Abstract

Approximately 75% of the endogenous norepinephrine content of rabbit thoracic aorta resides in the adventitia; the remainder resides in the media-intimal layers. Approximately 75 to 90% of the capacity of sortie strips to bind tritiated norepinephrine resides in the adventitia and is sensitive to inhibition by cocaine. The remaining capacity to bind norepinephrine resides in the media-intimal layers and is not sensitive to inhibition by cocaine. Sham removal of the adventitia does not significantly alter the responsiveness of aortic strips to norepinephrine or tyramine. Actual removal of the adventitia drastically reduces the responsiveness of strips to tyramine and moderately reduces their responsiveness to norepinephrine. It is concluded that removal of the adventitia effectively denervates rabbit aorta. It is further concluded that the localization of the innervation of the rabbit aorta within the adventitia makes it unlikely that the innervation can effectively limit the concentration of norepinephrine throughout the entire media. The failure of the strips from which the adventitia has been removed to become hyperresponsive to norepinephrine supports this latter conclusion.