Preliminary pharmacological characterization of the isolated circular strips of gastric muscularis muscle of Bufo marinus: a new preparation.

This paper describes a preliminary pharmacological study of isolated circular strips of gastric muscularis muscle of Bufo marinus under isometric conditions. The stomach of Bufo marinus was surgically removed and the muscularis muscle was isolated and divided into 12 equal parts from the fundus to the pylorus. The preparation contracted to acetylcholine (ACh), DL-muscarine, and K+. Histamine and 5-hydroxytryptamine had no effect, while dopamine caused relaxation. Prostaglandin E2 (PGE2) caused relaxation of the tonic contractions and potentiation of spontaneous contractions. A challenge of the preparation with ACh (1.5 X 10(-5) M) initiated tonic and spontaneous contractions, of which three types were identified. These were: type A (predominantly tonic contractions on strip #1); type B (tonic contractions over which spontaneous contractions were superimposed on strips #2-8; and type C (mostly tonic contractions and some superimposed spontaneous contractions on strips #9-12). Lower concentrations of ACh (1.0 X 10(-6)M) elicited tonic contractions, while higher concentrations of ACh (3.0 X 10(-5)M) were necessary for the initiation of tonic and spontaneous contractions in type B preparations.