Effects of reserpinization, surgical denervation and in vitro chemical denervation with 6-hydroxydopamine on the contractile response of isolated rabbit ear artery to propranolol.

The contractile effect of propranolol in isolated rabbit ear artery was assessed in reserpinized and in surgically and chemically denervated blood vessels. Reserpinization and surgical denervation either had no effect on or enhanced the ear artery contractile response to 10(-6) to 10(-4) M propranolol. In contrast, the contractile response to propranolol was nearly abolished after denervation of the ear artery in vitro with 6-hydroxydopamine (6-OHDA). Dose-response curves to norepinephrine were shifted to the left by factors of 4.9 in 6-OHDA denervated ear arteries and 15.6 in untreated arteries in the presence of 10(-7) M desipramine. The diluent for 6-OHDA shifted both the norepinephrine and propranolol dose-response curves to the right. It is proposed that propranolol caused a contractile response in ear artery by an action on the postsynaptic tissues of this vessel. 6-OHDA denervation caused nonspecific desensitization in rabbit ear artery leading to the loss of response of this vessel to propranolol.