Scientists have discovered a biological brake for a hunger hormone: a competing hormone that seems to counter the urge to eat. The substance, named obestatin, has been tested just in laboratory rats so far. But if it pans out, the discovery of the dueling hormones could lead not only to a new appetite suppressant, but also help unravel the complex ways that the body regulates weight.It turns out that the same gene sparks production of the two opposing hormones, Stanford University researchers say in Friday’s edition of the journal Science.