The present study examines the effects of the diterpene ENT-pimara-8(14),15-dien-19-oic acid (PA) on rat thoracic aorta. PA (10(-5), 3 x 10(-5) and 10(-4) mol/l) caused concentration-dependent inhibition of phenylephrine (Phe)-induced contraction in either endothelium-intact or endothelium-denuded