Time course of the development of pre- and postjunctional supersensitivity in the rabbit ear artery after decentralization.

Changes in the sensitivity of the rabbit ear artery to exogenous norepinephrine and potassium and to sympathetic nerve electrical stimulation were examined in vitro following decentralization which was performed by removing the unilateral preganglionic nerve proximal to the superior cervical ganglion. The contralateral side was left intact as a control. The postjunctional supersensitivity to exogenous norepinephrine and potassium had fully developed one week after the decentralization and was sustained for at least 8 weeks; the arteries decentralized for 1-8 weeks were about 2.1- and 1.3-fold supersensitive to norepinephrine and potassium, respectively, as compared with the contralateral control arteries. The frequency-response curve of the electrically stimulated decentralized artery shifted gradually to the left of the control within weeks after decentralization. Since the response to electrical stimulation was attributed to endogenous norepinephrine released from the sympathetic nerve terminals within the adventitial-medial junction, the leftward shift of the frequency-response curve in the decentralized artery probably reflects a gradual increase in the released norepinephrine per pulse by electrical stimulation, i.e., the prejunctional supersensitivity to electrical stimulation. It is concluded that the prejunctional sympathetic supersensitivity to electrical stimulation develops slower than the postjunctional nonspecific supersensitivity in the rabbit ear artery. The change in the sensitivity of the denervated postganglionic neuron, including the superior cervical ganglion is also discussed with regard to the "law of denervation supersensitivity".