Figure 6. Competition for [sup 3 Hydrogen] prazosin binding by phentolamine and selected neuroleptics. Various concentrations of chlorpromazine (closed triangle), haloperidol (closed square), phentolamine (open circle), trifluoperazine (open triangle), and imipramine (closed circle) were incubated with aortic membranes and [sup 3 Hydrogen] prazosin (0.1 nM) for 30 min at 25 degrees Celsius. The values are the means plus/minus SE of 3-5 experiments determined in duplicate or triplicate, from 3-5 different preparations of membranes. On the vertical axis, the data are expressed as percentage of control-specific [sup 3 Hydrogen] prazosin binding.