THE RESPONSE OF RABBIT VASCULAR TISSUE TO ELECTRICAL AND DRUG STIMULATION

¹ Department of Pharmacology, University of Alberta, Edmonton, Canada, and Laboratory of Psychopharmacology, Yale University School of Medicine, New Haven, Connecticut

The secondary contraction of isolated rabbit aorta and carotid artery preparations, which normally follows the cessation of electrical stimulation, has been shown to be blocked by pretreatment of the animals with 2 mg of reserpine per kg, given intravenously either 24, 4 or 2 hours before removal of the vascular tissues. At each time of pretreatment, this dose of reserpine significantly reduced the amount of catecholamines present in the carotid artery. The lowering of the mean concentration of catecholamine in the aorta was statistically significant, however, only when reserpine was given 2 or 4 hours before excision of the tissue. Attempts to restore the response to normal by the addition of norepinephrine, epinephrine or dopamine to the bathing medium or by the administration of norepinephrine or dopamine before sacrifice were unsuccessful. The secondary response to electrical stimulation of tissue from untreated animals was reversibly blocked by either piperoxan or bretylium. These observations can be explained by assuming, with Furchgott (1952), that the secondary contraction is attributable to the liberation of catecholamine from the vessel wall. Isolated aorta from reserpine-treated rabbits showed a 30-fold increase in sensitivity to a range of concentrations of both norepinephrine and epinephrine.