High‐ and Low‐Affinity Binding of [3H]Imipramine in Rat Hypothalamus

Abstract

In the rat hypothalamus [³H]imipramine binding is inhibited by tricyclic and nontricyclic antidepressant drugs in a complex manner, with biphasic curves and Hill coefficients 3H]-imipramine binding sites as the [³H]imipramine concentration was raised. In the absence of sodium ions, IC₅₀ values for the inhibition by tricyclic and nontricyclic antidepressants were increased by approximately 1,000-fold, and the inhibition curves became classically monophasic with Hill coefficients close to 1.0. These data are interpreted as suggesting that [³H]imipramine binds to two independent sites in the rat hypothalamus. One site is sodium-dependent with a high affinity for the drugs tested; the other is sodium-independent and has a low affinity for these drugs.