ARTERIOLAR RESPONSES TO EXTRACELLULAR ATP IN STRIATED

Blood flow and its distribution must be appropriately regulated to ens ure that perfusion is matched to local tissue demands. We investigated the role of ATP in triggering a conducted alteration in arteriolar di ameter in the Saran-covered cheek pouch retractor muscle of anesthetiz ed hamsters (n = 60). Vascular responses were observed using in vivo v ideo microscopy upstream from the site of micropressure application of ATP (10(-8)-10(-4) M) either into the lumen or just outside the wall of first- and second-order arterioles. The role of nitric oxide (NO) i n the vascular responses to ATP was determined by inhibiting NO syntha se activity with N-omega-nitro-L-arginine methyl ester (L-NAME) with a nd without coadministration of an excess of L-arginine. Intraluminal a pplication of ATP led to a concentration-dependent vasodilation, which was conducted upstream along the arteriole. The dilatory response was blocked by systemic pretreatment with L-NAME and was maintained in th e presence of an excess of L-arginine. In contrast, ATP introduced ext raluminally resulted in a conducted vasoconstrictor response that was enhanced by pretreatment with L-NAME. The dilator response to intralum inal ATP, in the context of ATP release from erythrocytes under condit ions associated with decreased supply relative to demand, supports a r ole for the erythrocyte in communicating local tissue needs to the vas culature, enabling the appropriate matching of oxygen supply to demand .