The mechanism of the bronchoconstriction induced by unilateral orthodromic stimulation of the carotid sinus nerves.

Unilateral stimulation of carotid sinus nerve afferents at 2 and 4 V produced pulse duration-dependent reflex bronchoconstriction which was unaffected by midcervical, bilateral vagotomy. The bronchoconstriction consisted of two pharmacologically distinct components. One component was blocked by atropine or atropine methiodide, and other was blocked by either mepyramine or disodium cromoglycate. Combinations of atropine or atropine methiodide with mepyramine or disodium cromoglycate completely eliminated bronchoconstrictor responses to nerve stimulation. These data indicate that two separate bronchoconstrictor reflexes, possibly resembling serotonin- and diazoxide-induced reflex bronchoconstriction are activated by stimulation of afferent fibers in the carotid sinus nerves.