Sensitization of Arteries, Veins, and Small Vessels to Norepinephrine After Cocaine

• Cocaine augments the pressor effect of norepinephrine in dogs.1 It is not known whether this greater pressor effect is caused by a greater cardiac output or greater vascu-lar resistance or both. Macmillan's observa-tions on the perfused ear of rabbit suggest that norepinephrine causes a greater increase in vascular resistance after cocaine.2 The effect of norepinephrine on veins, arteries, and small vessels after cocaine has not been reported. Veins, arteries, and small vessels in-terpose independent resistances which con-tribute in varying degrees to total resistance/1 It is possible that a greater increase in total resistance to blood flow in response to the catecholamine may be caused by greater con-striction of only one of the vascular segments. If such selective sensitization occurred after cocaine it might have important physiologic and pharmacologic implications. The present experiments were done to meas-ure vascular responses to norepinepinine after cocaine and to determine whether changes in responses of veins, arteries, and small vessels in the perfused foreleg of dog were similar