EFFECTS OF CALCIUM-CHANNEL BLOCKERS ON COLD-INDUCED VASODILATATION AND ELEVATED SYMPATHETIC TONE IN THE CANINE INTERNAL MAXILLARY ARTERY BED

This study was concerned with the interactive effects of cold-induced vasodilatation, blockade of voltage-sensitive Ca2+ channels and sympat hetic 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 micros phere technique in combination with electromagnetic flowmetry was used . Intraarterial infusion of verapamil resulted in a dose-dependent vas odilatation and a redistribution of the internal maxillary artery bloo d flow in favor of the capillary fraction, at the expense of the AVA f raction. Cold exposure of the nasal and facial tissues was followed (a s a result of a marked dilatation of the AVA) by a prompt increase in internal maxillary artery blood flow. Simultaneously applied electrica l stimulation of the cervical sympathetic trunk resulted in a signific ant 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 capill ary flows were affected in different manners, depending on the sequenc e of the stimulations. Analysis of capillary flow data in the various nasal and facial tissue compartments indicates that cold exposure, blo ckade of the voltage-dependent Ca2+ channels and an elevated sympathet ic tone modify the local nutritive blood flow.