Electrical and mechanical response of arteries to stimulation of sympathetic nerves.

1. When common carotid arteries of sheep were studied in vitro by the sucrose-gap method, application of acetylcholine or nicotine caused small irregular spikes of depolarization. The discharge was prevented by hexamethonium, Hydergine, phentolamine, or chronic denervation, indicating that it represented electrical activity of groups of smooth muscle cells induced by the stimulation of sympathetic nerve fibres.2. The size of spikes produced by acetylcholine or nicotine, together with counts of the total number of smooth muscle cells in cross-sections of the arterial strips, indicated that the larger groups of smooth muscle cells activated by one sympathetic nerve fibre contained approximately 1300 cells.3. Sections of arteries treated with hot formaldehyde vapour contained numerous fluorescent fibres which were intensified by previous injection of noradrenaline into the animal and were scanty or absent after chronic sympathetic denervation. They are therefore believed to be post-ganglionic sympathetic nerve fibres.4. Most of these fibres ran circularly in the outer (1/2)-(3/4) of the media. A few ran longitudinally in the adventitia. There were none in the inner (1/4)-(1/2) of the media.5. Electrical stimulation of the cervical sympathetic nerve of anaesthetized sheep caused large contractions of the common carotid artery of the same side, reducing its external diameter by 30-39%.