There are two types of diabetes. The most common is called sugar diabetes or diabetes mellitus and is common in cats and dogs especially if they are overweight. It is caused by the pancreas secreting insufficient insulin, the hormone that controls the amount of glucose in the blood. If insulin secretion is inadequate, the concentration of glucose in the blood increases. Any increase in the glucose in the blood automatically leads to an increase in glucose in the fluid filtered into the kidney tubule. Normally the kidney removes all the glucose filtered into it, but these high concentrations swamp this removal mechanism and urine containing glucose is produced. The main symptoms of this type of diabetes are the production of large amounts of dilute urine containing glucose, and excessive thirst.
The second type of diabetes is called diabetes insipidus. The name comes from the main symptom, which is the production of large amounts of very dilute and “tasteless” urine. It occurs when the pituitary gland produces insufficient ADH, the hormone that stimulates water re-absorption from the kidney tubule. When this hormone is lacking, water is not absorbed and large amounts of dilute urine are produced. Because so much water is lost in the urine, animals with this form of diabetes can die if deprived of water for only a day or so.