Neuropeptides

It has long been known that type 1 diabetes is caused by the destruction of insulin producing cells in the pancreas by the body’s own immune system. This is not so much due to antibodies but a type of white blood cell called CD8+ lymphocytes. They are very important in protecting the body from infections but at times they can attack the body’s own tissues.

Scientists have studied type 1 diabetes in a strain of mice known as NOD. This stands for non-obese diabetic. This is a specially bred strain that has a tendency to develop inflammation of the pancreas and type 1 diabetes. It occurs spontaneously in about 60-80% of females and 20-30-% of males. Researchers at the Hospital for Sick Children in Toronto, Canada found that injecting a chemical called substance P into the artery to the pancreas stopped and reversed the process for weeks. In addition it reversed the resistance to insulin that is found in these diabetic mice.

Substance P is called a neuropeptide or a neurotransmitter. This means that it is involved with the transmission of impulses between nerves. It has a number of functions but usually it especially important in the sensation of pain.

The importance of this finding is that it suggests that the cause of the destruction of insulin producing cells is not simply the immune system but nerves appear to be involved too. If injecting substance P or a similar substance into the pancreas could stop or even reverse the destruction of insulin producing cells in type 1 diabetes, this would be a great advance.

There is already evidence that neuropeptides play a part in the production of diabetic neuropathy. This is damage to nerves caused by diabetes. This is the first time that neuropeptides have been implicated in the underlying process of destruction of insulin producing cells that causes diabetes.

Although this research was published late in 2006 it is important to realise that it does not mean that the end of type 1 diabetes is in sight. The findings relate to inbred experimental mice and may not be applicable to humans.

In the human, the islets of Langerhans that contain the cells that produce glucagon and insulin, are richly supplied by autonomic nerves. These are the nerves of the sympathetic and parasympathetic nervous system and they stimulate polypeptide secretion from the nerves in the pancreas. The parasympathetic nerves and administration of their transmitting chemicals stimulate insulin and glucagon secretion. The sympathetic nerves and administration of their transmitters inhibit insulin but stimulate glucagon secretion.

Dr Tony Woolfson MB BS DM MRCP(UK)
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