Vasopressin Response to Osmotic Stimulation in 18 Young Dogs with Polyuria and Polydipsia

Abstract

Common disorders of water homeostasis leading to polyuria include a variety of endocrine, metabolic, and renal disturbances. After exclusion of most of these conditions, the diagnostic dilemma of differentiating between central diabetes insipidus, primary polydipsia, and nephrogenic diabetes insipidus may remain. Here, we report on 18 young dogs with polyuria that had been present in most cases since the dogs were puppies. The conditions were categorized according to the plasma vasopressin (VP) response to hypertonicity. The VP response to osmotic stimulation was tested by IV infusion of 20% NaCl for 2 hours. The VP response in all dogs was abnormal. Three categories could be distinguished: an exaggerated response (n = 3), a subnormal response (n = 4), and a nonlinear response with high plasma VP concentrations unrelated to increases in plasma osmolality (n = 11). The VP response to hypertonicity did not consistently distinguish among different clinical entities. In the 9 dogs with variations in urine osmolality compatible with primary polydipsia, exaggerated, subnormal, and nonlinear responses were observed. Examination of the present data questions the generally accepted notion that VP measurements during hypertonic saline infusion are the "gold standard" for the diagnostic interpretation of causes of polydipsia and polyuria. Studies of the peripheral reflection in plasma of the pulsatile VP release in healthy and polyuric individuals, with and without osmotic provocation, should be performed.

Aquaporin‐2 regulation in health and disease

“…The proteome of urinary exosomes has been elucidated and is publicly available in an online database (http://dir.nhlbi.nih.gov/papers/lkem/exosome/). Multiple publications have reported measurement of urinary AQP2 excretion as an indicator of the state of the kidney with regard to AQP2 regulation . The results of these studies are consistent with the conclusion that vasopressin increases AQP2 excretion, suggesting that the increase in AQP2 in the kidney is not due to an effect of vasopressin to decrease its elimination via exosomal secretion.…”

“…Other tumors of the central nervous system (CNS) that have been implicated in the development of CDI in the dog include lymphoma and metastatic carcinoma . Congenital CDI in dogs has been reported rarely . The majority of the reported cases of CDI in cats were the result of head trauma or were idiopathic with rare reports of congenital CDI or CDI secondary to neoplasia …”

“…Urine concentrating ability in response to water deprivation is intact, and even under conditions of free access to water, urine specific gravity and osmolality may fluctuate from dilute to concentrated over a 24‐hour period . There is considerable variation in baseline serum sodium concentration, baseline circulating vasopressin, and vasopressin response to hypertonic saline infusion . Systemic diseases that may trigger primary polydipsia in dogs include hepatic disease and gastrointestinal disease .…”

Desmopressin acetate-induced water intoxication in a dog with psychogenic polydipsia

“…After exclusion of causes for acquired nephrogenic DI, the differentiation between central DI, primary nephrogenic DI and psychogenic PD is based on results of the MWDT, response to DDAVP trial therapy and measurement of plasma osmolality 1. Measurement of plasma vasopressin concentrations under osmotic stimulation has been called into question, as findings were inconsistent and could not distinguish between different disorders 17. Although the MWDT is considered the best differentiating tool, it is time‐consuming, expensive and unpleasant for the patient.…”

Comparative quantitation of aquaporin-2 and arginine vasopressin receptor-2 localizations among chronic kidney disease and healthy kidney in dogs

“…Azotemia, uremia, proteinuria, hypertension, polyuria, and water and electrolyte imbalance were the clinical signs [ 1 ]. The most common disorder caused by the kidney’s failure to conserve water is polyuria [ 8 ]. These could be related to a protein that functions as a water channel.…”