We investigated the impairment of KATP channels in aortic smooth muscle cells (ASMCs) from hypertrophied rabbits. The amplitude of KATP channels induced by the KATP channel opener pinacidil was greater in ASMCs from control than from hypertrophied animals (P<0.05, n=6). In phenylephrine pre-constricted aortic rings, pinacidil induced relaxation in a dose-dependent manner. The dose-dependent curve was shifted to the right in the hypertrophied compared with the control model (P<0.05, n=4). Although the level of Kir6.2 subtype expression did not differ between ASMCs from the control and hypertrophied models (n=5), those of the Kir6.1 and SUR2B subtypes were decreased in the hypertrophied model (P<0.05, n=4). Application of the CGRP and forskolin induced a KATP current in both control and hypertrophied animals; however, the KATP current amplitude did not differ between the two groups (n=5). Furthermore, PKA expression was not altered (n=5). These results suggests that the decreased KATP current amplitude and KATP channel-induced vasorelaxation in the hypertrophied animals were attributable to the reduction in KATP channel expression, but not to changes in the intracellular signaling mechanism that activates the KATP current. (P<0.05 was regarded significant, and data analysis was done with student t-test.)