Last Updated: 2002-08-07 14:37:44 -0400 (Reuters Health)
By Amy Norton
NEW YORK (Reuters Health) - A hormone naturally produced in the intestines after a meal has been found to quell people's appetites and cut their food intake when given before eating.
The study of 12 healthy volunteers found that those who received infusions of the hormone shortly before an all-you-can-eat buffet ate one third less than those given only saline.
The hormone, known as PYY3-36, is normally released into the blood from the intestines after a meal and in proportion to calorie intake. The new research, reported in the August 8th issue of Nature, suggests that PYY3-36 sends signals to specific receptors in the brain that in turn curb the appetite.
It also points to the PYY3-36 "system" as a new target in fighting obesity, according to the study authors, led by Stephen R. Bloom of Imperial College in London.
Bloom's team used rat experiments to first show that injections of PYY3-36 cut food intake and lead to weight loss. They also found evidence that the hormone acts via specific receptors in the brain's hypothalamus, which is known to regulate food intake. Rats genetically engineered to lack the receptor--called the Y2 receptor--were unaffected by injections of PYY3-36.
In the human phase of the study, volunteers were infused with either saline or enough PYY3-36 to match concentrations that would normally be in the blood after a meal. The hormone infusion decreased participants' hunger, and, at an open buffet 2 hours later, kept their calorie intake more than one third lower than that of those who received saline. And the difference in food intake between the two groups lasted for 12 hours after infusion.
If the hormone turns out to be a viable weight-loss agent, Bloom told Reuters Health, the best way to give it would be via injection--which could make it less than appealing.
And much more research needs to be done. Bloom said his team plans to test the hormone among obese study participants and also try to hunt for foods that naturally trigger a greater release of PPY3-36 into the blood.
Dr. Michael W. Schwartz of the University of Washington in Seattle agreed that it is "reasonable" to expect that PPY3-36 or other agents that activate the Y2 receptor could cut food intake and body weight.
But a range of hormones--including the blood-sugar regulator insulin and the so-called obesity hormone leptin--control appetite and weight in humans, noted Schwartz, who wrote an editorial accompanying the report.
"The control of body weight is highly redundant," he told Reuters Health, "and most interventions that cause weight loss will eventually trigger adaptive responses that counter the weight-reducing benefit."
So, Schwartz said, drug combinations that target various players in the body's weight-control system may be necessary. In addition, he noted, such medications may be most effective for preventing weight rebound in people who have already shed pounds, rather than spurring weight loss on their own.
SOURCE: Nature 2002;418:650-654,595-597.