Thirst and polyuria, with a note on the effects of potassium deficiency and calcium excess

Impaired Distal Tubular Acidification, Renal Cysts and Nephrocalcinosis in Monogenic Hypertension

Monogenic defects in tubular sodium handling contribute a small proportion to hypertension in childhood. Presentation varies from severe hypertension manifesting at birth to asymptomatic hypertension and hypokalemic metabolic alkalosis detected incidentally in adulthood. A 12-y-old girl presenting with polyuria, polydipsia, severe hypertension and seizures, was found to have hypokalemia, renal medullary cysts and nephrocalcinosis. Clinical exome revealed a homozygous variation of unknown significance in exon 5 of the HSD11B2 gene, indicating the diagnosis of apparent mineralocorticoid excess. Therapy with spironolactone was associated with resolution of hypokalemia and normal blood pressure during two-year follow up.

Hypernatremia in the geriatric population

Hypernatremia in the geriatric population is a common disorder associated with significant morbidity and mortality. Older people are predisposed to developing hypernatremia because of age-related physiologic changes such as decreased thirst drive, impaired urinary concentrating ability, and reduced total body water. Medications may exacerbate this predisposition. Hypernatremia and dehydration occurring in nursing homes are considered indicators of neglect that warrant reporting, but there are other nonavoidable causes of hypernatremia, and consideration at time of presentation is essential to prevent delay in diagnosis and management. We describe a case illustrating the importance of the consideration of alternate explanations for hypernatremia in a nursing home resident, followed by a review of hypernatremia in the elderly population, to underscore that neglect is the etiology of exclusion after alternatives have been considered.

Hypercalcemia reduces renal medullary content of organic osmolytes

Hypercalcemia is often associated with a urinary concentration defect. During antidiuresis, organic osmolytes [sorbitol, myo-inositol, taurine, and glycerophosphorylcholine (GPC)] accumulate in the renal inner medulla and are essential for urinary concentration. To clarify the relationship between organic osmolytes and urinary concentration defect in hypercalcemia, examination was made of the effects of hypercalcemia on renal medullary osmolytes content. Rats were put in a state of hypercalcemia by a calcium-rich diet supplemented with CaCO3 (2.5%/wt) and daily s.c. injection of 1.25(OH)2VitD3 (1.6 micrograms/kg). They were killed on days 7 and 14. Hypercalcemia induced a urinary concentration defect. Myo-inositol, sorbitol, and GPC contents in the renal medulla were significantly reduced. Aldose reductase activity decreased significantly. Hypercalcemia would thus appear to directly affect renal medullary content of organic osmolytes, thereby modifying renal concentration ability.

Drinking, thirst and water intoxication

Drinking is an activity determined partly by oropharyngeal stimulation and gastrointestinal sensations as well as biochemical changes, and thirst need not be involved. It is sometimes disturbed in mania or depression. Overdrinking (polydipsia) is common in long-stay in-patients, but only gives rise to water intoxication when there is a variable functional renal abnormality such as SIADH causing water retention. In contrast, in affective disorders, disturbance of sodium retention may be seen, possibly representing failure of nervous vascular control as part of the mental illness.

Non-psychogenic primary polydipsia in autoimmune chronic active hepatitis with severe hyperglobulinaemia

The association of hyperglobulinaemia with renal tubular acidosis and nephrogenic diabetes insipidus is well established. A patient with marked hyperglobulinaemia due to autoimmune chronic active hepatitis is described who presented with severe polydipsia and polyuria but had entirely normal renal tubular function indicating a primary thirst disorder.

Effect of dietary calcium levels near the time of sexual maturity on water intake and excreta moisture content

Three trials were conducted to investigate the effect of dietary calcium on water balance of leghorn pullets. Trial 1 involved introduction of a 4% calcium layer diet at 112, 123, 134, or 144 days of age. Introducing the layer diet early had an early but transitory effect on water intake (P less than .05) and absolute quantity of excreta moisture, although the pattern of percentage excreta moisture was not clearly defined. In a second trial, birds were moved to laying cages at 105 days, with diet change from 1 to 4% calcium occurring at 112 or 142 days. When the layer diet was offered at 112 days, percentage excreta moisture was higher from 113 to 142 days, although no difference was seen after this time. In a final experiment, introduction of a 4% calcium layer diet at either 112 or 133 days of age resulted in higher percentage excreta moisture at four measurement periods to 245 days of age, although this effect was significant only at 147 days (P less than .05). These results suggest there is a transitory effect of dietary calcium on water intake and excreta moisture content. This affect may be of concern within controlled environment buildings and with certain manure-handling systems. In commercial situations, such dietary changes are often confounded with increased dietary protein concentration, another factor known to influence water balance in pullets.

Severe depressive illness in the context of hypervitaminosis D

Hypercalcaemia, whether due to undiagnosed hyperparathyroidism or some other cause, can lead to clinical depression. The patient described here developed a severe depressive illness in the setting of hypervitaminosis D after 15 years of inappropriate therapy with calcium gluconate and strong calciferol. The importance of monitoring serum calcium levels in anyone on vitamin D therapy is stressed.

DDAVP and urine osmolality in refractory enuresis

A double blind crossover trial of 20 micrograms intranasal 1-deamino-8-d-arginine vasopressin (DDAVP) versus placebo was carried out in 17 children with intractable enuresis aged between 6 and 13 years who had failed to respond to drugs and an enuresis alarm. Fluid intake was not restricted. There was a significant reduction in the number of wet nights. Seven children (41%) were cured or showed considerable improvement, with strong evidence against any placebo effect. The best response was seen in children aged 10 years or over and if urine osmolality after DDAVP reached beyond 1000 mmol/kg or was already at this concentration. The degree of overnight rise in urine osmolality after treatment with DDAVP was not predictable but correlated well with the clinical improvement in nocturnal diuresis present in eight of the children. A further 12 children with equally refractory enuresis were given 20 micrograms of the active drug to take during their school journeys or holidays. Six of them had previously normal overnight urine osmolalities with only two successes, but of the six who had nocturnal diuresis before treatment, five became dry, suggesting that DDAVP acts largely by anti-diuresis and might be most useful in children with nocturnal polyuria.

Vasopressin function in hypercalcaemia

Vasopressin function and thirst were studied in fourteen hypercalcaemic patients (ten hyperparathyroid and four disseminated malignant disease). Ten patients had decreased renal concentrating ability which reversed within a few days in the majority of patients whose hypercalcaemia was corrected by parathyroidectomy. Although eight patients complained of thirst, none showed a lowered threshold of thirst appreciation during hypertonic saline infusion. Osmoregulation of vasopressin secretion was not reduced in any patient, but the hyperparathyroid group had an exaggerated vasopressin response to osmotic stimulation. We conclude that a partial, reversible nephrogenic diabetes insipidus occurs in at least 70% of hypercalcaemic patients irrespective of cause, which accounts for the polyuria induced by hypercalcaemia.

Water metabolism

Total body water is finely regulated and controls of intake and output are maximally activated by small osmotic changes. Sensors in the hypothalamus invoke the fluid repletion or depletion reactions through changes in thirst, urine concentration and solute intake. Antidiuretic hormone controls urinary concentration and is released mainly in response to osmotic stimuli. However, the threshold and sensitivity of this response are affected by non osmotic stimuli. Urine concentration varies in response to antidiuretic hormone only if the distal tubule, collecting duct and hypertonic medullary interstitum are intact. The capacity to conserve or excrete water depends on the osmolar load and an efficient urinary concentrating or diluting mechanism.

Disorders of thirst are uncommon and often associated with abnormal antidiuretic hormone secretion. Disorders of urine concentration and dilution are common in illness and reflect abnormalities of antidiuretic hormone secretion or the renal mechanisms generating the osmotic gradient. When urine concentrating capacity is impaired ( true or nephrogenic diabetes insipidus) water depletion occurs only when thirst fails or access to water is denied. When urine diluting ability is impaired, water excess occurs when the osmolar load and minimum urinary osmolality generated are inadequate for the fluid intake.

Hyper-osmolality and hypo-osmolality are usually caused by abnormal water metabolism although they may be associated with abnormalities of solute metabolism. The various clinical syndromes are determined by the primary disease, and the associated fluid volume and osmolar abnormalities.