Aim: 

Testosterone is a steroid hormone produced mainly by the gonads, which acts throughout the body and in the brain. We have already shown in vivo, in male rats and in vitro, in C6 rat glioma cells, that the administration of a single dose of morphine results in a decrease of testosterone levels in the blood and in the brain of animals and in the cells probably trough the morphine-induced increase of the aromatase actvity.However opioids are used to treat pain and pain need to be considered as variable.

Methods: 

Thus, in this experiment, the morphine modulation of testosterone levels was analyzed in rats subjected to the formalin test (50 ul, 10%) 3-hr after morphine injection. Morphine serum levels were determined by LC-MS-MS. Testosterone blood and brain levels were determined by radioimmunoassay.

Results: 

The formalin-induced behavioral responses (licking and paw jerk) were decreased in rats treated with morphine with respect the saline group. LC-MS-MS analysis of morphine serum levels showed no significant differences between MF sham and MF form groups. Morphine administration determined a decrease of testosterone serum and brain levels, independently on formalin injection, while in saline-treated animals testosterone shows a tendency to lower levels in formalin treated animals than in the sham one's in both blood and brain.

Conclusion: 

our findings show that morphine treatment decreases testosterone levels independent on pain; moreover pain per se appears to be able to affect testosterone blood and brain levels.