The first occurs at the brain. With the onset of stress, two important classes of hormones, the endorphins and enkephalins (mostly the former), act to block the release of LHRH from the hypothalamus. As will be discussed in chapter 9, endorphins play a role in blocking pain perception and are secreted in response to exercise (helping to account for the famed “runner’s high” or “endorphin high” that hits many hardy joggers around the 30-minute mark).
