Myogenic response of isolated pressurized rabbit ear artery is independent of endothelium

Central ear artery segments, removed from urethan-anesthetized rabbits, were used to assess whether distention activation was dependent on intact and functional endothelium (ENDO). Changes in external arterial diameter were measured with light-dependent diode array mounted above the vessel. After constriction with norepinephrine, slow increases in pressure from 60 to 80 or 100 mmHg performed over 120 s (pressure ramps) failed to initiate distention, but initial diameter was maintained. Rapidly applied (500 ms) pressure increases (pressure jumps) across same pressure ranges gave rise to initial distention and a myogenic response resulting in a return to almost initial diameter while new pressure was maintained for 120 s. Myogenic activity was measured from extent of recovery of vessel to its initial diameter during maintenance of pressure jumps or ramps. Rapid jumps and slow ramps were performed in presence of an intact ENDO and again after ENDO was removed by passage of intraluminal gas. With pressure jumps 60 to 80 mmHg, degree of recovery in ENDO-denuded vessels was 91.9% compared with 89.5% in ENDO intact vessels. For pressure jumps 60 to 100 mmHg, extent of recovery was 87.4 and 89.6%. During application of pressure ramps of 20 or 40 mmHg, vessel diameter did not increase by greater than 5%. There are no significant differences in these data, and we conclude that myogenic response in rabbit ear artery is mediated independently of endothelial-derived factors, irrespective of whether myogenic activation is induced by pressure jumps or ramps.