Effects of volatile anesthetics on response to norepinephrine and acetylcholine in guinea pig atria

The in vitro chronotropic and inotropic effects of norepinephrine and acetylcholine in isolated right and left guinea pig atria were examined in the absence and presence of halothane, isoflurane, and enflurane (0.6 and 1.2 MAC). All three anesthetics elicited dose-dependent reductions in contractile force and spontaneous pacemaker activity. The maximal developed tension observed in the presence of norepinephrine was not altered by the anesthetics and corresponding ED50 values increased only in the presence of 1.2 MAC halothane and 1.2 MAC isoflurane. The anesthetics did not affect (a) the maximal positive chronotropic effect of norepinephrine, (b) the ED50 values for its positive chronotropic effect, and (c) acetylcholine-induced negative inotropic and chronotropic actions and did not induce arrhythmic activity even in the presence of the maximally effective neurotransmitter concentrations. These findings indicate that in isolated guinea pig atria volatile anesthetics, in concentrations up to 1.2 MAC, do not alter the inotropic and chronotropic effects of norepinephrine or acetylcholine and do not induce arrhythmogenic action in the presence of the neurotransmitters. These data suggest that altered atrial responsiveness to adrenergic or muscarinic stimulation does not contribute to the development of anesthetic-induced cardiac arrhythmias.