Platelet alpha 2-adrenergic receptor binding and the effects of d-amphetamine in boys with attention deficit hyperactivity disorder.

Presynaptic inhibitory alpha-adrenergic receptors are involved in regulating the release of norepinephrine (NE) through a negative feedback mechanism mediated by NE. Increased alpha2-adrenergic receptor activity suggests decrease NE release and activity, while decreased alpha2-adrenergic activity suggests increase NE release and activity. A large body of evidence suggests the involvement of a disturbance in NE activity in the pathophysiology of attention deficit hyperactivity disorder (ADHD) in childhood. Platelet alpha2-adrenergic receptor binding was compared in 23 boys aged 7-12 with the diagnosis of ADHD and 11 normal controls. The ADHD boys tended to have lower levels of alpha2-binding than controls. The administration of d-amphetamine in a double-blind placebo-controlled crossover design did not have any effect on alpha2-receptor binding in ADHD boys. Nonresponders to d-amphetamine had the lowest alpha2-receptor binding compared to responders and controls. These findings suggest a normal alpha2-adrenergic activity in ADHD boys responders to d-amphetamine and a possible increase in NE release in ADHD boys nonresponders to d-amphetamine due to decreased alpha2-adrenergic receptors.