Effect of oestradiol replacement on swim-induced antinociception in ovariectomized mice

1. A 30 s swim in water at 30 degrees C reduced the number of abdominal constrictions produced in female mice by intraperitoneally administered acetic acid and this antinociceptive effect was antagonized by naloxone. 2. Oophorectomy abolished the development of antinociceptive activity in response to swim. 3. The development of antinociceptive activity and naloxone antagonism were restored in oophorectomized mice maintained on daily oestradiol injection. 4. The present study indicates that the increase in abdominal constriction response to acetic acid in oophorectomized mice was due to the removal of the source of female sex hormone.