Effect of 4 Weeks of Progressive Resistance Training on Plasma Levels ofOmentin-1 and Metabolic Factors in Diabetic Male Rats

Obesity is one of the main problems in the world [1]. A wide range of genetic, biological, behavioral, and environmental factors can lead to obesity [2]. Obesity is mostly related to chronic cardiovascular disorders and type 2 diabetes mellitus (T2DM) in middle-aged and old people [1]. People with obesity, T2DM or metabolic syndrome face various problems when performing sports activities which are often recommended as a non-pharmacological treatment for obesity [3]. Omentin-1 is a recently found adipokine that is expressed in visceral adipose tissue. It is synthesized and secreted in the adipose tissue stem cells and can have a role in increased glucose transport in adipose tissue by insulin. It may also play a role in regulating insulin sensitivity in a paracrine or endocrine manner. In addition, it is involved in the regulation of lipid metabolism and body fat distribution. Diabetes is associated with decreased Omentin-1 levels. Pan et al. [12] showed that Omentin-1 level increases after weight loss. A study also reported that Omentin-1 level has a negative relationship with body mass index, fasting insulin, homeostasis model of insulin resistance, and plasma level of glucose [13]. Physical activities have been suggested to have a role in controlling Omentin-1 level and insulin resistance. This study aims to investigate the effect of progressive resistance training (PRT) on the lipid profile, Omentin-1 level, and insulin resistance in diabetic rats.

In this study, 24 male Wistar rats aged 8 weeks (Mean weight=22±228 g) were selected as samples. The animals were kept at a temperature of 22±2°C, a humidity of 50±5%, and in a 12:12 light cycle. One week after their transfer to the laboratory, diabetes was induced. Then, they were randomly divided into three groups matched for weight including diabetic (n=8), diabetic+PRT (n=8), and healthy control (n=8). The rats in the control group did not have any exercise. The PRT was performed for four weeks, three days a week. Forty-eight hours after the last training session, rats were anesthetized with ketamine, and their blood samples were taken directly from their heart to measure the serum concentrations of omentin-1, glucose, and insulin. Descriptive statistics including mean and standard deviation were used to describe the data, and one-way analysis of variance (ANOVA) was used to examine the difference among the three groups, followed by the least significant difference (LSD) post hoc test. Analyses were done in SPSS software, version 22. The significance value was set at 0.05.

The results of one-way ANOVA showed that there was a significant difference between the study groups in the levels of omentin-1 (F=16.788, P<0.05), glucose (F=249.13, P<0.05), insulin (F=15.68, P<0.05) P<0) and triglyceride (F=7.895, P<0.05), but not in the levels of high-density lipoprotein (F=0.318, P>0.05), low-density lipoprotein (F=0.612, P>0.05), and cholesterol (F=0.049, P>0.05). The results of the LSD post hoc test showed that there was a significant difference in the plasma concentration of omentin-1 between the healthy control and diabetic control groups (P=0.001), between the healthy control and  exercised diabetic groups (P=0.004) and between the diabetic control and exercised diabetic groups (P=0.017). Regarding the glucose level, the results of LSD post hoc test showed a significant difference between the healthy control and diabetic groups (P=0.001) and between the healthy control and diabetic+PRT groups (P=0.001), while no significant difference was found between diabetic+PRT and diabetic groups (P=0.92). Regarding the insulin level, the results of the LSD post hoc test showed a significant difference between the healthy control and diabetic groups (P=0.001) and between the healthy control and diabetic +PRT groups (P=0.001), while no significant difference was found between diabetic+PRT and diabetic groups (P=0.9). Regarding the triglyceride level, the results of the LSD test showed a significant difference between the healthy control and diabetic groups (P=0.001), between the diabetic and diabetic+PRT groups (P=0.001) and between healthy control and diabetic+PRT groups (P=0.017).

The findings of the present study indicated an increase in the plasma level of omentin-1 in diabetic rats performed PRT compared to diabetic rats without training. This result may indicate the improvement of insulin sensitivity after training and the anti-inflammatory role of PRT. However, the PRT had no significant effect on glucose level and lipid profile. According to the effect of PRT on the omentin-1 level, it seems that PRT reduces adipokine factors and the resulting inflammation in diabetic people. In vitro studies have shown that omentin-1 increases insulin transduction by activating the Akt protein kinase B and increasing insulin-stimulated glucose transport in isolated human adipocytes [29]. Therefore, it can be assumed that omentin-1 improves glucose homeostasis and insulin sensitivity through the activation of Akt signaling [28]. Therefore, since about 82-85% of blood glucose is taken up by skeletal muscles and omentin-1 plays a role in stimulating the insulin receptors of skeletal muscles and glucose uptake [31], it seems that the increase in plasma level of omentin-1 after PRT in diabetic patients or those with insulin resistance are important in controlling hyperglycemia. The most important physiological event in diabetes is the increase in blood sugar (hyperglycemia), which can be reduced by regular exercise. However, the exact mechanism of the effect of PRT on the omentin-1 level in human and animal samples is still unknown, and there is a need for more studies in this field.