4-Aminopyridine Reversal of Sympathetic Ganglionic Blockade in the Anesthetized Cat

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Abstract
The effects of 4-aminopyridine [4-AP] on the blockades of transmission of the superior cervical ganglion produced by hexamethonium [HM], d-tubocurarine [d-TC], and polymyxin B [PM-B] were investigated in 15 anesthetized cats. Isometric contractions of the nictitating membrane resulting from pre- and postganglionic stimulation were quantified. A 75-85% ganglionic blockade produced by HM, 3 mg/kg, or by d-TC, 1.0 to 1.2 mg/kg, was completely reversed by 4-AP, 1 mg/kg. After injection of 4-AP the times required for the contractions of the nictitating membrane to increase from 25 to 75% of control with preganglionic stimulation were 6 .+-. 3 (mean .+-. SEM) and 7 .+-. 2 min for HM and d-TC, respectively. Both values are significantly shorter than their respective control spontaneous recovery times of 26 .+-. 8 and 25 .+-. 7 min. PM-B, 20-35 mg/kg, depressed the contractions of the nictitating membrane resulting from pre- and postganglionic stimulation by 84 .+-. 2 and 66 .+-. 10%, respectively. 4-AP, 1 mg/kg, lessened the PM-B-induced depression of the contractions of the nictitating membrane resulting from preganglionic stimulation to 50 .+-. 13%, but had less effect, 61 .+-. 13%, on the contractions resulting from postganglionic stimulation. Apparently 4-aminopyridine rapidly and completely reverses the sympathetic ganglion blockade produced by HM or d-TC, and is partially effective in the reversal of the autonomic effects of PM-B.

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