The canine internal carotid system: regional differences in reactivity to nerve stimulation, noradrenaline and 5–hydroxytryptamine

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Abstract
Nava‐Hernandez, E., Valle, J., Garcia‐Villalon, A. L., Garcia, J. L., Monge, L., Gomez, G. & Dieguez, G. 1992. The canine internal carotid system: regional differences in reactivity to nerve stimulation, noradrenaline and 5–hydroxytryptamine. Acta Physiol Scand144, 4455452. Received 22 July 1991, accepted 5 November 1991. ISSN 0001–6772. Departamento de Fisiología, Universidad Autónoma de Madrid, Spain.Reactivity of the canine internal carotid system to field electrical stimulation, noradrenaline and 5–hydroxytryptamine was determined isometrically using 4–mm cyclindrical rings from the cervical and cavernous portions and middle cerebral artery. Electrical stimulation at supramaximal voltage (0.54 Hz, 0.2 ms duration) produced a frequency‐dependent contraction that was similar in cervical and cavernous portions and lower in the middle cerebral artery. This response was blocked by tetrodotoxin (10‐6m)or phentolamine (10‐6m). Noradrenaline (10‐9‐3 × 10‐4m)produced concentration‐dependent contractions and the sensitivity was: cervical portion = cavernous portion > middle cerebral artery, and this effect was blocked by phentolamine (10‐6m). 5–hydroxytryptamine (10‐9‐‐10‐5m)caused concentration‐dependent contractions and the sensitivity was: cervical portion < cavernous portion < middle cerebral artery. This response was depressed by lysergic acid diethylamide (10‐6m). The results indicate that reactivity of the internal carotid system: (a) to alpha adrenergic activation by endogenous and exogenous noradrenaline is lower in the distal segment (middle cerebral artery) than in the proximal segments (cervical and cavernous internal carotid artery) and (b) to tryptaminergic activation increases as it courses toward the brain. Therefore, functional characteristics could be related to embryological origin which the segments of this vascular system are derived from.