The response to analgesia testing is affected by gonadal steroids in the rat.

The effect of gonadal steroids on the response to analgesia testing was determined in castrated male and female rats and castrated male and female rats treated with testosterone propionate (TP) and estradiol benzoate (EB), respectively. The time to respond to a noxious somatic stimulus in the form of heat was assessed using the tail withdrawal test (tail withdrawal from hot water) and hot plate test (the time to paw lick or jump). In male rats, castration resulted in a significant reduction of the reaction time for tail withdrawal. This effect was reversed by treatment with TP. The time to paw lick or jump in male rats was also diminished by castration. Treatment with TP resulted in a partial reversal of the effect of castration on this response. In castrated female rats, the time required for tail withdrawal was decreased by castration and increased by treatment with EB. The reaction time to the hot plate in female rats was diminished by castration and further reduced by EB administration. These data indicate that gonadal steroids influence the response to a noxious heat stimulus in male and female rats and that the effect may vary according to sex and the way in which the stimulus is applied.