The potential of
mitragynine to produce physiological dependence (withdrawal) was assessed using a rapid assessment procedure with male ICR mice exposed to
heroin-admixed food followed by
naloxone (subcutaneously, s.c.) precipitation of withdrawal. Initial studies indicated that 3 days of exposure to 3.0 mg/g of
heroin-admixed food followed by
naloxone (0.6 mg/kg) reliably precipitated withdrawal jumping and
weight loss. Lower concentrations of
heroin-admixed food and lower doses of
naloxone produced fewer withdrawal signs. A longer exposure to
heroin-admixed food did not produce significantly greater amounts of jumping or
weight loss. Further, these withdrawal signs were dose-dependently reversed by s.c. administration of
heroin immediately following
naloxone administration.
Mitragynine (s.c.) also dose-dependently suppressed
naloxone-precipitated withdrawal signs. Additionally, both jumping and
weight loss were suppressed over a comparable range of
mitragynine doses when administered by gavage with a noticeably, but not significantly, higher potency than with s.c. administration. The ED50 values for
mitragynine for the suppression of withdrawal by any route (354-911 μmol/kg) were greater than the minimally effective dose that decreased locomotor activity (251 μmol/kg) and from 40- to 104-fold greater than those for
heroin. The results suggest inherent
opioid dependence liability of
mitragynine. The in vivo potency relations between
mitragynine and
heroin are consistent with a conclusion of dependence-producing effects, indicated by the suppression of withdrawal, comparable to standard
opioid μ-receptor agonists, differing primarily in terms of potency. The present paper provides a method for the rapid assessment of physiological dependence liability applicable to other kratom plant constituents or any potential
opioid dependence-producing agents.