4-Aminopyridine reversal of sympathetic ganglionic blockade in the anesthetized cat.

The effects of 4-aminopyridine on the blockades of transmission of the superior cervical ganglion produced by hexamethonium, d-tubocurarine, and polymyxin B were investigated in 15 anesthetized cats. Isometric contractions of the nictitating membrane resulting from pre- and postganglionic stimulation were quantified. A 75-85 per cent ganglionic blockade produced by hexamethonium, 3 mg/kg, or by d-tubocurarine, 1.0 to 1.2 mg/kg, was completely reversed by 4-aminopyridine, 1 mg/kg. After injection of 4-aminopyridine, the times required for the contractions of the nictitating membrane to increase from 25 to 75 per cent of control with preganglionic stimulation were 6 +/- 3 (mean +/- SEM) and 7 +/- 2 min for hexamethonium and d-tubocurarine, respectively. Both values are significantly (P less than 0.05) shorter than their respective control spontaneous recovery times of 26 +/- 8 and 25 +/- 7 min. Polymyxin B, 20-35 mg/kg, depressed the contractions of the nictitating membrane resulting from pre- and postganglionic stimulation by 84 +/- 2 and 66 +/- 10 per cent, respectively. 4-Aminopyridine, 1 mg/kg, lessened the polymyxin B-induced depression of the contractions of the nictitating membrane resulting from preganglionic stimulation to 50 +/- 13 per cent, but had less effect, 61 +/- 13 per cent, on the contractions resulting from postganglionic stimulation. It is concluded that 4-aminopyridine rapidly and completely reverses the sympathetic ganglion blackade produced by hexamethonium or d-tubocurarine, and is partially effective in the reversal of the autonomic effects of polymyxin B.