Disturbed Vasopressin Release in 4 Dogs with So-Called Primary Polydipsia

Abstract

Primary polydipsia is characterized by a marked increase in water intake and secondary polyuria, and in dogs often is described as a behavioral problem or a psychological disorder. We describe 4 dogs with primary polydipsia, diagnosed on the basis of a modified water deprivation test, in which further examination included serial measurements of urine osmolality (UOsm) and plasma vasopressin (VP) measurements during water deprivation and hypertonic saline infusion. The dogs, ranging in age from 4 months to 4 years, all were presented for evaluation of polyuria and polydipsia. Physical examination, routine blood chemistry, and urinalysis disclosed no specific cause for the polyuria and polydipsia. During serial measurements UOsm spontaneously reached high concentrations in 2 dogs, whereas in the other 2 dogs UOsm also fluctuated but on no occasion exceeded 1,000 mosm/kg. Primary polydipsia was diagnosed when UOsm exceeded 1,000 mosm/kg at the end of the modified water deprivation test and plasma osmolality did not exceed the upper limit of the reference range during testing. During water deprivation, plasma VP concentrations remained relatively low. The VP response to hypertonic saline infusion was abnormal, with an increased threshold value in 3 dogs, an increased sensitivity in 2 dogs, and an exaggerated response in 1 dog. It is concluded that some dogs fulfilling current criteria for primary polydipsia produce concentrated urine spontaneously throughout the day in a pattern similar to what has been observed in healthy pet dogs. This finding can be regarded as diagnostic and precludes the need for a water deprivation test. During water deprivation testing, all 4 dogs produced highly concentrated urine in the face of low basal plasma VP concentrations. The observed abnormal VP release in response to hypertonic stimulation may be interpreted as a primary disturbance in the regulation of VP secretion, although it might also be the result of overhydration caused by a primary abnormality in drinking behavior.

Probable primary polydipsia in a domestic shorthair cat

“…1,2,4 Plasma and urine osmolality have also been shown to vary throughout the day in dogs with PP, and both hyponatremia and normal serum sodium levels have been reported in humans and dogs with this disease. 21,24 With the cat featured in this case study, serum sodium levels were always normal (RI 145-158 mmol/l) 6 and plasma osmolality levels were either in the normal range or elevated. As mentioned previously, human patients diagnosed with dipsogenic diabetes insipidus have an osmotic thirst threshold that is set lower than the threshold for AVP release.…”

“…1,2,4,24 Although uncommon, PP has been briefly described in dogs as a psychological disorder and behavioral problem but no reports yet exist in cats. 2,4,21 In dogs this syndrome may be a result of a concurrent disease or a learned behavior due to a change in environment. Treatment for dogs diagnosed with psychogenic polydipsia centers around gradual water restriction with or without the addition of salt to the diet and changes in the environment to provide additional enrichment to the dog's daily routine.…”

“…A study by van Vonderen et al showed that four dogs previously diagnosed with PP had decreased AVP responses during a MWDT, and that two of four dogs had plasma osmolality and serum sodium levels at the upper limits of normal, indicating that a non-linear relationship between AVP and plasma osmolality levels may exist in some dogs with PP. 21 Plasma osmolality and serum sodium levels that are not decreased in a PU/PD animal should not necessarily rule out PP and emphasizes the fact that multiple diagnostic tests may be needed before reaching a final diagnosis. Although helpful in diagnosing CDI in one feline case, there are no published AVP reference intervals in cats.…”

“…PP is defined as a marked increase in water intake that cannot be explained as a compensatory mechanism for excessive fluid loss. 21 In humans this can be further subdivided into dipsogenic diabetes insipidus and psychogenic polydipsia. The underlying physiological disorder with dipsogenic diabetes insipidus appears to be an osmotic threshold for thirst that is abnormally low.…”

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

“…Associations with medical problems such as liver diseases, especially hepatoencephalopathy,10–12 and gastrointestinal diseases13 are reported. In the absence of underlying diseases, primary PD has been linked to behavioural problems or stressful events, although these may not always be obvious 2 14 15. Generally, psychogenic PD is rarely diagnosed in dogs.…”