We previously reported that isolated perfused hearts from streptozotocin (STZ)-induced diabetic rats exhibited increases in the sensitivity of the coronary vasoconstriction induced by acetylcholine (ACh) infusion (versus age-matched controls) (Kamata et al., 2008). Here, we examined the ACh-induced coronary vasoconstriction in perfused hearts taken from Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a type 2 diabetes model, at the chronic stage of diabetes (38-40 weeks old). The ACh-induced vasoconstriction was greatly enhanced in such rats [versus age-matched control Long-Evans Tokushima Otsuka (LETO) rats]. This enhancement was improved by the chronic administration of the angiotensin II type I receptor (AT(1)-receptor) antagonist losartan (25 mg kg(-1), p.o., for 4 weeks). Further, the enhancement of the ACh-induced vasoconstriction seen in the OLETF group was suppressed by tempol, a superoxide dismutase mimetic. These results suggest that the coronary artery contractile response to ACh is enhanced in type 2 diabetic OLETF rats, and that this enhancement may be attributable to increased AT(1) receptor-mediating signaling and/or to increased oxidative stress.