THE EFFECT OF SYMPATHETIC NERVE STIMULATION ON ISOLATED ATRIA OF GUINEA PIGS AND RABBITS PRETREATED WITH RESERPINE

¹ Department of Pharmacology, Harvard Medical School, Boston, Massachusetts

Isolated atria obtained from guinea pigs and rabbits pretreated with 5 mg/kg of reserpine were exposed to norepinephrine in order to "refill" their norepinephrine stores. While this procedure restored the response of the atrial pacemaker to tyramine, it had no effect on its response to electrical stimulation of the right accelerans nerve. It appears that under these experimental conditions tyramine and nerve impulses do not act on the same compartment of the total store.

Isolated atria of reserpine-pretreated guinea pigs failed to respond to tyramine. Although their response to sympathetic stimulation was diminished, it was not abolished. A similar response to sympathetic stimulation was observed in open-chest guinea pigs under sodium pentobarbital anesthesia. it is suggested that guinea pigs have a compartment in their cardiac norepinephrine stores that is accessible to nerve impulses but neither to reserpine nor to tyramine. This seems to be species-dependent, since rabbit atria had virtually no response to sympathetic stimulation after pretreatment with reserpine.

Isolated atria obtained from reserpine-pretreated rabbits responded to tyramine more strongly when the animals were killed with ether than when they were killed by a blow on the head. Agonal uptake of circulating catecholamines may be responsible for this difference.