Tension developed by papillary muscles from hypertrophied rat hearts.

TO DETERMINE whether, in certain aspects, hypertrophied heart muscle behaves differently from normal heart muscle simple observations were performed. Papillary muscle strips from the left ventricle of rats, the hearts of which had been caused to hypertrophy, were compared with papillary strips from normal rat hearts by measuring tension developed at various weights in a perfused isolated muscle strip preparation. Having parallel muscle fibers and sharing in hypertrophy of the left ventricle,papillary muscle is well suited to studies of isometric contraction. Methods Hypertrophy of the left ventricle was achieved by the method of Hajdu and Beznak. Silver rings of an internal diameter of 1.50 mm. were snugly placed about the ascending aorta of male rats between the ages of 30 and 90 days weighing 150 to 250 Gm. Blue Spruce Farm Sprague-Dawley rats were used for operation and for control animals. Between 21 and 90 days after placement of the ring, the rat hearts were tested. Animals failing to gain weight normally were discarded. The animal was weighed, given ether anesthesia, and the heart quickly removed. Following the method of Hoffman and Kelly, the actively beating fresh heart was transferred to oxygenated Tyrode's solution, the left ventricle opened, and a papillary muscle, gently handled, was tied at its apex with 0000 silk and excised at its base. The muscle was inserted into a plastic muscle holder and its base firmly pressed against two pin-point platinum stimulating electrodes. The strip was then placed