(+)-T-Cadinol is a sesquiterpene with smooth muscle relaxing properties. In the isolated rat aorta, T-cadinol relaxed contractions induced by 60 mM K+ in a concentration-dependent fashion. The dihydropyridine calcium antagonist nimodipine was approximately 4,000 times more potent than T-cadinol. While both drugs nearly abolished the K(+)-induced contractions, they only partially relaxed contractions induced by phenylephrine. The relaxation induced by T-cadinol and nimodipine in K(+)-contracted aortic rings, was completely reversed by the calcium channel activator Bay K8644. In aortic preparations partially depolarized by 20 mM K+, Bay K8644 induced a concentration-dependent contraction. Nimodipine shifted the Bay K8644 concentration-response curve to the right in a parallel manner, consistent with a competitive mode of inhibition. T-cadinol at concentrations less than 10(-3.5) M also produced a right-ward shift of the Bay K8644 concentration-response curve with a maintained maximum response. However, the highest T-cadinol concentration used 10(-3.5 M) significantly reduced the maximum response. In conclusion, although T-cadinol and nimodipine display marked structural differences, their pharmacological profiles of action have several features in common, suggesting that T-cadinol is a calcium antagonist, possibly interacting with the dihydropyridine binding sites on the calcium channels.