“… [3H]idazoxan … guanidines with the following rank order of potency which conforms to the characteristics of the previously defined I2-IBS (in parentheses: Ki, nmol/l): …-ylamino) isoindoline) > BDF 6100 (563; 2-(2-imidazolin-2-ylamino)-isoindoline) ≥ BDF 7579 (868; (4-chloro-2-isoindolinyl)guanidine) > phentolamine (1424) = naphazoline (1451).”