Ethanol inhibits the binding of substance P to rat brain cortex NK1 receptors

The binding of 125I-labeled substance P (SP) to rat brain cortex membranes has been studied under control conditions and in the presence of ethanol. The binding of SP at low concentrations (20-1000 pM) gave two components, one with a KD value of 80 pM and another one with a KD of 500 pM. The higher-affinity component is due to NK1 receptors, as confirmed by the inhibition of the SP binding by the rodent NK1 specific agonist [Sar9 Met(O2)11]SP. Ethanol (1.7 mM) added to the binding assays inhibited by more than 50% the specific binding at a very low SP concentration (20 pM); however, it had no effect at SP concentrations ranging from 50 to 120 pM. This suggests a decrease by ethanol of the affinity of SP to the NK1 receptors involved in this binding component. The ethanol effect disappeared at [EtOH] < or = 0.17 mM.