Structural relationships and vasorelaxant activity of monoterpenes

Contractions of the vessels were induced with 10？μM of phenylephine (Phe) in rings with endothelium. During the tonic phase of the contraction, the monoterpenes (10-8 - 10-3, cumulatively) were added to the organ bath. The extent of relaxation was expressed as the percentage of Phe-induced contraction.The results from the present study showed that both oxygenated terpenes (rotundifolone, (+)-limonene epoxide, pulegone epoxide, carvone epoxide, and (+)-pulegone) and non-oxygenated terpene ((+)-limonene) exhibit relaxation activity. The absence of an oxygenated molecular structure was not a critical requirement for the molecule to be bioactive. Also it was found that the position of ketone and epoxide groups in the monoterpene structures influence the vasorelaxant potency and efficacy.The results suggest that the presence of functional groups in the chemical structure of rotundifolone is not essential for its vasorelaxant activity.The essential oils are natural products extracted from species of aromatic plants and exhibit a variety of biological properties [1-6]. These effects are attributed mainly to the terpenes, which are the major chemical components of these oils. The cardiovascular activity of essential oils has been reported [7-10]. Some studies showed that the main chemical components of these oils are bioactive [7,10-12].The antihypertensive activity of some plants also has been related to the presence of terpenes. Extracts and diterpenoids of Salvia species have shown cardiovascular activity, such as ferruginol and 7-oxo-abieta-9,12,14-triene [13]. In another work, in normotensive anaesthetised rats, the cardiovascular effect of the essential oil of Mentha x villosa and its main constituent, rotundifolone, suggests that hypotensive activity may result from its vasodilatory effects directly upon vascular smooth muscle [11]. Additional studies showed that the hypotensive activity of the monoterpene rotundifolone is related to decrease in heart rate and periph