Circadian Rhythms: Variation in Sensitivity of Isolated Rat Atria to Acetylcholine

Abstract
Experiments were performed at 2 time points in the 24-hr, cycle to determine whether isolated right atria of rats would vary in sensitivity, with a circadian rhythm, to 2 concentrations of acetylcholine. The beating rate of the atria decreased ore in response to the drug if the atria were isolated at 1100 than if isolated at 2300 hrs.