Effects of Training on Atrial Rate and Sensitivity of Isolated Rat Atria to Catecholamines and Acetylcholine

Abstract

Thirty five male rats were subjected to a treadmill running program and body weight heart weight and effects of neurotransmitters were measured. Rats engaged in training programs show a lower body weight, a lower heart rate and lower intrinsic heart rate. The response of all isolated rat atria to different drugs were observed. Epinephrine in concentrations of 1 X10-5M, 1X10-6M and 1X10-7M increased the atrial rate in trained rats by averages of 41.3%, 20.04% and 15.3% respectively, and in control animals by averages of 18.6%, 11.1% and 8.6% respectively. Norepinephrine in concentrations of 1X10-6M and 1x10-7M increased the atrial rates of trained animals by averages of 13.3% and 8.3% respectively. Acetylcholine of 1x10-6M decreased the atrial rate in trained rats averages of 48.4% and 28.2% in control animals. Atrophine in concentrations of 1x10-5M, x 10x10-6M, and 1x10-7M increased the atrial rates in all preparations, but the percent change was higher in trained rats. 1x10-5M atropine added to isolated rat atria of trained rats increased the atrial rate to a rate almost identical to the basal atrial rate of control rats. A biphasic response of atrial rate was observed when equimolar concentrations of acetylcholine and norepinephrine were added to isolated rat atria. It is concluded that trained rats have a lower resting heart rate and a lower intrinsic heart rate than control rats. The isolated rat atria of trained animals were more sensitive to catecholamines, acetylcholine and atropine. Increased stores of acetylcholine in the region of the pacemaker may account for the lowered heart rate. The negative chronotropic action of acetylcholine was blocked and the heart rate was brought to the basal rate of control animals in the presence of 1x10-5M atropine.