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 ≧ 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 1-200 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.
The effects of the close arterial infusion of histamine upon the microcirculation of facial and nasal tissues were examined in dogs. Blood flow through arteriovenous anastomoses (AVA flow), capillaries (CAP flow) and collaterals (COL flow) were determined by electromagnetic flowmetry and the tracer-microsphere technique following an infusion of histamine at doses ranging from 0.5 to 50 nmol/min. Low doses of histamine (0.5-5.0 nmol/min) resulted in an increase in blood flow through the ipsilateral internal maxillary artery (IMA), which could be mainly attributed to a significant elevation of the CAP flow. A concomitant marked increase in AVA flow was observed only after the administration of higher doses (20-50 nmol/min). Significant changes in systemic blood pressure, heart rate and cardiac output occurred only after the infusion of histamine at doses of 20 and 50 nmol/min. Significant increases in the CAP flow of tissues with relatively low perfusion were observed after the infusion of histamine at lower doses. The CAP flow of structures which play an essential role in conditioning the inspired air and exhibit high perfusion rates under control conditions exhibited significant increases only after the administration of higher doses. The present experiments provide direct evidence for a dose-dependent vasodilatory effect of histamine on different microcirculatory compartments of cutaneous and mucosal vascular beds supplied by the IMA in the dog. The results indicate that at low blood histamine levels, an increase in CAP flow predominates, and at higher doses, both elevated CAP flow and elevated AVA flow contribute to the vasodilatory response to histamine. The investigation suggests that histamine is not involved directly in a selective dilation of the AVA of the facial and nasal vasculature which is characteristic for cold-induced vasodilation.
This study was concerned with the interactive effects of cold-induced vasodilatation, blockade of voltage-sensitive Ca2+ channels and sympathetic nerve stimulation in the nasal vascular bed of anesthetized dogs. To estimate the distribution of the internal maxillary artery blood flow to capillaries and to arteriovenous anastomoses (AVA), the microsphere technique in combination with electromagnetic flowmetry was used. Intraarterial infusion of verapamil resulted in a dose-dependent vasodilatation and a redistribution of the internal maxillary artery blood flow in favor of the capillary fraction, at the expense of the AVA fraction. Cold exposure of the nasal and facial tissues was followed (as a result of a marked dilatation of the AVA) by a prompt increase in internal maxillary artery blood flow. Simultaneously applied electrical stimulation of the cervical sympathetic trunk resulted in a significant fall in blood flow, caused mainly by a decrease in capillary flow. Verapamil infusion combined with cold exposure led to a simultaneous elevation of the AVA and capillary flows. When electrical stimulation of the cervical sympathetic trunk was also applied, the AVA and capillary flows were affected in different manners, depending on the sequence of the stimulations. Analysis of capillary flow data in the various nasal and facial tissue compartments indicates that cold exposure, blockade of the voltage-dependent Ca2+ channels and an elevated sympathetic tone modify the local nutritive blood flow.
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