In response to various stimuli, along with other adaptive mechanisms, the heart has developed an ability to modulate the systolic and diastolic volumes of the left ventricle as an adaptive mechanism against damaging factors [1-4]. This alteration in contraction strength and volume occurs in response to both pathological conditions (e.g., valvular defects and cardiomyopathies) and physiological stimuli, such as dosed loading with physical exercise [5-7]. The molecular basis for changes in heart rhythm and left ventricular volumes remains partially unclear, with some authors suggesting the interplay of genetic and environmental factors [8-10]. Dosed long-term exercise in rats elicits changes in key cardiological parameters such as left ventricular systolic and diastolic volumes, cardiac output, left ventricular weight, and ventricular wall thickness [11-13]. The heart's adaptive response to physical exertion hinges on the intensity, duration, and variations in left ventricular systolic and diastolic volumes [14-16]. Swimming exercise is considered as an optimal physiological trigger for studying alterations in rat cardiac parameters [17, 18]. In our study, we subjected 12-13-week-old male rats to a 6-week dosed swimming exercise regimen and conducted weekly echocardiographic monitoring [19, 20].
Materials and Methods
Our research material consisted of 12-13-week-old male rats (n=12), which were housed under standard conditions (12-hour light/dark cycle, 22 °C temperature, feeding according to a specific diet , and unlimited water access). The loading was administered during the rats' dark phase circadian rhythm (07:00-19:00 in our study). The rats were divided into two groups: (1) a control group that did not undergo any load (n=6); and (2) a study group that was subjected to a daily 60-minute swimming exercise for 6 weeks, with a load equivalent to 4% of their body weight attached to their tails. All procedures carried out on the rats complied with internationally recognized guidelines and ethical norms.
All rats were weighed weekly to accurately assess weight fluctuations and calculate the weight to be attached to the rat's tail during swimming (4% of body weight).
Control group rats were placed in the swimming apparatus thrice weekly, ensuring the environment emulated the one designated for the study rats. Weekly monitoring was conducted using an echocardiograph specifically designed for experimental animals, adhering to international guidelines for rat echocardiographic research [21 ,22].
The animal studies adhered to the bioethics protocols provided by the World Medical Association's Helsinki Declaration of 2013.
Data from the study were analyzed using specialized software. Metrics from each of the two groups in the study were independently evaluated before conducting a comparative analysis.
Results and Discussion
The study investigated the effect of prolonged physical exertion on the cardiac adaptation capabilities of 12-13-week-old male rats, with a specific focus on alterations in the left ventricular systolic and diastolic volumes. The participating rats, which had an average weight of 250 g, were subjected to a six-week regimen of swimming exercise, with a load equivalent to 4% of their body weight for 60 minutes daily.
The obtained results demonstrate a consistent decrease in both diastolic and systolic volumes of the left ventricle in all rats over the six-week period. The control group's decline appeared more gradual, while the study group, subjected to a sustained exercise load equivalent to 4% of their body weight, exhibited a more pronounced decrease.
When comparing the two groups, the control group had a relatively stable reduction trend in the left ventricular diastolic volume (Figures 1 and 2). For example, Rat 1 in the control group showed an average weekly reduction of 0.075 ml, while Rat 1 from the study group displayed a more rapid decrease, averaging about 0.108 ml per week (Table 1 and 2).
An identical trend was observed in the systolic volume changes (Figures 3 and 4). Here, the weekly average decrease for Rat 1 in the control group was around 0.04 ml, while Rat 1 from the study group had a more significant average decrease of 0.073 mL (Table 3 and 4).
The present study underscores the potential of dosed swimming exercise in driving alterations in left ventricular systolic and diastolic volumes in 12-13-week-old male rats. Following a six-week regimen of daily, 60-minute swimming exercise, carrying a load equivalent to 4% of their body weight, the experimental group exhibited significant changes in their left ventricular volumes. This change was apparent from the second week onward, with a trend towards a decrease in both systolic and diastolic volumes. By the fourth week, coinciding with the onset of hypertrophy, a pronounced decrease in left ventricular volume was noticed.
These findings offer a crucial insight into how sustained physical exercise, specifically in the form of dosed swimming, may induce physiological adaptations in the heart. It particularly sheds light on the change dynamics in systolic and diastolic volumes of the left ventricle. The results thus contribute significantly to our understanding of the heart's adaptive response under physical exertion, adding to our knowledge about pathogenic mechanisms linked with alterations in myocardial contractile force and ventricular volumes.
Therefore, the main added value of this study is providing an experimental model for exploring cardiac adaptations to physical stress. This model can be instrumental in advancing our understanding of cardiac health and diseases, potentially leading to improved preventative and therapeutic strategies. Moreover, the study highlights the need for further investigations to elucidate the molecular basis behind these exercise-induced changes, which remain partially unclear.
The authors would like to express their profound gratitude to Tbilisi State Medical University for their invaluable support in fostering the pursuit of doctoral studies. Their efforts in heightening the allure of advanced research and studies, as well as their provision of essential scientific grants for conducting experimental work, are greatly appreciated. Further appreciation is extended to the Department of Normal Human Anatomy at Tbilisi State Medical University for their unwavering support and collaboration throughout this endeavor.
No potential conflict of interest was reported by the authors.
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
All authors contributed to data analysis, drafting, and revising of the paper and agreed to be responsible for all the aspects of this work.
HOW TO CITE THIS ARTICLE
Nikoloz Vachadze, Anzor Gogiberidze, Ramaz Khetsuriani, Marina Pailodze, Elene Shvangiradze, Nino Pruidze. Alterations in Left Ventricular End-Systolic and End-Diastolic Volumes in 12-13-Week-Old Laboratory Rats Subjected to Dosed Swimming Exercise. J. Med. Chem. Sci., 2023, 6(11) 2727-2734.