Chemoreflexes in rabbits

Criteria defining chemoreflexes (called responses) in rabbits have been established in relation to right atrial injection of 16 chemicals, and compared with previously-defined chemoreflexes of cats. A vagally mediated 'pulmonary' response elicited at latencies less than 1.6 sec consists only of an increased frequency of breathing due primarily to decrease of expiratory duration. A vagally mediated 'cardiac' response at latencies of 2-3 sec consists of bradycardia, hypotension and a respiratory component of decreased tidal volume. A 'non-vagal excitatory' response probably from the carotid bifurcation region consists predominantly of increased tidal volume, commencing at latencies greater than 2 sec. Stimuli eliciting 'pulmonary' responses were acetic, propionic, butyric, glycolic, lactic, glyoxilic and pyruvic acids, sodium dithionite and phenyl diguanide, and all also elicited the 'non-vagal excitatory' response. Phenyl diguanide additionally elicited the 'cardiac' response. No responses were elicited either by amino-substituted acids (glycine, beta- and L-alanine, 2-amino-butyric acid and GABA) or sodium salts of lactic and acetic acids, except occasionally beta-alanine and GABA elicited a 'non-vagal excitatory' response.