[Different effects of testosterone on acute and chronic pain in gonadectomized male rats]

ABSTRACT

Nociception and behavioral responses to noxious stimuli are different in males and females. It seems that these differences are due to the effects of sex hormones on the pain mechanisms. The aim of the current study was to evaluate the effect of testosterone administration on nociception by formalin test in gonadectomized rats. In this study 32 male wistar rats were divided into four groups [n=8]; the control rats without receiving any drug or surgical operation, the sham - operated animals with surgical stress, the gonadectomized rats receiving 0.5 ml vehicle [olive oil] i.p., and the gonadectomized rats receiving testosterone enantate [6 mg/100 gr body weight in 0.5 ml vehicle i.p.]. On the sixth day after gonadectomy operation, formalin test was done in all rats. Pain scores in formalin test were statistically analyzed by SPSS and ANOVA. The results showed that testosterone caused an increase in pain score in acute phase of formalin test in gonadectomized rats compared with sham-operated group [p<0.001]. However, pain score in chronic phase was significantly reduced in testosterone received rats [p<0.001]. It can be concluded that testosterone increases nociception in acute phase of formalin test in gonadectomized rats. On the other hand, testosterone relieved pain during chronic phase. Anti-nociceptive effects of testosterone in chronic phase may be through central nervous system by interacting with endogenous pain modulatory systems