You've just finished dining at the local burger joint, and you feel the need to check into the Heartburn Hotel.

Heartburn and acid reflux are caused primarily by the overproduction of gastrin, a hormone that initiates stomach acid production. Sometimes too much gastrin is produced during the digestive process, resulting in that familiar burning sensation.

But research conducted by Medical School Prof. Juanita Merchant, indicates that gastrin may also play a vital role in the immune system.

Scientists are studying gastrin to better understand how the gastric system is regulated. In essence, the same hormone that aids in digesting those greasy fries you just consumed for lunch may also be protecting you from harmful bacterial invasions.

The hormone gastrin appears to be one of the initial respondents in the innate immune system, the body's first line of defense against harmful bacteria. It tells the stomach cells to start producing acid, which, in addition to Gastrin's digestive responsibilities, can also destroy foreign microbes.

Some trickier bacteria, such as Helicobacter pylori, has adapted to survive within the harsh acidic conditions of the stomach. When this type of resistant bacteria infects the stomach, it causes an increase in acid production, leading to inflammation. Merchant explained that third-world populations are more susceptible to such bacteria because of poor sanitary practices.

There are many drugs on the market today to combat bacteria like these. Leading brands, including Prilosec and Prevacid, are available by prescription. These drugs essentially stop the production of stomach acid. Merchant said the drugs effectively relieve gastric conditions such as heartburn or ulcers, but has some concerns regarding their extended use. Long-term suppression of acid production could weaken the immune system response. Many bacteria would have a better chance of surviving in weakened acidic conditions. Merchant suggested that the best way to determine long-term effects is to "keep an eye on pediatric patients."

Merchant used "knock-out" mice in her study to test the effects of suppressing gastrin production. These mice, created by another Medical School Prof. Linda Samuelson, were genetically engineered so that they could not produce gastrin.

According to Samuelson, the use of such mice is quite common.

"(The mice) have really given us an insight into many fields of mammalian biology," Samuelson said.

The University has a Transgenic Animal Model Core that creates genetically engineered mice for researchers. Merchant's lab used mice that were already being studied by Samuelson in her own lab.

Although scientists have yet to see the long-term implications of stopping acid production in humans, Merchant's research revealed that the mice that had been genetically engineered not to produce acid developed cancerous tumors.

But Merchant stressed that there is no definitive evidence correlating cancer with decreased stomach acid production.

Even if scientists could prove causation in mice, only clinical trials could prove any correlation in humans, because of the extreme differences in genetic makeups between the two organisms.

Fast facts about the stomach:

- During digestion, a hormone called gastrin initiates the production of stomach acid.

- Too much gastrin can cause too much stomach acid to be produced. This can cause heartburn or acid reflux.

- Gastrin could also be responsible for defending against harmful bacteria, by triggering the production of stomach acid that can break down food and kill harmful microbes.

- Helicobacter pylori is a type of bacteria that has adapted to survive in highly acidic environments. If a person is infected with this kind of bacteria, it can cause the body to increase its acid production, in order to eliminate the bacteria.

- New research implies that halting stomach acid production can lead to cancer, though no clinical trials have been performed yet.