A comparison of the binding of nicotine and nornicotine stereoisomers to nicotinic binding sites in rat brain cortex.

Naunyn-Schmiedeberg's archives of pharmacology

PubMedID: 2067586

Copeland JR, Adem A, Jacob P, Nordberg A. A comparison of the binding of nicotine and nornicotine stereoisomers to nicotinic binding sites in rat brain cortex. Naunyn Schmiedebergs Arch Pharmacol. 1991;343(2):123-7.
Both stereoisomers of nicotine and nornicotine were tested for their ability to competitively displace 3H-(-)-nicotine and 3H-acetylcholine (in the presence of atropine), in rat cortex tissue. 3H-acetylcholine was displaced from two binding sites, super-high and high, by (+)-nicotine, (-)-nornicotine and (+)-nornicotine but from a high affinity site by (-)-nicotine. 3H-nicotine was displaced from two sites, high and low affinity by nicotine and nornicotine stereoisomers. The high-affinity 3H-(-)-nicotine binding site showed similar binding characteristics to one of the sites labelled by 3H-acetylcholine. IC50 values showed (-)-nicotine to be 13 and 25-fold more potent than (+)-nicotine for displacing 3H-(-)-nicotine and 3H-acetylcholine, respectively, but no difference was observed for nornicotine stereoisomers. While (-)-nicotine preferentially bound to the high affinity site of 3H-(-)-nicotine (+)-nicotine preferred the low affinity site. The study provides further evidence for multiple nicotine receptors in brain.