Effects of aortic pressure and vasoactive agents on the vascular resistance of the vasa vasorum in canine isolated thoracic aorta.

1. We have developed a new preparation for continuously measuring changes in vascular resistance of the vasa vasorum of the canine isolated thoracic aorta perfused at a constant flow rate with Krebs-bicarbonate solution. 2. An increase of more than 150 mmHg in aortic pressure caused a significant increase in the vascular resistance of the vasa vasorum. 3. 5-Hydroxytryptamine (5-HT), noradrenaline (NA), adrenaline and dopamine caused dose-dependent increases in the vascular resistance of the vasa vasorum. The decreasing order of potency in the vasoconstrictor responses was as follows: 5-HT >> NA = adrenaline >> dopamine. The 5-HT- and adrenaline-induced vasoconstrictor responses were inhibited by methysergide and by phentolamine plus propranolol, respectively. 4. Acetylcholine (ACh), isoprenaline (ISP), histamine (His), ATP, ADP and adenosine produced dose-related decreases in the vascular resistance of aortic vasa vasorum perfused with the Krebs solution containing 10(-5) M-NA. The decreasing order of potency in the response was as follows: ACh = ISP > His >> adenosine = ATP = ADP. The ACh-, ISP- and His-induced vasodilator responses were antagonized by atropine, propranolol and famotidine, respectively. 5. The results suggest that the preparation described is useful for studying the regulation of vascular resistance of aortic vasa vasorum and that aortic pressure and vasoactive compounds may directly regulate the vascular resistance of the vasa vasorum in canine isolated thoracic aorta.