Biochemical effects of the antidepressant paroxetine, a specific 5-hydroxytryptamine uptake inhibitor.
Paroxetine was shown to be a potent (Ki = 1.1 nM) and specific inhibitor of [3H]-5-hydroxytryptamine (5-HT) uptake into rat cortical and hypothalamic synaptosomes in vitro. Lineweaver-Burk kinetic analysis determined that this inhibition was competitive in nature, implying a direct interaction with the 5-HT uptake transporter complex. Oral administration of paroxetine produced a dose-related inhibition of [3H]-5-HT uptake (ED50 = 1.9 mg/kg) into rat hypothalamic synaptosomes ex vivo with little effect on [3H]-l-noradrenaline (NA) uptake (ED50 greater than 30 mg/kg). This selectivity for 5-HT uptake was maintained after oral dosing for 14 days. Paroxetine (ED50 1-3 mg/kg PO) prevented the 5-HT depleting effect of p-chloroamphetamine (PCA) in rat brain, demonstrating 5-HT uptake blockade in vivo. Radioligand binding techniques in rat brain in vitro showed that paroxetine has little affinity for alpha 1, alpha 2 or beta adrenoceptors, dopamine (D2), 5-HT1, 5-HT2 or histamine (H1) receptors at concentrations below 1000 nM. Paroxetine demonstrated weak affinity for muscarinic receptors (Ki = 89 nM) but was at least 15 fold weaker than amitriptyline (Ki = 5.1 nM). Paroxetine, therefore, provides a useful pharmacological tool for investigating 5-HT systems and furthermore should be an antidepressant with reduced tricyclic-like side-effects.
D000818:Animals; D000928:Antidepressive Agents / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009638:Norepinephrine / Q000378:metabolism; D017374:Paroxetine; D010880:Piperidines / Q000494:pharmacology*; D051381:Rats; D012701:Serotonin / Q000378:metabolism*; D012702:Serotonin Antagonists / Q000494:pharmacology; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism; D010133:p-Chloroamphetamine / Q000494:pharmacology
D000928:Antidepressive Agents; D010880:Piperidines; D012702:Serotonin Antagonists; D012701:Serotonin; D017374:Paroxetine; D010133:p-Chloroamphetamine; D009638:Norepinephrine