A comparative study of guinea pig and rat tracheal reactivity

Species differences in behavior and responses of guinea pig (GPT) and rat (RT) tracheal smooth muscle to electrical field stimulation (EFS) and chemicals were investigated under semi-isometric conditions. Indomethacin augmented and papaverine reduced the contractions elicited by EFS in both tissues. They relaxed the GPT and did not affect the tone decline in the RT. Experiments with different load, cartilage content, thread and rubber strips suggest the role of elastic elements in passive elongation of the RT. This was independent of muscarinic, adrenergic, histaminergic and serotoninergic receptors, nitric oxide, eicosanoids and metabolic processes. The second response on repeated administration of acetylcholine was augmented and that of serotonin attenuated in both GPT and RT. Upon repeated elevation of [K+]o the tissues responded in an opposite manner. Further data are provided on similarities (modulation of cholinergic transmission by prostaglandins, sensitization to acetylcholine and desensitization to serotonin) and differences (innervation, responses to repeated elevation of [K+]o, presence/absence of prostaglandin-regulated basal tone and spontaneous activity) in reactivity of GPT and RT.