Temporal variation of chemical composition and relaxant action of the essential oil of Ocimum gratissimum L. (Labiatae) on guinea-pig ileum

The medicinal plant Ocimum gratissimum L. (Labiatae) is widely encountered in the Northeast of Brasil where it is used to treat digestive problems. Its leaves have an essential oil (EOOG) content whose chemical composition varies according to the time of plant collection. We have compared the effects of the EOOG, collected at 08:00 a.m. (EOOG(8)) and at 12:00 a.m. (EOOG(12)), on the relaxation of guinea-pig isolated ileum. Both EOOG(8) and EOOG(12) (30-300 mu g/ml) reversibly relaxed the spontaneous tonus of the guinea-pig ileum in a concentration-dependent manner, with similar IC50 values (49.3 and 23.8 mu g/ml, respectively). The magnitude of the decrease in resting tonus was similar to that of the recognised smooth muscle relaxant papaverine. EOOG(8) and EOOG(12) relaxed 60 mM KCl-precontracted preparations similarly (38.33 +/- 9.91 mu g/ml and 35.53 +/- 6.70), whereas a significantly more potent relaxant effect of EOOG(12) compared to EOOG(8) was observed when tissues were contracted using 10 mu M acetylcholine (IC50 values of 69.55 +/- 4.93 and 128.16 +/- 15.70 mu g/ml, respectively; p < 0.05). The principal constituents of the essential oil, eugenol and cineole, also relaxed KCI-precontracted preparations, although they were less potent than EOOG, suggesting that they alone were not responsible for EOOG-induced relaxations. Our results show that the essential oil extracted from the leaves of O. gratissimum L., collected at different time periods, exerts significant relaxant effects on isolated guinea-pig ileum which may underlie the therapeutic action of the plant. (c) 2005 Elsevier GmbH. All rights reserved.