LOCALIZATION OF HYPOTENSIVE EFFECT OF 2-(2-6-DICHLOROPHENYLAMINO)-2-IMIDAZOLINE HYDROCHLORIDE (ST-155 CATAPRESAN)

Transection experiments and injection into the cerebral cavities were carried out in order to localize the site of action of St 155 in dogs and cats. Intercollicular decerebration and transection of the brain stem above the medulla oblongata did not change the bradycardia and hypertension followed by hypotension caused by St 155 nor was the reduction of the sympathetic discharges brought about by the drug affected. In contrast, transection of the spinal cord at C1 level lowered blood pressure, abolished splanchnic discharges and suppressed the hypotensive effect of St 155. It is concluded that the medulla oblongata is the main site of the hypotensive and bradycardic actions of St 155. Low doses of St 155 injected into the cisterna magna or into the cerebral ventricle, lowered blood pressure, heart rate and reduced sympathetic discharges, but after a long latency period which precluded any conclusion about the localization of the site of action. It is suggested that this long latency period was due to the slow passage of the drug from the cerebro spinal fluid into the nervous tissue. Thus the central action of St 155 was confirmed and the medulla oblongata was found to be the main site of this action. © 1969.