Circulatory Effects Caused by Intra-Arterial Infusion of AMP, ADP and ATP in the Canine Facial and Nasal Vascular Beds

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Abstract
The effects of the intra-arterial infusion of ATP, ADP and AMP into the internal maxillary artery (IMA), which provides the blood supply to the nasal and forehead regions of the dog, were analyzed. Total blood flow and perfusion pressure measurements in the IMA after administration of each adenyl compound indicated dose-dependent and active vasodilatory responses that were restricted to the ipsilateral vessels. The rank order of potency was ADP greater-than-or-equal-to ATP > AMP. In order to determine the microcirculatory effects caused by ADP, the tracer microsphere technique combined with absolute blood flow measurement was used. Intra-arterial infusion of ADP in the range 1200 nmol/min produced elevations in the IMA flow on the stimulated side that ranged between 11 and 74%. The responses to low doses of ADP were mainly confined to the capillaries (CAP), whereas the arteriovenous anastomoses too were sensitive to high doses. The relative contributions of the anatomically and functionally different compartments of the forehead and nose to ADP-produced relaxations of the CAP were dependent upon their location. The CAP flows in the tissues which play a crucial role in conditioning the inspired air increased significantly, while the compartments of the furred surfaces were less sensitive to ADP. The results suggest that, since ATP, ADP and AMP are effective vasodilatory agents in all the regions examined, purines could have a regulatory or modulatory role in the complex vascular regulation of the nasal and forehead regions.