The Effect of Umbellularia californica Essential Oil on Blood Vessel Diameter in Frogs

Plant essential oils contain many chemicals that are physiologically active in vertebrates. Terpenoids, which represent the largest category of these compounds, have been shown to lower blood pressure by reducing cardiac output and causing vasodilation. Most studies on the vasoactivity of terpenoids have been done on aortic rings and mesenteric artery preparations, and little is known about their effects on microvasculature. We applied Umbellularia californica essential oil, which contains several different terpenoids, to the cutaneous microvasculature of frogs and measured changes in blood vessel diameter. The U. californica oil caused a sustained, reversible vasoconstriction of these blood vessels, whereas no significant change in diameter was caused by medical grade sesame oil, which served as our control. The vasoconstriction we observed was therefore induced by compounds in the U. californica oil, many of which have previously been shown to cause vasodilation in arteries. Our results suggest that the vasoactive effects of terpenoids may differ across blood vessel types, and are more variable than previously thought. KEYWORDS: Cardiovascular; Terpenoid; Vasoactive; Arteriole; Secondary Metabolite; Vasoconstriction; Essential Oil; Microvasculature