Epinephrine release in response to sexual activity in male versus female rats

Sequential blood samples were collected from adult male and female rats before, during and after they interacted with either a sexually-active or a gonadectomized adult of the opposite sex. As assessed by plasma levels of epinephrine, both sexes showed a much greater response to a sexual encounter than they did to a nonsexual encounter. The release of epinephrine in response to sexual activity differed in males and females in at least two ways, however. First, a sexual encounter caused an absolutely greater but a proportionally smaller response in females. Second, plasma levels of epinephrine in males but not in females reflected the alternating periods of copulation and noncopulation that characterize sexual activity in this species. Blood levels of epinephrine were low and stable in males between copulatory bouts and relatively high during these bouts. In contrast, circulating levels of epinephrine in females were almost as high in the interval between copulatory bouts as they were during copulation.