Blocking alpha2A adrenoceptors, but not dopamine receptors, augments bupropion-induced hypophagia in rats.

Objective: Anti-obesity drugs have adverse effects which limit their use, creating a need for novel anti-obesity compounds. We studied effects of dopamine (DA) and norepinephrine (NE) reuptake inhibitor bupropion (BUP), alone and after blocking α1- or α2-adrenoceptors (AR), D1/5, D2/3, or D4 receptors, to determine which receptors act downstream of BUP.

Design And Methods: Effects on caloric intake, meal patterning and locomotion were assessed, using an automated weighing system and telemetry in male rats with 18-h access to Western Human style diet.

Results: BUP (30 mg/kg) induced hypophagia by reducing meal size and postponing meal initiation. WB4101 (α1-AR; 2 mg/kg) and imiloxan (α2B-AR; 5 mg/kg) attenuated BUP's effect on meal size, while WB4101 and BRL 44408 (α2A/D-AR; 2 mg/kg) counteracted effect on meal initiation. Atipamezole (α2-AR; 1 mg/kg) and imiloxan further postponed initiation of meals. SKF 83566 (D1/5; 0.3 mg/kg), raclopride (D2/3; 0.5 mg/kg) and to a lesser extent FAUC 213 (D4; 0.5 mg/kg), attenuated BUP-induced hypophagia. BUP stimulated locomotion, which was blocked by all antagonists, except FAUC 213 or BRL 44408.

Conclusions: Alpha1-, α2A/D- and α2B-ARs, and DA receptors underlie BUP's effects on size and initiation of meals, while blocking pre-synaptic α2-ARs enhanced BUP-induced hypophagia. An inverse agonist of (pre-synaptic) α2A-ARs could enhance BUP-induced anorexia and treat eating disorders and obesity.