[Contractile function of the heart of guinea pigs after long-term continuous stress]

Guinea-pigs exposed to 60- and 100-day biosocial stress were used to examine the contractile function of the heart in the whole body and in an isolated state. A 60-day stress effect caused adaptation which included increases in the intensity of heart contractility and in its weight unit by 29% and 38%, respectively. Measurement of resistance of such an adapted heart to isometric load produced by a short-term aortic occlusion showed increases in maximal rates of its contraction and relaxation by 34-35%. After a 100-day stress-effect the strength and velocity of heart contraction and resistance to isometric load returned to normal; however, the intensity of the function of the weight unit increased by 27-32%. The effect of adaptation was also seen in an isolated heart: after a 100-day exposure the isolated hearts did not lose their ability to react to a greater preload according to Starling's law; moreover at the filling pressure 15 cm H2O their cardiac output increased by 50% as compared to the baseline. This observation suggests that the process of adaptation of guinea-pig hearts to chronic stress involves not only activation of central mechanisms of regulation but also enhancement of mechanisms of self-regulation but also enhancement of mechanisms of self-regulation.