A vasoactive intestinal peptide, or VIP, is a hormone which was originally discovered in the intestine but has since been found to occur throughout the body. As digestive system hormones, VIPs enable relaxation of muscles in the gut, decrease food absorption and gastric acid production and increase the amount of water in digestive juices. Vasoactive intestinal peptide also has effects on the brain, heart, lungs, reproductive and immune systems. It is involved in regulating sleep, embryo development, and the control of the body's endocrine, or hormone, system. Drugs which mimic or block the effects of VIP could have the potential to treat many different diseases.
Structurally, a vasoactive intestinal peptide is made up of 28 amino acids. It causes its effects by binding to a vasoactive intestinal peptide receptor on a cell in the target tissue. The name vasoactive intestinal peptide arose because scientists first found the hormone in extracts taken from the intestine, and it was shown to have an effect on blood vessels, causing them to dilate, or widen. VIP also acts to relax smooth muscle in the gut, including the muscle in the walls of the stomach and gallbladder and the muscular valve, or sphincter, at the bottom of the esophagus.
In the lungs, vasoactive intestinal peptide causes widening of the airways. It may suppress the immune system, and it has a number of actions in the brain. The endocrine system is controlled by the hypothalamus in the brain, and VIP may be released along with other hypothalamus hormones, influencing the system as a whole. In the nervous system, VIP hormones transmit signals along nervous pathways. It is thought that vasoactive intestinal peptide may have an influence on behavior as well as sleep patterns, and the hormone may influence the course of diseases such as cancer and Alzheimer's.
A rare type of cancerous tumor known as a VIPoma may sometimes develop in the pancreas. The tumor secretes large amounts of vasoactive intestinal peptide, causing symptoms such as diarrhea, which is watery and may occur in great quantities. Other symptoms may include pain and cramping in the abdomen, weight loss and nausea, and flushing of the face.
The excessive diarrhea associated with a VIPoma usually leads to dehydration. Treatment initially involves rehydrating the patient by giving fluids through a vein, together with medication to control the diarrhea. The tumor may then be removed surgically. If a VIPoma can be removed before it has a chance to spread, the outlook is positive and the patient may be cured.