"per2" contains glucocorticoid response elements (gres) and a gre within the core clock gene "per2" is continuously occupied during rhythmic expression and essential for glucocorticoid regulation of per2 in vivo. mice with a genomic deletion spanning this gre expressed elevated leptin levels and were protected from glucose intolerance and insulin resistance on glucocorticoid treatment but not from muscle wasting. per2 is an integral component of a particular glucocorticoid regulatory pathway and that glucocorticoid regulation of the peripheral clock is selectively required for some actions of glucocorticoids.