Gender-specific and gonadectomy-specific effects upon swim analgesia: role of steroid replacement therapy.

Both gender-specific and gonadectomy-specific effects have been observed for the analgesic responses following continuous and intermittent cold-water swims (CCWS and ICWS respectively): female rats display significantly less analgesia than males, and gonadectomized rats display significantly less analgesia than sham-operated controls. The present study evaluated the effects of steroid replacement therapy with testosterone propionate (TP: 2 mg/kg, SC) upon CCWS and ICWS analgesia on the tail-flick and jump tests and hypothermia in sham-operated or gonadectomized male and female rats. Thirty days following surgery, rats received either no treatment, a sesame oil vehicle or TP for 14 days prior to, and then during testing. Relative to the no treatment condition, repeated vehicle injections in sham-operated rats eliminated the gender-specific, but did not affect the gonadectomy-specific effects upon CCWS and ICWS analgesia. TP reversed the deficits in CCWS and ICWS analgesia observed in both castrated and ovariectomized rats on both pain tests. TP only potentiated CCWS analgesia in sham-operated males on the tail-flick test. TP potentiated CCWS and ICWS hypothermia in gonadectomized rats and in male sham-operated rats. These data indicate that gonadal steroids play a major modulatory role in the etiology of swim analgesia, and that the observed gender effects are sensitive to possible adaptational variables.