Abstract
A new antihypertensive drug, 2-(2, 6-dichlorophenyl-l-amino)-imidazoline hydrochloride (ST-155) (1-5) which structurally resembles tolazoline has been reported to possess no adrenergic alpha-receptor blocking action as does tolazoline (1). Clinical trials show that ST-155 effectively reduces the blood pressure level of hypertensive patients who have not responded to any other antihypertensive drugs (2). Peripheral vascular resistance is decreased (2) and cardiac work is considerably reduced (4) in correspondence with the manifestation of a blood pressure fall in hypertensive patients.
Nayler et al. (6) have postulated that the beta-adrenergic mechanism is involved in the hypotensive action of ST-155 from results observed in dog heart-lung bypass preparations (7) in which the hypotensive action is blocked by propranolol and pentolinium. In the present experiments the mode of hypotensive actions of ST-155 was investigated more extensively on anesthetized rabbits, since this species always exhibited the marked and consistent depressor response to the drug. The results preclude the participation of the beta-adrenergic mechanism in hypotensive action. Actions of ST-155 on central and peripheral cardiovascular mechanisms were postulated to be responsible for its hypotensive action in anesthetized rabbits.
