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.

Hyponatremia in dogs and cats

“…Excessive ingestion of water (primary polydipsia) is a rare cause of hyponatremia, where an animal ingests enough water to overwhelm the normally functioning kidney's ability to excrete the excess water . Excess water ingestion can be a behavioral issue (psychogenic polydipsia) or can occur as a result of neurological disease or iatrogenic supplementation . A full patient history and evaluation of water intake are necessary to identify this cause of hyponatremia.…”

Aquaporin‐2 regulation in health and disease

“…Lack of exercise, boredom, or stress may fuel compulsive drinking in dogs . 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 .…”

Diabetes insipidus

“…Psychogenic polydipsia has been reported in dogs, with no specific breed or gender predisposition; it has not been documented in cats. 4 When considering diabetes insipidus as a diagnostic differential in a patient that has PU/PD, it is important to first rule out the more common causes (see the box on page 44).…”