polyuria in Patients With Nocturia: A Diurnal Variation in Arginine Vasopressin Secretion and its Relevance to Mean Blood Pressure

PURPOSE

Nocturia is a common lower urinary condition in the elderly population and nocturnal polyuria is recognized as a major factor responsible for nocturia. A functional change in osmotic or nonosmotic control regarding the water-salt balance with aging may contribute to nocturnal polyuria. This study evaluated plasma arginine vasopressin secretion function in symptomatic patients with nocturnal polyuria and the impact of mean blood pressure on nocturnal polyuria.

MATERIALS AND METHODS

A total of 29 patients who had nocturnal polyuria with 3 or more voids nightly and were screened with a 24-hour voiding diary were evaluated for their diurnal rhythm of arginine vasopressin secretion and osmotic response during a 5% hypertonic saline infusion test. Moreover, the relationships between the severity of nocturnal polyuria, ie the nocturnal polyuria index, or mean voided volume and mean blood pressure were assessed.

RESULTS

Decreased nocturnal baseline arginine vasopressin according to plasma osmolality was found in 11 patients (38%) and the lack of a diurnal rhythm for arginine vasopressin secretion was observed in high proportion. A positive correlation between plasma arginine vasopressin and plasma osmolality was described with a linear regression line, expressed as arginine vasopressin = 0.27 (plasma osmolality - 285), resulting in a 2 to 3 mmol/l upward shift in the threshold of overall plasma arginine vasopressin secretion, although various osmotic sensitivities in arginine vasopressin secretion were observed in individuals. Mean voided volume increased during the night more than during the day (p <0.0001). A significant positive correlation of mean blood pressure with the mean daytime-to-nighttime single voided volume ratio and the nocturnal polyuria index was found (p = 0.0343 and 0.0109, respectively).

CONCLUSIONS

An abnormal diurnal variation in arginine vasopressin secretion is highly prevalent in nocturnal polyuria. Moreover, it is relevant to mean blood pressure or sympathetic tone, such that the effects of nonosmotic control seem clinically implicated. Particular emphasis has been applied to the importance of considering comprehensive assessments not only of arginine vasopressin secretion function, but also of the possible underlying cardiovascular condition or hypertension in the treatment modality of nocturnal polyuria.

Fluid and electrolyte homeostasis in the elderly: physiological changes of ageing and clinical consequences

Characteristic of the normal ageing process are changes in the renal, hormonal and thirst regulatory systems involved in the control of sodium and water balance. In the presence of disease or drug use, the ageing changes put the elderly person at increased risk of either sodium retention or loss and of water retention or loss. Clinically, these alterations in water and sodium balance are commonly expressed as either hyponatraemia or hypernatraemia with central nervous system dysfunction as the symptomatic expression. Thus, the impaired homeostasis of the many systems affecting fluid balance in the elderly is readily influenced by many of the disease states and medications which are often present in the elderly with resultant adverse clinical consequences. Awareness of these age-associated circumstances can allow the physician to anticipate the impact of illnesses and drugs and to implement a rational approach to therapeutic intervention and management.

Urinary arginine vasopressin (AVP) measurement in children: water deprivation test incorporating urinary AVP

The value of a water deprivation test incorporating urinary arginine vasopressin (AVP) measurement was investigated in 13 patients with polydipsia and/or polyuria (complete central diabetes insipidus [CCDI] in four; incomplete central diabetes insipidus [ICDI] in five; secondary nephrogenic diabetes insipidus [NDI] in three; compulsive water drinking [CWD] in one) and a group of 25 control subjects (C). Urine samples were collected after water deprivation during sleep and the urinary osmolalities and AVP concentrations were measured. Analysis of the results of 104 urine samples from the 25 control subjects demonstrated a close correlation between urinary osmolality and AVP (r = 0.89, P < 0.001). After water deprivation during sleep, the respective mean maximal urinary osmolalities and AVP concentrations were: 127.4 +/- 34.4 mOsm/kg and 1.1 +/- 0.5 pg/mL in the patients with CCDI (14 samples, four children); 410.3 +/- 101.8 and 6.1 +/- 3.5 in those with ICDI (16 samples, five children); 348.7 +/- 71.2 and 100 +/- 45.1 in those with NDI (nine samples, three children); 541.5 +/- 143.5 and 43.6 +/- 33.2 in the patient with CWD (two samples, one child) and 898.8 +/- 186.3 and 97.4 +/- 50.4 in group C (54 samples, 18 children). Furthermore, the urinary AVP level relative to the osmolality in each patient varied depending on the AVP secretion status and renal concentrating ability. Each patient, except the one with CWD, could be discriminated from the normal subjects using this test. It seems that this test is easy to perform and useful for diagnosis and follow-up of patients with partial/complete posterior pituitary function defects and those with renal concentration impairment.

Role of the opioid system in the hypodipsia associated with aging

OBJECTIVE

To compare the effects of the opioid antagonist, naloxone, on fluid ingestion in young and older males, in order to estimate the role of the opioid system in hypodipsia of older men.

DESIGN

Single-blinded, randomized, cross-over, placebo-controlled study.

SETTING

Outpatient Department of Veterans Affairs.

STUDY PARTICIPANTS

Sixteen young subjects (aged 23 to 39) and eight older subjects (aged 69 to 75). All subjects were healthy, community-dwelling, non-smoking men, on no medications.

INTERVENTION

Subjects were randomized to receive either placebo or naloxone on day one. Whichever substance the subject did not receive was given on day two with days one and two separated by at least a 2-week washout period.

MAIN OUTCOME MEASURES

Fluid intake after overnight food and fluid deprivation, with placebo or naloxone injected in the morning.

RESULTS

After overnight fluid deprivation, older individuals consumed 29% less fluid in 2 hours compared with younger individuals (ns). After overnight fluid deprivation and injection with naloxone 100 micrograms/kg, fluid intake was diminished by 42% (P less than 0.05) in young subjects compared with placebo, but only by 7% (ns) in older subjects. Subjective ratings did not differ significantly between young and old subjects.

CONCLUSIONS

These preliminary data suggest that the opioid system plays a role in the drinking response in young subjects while failing to alter fluid intake in older subjects. Hypodipsia in older individuals may be due to a deficit in the opioid drinking drive.

Hyponatremia and inappropriate secretion of vasopressin (antidiuretic hormone) in patients with hypopituitarism

Severe hyponatremia occurs in some patients with untreated hypopituitarism, but it is not known whether such hyponatremia is caused by the hypersecretion of vasopressin (antidiuretic hormone). This report describes severe, symptomatic hyponatremia in five women 59 to 83 years old (serum sodium, 111 to 118 mmol per liter) who presented with hypopituitarism (which had been previously undiagnosed in four). Plasma vasopressin was inappropriately high (1.3 to 25.8 pmol per liter [1.4 to 28 ng per liter]) in relation to plasma osmolality (236 to 260 mOsm per kilogram of body weight). All five patients had normal renal function and no signs of dehydration or volume depletion. The hyponatremia was resolved within a few days after the institution of hydrocortisone therapy, after infusion of normotonic or hypertonic saline had been found to be less effective. When four of the patients were later restudied while receiving maintenance hydrocortisone treatment, the relation between plasma vasopressin and osmolality was normal. We conclude that ACTH deficiency may cause the syndrome of inappropriate secretion of antidiuretic hormone. The beneficial effect of hydrocortisone is probably exerted through the suppression of vasopressin secretion.

Vasopressin and oxytocin excretion in the Brown-Norway rat in relation to aging, water metabolism and testosterone

There is considerable disagreement in the literature on changes in the hypothalamo-neurohypophyseal system (HNS) with aging: some reports support HNS degeneration, whereas others claim an activation of this system in senescence. In order to study age-related changes in vasopressin (VP) and oxytocin (OT) excretion in relation to water metabolism, six young (4 months) and 12 aged (34 months) male Brown-Norway rats were placed in metabolism cages. Since plasma testosterone levels have been reported to affect HNS activity and to decline progressively with age, half of the aged animals were given subcutaneous testosterone implants. Urine volume and water intake were significantly increased in aged animals, while urine osmolality was significantly reduced. These changes could not be attributed to diminished VP secretion, since 24-h urinary excretion of this peptide was elevated in the aged animals. In addition, 24-h OT excretion was elevated in the aged animals, indicating an overall activation of the HNS in senescence. VP excretion was significantly correlated with urine osmolality, urine volume and urinary VP concentration. No significant differences were observed between testosterone- and sham-implanted aged rats. It is concluded that the moderate polyuria/polydipsia in the senescent Brown-Norway rat is probably due to renal changes and is accompanied by a compensatory rise in both VP and OT secretion. Testosterone does not affect these changes.

Activation of vasopressin neurons in the human supraoptic and paraventricular nucleus in senescence and senile dementia

A recent study has shown that vasopressin (AVP) cells in the human supraoptic (SON) and paraventricular (PVN) nuclei increase in size after 60 years of age, suggesting that AVP production is increased in senescence. In the present study, the same brain material was used for the determination of nucleolar size in immunocytochemically identified AVP and oxytocin (OXT) neurons as an additional parameter for peptide production. A strong correlation was found between nucleolar size and cell size, both in AVP and OXT neurons. Nucleolar size of AVP but not of OXT neurons increased significantly in senescence. Observations in brains from patients with senile dementia of the Alzheimer type (SDAT) were commensurate with their ages. These results strongly support the hypothesis that AVP neurons in the SON and PVN are activated in old age.

Evidence of age-related variation in plasma vasopressin of normotensive men

The influence of age on plasma arginine vasopressin was examined in three groups of healthy men, 25 +/- 1 (n = 12), 40 (n = 23) and 50 years of age (n = 13), respectively. The three groups were comparable in body height, weight, blood pressure, heart rate, serum and urine osmolality, electrolytes and endogenous creatinine clearance. Compared to the 25-year olds, the 50-year old men had more than three times higher basal plasma vasopressin (7.8 +/- 1.4 vs. 2.5 +/- 0.6 ng/l, p less than 0.01), only one-third the plasma renin concentration (0.36 +/- 0.05 vs. 1.10 +/- 0.33 G.U. X 10(-4)/ml, p less than 0.01) and a significantly higher plasma noradrenaline (267 +/- 21 vs. 199 +/- 19 ng/l, p less than 0.05) while plasma adrenaline remained essentially unchanged. The 40-year olds had intermediate plasma vasopressin concentrations (4.2 +/- 0.6 ng/l). Thus, age is a variable with a substantial effect on plasma concentrations of vasopressin in addition to the well-known effect on renin and noradrenaline. Age must be taken into account in further clinical studies on vasopressin.