[Post-radiation changes in cardiac contractility and responses mediated by beta adrenergic receptors in mature and old age].

Experiments were performed on isolated perfused hearts of rats of the middle and old age. The animals were irradiated with 60Co gamma-rays at a dose of 1 Gy and a dose rate of 2.7 x 10(-4) Gy/s. This exposure enhanced pacemaking activity and attenuated contractile activity of rat hearts. The biomechanical changes were most distinct in adult rats. It can be assumed that the mechanisms responsible for heart contraction and relaxation as well as for their self-regulation are more resistant to ionizing radiation in old-aged animals. Post-radiation changes of neurohormonal regulation show different age-related features. In adult rats, the exposure caused only a decline of the chronotropic response to stimulation of beta-adrenoreceptors whereas in old animals it produced a decline of inotropic and coronary responses. It is postulated that mechanisms underlying adrenergic effects at the level of the receptor apparatus of coronary vessels and cardiomyocytes experience greater changes in old-aged animals exposed to irradiation.