Abstract
Concomitant treatment with phentolamine, an α-blocker, or with propranolol, a β-blocker, suppressed the development of morphine tolerance in shamoperated (Sham) mice. In adrenalectomized (ADX) mice, daily morphine developed tolerance as well as in the Sham group, and concurrent phentolamine suppressed the development of tolerance, whereas such suppression by propranolol was abolished. Supplemental treatment of ADX mice with dexamethasone did not restore the suppressive effect of propranolol. These results suggest that defferent mechanisms underlie the prevention of tolerance development by α- and β-blockers, and that adrenal cortex does not seem to participate in the suppression by β-blockers.
