Tension Developed by Papillary Muscles from Hypertrophied Rat Hearts

Abstract

O 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, 1 -2 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.3 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, 4 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 Prom the Medical Service, Veterans Administration Hospital, and the Department of Medicine, State University of New York, Upstate Medical Center, Syracuse, jSTew York.Supported in part by grants from Xew York Heart Assembly and Heart. Association of Onondaga County.Drs. Giambattista and Winterberger were recipients of student research fellowships during the summers of 1958 and 1959.Received for publication August 5, 1960. in a muscle warmer and perfused at a rate of 3 ml./min. with Tyrode's solution (XaCl, 142 niM/ L.; KCL, 2.7; dextrose, 5.5; XaHCO 3 , 12.5; MgClo, 0.5; XaH 2 PO 4 , 3.7). A mixture of 95 per cent O 2 and 5 per cent CO 2 was delivered through a sintered disk at the bottom of the muscle warmer at a rate of 6 ml./min. The muscle warmer was surrounded by a constant temperature bath kept at 27 C. The suture from the apex was attached vertically to a horizontally placed Grass force displacement transducer (Model FT 0.03). Gram weights were used to calibrate the displacement of the transducer which was connected through a preamplifier to a channel of a Grass recorder. A micrometer screw adjustment was used to tighten the suture and the muscle was placed under 1 Gm. of tension. The preparation was then left in the muscle bath for one hour before stimulation. A Grass stimulator (Model S4C) and isolation unit were used. The muscle was stimulated at 5-second intervals with a rectilinear pulse of 10-msec. duration. Voltage was increased until a maximum response was evoked. Resting tension ...

Time course of changes in the mechanical properties of the canine right and left ventricles during hypertrophy caused by pressure overload.

“…This is in agreement with a number of previous studies (among others, Alpert et al, 1974;Bing et al, 1971;Ring et al, 1978). However, the results conflict with those of Kerr et al (1961), Grimm et al (1963), andWilliams andDeiss (1978). Furthermore, the recent clinical studies by Peterson et al (1978) indicate that, on the average, muscle stiffness remains normal in patients with aortic stenosis although there were isolated cases in which muscle stiffness was abnormal.…”

“…It always has been assumed that right and left ventricular muscles have similar mechanical properties (Alpert et al, 1974;Bing et al, 1971;Grimm et al, 1963;Kerr et al, 1961); however, this has never been quantified. Figure 4 demonstrates that normal right and left ventricular muscle stiffness is not statistically different over the stress range 5-25 g/cm 2 .…”

Normal Contractile State of Hypertrophied Myocardium after Pulmonary Artery Constriction in the Cat

“…Although earlier studies reported that contractile function of hypertrophied myocardium was normal or even "supernormal" (1)(2)(3)(4), the methods used to assess contractile state and the manner in which this function was corrected for differences in muscle mass have been criticized. More recently, Spann, Received for publication 10 May 1974 and in revised form 16 August 1974.…”

Left ventricular function in patients with chronic obstructive pulmonary disease

“…Evidence to support this impression has been gained primarily from the observation that patients dying with COPD often have left ventricular hypertrophy at postmortem examination (2)(3)(4)(5)(6)(7), and the possible mechanisms for this have been summarized (7). However, the presence of myocardial hypertrophy does not necessarily indicate depressed myocardial function since it has been demonstrated that the hypertrophied myocardium can function normally (8) or even supernormally (9)(10)(11)(12)(13). Furthermore, definitive conclusions concerning left ventricular function in these patients cannot be made from the vast amount of hemodynamic data accumulated from cardiac catheterization studied which have been summarized recently (14).…”