NCIt definition : The mesylate salt of a synthetic imidazoline with alpha-adrenergic antagonist activity.
As a competitive alpha-adrenergic antagonist, phentolamine binds to alpha-1 and alpha-2
receptors, resulting in a decrease in peripheral vascular resistance and vasodilatation.
This agent also may block 5-hydroxytryptamine (5-HT) receptors and stimulate release
of histamine from mast cells.;