Pharmacological assays on the isolated esophagus of an amphibious snail, Pomacea lineata (Spix, 1827) (mollusca, gastropoda, prosobranchia)

Abstract

1. 1. Choline esters, cholinomimetic drugs, serotonin and histamine elicit sustained contractions in both the quiet and spontaneously active isolated esophagus of Pomacea lineata; adrenaline relaxes it. 2. 2. On an equimolar basis, the actions of choline esters and cholinomimetic drugs decrease with the decreasing degree of their muscarinic activity; nicotine is inactive. The results suggest that the acetylcholine receptors in the post-synaptic membrane of the neuromuscular junctions are of a muscarinic nature. 3. 3. A further evidence of this view is the fact that the responses to acetylcholine are blocked by atropine in a dose dependent manner, but not by d-tubocurarine or mytolon. 4. 4. The responses to acetylcholine are dose dependent and, in a dose-effect assay, followed a straight line. The responses of both the active and quiet esophagus are enhanced by previous incubation in eserine. 5. 5. The esophagus respond also to serotonin and histamine in a dose dependent manner, but the responses are less regularly blocked by specific antagonists (BOL, neoantergan, antazoline). 6. 6. The fact that both the gastropod esophagus and the vertebrate intestine respond to acetylcholine, serotonin and histamine and are relaxed by adrenaline is in accordance with the analogy of the innervation pattern of the two structures.