Trimetoquinol (TMQ) and its analogs are known to have thromboxane A₂ antagonistic action. We also reported that GS389, chemically similar to TMQ, has competitive antagonistic action in rat aorta and human platelets. In the present study, we investigated the pharmacological characteristics of GS283 and GS386, analogs of GS389, using vascular smooth muscle, human platelets and rat brain homogenates. In isolated pig coronary artery (PCA), both of GS283 and GS386 relaxed U46619-contracted rings in concentration dependent manner. Pretreatment with several concentrations of GS283 and GS386 shifted the dose-response curves to the right, and reduced of maximum contration dose-dependently. Furthermore, GS283 and GS386 strongly inhibited Ca^(2+)-induced contraction in the PCA. In human platelets, U46619- and A23187-induced platelet aggregation was inhibited by GS283 and GS386, concentration-dependently. Anti-platelet aggregation was related to the compound`s ability to inhibit ATP release at each stimulation. In rat brain homogenates, receptor-binding assay resulted that both GS283 and GS386 have a relative affinity to α-adrenergic receptor. Taken together, we concluded that the mechamism of action of GS283 and GS386 is not related with in TXA₂ receptor but concerned with calcium antagonistic action and α-blocking action.