Influence of chronic stellectomy on reactivity to serotonin in the dog external carotid bed.

The influence of chronic stellectomy on external carotid flow responses to i.a. serotonin (5HT) was determined in dogs in which both stellate ganglia had been removed 1, 2, 4 or 8 weeks previously. The effect of this maneuver on carotid and heart rate responses to i.a. and i.v. norepinephrine (NE), respectively, was also assessed for comparison. Constrictor responses to NE in the carotid were moderately increased at 2 and 4 weeks, while its positive chronotropic effects were markedly augmented throughout the observation period. Dilator responses to 5HT increased at 4 and specially at 8 weeks after stellectomy. Results obtained with NE were considered compatible with supersensitivity induced by decentralization in the carotid and by denervation in the heart. Changes in carotid responses to 5HT were interpreted as being due to a prejunctional mechanism similar to that responsible for supersensitivity to NE. Differences in the time course of development of supersensitivity to both amines were attributed to masking of 5HT dilatation by NE released by the indoleamine at the time of increased sensitivity to constriction by the catecholamine.