Diabetes in Monogastric Animals and its Management
Sriti Pandey 1, Abhishek Rajput 2, Aditya Agrawal 1, Swagatika Priyadarsini 1, Nikhil K.C. 1, Manoj Kumar Ahirwar 1
- College of Veterinary Science and Animal Husbandry, Rewa (M.P.)
- Department of Animal Husbandry and Dairying, Bhopal (M.P.)
Introduction
The relationship between energy metabolism, endocrinology, and immunology is a key to understanding metabolic disorders in animals. Lifestyle-related metabolic diseases, such as obesity, hyperlipidemia, and diabetes mellitus have increased in prevalence in dogs and cats. Diabetes mellitus has been reported to occur in a wide variety of species; however, it is a common ailment of humans, dogs, and cats. Animals with diabetes all exhibit the following characteristics: high blood glucose concentration and consequently large amounts of glucose in the urine. The blood glucose is increased because of reduced entry of glucose into muscle and adipose tissue and because of increased production of glucose by the liver from excessive glucagon stimulation. During diabetes, the muscles of the body are essentially starving for energy despite the fact that they are surrounded by glucose. Insulin is required to drive glucose across the cell membrane of muscle, adipose tissue, and α cells of the pancreas. Nervous tissue, erythrocytes, hepatocytes, intestinal epithelium, mammary gland, and cells of the renal cortex are insulin-independent and do not require insulin for uptake of glucose from the blood. If insulin is not produced in adequate amounts or if it is unable to act on its target tissues, glucose does not enter the insulin‐dependent tissues and they must utilize fatty acids, ketones, and amino acids as alternative sources of energy. Glucose builds up in the blood of the animal since it is not being utilized by the tissues of the body. The concentration of glucose in the blood of the diabetic animal will usually exceed the renal threshold for tubular glucose reabsorption and therefore it is common to find large amounts of glucose in the urine of the diabetic animal. The osmotic pressure exerted by the presence of so much glucose in the urine also increases water loss via the urine. This reduces blood volume and causes thirst in the diabetic patient, often one of the first clinical symptoms observed by the owner of a diabetic animal.
Exacerbating the situation is the fact that the α cells of the pancreatic islets require insulin, and when insulin is not available the α cells do not recognize that blood glucose levels are above normal. The α cells interpret the inability to take up glucose from the plasma to mean that blood glucose concentrations must be low and therefore glucagon secretion is increased. Glucagon stimulates gluconeogenesis, which acts to raise blood glucose concentrations even further.
Forms of Diabetes Mellitus
Type I or juvenile diabetes
In this form of diabetes, the β cells of the pancreatic islets fail to produce adequate insulin. In humans, it is well known that there is a genetic component to development of juvenile diabetes mellitus as the disorder tends to follow familial lines. However, it is also recognized that the disease appears to be a disorder with an autoimmune component. The β cells within the pancreatic islets of type I juvenile diabetes victims become mistaken by the immune system as a foreign tissue and are destroyed. Why this occurs is unknown, though it is speculated that exposure to certain viruses may cause the body to mistake islet cell components as viral antigens. With destruction of the β cells, the ability to produce insulin is lost.
Type II or adult‐onset diabetes
In this form of diabetes, the β cells do produce insulin (at least initially). However, the tissues fail to respond to insulin as they usually do. In humans, the failure to respond to insulin is associated with a decline in the number of receptors for insulin on the surface of target cells. In most cases, this is associated with obesity. The tissues of the body can still respond to insulin but the concentration in the blood must be raised considerably over normal levels to allow adequate uptake of glucose by the tissues. Initially, the β cells of the pancreas respond by producing the higher levels of insulin needed to maintain normal blood glucose concentrations. However, prolonged production of high amounts of insulin eventually leads to exhaustion and atrophy of the β cells. It is at this point that the patient develops hyperglycemia.
Gestational diabetes
Female dogs can also develop temporary insulin resistance while in heat or pregnant.
Causes of Diabetes
The exact cause of diabetes is unknown. However, autoimmune disease, genetics,obesity, chronic pancreatitis, certain medications and abnormal protein deposits in the pancreas can play a major role in the development of the disease. Type 1 diabetes mellitus (T1DM) is an autoimmune disease and its etiology is incompletely understood but environmental agent(s) are thought to trigger T1DM in the genetically at-risk. Humans are widely exposed to Mycobacterium avium subspecies paratuberculosis (MAP), a proven multi-host chronic enteric pathogen that is mostly studied in ruminant animals and causes the inflammatory disease paratuberculosis or Johne’s disease. MAP-induced enteric inflammation has been found in monogastric animals including dogs and pigs as well as four different types of subhuman primates— macaques, baboons, gibbons and cotton-top tamarins.’’
Signs of Diabetes
Early signs- The owner will sometimes notice certain symptoms that can be early signs of diabetes:
- Excessive thirst- The dog may drink frequently and empty the water bowl more often.
- Increased urination- The dog may ask to go outside frequently and may start having “accidents” in the house. Increased urination (and increased thirst) happens because the body is trying to get rid of excess sugar by sending it out through urine, along with water that bond to the sugar.
- Weight loss- The dog can lose weight despite eating normal portions. This is because the dog isn’t efficiently converting nutrients from its food.
- Increased appetite- The dog can be very hungry all the time because the body’s cells aren’t getting all the glucose they need, even though the dog is eating a normal amount.
Advanced signs- In more advanced cases of diabetes, symptoms can become more pronounced and can include:
- Loss of appetite
- Lack of energy
- Depressed attitude
- Vomiting
Threats to health- Uncontrolled diabetes can lead to devastating effects on the dog’s body, which is why early detection and proper treatment are crucial. Effects of diabetes on the dog’s health can include:
- Cataracts (leading to blindness)
- Enlarged liver
- Urinary tract infections
- Seizures
- Kidney failure
- Ketoacidosis, a potentially life-threatening acute condition that can be accompanied by rapid breathing, dehydration, lethargy, vomiting, or sweet-smelling breath; can be triggered by factors such as stress, surgery, fasting, infection, or an underlying health condition combined with low insulin level. Owners of diabetic animals should always have on hand ketone testing sticks and should test their dog’s urine if any of the above occurs. If the dog’s urine tests positive for ketones, an emergency vet should be called immediately.
Management of Diabetes
Initial treatment may consist of drugs such as tolbutamide, which stimulate the remaining β cells to increase their production of insulin. However, in most cases, therapy will involve the exogenous administration of insulin. This is generally the situation in veterinary medicine as the condition is rarely diagnosed before the β cells of the pancreas are reduced to numbers that will not sustain adequate insulin production. In people diagnosed very early in the course of this disease, simply losing weight will improve the insulin responsiveness of the tissues. In human medicine, the success of therapy with insulin is often determined by monitoring blood glucose concentration. Also, it is the general practice in human medicine to administer insulin after each meal to help drive absorbed glucose into the cells. In veterinary medicine, it is common to give the diabetic patient just one meal per day and to administer insulin just once each day at the time of the meal. Most protocols involve feeding and administering insulin in the morning. Monitoring blood glucose is generally impractical and is only used in the veterinary hospital to establish a dose of insulin to be administered to the animal. After being released from the hospital, the status of the animal is generally assessed by the owner who monitors urine glucose appearance each morning. It is assumed that if there is no glucose in the urine that blood glucose remained below the renal threshold (180 mg/dL) during the night hours. When glucose appears in the urine, it is assumed that the animal is getting an inappropriate insulin dose. The initial assumption would be that the animal was not being given enough insulin. This is not always a safe assumption. It is also possible that the animal has been given too much insulin. When too much insulin has been given the animal develops hypoglycemia 6–12 hours after the insulin injection. The body reacts by increasing secretion of cortisol and glucagon to increase blood glucose. Since this effect begins about the time the effects of the insulin injection are wearing off, the animal can develop hyperglycemia during the night that results in the appearance of glucose in the morning urine. This phenomenon is known as the Somogyioverswing. Misinterpreting the appearance of glucose in the urine as an automatic indication of insulin under-dosing could lead the veterinarian or owner to increase the dose of insulin administered to the animal, possibly resulting in fatal hypoglycemia as a result of insulin shock.
Conclusion
Lifestyle-related metabolic diseases, such as obesity, hyperlipidemia and diabetes mellitus have increased in prevalence in dogs and cats, as in human beings. Understanding of their causes and symptoms is important for early and better treatment. Early treatment of metabolic disorders includes the development of customized food, supplements, and drugs. Recently, good candidates of supplements and drugs for treating obesity in human medicine were developed, and these compounds will now be studied and utilized in veterinary medicine.
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