In Vivo Evidence for an Increase in 5alpha-Reductase Activity in the Rat Central Nervous System Following Morphine Exposure

The study investigated the effects of morphine on testosterone levels in rats, revealing that both acute and chronic morphine exposure significantly reduced testosterone in the serum and central nervous system (CNS), particularly in the spinal cord and brain. The reduction was more pronounced in the CNS, suggesting increased local metabolism rather than just peripheral decline. This was supported by the finding that finasteride, a 5alpha-reductase inhibitor, blocked testosterone elimination in the CNS after morphine exposure. Additionally, chronic morphine exposure increased serum levels of 5alpha-reduced testosterone metabolites, which was not observed with finasteride co-treatment. The study concluded that morphine exposure increased CNS 5alpha-reductase activity, a key enzyme in testosterone metabolism.