[Daily 1 h standing can prevent depression of myocardial contractility in simulated weightless rats].
Objective. To observe and compare the effect of daily standing of rats for different durations in alleviating the depression of myocardial contractility induced by simulated weightlessness. Method. Fifty male Sprague-Dawley rats were randomly assigned to five groups: simultaneous control (CON), four-week tail-suspension (SUS), SUS plus daily 1 h standing (STD1), SUS plus daily 2 h standing (STD2) and SUS plus daily 4 h standing (STD4). Four weeks later, wet weights of the left soleus, testis and adrenal gland were measured, and the isometric contractile tension and its time parameters of isolated perfused papillary muscles from rats of various groups were examined. Result. Compared with CON, the wet weights of testis in different treatment groups decreased significantly (P<0.05). The wet weight of soleus in SUS decreased by 58.9% (P<0.01); but in STD1, STD2 and STD4, decreased by 38.5%, 24.0% and 11.0% (P<0.01, or P<0.05) respectively. The relative protections were 34.7%, 59.2% and 81.4% (P<0.01) respectively. In SUS group, developed tension (DT), peak rate of tension rise (+dT/dtmax) and peak rate of tension fall (-dT/dtmax) decreased by 32.2%, 29.2% and 30.7% (P<0.05), and time to peak rate of tension rise (TPP) and time to peak tension (TPT) prolonged by 21.2% and 11.0% (P<0.05), respectively. Whereas in STD1, STD2 and STD4, all the parameters reflecting myocardial contractility (like DT, + dT/dtmax, -dT/dtmax and TPP), did not show any significant change as compared with those of CON. However, being an exception, TPT still showed obvious prolongation (P<0.05) in STD1. Conclusion. Daily 1 h standing could prevent depression of myocardial contractility in rat induced by medium-term simulated weightlessness. However, with respect to prevention of atrophic changes in soleus muscle and testis, daily standing for 1 h, 2 h, or 4 h was only partially effective and even totally devoid of any effect, respectively.
Sun
B
B
Department of Aerospace Physiology, The Fourth Military Medical University, Xi'an, China.
Yu
Z B
ZB
Zhang
L F
LF
D000818:Animals; D019417:Hindlimb Suspension / Q000009:adverse effects; D008297:Male; D018482:Muscle, Skeletal / Q000033:anatomy & histology*; D009133:Muscular Atrophy / Q000209:etiology / Q000503:physiopathology / Q000517:prevention & control*; D009200:Myocardial Contraction / Q000502:physiology*; D009929:Organ Size; D010210:Papillary Muscles / Q000503:physiopathology; D011187:Posture / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013737:Testis / Q000033:anatomy & histology*; D013997:Time Factors; D018544:Weightlessness Countermeasures; D018474:Weightlessness Simulation / Q000009:adverse effects*