effect of food deprivation on formalin-induced nociceptive behaviors and beta-endorphin and sex hormones concentration in rats

background: the present study examined the possible role of endogenous opioidergic system in effect of food deprivation on formalin-induced nociceptive behaviors in male and female rats. also, we investigated the effect of food deprivation on the plasma level of beta-endorphin and sex hormones. methods: food was withdrawn 48 h prior to performing the formalin test, but water continued to be available ad libitum. the formalin was injected into hind plantar paw. results: there is significant difference between male and female control rats during phase 2b. following 48-h food deprivation, both male and female rats exhibited enhanced nociceptive behavior in response to formalin. food deprivation for 12 and 24 h increased and for 48 h decreased beta-endorphin level in male and female rats. food deprivation for 24 h decreased testosterone level in male, while it had no significant effect on female rats and food deprivation for 48 h decreased testosterone level in both sexes. food deprivation for 24 h increased estradiol level in female and that for 48 h had no significant effect on male and female rats. conclusions: the present study demonstrates the existence of food deprivation for 48 h causes enhancement of nociception in the formalin test in male and female rats that has correlation with decrease in plasma beta-endorphin and testosterone levels.