CONDUCTED VASCULAR-RESPONSES - COMMUNICATION ACROSS THE CAPILLARY BED

Conducted vasomotor responses are important for the effective distribu tion of blood flow, although the mechanism by which these responses ar e initiated is not well understood. ATP, a substance which is released from circulating red blood cells in response to low P-O2 and low pH, two conditions which are associated with decreased supply relative to demand, has been shown to initiate conducted vasodilation following it s intraluminal application in first and second order arterioles. Since such low P-O2 and low pH conditions would most likely occur on the ve nous side of the vasculature, we evaluated the response of the arterio lar and capillary networks to application of ATP into venules in the S aran-covered hamster cheek pouch retractor muscle using in vivo video microscopy. Intraluminal application of 40 and 400 pi of 10(-6) M ATP resulted in dose-dependent increases in arteriolar diameter >450 mu m upstream from the site of application. These changes in arteriolar dia meter were accompanied by significant increases in red blood cell flux . In capillaries, red blood cell flux doubled in response to ATP admin istration. Since NO was previously determined to be involved in the va scular response to intraluminal ATP in arterioles, we evaluated its ro le in these responses. We found that systemic administration of L-NAME prior to ATP application eliminated any conducted response and this e ffect of L-NAME was reversed by the systemic administration of L-argin ine. These data suggest that ATP, which is released from red blood cel ls in response to low P-O2 and low pH, conditions which would be found in the venular microvasculature, may serve a role in distributing per fusion in response to alterations in supply. (C) 1998 Academic Press.