Maintaining the volume and composition of body fluids at adequate levels is possible thanks to systems that control water intake and urine output. When these control mechanisms are altered, polyuria (increased urine production) and polydipsia (increased water intake) appear. Polyuria and polydipsia are clinical signs that can occur in different pathologies, therefore, it will be necessary to make a diagnosis of the disease that causes them in order to correct them.
If you want to know what are the causes of polyuria and polydipsia in dogs and what to do in each case, keep reading this article from our place.
What is polyuria in dogs?
Polyuria consists of an increase in diuresis above normal, or what is the same, an increase in urine productionPolyuria in dogs is considered to exist when they produce more than 50 ml of urine per kilogram of weight per day (50 ml/kg/day). That is, to calculate if your dog has polyuria you must multiply his weight in kg by 50. The result will be the maximum milliliters of urine that he should produce per day. If the output is higher, he will have polyuria
Diuresis is regulated by antidiuretic hormone or ADH, which promotes the reabsorption of water in the kidneys (specifically through level of the renal tubules). Therefore, in pathologies in which the synthesis or action of this hormone is altered, polyuria occurs.
What is polydipsia in dogs?
Polydipsia consists of an increase in water intake In dogs, polydipsia is considered when water intake exceeds100 ml per kg of weight per day (100ml/kg/day). That is, to calculate if your dog has polydipsia, you must multiply his weight in kg by 100. The result will be the maximum number of milliliters of water he should drink per day. If the intake is higher, he will have polydipsia
It should be remembered that water intake is regulated by the Thirst Center , located at the hypothalamic level. Therefore, in those pathologies in which the Thirst Center is stimulated, we will observe polydipsia.
Polyuria-polydipsia syndrome
When an individual urinates more and drinks more, we say that they have polyuria-polydipsia syndrome (PU/PD syndrome). Actually, one sign gives rise to the other, and vice versa. That is, if an individual urinates more, he will need to increase his water intake so as not to become dehydrated. In the other direction, if an individual drinks more, he will also urinate more to avoid overhydration.
The most common is that polyuria (increased diuresis) occurs primarily and this is the cause of secondary polydipsia (increased water consumption). However, although it is much less frequent, the opposite can also occur in which a primary polydipsia causes a secondary polyuria.
At this point it is important to point out that both polyuria and polydipsia are clinical signs, they are not diseases in themselves. When a dog presents these clinical signs, it will be necessary to diagnose the pathology that is causing such signs in order to correct them.
Why do polyuria and polydipsia occur in dogs?
Causes of primary polyuria in dogs
We must differentiate between two types of polyuria based on the osmolarity of the urine, since the causes will be different.
1. Watery polyuria. The causes can be:
- Decrease in ADH synthesis and secretion: as we have already mentioned, this hormone promotes water reabsorption in the kidneys. If its synthesis and secretion decrease, less water will be reabsorbed in the renal tubules and the volume of urine will increase.
- Renal failure to respond to ADH: although ADH is synthesized, the renal tubules are not sensitive to it, so it does not produce its effect.
two. Osmotic polyuria: is caused by decreased reabsorption of water due to the presence of osmotically active solutes in the renal tubules, which are not reabsorbed and drag water.
Causes of primary polydipsia in dogs
- Behavioral disorders that cause animals to drink compulsively
- Pathologies that stimulate the Thirst Center at the level of the Central Nervous System
Diseases that cause polyuria and polydipsia in dogs
1. Watery polyuria
- Central diabetes insipidus: occurs in young animals due to an unknown cause (idiopathic) or secondary to lesions in the Central Nervous System that cause less synthesis and/or secretion of ADH.
- Nephrogenic diabetes insipidus: due to a lack of response to ADH. It can be primary (due to a congenital kidney anomaly) or secondary to other pathologies.
The pathologies that can lead to secondary nephrogenic diabetes insipidus are:
- Pyometra: is a purulent infection at the level of the uterus. Toxins produced by the bacteria causing the infection interfere with the action of ADH.
- Pyelonephritis: is an inflammatory and infectious process at the level of the renal pelvis in which blood flow to the renal medulla increases, decreasing its osmolarity and preventing the reabsorption of water in the renal tubules. In addition, bacterial toxins can interfere with the action of ADH.
- Hyperadrenocorticism or Cushing's Syndrome: excess glucocorticoids decrease ADH synthesis, interfere with ADH action and decrease permeability of the renal tubules.
- Hypoadrenocorticism or Addison's Syndrome: mineralocorticoid deficiency decreases the osmolarity of the renal medulla, which prevents the reabsorption of water and increases the volume of urine.
- Pheochromocytoma: is a tumor of the adrenal glands in which the excess of catecholamines causes arterial hypertension and an increase in renal flow, causing polyuria.
- Hypercalcemia: the increase in calcium in the blood interferes with the action of ADH. Hypercalcemia can be seen in neoplasms, hyperparathyroidism, chronic kidney disease, vitamin D intoxication, and granulomatous diseases.
- Hypokalaemia: the lack of potassium in the blood decreases the release of ADH, decreases the osmolarity of the renal medulla and interferes with the action of ADH. Hypokalemia can be seen in patients with vomiting/diarrhoea, kidney disease and diabetes.
two. Osmotic polyuria
- Diabetes Mellitus: the presence of glucose in the renal tubules prevents the reabsorption of water, which increases urine production.
- Chronic kidney disease: The number of functional nephrons decreases and, as a compensatory mechanism, the surviving nephrons increase their filtration. Consequently, osmotically active solutes accumulate in the renal tubules, preventing water reabsorption and increasing urine output.
We must remember that both aqueous and osmotic polyuria will secondarily cause polydipsia to avoid dehydration.
3. Polydipsia
- Psychogenic polydipsia: this is a behavioral disorder in which the animal begins to drink compulsively. It can occur in stressful situations or in confined dogs that require a lot of physical activity.
- Brain tumors, head injuries or cerebrovascular accidents: these are pathologies that can stimulate the Thirst Center at a central level.
- Hepatic encephalopathy: compounds that should be metabolized by the liver accumulate in the blood, which stimulate the Thirst Center.
In the same way, we must remember that a primary polydipsia will lead to a secondary polyuria to avoid excessive hydration.
Treatment for polyuria and polydipsia in dogs
As we have mentioned, polyuria and polydipsia are clinical signs that accompany certain diseases. Therefore, to correct these clinical signs it will be necessary to treat the specific pathology that is causing them:
- Central diabetes insipidus: Treat with desmopressin, a synthetic analog of ADH.
- Nephrogenic diabetes insipidus: treated with thiazide diuretics that decrease sodium reabsorption, which causes plasma sodium to be reduced, reducing water consumption and, consequently, the volume of urine. In addition, in the case of secondary nephrogenic diabetes, it will be necessary to establish a specific treatment based on the primary pathology. Infections such as pyometra or pyelonephritis will be treated with antibiotics and anti-inflammatories. Cushing's Syndrome will be treated with trilostane (if it is pituitary) or by adrenalectomy (if it is adrenal). Addison's Syndrome will be treated with glucocorticoids (hydrocortisone or prednisone) and mineralocorticoids (fludrocortisone or deoxycorticosterone privalate). Pheochromocytoma will be treated with toceranil phosphate or adrenalectomy. Electrolyte disorders such as hypercalcaemia or hypokalaemia will be corrected by treating the primary pathologies that produce them.
- Diabetes Mellitus: Treatment is based on insulin administration, regular exercise, and a low-fat, high-fiber diet.
- Chronic kidney disease: there is no curative treatment, so we have to limit ourselves to administering a symptomatic and nephroprotective treatment. It is normally based on the administration of ACEI vasodilators and a renal diet (low in protein, sodium and potassium, and rich in omega 3 fatty acids, soluble fiber and antioxidants).
- Psychogenic polydipsia: avoid stressors that trigger compulsive water consumption.
- Hepatic encephalopathy: Usually caused by portosystemic shunts that are surgically closed.
