ESSENTIAL OIL OF CROTON NEPETAEFOLIUS AND ITS MAIN CONSTITUENT, 1,8-CINEOLE, BLOCK EXCITABILITY OF RAT SCIATIC NERVE IN VITRO
SUMMARY
- 1
The effects of the essential oil of Croton nepetaefolius (EOCN) and its major constituent, 1,8-cineole, on the compound action potential (CAP) of nerve were investigated.
- 2
Experiments were performed in sciatic nerves dissected from Wistar rats, mounted in a moist chamber and stimulated at a frequency of 0.2 Hz, with electric pulses of 100 µs duration at 20–40 V. Evoked CAP were displayed on an oscilloscope and recorded on a computer. The CAP control parameters were as follows: peak-to-peak amplitude 8.1 ± 0.6 mV (n = 15); conduction velocity 83.3 ± 4.2 m/s (n = 15); chronaxie 58.0 ± 6.8 msec (n = 6); and rheobase 2.8 ± 0.1 V (n = 6).
- 3
Lower concentrations of EOCN (100 and 300 µg/mL) and 1,8-cineole (153 and 307 µg/mL; i.e. 1 and 2 mmol/L, respectively) had no significant effects on CAP control parameters throughout the entire recording period. However, at the end of 180 min exposure of the nerve to the drug, peak-to-peak amplitude was significantly (P < 0.05) reduced to 27.4 ± 6.7 and 1.7 ± 0.8% of control values by 500 and 1000 µg/mL EOCN, respectively (n = 6), and to 76.5 ± 4.4, 70.0 ± 3.9 and 14.8 ± 4.1% of control values by 614, 920 and 1227 µg/mL (i.e. 4, 6 and 8 mmol/L) 1,8-cineole, respectively (n = 6). Regarding conduction velocity, at the end of the 180 min exposure period, this parameter was significantly reduced to 85.8 ± 7.3 and 48.7 ± 12.3% (n = 6) of control values by 500 and 1000 µg/mL EOCN, respectively, and to 86.4 ± 4.5 and 76.1 ± 5.2% (n = 6) by 920 and 1227 µg/mL 1,8-cineole, respectively. Chronaxie and rheobase were significantly increased by the higher concentrations of both EOCN and 1,8-cineole.
- 4
It is concluded that EOCN and its main constituent 1,8-cineole block nerve excitability in a concentration-dependent manner, an effect that was totally reversible with 1,8-cineole but not with EOCN. This suggests that other constituents of EOCN, in addition to 1,8-cineole, may contribute to the mediation of this effect of EOCN.
