Antidepressants given repeatedly increase the alpha 1-adrenoceptor agonist affinity in the rat brain.

Several different antidepressant drugs (AD): imipramine, amitriptyline, citalopram and mianserin were administered to rats at a dose of 10 mg/kg po, twice daily for 14 days. The competition studies showed that AD used enhanced the ability of alpha 1-agonist phenylephrine to inhibit the binding of [3H]-prazosin to its receptors (Ki values being decreased) in the cerebral cortex, thalamus and hippocampus. The present results show that the increase in the affinity of alpha 1-adrenoceptors for their agonist is responsible for the functional alpha 1-adrenergic hypersensitivity found after repeated treatment with different AD.