October - December 2009, Volume 5, Issue 4

Ahmadi R, Oryan S

Sex difference and effects of gonadal hormones on thermal pain thershold in rat

Acta Endo (Buc) 2009, 5 (4): 437-445
doi: 10.4183/aeb.2009.437

Various clinical and experimental studies indicate that gonadal hormones exert\r\nmodulatory effects on nociception and analgesia.\r\nThe aim of the present study was to investigate the role of gonadal hormones in the\r\nresponse by male and female rats to thermal nociceptive stimulation.\r\nMaterials and Methods. 7 week old albino (Wistar) rats were used in our study.\r\nAnimals were randomly divided into control, sham and ovariectomised or orchidectomised\r\ngroups. Thermal pain threshold was measured through tail immersion test before and 10, 20\r\nor 40 days after gonadectomy. The pain threshold was measured as the time required to elicit\r\na flick of the tail called analgesia time. Serum testosterone, estradiol, progesterone or\r\nprolactin levels were measured simultaneously.\r\nThe results showed that analgesia time was higher in female (5.11 min) than in male\r\n(4.93 min) intact animals (p<0.05) indicating sex difference in response to thermal\r\nnociception. Serum testosterone, estradiol or progesterone level as well as analgesia time\r\nwere not significantly reduced 10 days after gondectomy. In male animals, analgesia time\r\nwas significantly decreased (p<0.01) 20 or 40 days after orchidectomy (2.25 or 2.14 min,\r\nrespectively) compared with control rats (4.93 min). Serum testosterone concentration was\r\nsignificantly reduced (p<0.05) 20 or 40 days after orchidectomy (0.08 or 0.09 ng/mL,\r\nrespectively) compared with control serum testosterone level (2.14 ng/mL). In female rats,\r\nanalgesia time was significantly decreased (p<0.001) 20 or 40 days after ovariectomy (2.87\r\nor 2.66 min, respectively) compared with control rats (5.11 min). Serum estradiol\r\nconcentration was significantly reduced (p<0.001) 20 or 40 days after ovariectomy (3.17 or\r\n0.87 ng/mL, respectively) compared with control serum estradiol level (19.95 ng/ml). Serum\r\nprogesterone level was also decreased (p<0.001) 20 or 40 days after orchidectomy (5.27 or\r\n0.55 ng/mL, respectively) compared with control serum estradiol level (17.66 ng/mL).\r\nSerum prolactin level was not significantly enhanced during experiment indicating that there\r\nwas not heat stress influencing the procedure.\r\nConclusively, our findings clearly indicate that depletion of gonadal hormones 20 or 40 days\r\nafter gonadectomy modulates the pain-induced behavioral responses related to thermal nociception.

Keywords: sex difference, gonadal hormones, thermal pain

Correspondence: Rahim Ahmadi, PhD, Islamic Azad University, Hamedan Branch, Hamedan, Iran. Phone: +98-9126120353; Fax: +98-8114290977. E-mail: rahahmadi2001@yahoo.com