Extended Abstract
1. Objectives
Appetite is among the most influential factors in energy homeostasis and its regulation plays an important role in controlling energy balance [1]. The environmental factors involved in energy homeostasis and appetite regulation are often controlled by long-term signals such as ghrelin, cholecystokinin, and peptide YY [2]. Ghrelin, an acylated upper gastrointestinal peptide, is the only known orexigenic hormone [2]. According to studies, of 3 types of mutations in the preproghrelin gene, only 1 is associated with obesity in humans [3]. Thus, overweight and obesity and its related diseases have become a major economic problem in many countries due to their high health and medical costs. The positive effects of exercise and physical activity on preventing obesity and overweight have been reported [4]. The current study evaluated the effect of aerobic training on plasma ghrelin level and the expression of ghrelin lymphocyte gene in elderly men.

2. Methods and Materials
In this quasi-experimental study, 30 elderly men with an average age of 60-70 years and Body Mass Index (BIM) of 25-30 kg/m2 participated. The subjects were selected using convenience and purposeful sampling methods. They were then randomly divided into 2 groups of training (n=15) and control (n=15). Those in the training group received aerobic training for 8 weeks; 4 sessions per week. The duration of each session was 50-60 minutes. The intervention program included: 1. A 10-minute warmup; 2. Aerobic training for 50-60 minutes with an intensity of 60-85% of the maximum heart rate. The training time gradually increased from 20 minutes at the beginning to 45 minutes at the end; and 3. A 10-minute cool down. The intensity of training was measured by a heart rate sensor (Polar, England).
Blood samples were collected 48 hours before initiating the training and 24 hours after the last training session, to measure plasma ghrelin levels using ELISA method, and the expression of ghrelin lymphocyte gene using semiquantitative Reverse Transcription-Polymerase Chain Reaction (RT-PCR) analysis with the sequence of forward primer (5’-ATGTGGAACGCGACCCCCAGCGA-3’) and reverse primer (5′-ACCCCCAATTGTTTCCAGACCCAT-3′). The obtained data were analyzed by SPSS. The between-group and within-group comparisons were conducted using repeated measures Analysis of Variance (ANOVA). The obtained results were evaluated at a significance level of P<0.05. This paper was extracted from a master thesis and has been approved by the Ethics Committee of the Faculty of Sport Sciences at Ferdowsi University of Mashhad (code: 18731).

3. Results
According to the obtained results, no significant differences were found between the 2 study groups in terms of height, BMI, body fat percentage, plasma ghrelin level and the expression of ghrelin lymphocyte gene. ANOVA results presented in Table 1, indicated that an 8-week aerobic training with an intensity of 60-85% of the maximum heart rate could significantly reduce BMI from 27.57 to 26.90 kg/m2 (P=0.001) and body fat percentage from 24.31% to 21.43 % (P=0.001), and could significantly increase the expression of ghrelin lymphocyte gene from 16.87% to 24.92%. Moreover, plasma ghrelin level increased from 0.64 to 0.71 ng/mL; however, this increase was not significant.
The Independent t-test results regarding between-group comparison of posttest mean scores suggested no significant differences between the 2 groups in terms of BMI, body fat percentage, and the expression of ghrelin lymphocyte gene (P>0.05) after the intervention. However, in terms of plasma ghrelin level, a significant difference was observed between the groups. In other words, aerobic training had a significant effect on the increase of plasma ghrelin level in the elderly men.

 

 

4. Conclusion
An 8-week aerobic exercise resulted in a significant decrease in body fat percentage and BMI in the training group. However, the expression of ghrelin lymphocyte gene significantly increased. No significant difference was observed in plasma ghrelin level after the intervention. Therefore, regular aerobic exercise can be used as a non-pharmacological treatment in regulating the balance of peptide hormones, effective in the prevalence of obesity. Possibly, the aerobic exercise causes a negative energy balance in the body. In response to energy shortages, ghrelin stimulates food intake, resupplies lost energy resources, and restores energy balance to compensate for energy reserves in the body. Further studies are required for the recognition of main mechanisms responsible for the association of ghrelin with obesity and the role of physical activity on them.

Ethical Considerations
Compliance with ethical guidelines
All ethical principles were considered in this article. The participants were informed about the purpose of the research and its implementation stages; they were also assured about the confidentiality of their information; Moreover, They were allowed to leave the study whenever they wish, and if desired, the results of the research would be available to them. This paper has been approved by the Ethics Committee of the Faculty of Sport Sciences at Ferdowsi University of Mashhad (code: 18731).

Funding
The present paper was extracted from the MSc. thesis of the first author, in Department of Physiology, Faculty of Physical Education and Sports Sciences, Ferdowsi University of Mashhad.

Authors contributions
All authors contributed in preparing this article.

Conflict of interest
The authors declared no conflict of interest.




   

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