The effect of combined impact of simulated microgravity and ionizing radiation on the development of experimental myocardial infarction in rats for two weeks
Abstract
During space missions, a large number of new stressors, not previously encountered on Earth, act on a living organism. Ionizing cosmic radiation (IR) and microgravity are considered to be the main factors of space flight (SF), affecting the entire organism as a whole and causing an increase of compensatory and adaptive mechanisms, shifts in the homeostasis system, which ultimately can lead to long-term structural and functional changes, the occurrence of diseases, including those in the cardiovascular system. The rat model of isoproterenol myocardial infarction (MI) allows inducing heart damage similar to that observed in humans. The complex of isoproterenol-induced disorders leads to progressive myocardial dysfunction and to chronic heart failure later.
Purpose: To evaluate the influence of simulated factors of space flight (IR and microgravity) in two combinations on the development of experimental MI in rats for two weeks.
Methods: Two-week hindlimb unloading (HU), single acute gamma irradiation (γ) at a dose of 2 Gy, ECG, laser correlation spectroscopy, measurement of body and heart weight of rats.
Results: The decrease in body weight during 2 weeks of observation was more influenced by HU. Analysis of the characteristics of the PQRST complex revealed an increase in the amplitude of the following waves: P2 in the groups γ+MI and HU+γ+MI, R1 in the groups HU+γ+MI and γ+HU+MI groups on the next day, as well as T2 1 week after the last injection of isoproterenol.
After 2 weeks in the HU+γ+MI group an increase in R2 wave amplitude, an increase in the duration of the QTc interval in the groups γ+MI and γ+HU+MI, and a decrease in heart rate in all experimental groups were observed. A higher percentage of arrhythmias were recorded in the γ+HU+MI group, a negative Q wave was recorded in the γ+MI group. Analysis of the spectral characteristics of heart rate variability (HRV) showed an increase in VLF% waves in all experimental groups on the first day of observations and a shift in the autonomic balance towards sympathicotonia in the group γ+HU+MI, and a week later only a slight increase in the percentage contribution of LF and a decrease of HF waves were found. The greatest changes in serum homeostasis were present in the γ+MI and γ+HU+MI groups: an increase in the percentage contribution to the light scattering of particles with a radius of 20-28 nm. In the HU+γ+MI group, the percentage of particles with a larger hydrodynamic radius in the range of 67-122 nm was increased.
Conclusion: The effects of the simulated SP factors played a major role in reducing body weight gain in the experimental groups, caused shifts in serum homeostasis specific to each combination and electrophysiological changes. Depending on the sequence of SP factors was found that changes in the spectral parameters of HRV and the frequency of rhythm disturbances were more pronounced in the γ+HU+MI group, and prolongation of the QTc interval was in the HU+γ+MI group. The recorded increase in the amplitude characteristics of the P, R, T waves in groups of rats with combined exposure to simulated microgravity and ionizing radiation may be a consequence of more significant changes in electrical conductivity and manifestations of myocardial hypertrophy compared to the MI group.
