Vasorelaxation induced by (-)-α-Bisabolol in rat aorta is preferential to voltage-operated contractile pathways
(-)-α-Bisabolol (BIS) is a sesquiterpene alcohol found in the essential oil of Matricaria chamomilla L. Here, we investigated the underlying mechanism involved in its vasodilator effects. Ring-like preparations obtained from rat aorta were maintained in bath chambers for isometric trace recordings. BIS (1–1000µM) more preferentially relaxed K+ (60 mM)- than phenylephrine (PHE, 1µM)-induced contractions, as evidenced by the IC50 values (24.9 [17.0–36.5] µM (n=8) and 162.0 [91.0–288.2] (n=7), respectively). Potency of BIS for relaxing PHE contractions was not changed by L-NAME, ODQ, TEA, glybenclamide or indomethacin pretreatment. BIS did not reduce phasic contractions induced by caffeine or by PHE under Ca2+-free conditions. It did not alter contractions induced by Ca2+ restoration outside the cell after cyclopiazonic acid treatment. In presence of BIS (100µM), the contraction induced by Ca2+ (3 mM) corresponded to 73.3±5.7% (expressed as % of an initial reference response induced by 60 mM K+) when PHE was the contractile agent in presence of nifedipine, a value which was significantly higher (p<0.05) than that (16.0±2.1%) observed when the contractile agent was a depolarizing solution with a high K+ (60 mM) content. Simultaneous measurement by confocal microscopy in Fura-4 AM-loaded vessels showed that BIS (100µM) reduced intracellular Ca2+ levels in response to K+. Thus, BIS has a vasodilator property in rat aorta acting preferentially against electromechanical pathways.