The Response of the Heart to Stress

Abstract

The response of the myocardium to persistent stress involves an increase in mass and a restructuring of the cellular and subcellular elements. The experiments described in this article are designed to test the hypothesis that the restructuring of the various systems (contractile, excitation-contraction coupling, recovery, etc.) that occurs in adaptive hypertrophy is a coordinated (matched) process. When the restructuring of the systems in response to stress occurs in an uncoordinated fashion, congestive heart failure results. In addition to controls, three heart models with normal pump performance are used (control, C; pressure overload, P; thyrotoxic, T; and pressure overload plus thyrotoxic, PT4) and one with inadequate pump performance (pressure overload plus thyrotoxic, PT2). In this analysis the contractile and excitation-contraction coupling systems are evaluated. The former is assessed by sensitive myothermal measurement of tension dependent heat (TDH) normalized for the isometric tension time integral (integral of Pdt). The latter is assessed from measurement of the time to peak isometric tension (TPT). The TDH/integral of Pdt (mu cal/g.cm.s) and TPT (ms) for the C, P, T, PT4, and PT2 hearts are 2.4, 1.8, 5.2, 5.1, and 0.1, mu cal/g.cm.s and 627, 816, 352, 484, and 465 ms, respectively. According to the coordination or matching hypothesis, if TDH/integral of Pdt is low, then TPT should be increased, or if TDH/integral of Pdt is high, then TPT should be decreased. Relative to control hearts, matched restructuring of the contractile and excitation-contraction coupling systems occurred for the P, T, and PT4 preparations. In these animals the hypertrophy has been adaptive and the pump performance is adequate.(ABSTRACT TRUNCATED AT 250 WORDS)