LOCAL AND CONDUCTED VASOMOTOR RESPONSES IN ISOLATED RAT CEREBRAL ARTERIOLES

We tested the hypothesis that conduction of vasomotor responses occurs in cannulated and isolated rat cerebral penetrating arterioles. Both at the site of stimulation (local) and 500-650 mu m distant from it, w e observed the diameter responses and time courses thereof to pressure -ejected vasoactive stimuli. ATP locally caused an initial constrictio n (response onset at 0.3 s, average diameter 85% of control at 450-ms pulse with a maximum at 1.6 s after stimulation) followed by a seconda ry dilation (111% at 7 s). Conducted vasodilation of 111% was observed over a distance of 520 mu m. Prostaglandin F-2 alpha (PGF(2 alpha)) c onstricted the vessels locally (80%) and caused conducted vasodilation (110%). For both ATP and PGF(2 alpha) the local constriction occurred simultaneously to the conducted vasodilation. Adenosine dilated the v essels (123%) but produced only inconsistent conducted vasodilation. H ydrogen ions initially constricted the vessels (88%) and then dilated them to 113%. Thus, although ATP and PGF(2 alpha) are strong promoters of conduction, adenosine and hydrogen ions are not. Paradoxically, AT P and PGF(2 alpha) caused conducted vasodilation even though the initi al local response was a vasoconstriction, indicating that in cerebral arterioles conduction may be mediated through endothelial cell mechani sms rather than through smooth muscle cell communication.