Myogenic response causing remote vasoconstriction

In arterioles there is communication between parts of the vasculature such that pressure increases at one location can initiate constrictions that are remote from where the pressure increased. This study was performed to determine if the size of the remote response is related to the myogenic response of the arteriole. A section of arteriole (∼1400 μm long) in cheek pouch of anesthetized hamster was captured between two micro-occluders and pressure transients within the segment were created through a microcannulae. Arteriole diameters were measured within the segment and remotely. In the segment, pressure changes caused passive dilation followed about 10 sec. later with active myogenic constriction. Remotely, pressure changes caused a constriction contemporaneous with the segment myogenic response. A constant change in pressure (30 cm H₂O) was tested at varying starting pressures (0-50 cm H₂O) and the passive dilation decreased (13 to 4 μm), myogenic response did not change (∼ 4μm), and the remote constriction increased significantly (-1.5 to -2.5 μm) with increasing resting pressure (n=10). Next, using a constant resting pressure (20 cm H₂O), different transients pressures were used (10-40 cm H₂O). All response were found to significantly increase with the magnitude of the pressure transient: passive responses (1.8 to 4.5 μm), myogenic responses (0.5 to 2.4 μm), and remote constrictions (-1.4 to -2,5 μm) (n=7). Thus, remote constrictions caused by increases in pressure were closely related to the starting pressure and the size of the pressure change but not related to the passive dilation of the arteriole or the active myogenic response. This implies that remote responses are related to the level of stress in the vessel wall, and any changes wall stress, but not to the outward response of the arteriole to a change in pressure.