Predator induced stress and its analgesic potential on estrous and anestrus albino rats.

It has been established that physical stress induces antinociceptive effect. In the present study efforts were made to investigate the role of chronic intermittent psychological stress in the induction of the analgesic effect and the probable role of estrous cycle in modulating the antinociceptive response. Albino rats in regular estrous cycle (n = 15) and those in anestrus (n = 15) were exposed to psychological stress for a period of 20 min each day for 12 consecutive days. The predator (domestic cat) was used to induce the psychological stress. At the end of each session tail flick response time to heat was recorded as a measure of pain perception. It was observed that female estrous rats had a low pain threshold in the beginning but its tolerance increased gradually reaching a peak by 6th to 7th day and returned to control level by 11th day. The anestrus female had higher pain threshold at the beginning and showed a gradual decline to reach the control level as estrous females by 12th day. These results suggest that the ovarian hormones and the corticosterone may modulate the impact of stressor on endogenous pain inhibition and other stress responsive systems.