Effects of estragole on the compound action potential of the rat sciatic nerve

Estragole, a relatively nontoxic terpenoid ether, is an important constituent of many essential oils with widespread applications in folk medicine and aromatherapy and known to have potent local anesthetic activity. We investigated the effects of estragole on the compound action potential (CAP) of the rat sciatic nerve. The experiments were carried out on sciatic nerves dissected from Wistar rats. Nerves, mounted in a moist chamber, were stimulated at a frequency of 0.2 Hz, with electric pulses of 50-100-micros duration at 10-20 V, and evoked CAP were monitored on an oscilloscope and recorded on a computer. CAP control parameters were: peak-to-peak amplitude (PPA), 9.9 +/- 0.55 mV (N = 15), conduction velocity, 92.2 +/- 4.36 m/s (N = 15), chronaxy, 45.6 +/- 3.74 micros (N = 5), and rheobase, 3.9 +/- 0.78 V (N = 5). Estragole induced a dose-dependent blockade of the CAP. At 0.6 mM, estragole had no demonstrable effect. At 2.0 and 6.0 mM estragole, PPA was significantly reduced at the end of 180-min exposure of the nerve to the drug to 85.6 +/- 3.96 and 13.04 +/- 1.80% of control, respectively. At 4.0 mM, estragole significantly altered PPA, conduction velocity, chronaxy, and rheobase (P < or = 0.05, ANOVA; N = 5) to 49.3 +/- 6.21 and 77.7 +/- 3.84, 125.9 +/- 10.43 and 116.7 +/- 4.59%, of control, respectively. All of these effects developed slowly and were reversible upon a 300-min wash-out. The data show that estragole dose-dependently blocks nerve excitability.