Interaction effect of 4 weeks of endurance training and octopamine on gene expression of PGC-1α in brown adipose tissue of male rats fed with DFO

Obesity, as a primitive risk factor in type 2 diabetes, is recognized by the imbalance between absorption and energy expenditure. This imbalance is probably due to the combined effect of reduced physical activity and increased supply of fried foods and fast food at reasonable prices. Brown adipose tissue (BAT) has a substantial ability to dissipate excess energy as heat in a process called thermogenesis, which is activated in response to stimulants such as high-fat diets, cold and exercise training. Nowdays, the consumption of fried foods such as french fries has become very popular among human societies. The use of heat causes chemical changes, including oxidation, that can affect mitochondrial function. PGC-1α is the major regulator of brown adipose tissue thermogenesis. Low levels of PGC-1α gene expression increase ROS production and cause oxidative stress. Endurance training is used to prevent and treat obesity, insulin resistance, or type 2 diabetes because of its ability to improve mitochondrial function and fatty acid oxidation. One of the adaptations resulting from exercise is altered expression of the PGC-1α gene. Octopamine is an antioxidant and endogenous antioxidant biogenic amine that has properties similar to catecholamines such as norepinephrine. Octopamine has the ability to stimulate lipolysis and fat metabolism . The present study aimed to determine the interaction effect of 4 weeks of endurance training and octopamine on gene expression of PGC-1α in brown adipose tissue of male rats fed with DFO.

In an experimental study, 30 adult male Wistar rats weighing an average of 300 to 350 g and aged 8 weeks were purchased. All rats were kept in polycarbonate cages (5 mice per cage) at 22°C, 55% humidity and under the light and dark cycle for 12:12 hours without restriction on water and food. Rats were randomly divided into five groups: healthy control (n=6), deep frying oil (DFO, n=6), endurance training + DFO (n=6), octopamine + DFO (n=6) and endurance training + octopamine + DFO (n=6). Intraperitoneal injection of 10 ml/kg of octopamine and gavage of deep -frying oil were done five times a week and every day, respectively.To adapt the rats in the aerobic training group, before starting the main training program, the rats in this group ran at a speed of 9 m / min for 20 minutes for a week. The endurance training protocol consisted of 4 weeks of endurance training and 5 sessions a week week. The training session included 5 minutes of warm-up at 7 m / min and 5 minutes of cooling at 5 m / min. The intensity of training started in the first week with 50% vo2max and a speed of 16 m / min, and in the last week it reached 65% vo2max and a speed of 26 m / min. To prepare deep frying oil, 8 liters of sunflower oil was heated for 190 consecutive days at a temperature of 190 to 200 ° C for 4 consecutive days.48 hours after the last training session and 8 hours of fasting, all rats were anesthetized with chloroform and then sacrificed. The brown adipose tissue was immediately removed from the body and stored in a nitrogen tank at -80 ° C. Gene expression of PGC-1α was measured by Real time PCR. Independent t-test, two-way analysis of variance and Bonferoni post hoc tests were used to analyze the data. All the analyses were done by SPSS software version 21 and the charts were drawn using Microsoft Excel software version 16. The significance level was p<0.05.

The results showed that consumption of deep frying oil induced significant decrease in gene expression of PGC-1α (p<0.05) compared to the healthy control group. The endurance training caused a significant increase in gene expression of PGC-1α (p>0.05) compared to the DFO group. Effect of octopamine alone and the interaction effect of endurance training and octopamine caused the non-significant increase in PGC-1α gene expression in comparison with the DFO group (P>0.05).

The endurance training and octopamine may have influenced PGC-1α gene expression through their antioxidant and lipolytic properties. However, the octopamine group and the interaction group of endurance training and octopamine require changes in the dose, intensity, and duration of endurance training for their effects to be statistically significant. Probably, endurance training has affected PGC-1α gene expression by stimulating elevated levels of catecholamines (epinephrine), stimulation of beta-adrenergic receptors through the upregulation of orexin signals in adipose tissue, and activation of CREB transcription factors. In addition, exercise can increase the gene expression of PGC-1α by increasing and activating NRF2 and binding it to the Antioxidant response element (ARE) and finally the production of antioxidants.