[The role of vasopressin in dogs with polyuria]. / Onderzoek naar de rol van vasopressine bij honden met polyurie.

Polyuria and polydipsia (PUPD) occur frequently in dogs and may be caused by a variety of endocrine, metabolic, and renal disturbances. The studies described in this PhD Thesis, which was defended in January 2004 in Utrecht, investigated the role of the antidiuretic hormone vasopressin (VP) in the pathogenesis of different forms of canine polyuria. Experiments in healthy dogs demonstrated that the ranges of urine specific gravity and urine osmolality are much larger than previously thought. A water deprivation test is not required in all polyuric dogs, because serial measurements of urine osmolality may already lead to the diagnosis of primary polydipsia, in some cases. In dogs with primary polydipsia a wide variation in VP responses to hypertonic stimulation can be found, including a hyperresponse, a hyporesponse, and a non-linear response. The significance of the VP response to hypertonic saline infusion as the 'gold standard' for a diagnosis of canine polyuria is discussed. In the dog, VP is secreted in a pulsatile fashion with a wide variation in the number of VP pulses, VP pulse duration, and VP pulse amplitude and height. The occurrence of spontaneous VP pulses may severely hamper the interpretation of the curve describing the relationship between plasma osmolality and plasma VP concentration during osmotic stimulation. A radioimmunoassay to measure the VP-dependent water channel aquaporin-2 (AQP2) in urine was developed in dogs. In healthy dogs, urinary AQP2 excretion closely reflects changes in collecting duct exposure to VP. Measurement of urinary AQP2 excretion in polyuric dogs may be helpful to distinguish between central diabetes insipidus, nephrogenic diabetes insipidus, and primary polydipsia.

Urinary aquaporin-2 excretion in dogs: a marker for collecting duct responsiveness to vasopressin.

In humans, the urinary aquaporin-2 (U-AQP2) excretion closely parallels changes in vasopressin (VP) action and has been proposed as a marker for collecting duct responsiveness to VP. This report describes the development of a radioimmunoassay for the measurement of U-AQP2 excretion in dogs. In addition, the localization of AQP2 in the canine kidney was investigated by immunohistochemistry. Basal U-AQP2 excretion was highly variable among healthy dogs. Two hours after oral water loading, the mean U-AQP2/creatinine ratio decreased significantly from (231 +/- 30) x 10(-9) to (60 +/- 15) x 10(-9) (P = 0.01), while the median plasma VP concentration decreased from 4.2 pmol/l (range 2.2-4.8 pmol/l) to 1.2 pmol/l (range 1.0-1.9 pmol/l). Subsequent intravenous administration of desmopressin led to a significantly increased mean U-AQP2/creatinine ratio of (258 +/- 56) x 10(-9) (P = 0.01). Two hours of intravenous hypertonic saline infusion (20% NaCl, 0.03 ml/kg body weight/min) significantly increased the mean U-AQP2/creatinine ratio from (86 +/- 6) x 10(-9) to (145 +/- 23) x 10(-9) (P = 0.045), while the median plasma VP concentration increased significantly from 2.2 pmol/l (range 1.1-6.3 pmol/l) to 17.1 pmol/l (range 8.4-67 pmol/l) (P < 0.001). Immunohistochemistry revealed extensive labeling for AQP2 in the kidney collecting duct cells, predominantly localized in the apical and subapical region. As in humans, U-AQP2 excretion in dogs closely reflects changes in VP exposure. Urinary AQP2 excretion may become a diagnostic tool in dogs for the differentiation of polyuric conditions such as (partial) central or nephrogenic diabetes insipidus, primary polydipsia, and inappropriate VP release.

Pulsatile secretion pattern of vasopressin under basal conditions, after water deprivation, and during osmotic stimulation in dogs.

Measurement of plasma osmolality (Posm) and plasma vasopressin (VP) concentration in response to hypertonicity is regarded as the gold standard for the assessment of VP release in polyuric conditions. Yet the interpretation of the VP curve as a function of Posm may be hampered by the occurrence of VP pulses. To determine whether VP is secreted in a pulsatile fashion in the dog and whether stimulation of VP release changes the secretion pattern of VP, we measured VP at 2-min intervals for 2 h under basal conditions, after 12 h of water deprivation, and during osmotic stimulation with hypertonic saline (20%) in eight healthy dogs. Vasopressin was secreted in a pulsatile fashion with a wide variation in number of VP pulses, VP pulse duration, and VP pulse amplitude and height. After water deprivation, total and basal VP secretion, the number of significant VP pulses, as well as the pulse characteristics did not differ from the basal situation. During osmotic stimulation, there was a large increase in both basal and pulsatile VP secretion, and the number of VP pulses and VP pulse height and amplitude were significantly increased. The VP pulse amplitude correlated significantly with the basal plasma VP concentration during osmotic stimulation. It is concluded that VP is secreted in a pulsatile manner in healthy dogs. The basal and pulsatile VP secretion increases during osmoreceptor-mediated stimulation. The VP pulses may occur to the magnitude that they may be interpreted as erratic bursts, when occurring in the hypertonic saline infusion test.

Parathyroid hormone immunohistochemistry in dogs with primary and secondary hyperparathyroidism: the question of adenoma and primary hyperplasia.

In primary hyperparathyroidism, calcium homeostasis is disrupted by excessive synthesis and secretion of parathyroid hormone (PTH), which is usually caused by a solitary adenoma, or less often by nodular hyperplasia or carcinoma of the parathyroid glands. So far, the distinction between these forms of primary hyperparathyroidism has been made by histological examination. In this report clinical and histological findings, including PTH immunohistochemistry, are described in five dogs with primary hyperparathyroidism, three dogs with secondary hyperparathyroidism due to chronic renal failure, and eight control dogs. In the dogs with primary hyperparathyroidism, nodular adenomatous hyperplasia was found in two animals and parathyroid adenoma in three. The dogs with chronic renal failure had diffuse parathyroid gland hyperplasia. The parathyroid glands of the control dogs and the inactive cells surrounding the hyperplastic nodules showed slight to moderate, localized, paranuclear PTH immunolabelling. In the primary nodular and secondary diffuse hyperplasia, all parathyroid cells had a diffuse cytoplasmic PTH labelling pattern, sometimes in combination with localized paranuclear labelling. In parathyroid adenoma, areas with either paranuclear labelling or diffuse cytoplasmic labelling were observed. As both parathyroid adenoma and primary nodular parathyroid gland hyperplasia have characteristics of intrinsic autonomy (i.e., suppression of the remaining endocrine tissue), there would seem to be no functional difference between the two abnormalities. It is argued that primary (multi)nodular hyperplasia is a multiple form of parathyroid adenoma.

Aldosteronoma in a dog with polyuria as the leading symptom.

In a 10-year-old castrated male shorthaired German pointer polyuria was associated with slight hypokalemia, hypophosphatemia and alkalosis, as well as elevated plasma concentrations of a glucocorticoid-inducible iso-enzyme of alkaline phosphatase. Repeated measurements of urinary corticoids and normal suppressibility of the hypothalamus-pituitary-adrenocorticial axis excluded glucocorticoid excess. Urine osmolality (Uosm) did not increase during administration of the vasopressin analogue desmopressin. At the time water deprivation had caused Uosm to rise from 300 to 788 mOsm/kg, there was also plasma hypertonicity. During hypertonic saline infusion the osmotic threshold for vasopressin release was increased. The combination of elevated plasma aldosterone concentrations and unmeasurably low plasma renin activity pointed to primary hyperaldosteronism. As initially computed tomography (CT) did not reveal an adrenocortical lesion, the dog was treated with the aldosterone antagonist spironolactone. This caused Uosm to rise in a dose-dependent manner. However, well-concentrated urine was only achieved with doses that gave rise to adverse effects. Once repeated CT, using 2-mm-thick slices, had revealed a small nodule in the cranial pole of the left adrenal, unilateral adrenalectomy was performed which resolved the polyuria completely. Also the plasma concentrations of kalium, aldosterone and renin activity returned to within their respective reference ranges. The adrenocortical nodule had the histological characteristics of an aldosteronoma, with the non-affected zona glomerulosa being atrophic.In this dog with primary hyperaldosteronism the polyuria was characterized by vasopressin resistance and increased osmotic threshold of vasopressin release, similar to the polyuria of glucocorticoid excess. The possibility is discussed that the polyuria of glucocorticoid excess is actually a mineralocorticoid effect.

Cerebellar cortical abiotrophy in two Portuguese Podenco littermates.

Cerebellar cortical abiotrophy in two Portuguese Podenco littermates is reported and discussed. The disease is characterized by progressive cerebellar ataxia with an early onset of two to three weeks. Extensive loss, degeneration, and necrosis of Purkinje cells particularly involved the cerebellar hemispheres. An autosomal recessive pattern of inheritance is suspected.

Disturbed vasopressin release in 4 dogs with so-called primary polydipsia.

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.

Influence of veterinary care on the urinary corticoid:creatinine ratio in dogs.

Physical and emotional stresses are known to increase the production and secretion of glucocorticoids by the adrenal cortex in both humans and experimental animals. The urinary corticoid: creatinine (C:C) ratio is increasingly used as a measure of adrenocortical function. In this study we investigated whether a visit to a veterinary practice for vaccination, a visit to a referral clinic for orthopedic examination, or hospitalization in a referral clinic for 1.5 days resulted in increases of the urinary C:C ratio in pet dogs. In experiment 1, owners collected voided urine samples from 19 healthy pet dogs at specified times before and after taking the dogs to a veterinary practice for yearly vaccination. In experiment 2, 12 pet dogs were evaluated in a similar way before and after an orthopedic examination at a referral clinic. In experiment 3, 9 healthy pet dogs were hospitalized for 1.5 days and urine samples were collected before, during, and after this stay. Basal urinary C:C ratios in all experiments ranged from 0.8 to 8.3 x 10(-6). In experiment 1, the urinary C:C ratio after the visit to the veterinary practice ranged from 0.9 to 22.0 x 10(-6). Six dogs had a significantly increased urinary C:C ratio (responders), but in 5 of these dogs the ratio was < or = 10 x 10(-6). In experiment 2, 8 of 12 dogs responded significantly with urinary C:C ratios ranging from 3.1 to 27.0 x 10(-6). In experiment 3, 8 of 9 dogs had significantly increased urinary C:C ratios, ranging from 2.4 to 24.0 x 10(-6), in some or all urine samples collected during hospitalization. In 4 dogs urinary C:C ratios 12 hours after hospitalization were still significantly higher than the initial values. Thus, a visit to a veterinary practice, an orthopedic examination in a referral clinic, and hospitalization can be considered stressful conditions for dogs. A large variation occurs in response, and in individual dogs the increases in urinary C:C ratios can exceed the cutoff level for the diagnosis of hyperadrenocorticism. Therefore, urine samples for measurement of the C:C ratio in the diagnosis of hyperadrenocorticism should be collected in the dog's home environment, to avoid the influence of stress on glucocorticoid secretion.

Intra- and interindividual variation in urine osmolality and urine specific gravity in healthy pet dogs of various ages.

Urine specific gravity (Usg) and urine osmolality (Uosm) are used routinely to assess renal concentrating ability, but limited data on these variables are available for healthy dogs. Consequently, we studied the intra- and interindividual variations in Usg and Uosm in healthy dogs as well as the influence of age and gender on these variables. Dogs were selected for health and anestrus in female dogs through the use of a detailed questionnaire. Eighty-nine owners collected morning and evening urine samples from their dogs on 2 consecutive days. In 8 dogs in which the Uosm of different samples varied more than 50%, owners collected urine for 24 hours at 2-hour intervals during the day and at 4-hour intervals at night. The possible effect of changes in adrenocortical function with age was assessed by measurements of urinary corticoid/creatinine (C/C) ratios. Among all samples, Uosm ranged from 161 to 2,830 mOsm/kg and Usg from 1.006 to > 1.050. In the morning, Uosm (1,541 +/- 527 mOsm/kg, range 273-2,620 mOsm/kg) and Usg (1.035 +/- 0.010, range 1.009-->1.050) were higher than in the evening (Uosm 1,400 +/- 586 mOsm/kg, range 161-2,830 mOsm/kg; Usg 1.031 +/- 0.012, range 1.006-->1.050). The interindividual coefficient of variation in Uosm was 34.2% for morning urine samples and 41.9% for evening samples. In 8 dogs with large differences in urine concentration, there were 2- to 3-fold increases or decreases in Uosm during the day, and the intraindividual coefficient of variation was 33.0%. There was no relation between gender and urine concentration. Urine concentration in both the morning and evening samples decreased with age. Urinary corticoid/ creatinine ratios did not change with age. It can be concluded that Uosm and Usg vary widely among healthy dogs. Urine concentration is generally lower in the evening than in the morning and is not related to gender. Urine concentration decreases with age, and this cannot be ascribed to an associated increase in endogenous corticoids. In some dogs, Uosm varies widely during the day, with an intraindividual coefficient of variation approaching the interindividual coefficient of variation. This may be regarded as a biologic variation but also could represent an early undiagnosed clinical abnormality.

Polyuria and polydipsia and disturbed vasopressin release in 2 dogs with secondary polycythemia.

In dogs, secondary polycythemia (SP) may be associated with polyuria and polydipsia (PU/PD). The pathogenesis of this PU/PD has not yet been explained. We hypothesized that hyperviscosity and increased blood volume in SP might affect vasopressin (VP) release, resulting in PU/PD. This hypothesis was tested in 2 dogs with SP caused by renal neoplasia and PU/PD. Osmoregulation of VP release was studied by a modified water deprivation test and by investigating the VP response to hypertonic saline infusion. Water deprivation test results were consistent with an inability to produce concentrated urine despite increasing plasma osmolality. During hypertonic saline infusion, the osmotic threshold of VP release was markedly increased in both dogs, resulting in a delayed VP response to increasing plasma osmolality. The sensitivity of VP release was low normal in both dogs. We conclude that blood hyperviscosity and increased blood volume led to impaired VP release and polyuria.

[Evaluation of a test strip for the determination of urine specific gravity in the dog]. / Evaluatie van een teststrook voor de bepaling van het soortelijk gewicht van urine van de hond.

The specific gravity of 80 randomly chosen urine samples from healthy dogs without polyuria/polydipsia and from a few dogs with polyuria/polydipsia was measured by refractometry and by test strip method (sg test strip). Urine osmolality and pH were also measured and the urine samples were examined for the presence of glucose. In accordance with earlier observations, there was an excellent correlation between the specific gravity determined by refractory and the osmolality (r = 0.98). The results obtained with the sg test strip correlated poorly with those obtained by refractometry (r = 0.39) and poorly with the osmolality (r = 0.36). In 77.5% of the samples the specific gravity determined with the sg test strip differed by more than 0.005 from that determined by refractometry. After correction of the sg test strip results by +0.005 for urine pH > or = 6.5, this percentage decreased to 60%. The results for the refractometer and sg test strip were significantly different (P < 0.001). These results indicate that the sg test strip investigated is unsuitable for use to determination of the specific gravity of canine urine.