Behavioral effects and central nervous system levels of the broadly available κ-agonist hallucinogen salvinorin A are affected by P-glycoprotein modulation in vivo.
Active blood-brain barrier mechanisms, such as the major efflux transporter P-glycoprotein (mdr1), modulate the in vivocentral nervous system (CNS) effects of many pharmacological agents, whether they are used for nonmedical reasons or in pharmacotherapy. The powerful, widely available hallucinogen salvinorin A (from the plant Salvia divinorum) is a high-efficacy, selective κ-opioid agonist and displays fast-onset behavioral effects (e.g., within 1 min of administration) and relatively short duration of action. In vitro studies suggest that salvinorin A may be a P-glycoprotein substrate thus, the functional status of P-glycoprotein may influence the behavioral effects of salvinorin A or its residence in CNS after parenteral administration. We therefore studied whether a competing P-glycoprotein substrate (the clinically available agent loperamide 0.032-0.32 mgkg) or a selective P-glycoprotein blocker, tariquidar (0.32-3.2 mgkg) could enhance unconditioned behavioral effects (ptosis and facial relaxation, known to be caused by κ-agonists in nonhuman primates) of salvinorin A, as well as its entry and residence in the CNS, as measured by cerebrospinal fluid sampling. Pretreatment with either loperamide or tariquidar dose-dependently enhanced salvinorin A-induced ptosis, but not facial relaxation. In a control study, loperamide and tariquidar were inactive when given as a pretreatment to (()-(5α,7α,8β)-N-methyl-N-7-(1-pyrrolidinyl)-1-oxaspiro4.5dec-8-yl-benzeneacetamide (U69,593), a κ-agonist known to be a very poor P-glycoprotein substrate. Furthermore, pretreatment with tariquidar (3.2 mgkg) also enhanced peak levels of salvinorin A in cerebrospinal fluid after intravenous administration. These are the first studies in vivo showing the sensitivity of salvinorin A effects to modulation by the P-glycoprotein transporter, a major functional component of the blood-brain barrier.