Evidence for alpha-adrenergic innervation of the isolated canine thoracic duct

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Abstract
The excitatory innervation of isolated thoracic duct segments was studied using tissue bath techniques. No spontaneous activity was present in longitudinal or helical strips obtained from a portion of the thoracic duct cephalad to the hilum of the lung. Norepinephrine (10-8 to 10-5 M) and tyramine (3 .times. 10-5 M) produced contractions that were antagonized by phentolamine (2 .times. 10-5 M) and phenoxybenzamine (10-7 M). Acetylcholine (10-7 to 10-4 M) produced contractions that were antagonized by atropine (5 .times. 10-9 M). Thoracic duct strips contracted in response to field electrical stimulation, and maximal responses were obtained with a stimulus of 15 V, 15 Hz and 1-ms pulse duration. These electrically induced contractions were abolished by tetrodotoxin (5 .times. 10-7 M), phentolamine (2 .times. 10-5 M), phenoxybenzamine (10-7 M) and guanethidine (3 .times. 10-6 M), but not by atropine (10-6 M). Smooth muscle of the canine thoracic duct contains .alpha.-adrenergic and acetylcholine receptors, both of which cause contraction when stimulated. Only the .alpha.-receptors appear to be innervated.

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