University of Newcastle

Professor Baylis described how water intake and output are balanced in normal people. Water intake is governed by thirst and social drinking - and social drinking is the major stimulus to drinking in our society; output of water is regulated by the kidney.

This activity of the kidney is regulated by the hormone arginine Vasopressin, which is also known as antidiuretic hormone. As the body loses water and becomes dryer, special cells in the brain detect the change in the concentration of the blood and cause the pituitary to secrete vasopressin. This then circulates in the blood and sticks to the surface of kidney cells, allowing them to reabsorb water from the urine and making it more concentrated. Raised concentration of the blood also activates the brain to create the sensation of thirst, and the balance of increased drinking and decreased water in the urine normalises the blood concentration.

Adults with Diabetes Insipidus have a deficiency of vasopressin secretion (or in rare instances a kidney abnormality which does not allow them to respond to arginine vasopressin) and they pass more than three litres per day and sometimes up to 20 litres. Professor Baylis described how Desmopressin is a 'superdrug' which acts like vasopressin on the kidney, has few side effects and is long acting.

In the question and answer session, one major problem raised was with insurance companies who tend to confuse diabetes insipidus with diabetes mellitus. It was suggested that patients should not describe themselves as having DI, but say they are vasopressin deficient or insufficient. Professor Baylis was asked what happens if patients are not treated. He explained that large urine flows could eventually cause secondary problems with the bladder. This could in turn damage kidney function. He was asked about the relative merits of tablets and sprays. He tended to prefer the tablets, but there is a lot of variation between different patients. In reply to a question of whether spontaneous cures occured, the answer was that this is very rare and diabetes insipidus is effectively for life. However, after a head injury or certain diseases such as granulomas, recovery can sometimes occur. On being asked about the oldest person with DI, Professor Baylis replied that there was no evidence of any change in life expectancy for patients with this condition, so they could be very old. Professor Baylis discussed the great importance of MedicAlert bracelets. If a patient had an accident and the hospital did not know he or she had DI, this could prove to be very dangerous.

Finally, the problem of DDAVP overdose was discussed. Professor Baylis suggested that if one single dose of DDAVP was omitted once a week and the patient then passed a good volume of urine, this should help protect against the gradual development of diluted blood with low plasma sodium.