The effect of swimming-stress on tail-flick latency of normal and hypophysectomized rats.

The effect of swimming-stress on pain threshold was investigated in normal and hypophysectomized male rats of Long-Evans strain. The Tail-Flick Latency (TFL) was taken for determining the algesic sensitivity to noxious heat stimulation of the tail. The present study has shown that swimming-stress could prolong the TFL to thermal tail stimulation. In 15 intact control rats, the TFL were prolonged from 2.47 +/- 0.07 (Mean +/- S.E.) to 3.81 +/- 0.21 sec. In 10 sham-operated and 10 hypophysectomized rats, the TFL were also prolonged from 3.10 +/- 0.25 to 4.37 +/- 0.35 and 3.59 +/- 0.09 to 4.50 +/- 0.13 sec respectively after a 3 min swim. Therefore, the hypophysectomy did not appear to modulate the analgesic effect induced by swimming-stress. These experimental data implied that the hypophysis may not be important in the analgesic effect induced by the swimming-stress.