A single injection of morphine to fight persistent pain in male rats is able to strongly reduce the hormone testosterone in the brain and plasma [...] The study, led by Anna Maria Aloisi, M.D., showed that opioids had “long lasting genomic effects in body areas which contribute to strong central and peripheral testosterone levels” including the brain, the liver and the testis.
The study showed increases in aromatase, an enzyme that is responsible for a key step in the biosynthesis of estrogen. The findings are particularly important since testosterone is the main substrate of aromatase, which is involved in the formation of estradiol. [...]
Opioid induced hypogonadism can cause health complications to which patients with pain can be overly susceptible, including chronic fatigue, loss of stamina, emotional and sexual disturbances, as well painful skeletal and muscular complications. [...]
“Until a few years ago this condition was completely unrecognized by physicians although some reports clearly showed it in many kinds of patients,” notes Dr. Aloisi. (via.)
This is interesting, because it’s also been demonstrated that chronically anxious rat phenotypes have fewer steroid receptors (testosterone being a steroid, of course) in their brains. Additionally, exercise was one of the only things capable of reversing this phenotype. Exercise causes a rush of endorphins after training, which activate the same receptors (mu opioid) as morphine.