What role do kappa receptors hold in butorphanol's mechanism of action?

Butorphanol is a mixed opioid agonist-antagonist that interacts with various opioid receptors, including kappa receptors. In its mechanism of action, butorphanol acts primarily as an agonist at kappa receptors. This action leads to several analgesic effects while also contributing to a ceiling effect on respiratory depression, which can be an advantageous pharmacological property compared to pure opioid agonists.

The option indicating that kappa receptors are antagonized is indeed correct in the context that while butorphanol stimulates kappa receptors to provide analgesia, it has an antagonistic effect on mu receptors at higher doses. This antagonism helps mitigate some of the side effects typically associated with mu receptor activation, such as severe respiratory depression.

Kappa receptors play a crucial role in butorphanol’s profile by providing effective pain relief without the full risk of respiratory depression observed with full mu agonists, and that's why understanding their function is essential in appreciating butorphanol's therapeutic use in pain management.