Dextrallorphan is often used in research to block σ1 receptor sites so that σ2 receptor sites can be studied. It was hypothesized that both of these sigma receptors were opioid receptors, due to their affinity for psychoactive drugs. However, it is now understood that they are non-opioid receptors that bind to certain psychoactive drugs, like dextrallorphan. One example of dextrallorphan being used to mask σ1 receptor sites was seen in a study on the localization of the σ2 receptor in detergent-resistant lipid raft domains. It has also been used to mask σ1 receptor sites so that σ2receptor binding characteristics in the rat liver could be determined, by labeling σ2 receptor sites with l,3-di-o-tolylguanidine in the presence of 1 μM dextrallorphan solution.
Dextrallorphan was used in Spraque-Dawley rats to study cerebellar Purkinje neurons electrophysical responses to the drug when it was applied iontophoretically as a sigma receptor ligand. Dextrallorphan increased the firing rate by 14%, suggesting that sigma ligands alter the spontaneous firing of Purkinje neurons and cause motor effects. In another study, dextrallorphan, along with other opioid derivatives, was found to be a potent inhibitor of etorphine-inaccessible sites in the guinea-pig brain. Dextrallorphan was of the top three most potent opioid inhibitors of those studied, with a concentration of 67 nM required to show 50% inhibition.
History
In 1955, dextrallorphan has been used to study inhibition of cholinesterase's and to look at the relationship between analgetics and acetylcholine metabolism. It was found that dextrallorphan inhibits 25% of bovine erythrocyte cholinesterase at a dose of 10−3 mole/liter, which corresponds to a concentration of up to 0.2 mg/kg in dog intestine. However, at this dose the drug showed no effect on the gut tone. Dextrallorphan was classified as a potent inhibitor of the intestinal and red blood cell cholinesterase based on the concentration of the drug needed to inhibit these enzymes in the cholinesterase preparations from the animals systems utilized. Simultaneously, dextrallorphan showed no analgesia and no change in intestinal tone. With these results dextrallorphan helped proved that there is no correlation between the inhibition of cholinesterase systems and analgetic or intestinal effects. In 1979, dextrallorphan was found to have a half maximal inhibitory concentration for binding to the pituitary and brain receptor of 10,000 ± 1000 nM and 10,000 ± 1500 nM, respectively. While its stereoisomer, levallorphan, had a 10,000 times more potent dose, thus proving that binding to these receptors is stereospecific.
