Effects of stretch on tension development in frog atrium

¹ Department of Physiology, Seton Hall College of Medicine and Dentistry, Jersey City, New Jersey

Initial tension, isometric contractile tension, and the first derivative of the contractile response were recorded from the atrial wall of frog hearts. These hearts were stretched progressively from 0 to 25 g of initial tension at 25 C. Maximum peak isometric tension, maximum rate of tension development, and maximum rate of relaxation were attained at the relatively low stretching force of 2 g and at a 50% increase in length. Peak contractile tension remained near maximum under high initial tension, but the maximum rates of contraction and relaxation were markedly decreased. Stress relaxation was apparent in all preparations at all levels of initial tension. It appears to represent an alteration of the internal tension mechanism different from the alteration which accompanies the increase or decrease of the stretching force.