EFFECTS OF LOCAL ANESTHETICS ON MUSCARINIC SITES OF ISOLATED FROG VENTRICLE

Low concentrations of secondary and tertiary amine local anesthetics were found to increase the strength of contraction of the electrically driven frog ventricle. The positive inotropic effect occurred at concentrations of the local anesthetic that did not elevate the threshold for electrical stimulation. The enhanced contraction is shown to be due to a block of muscarinic receptors in the ventricle and a consequent reduction of the negative inotropic modulation of the myocardial contraction due to acetylcholine release during electrical stimulation. Acetylcholine in low concentrations depresses contraction; in intermediate concentrationss acetylcholine has a stimulatory action which is blocked by the beta adrenergic blocking agent, sotalol.{A table is presented}. © 1969.