[Obestatin and the regulation of energy balance in physical activity]

Obestatin, a peptide which is encoded by the same preproghrelin gene as Ghrelin, conveys information concerning the nutritional status and/or the energy stores to the central nervous system. In obese populations, circulating levels of the peptide are altered. Ghrelin, mostly acting through the GH secretagogue receptor GHS-R, is a potent GH secretagogue, an orexigenic peptide and a long-term regulator of energy homeostasis. Obestatin was described for its anorexigenic effects and it's binding to GPR39. However recent studies do not support the role of obestatin/GPR39 system in the regulation of energy balance. Because exercise training improves the health status of obese individuals and is associated with reduction of body weight, there is growing interest in the effects of exercise on obestatin and whether this peptide may provide better understanding of how exercise improves health. Obestatin levels do not increase in response to acute exercise, and therefore obestatin does not appear to regulate growth hormone [GH] release during exercise. There is some evidence that obestatin levels do not change in plasma following resistance exercise with higher GH concentrations during exercise and decreases in tissues following chronic exercise but not in plasma. This review is focuses on obestatin, by first summarizing it function and it relationship with hormonal and metabolic changes that affect energy balance, and then discussing the effects of acute and chronic exercise on plasma and tissues obestatin concentrations, and the potential mechanisms involved

effect of treadmill running on plasma and muscle agouti-related protein [AGRP] concentration in male rats

Appetite regulation is one of the most important issues in exercise physiology. AGRP is one of the most important neuropeptide in appetite regulation and energy homeostasis. The aim of this study was to investigate the effect of treadmill running on plasma and muscle [Soleus] concentration of AGRP in male Wistar rats. Forty rats were randomly assigned into two groups. The training group was given exercise on a motor-driven treadmill at 28 m/min [equal to 75% vo2max] for 60 min/day, 5 days/week for 10 weeks. After finishing the exercise protocol, each group was divided into 2 subgroups, the fasting and the fed [n=10] groups. Each subgroup was anesthetized and sacrificed after an overnight fast and the other, after 3 hours of food deprivation. The results showed muscle and plasma AGRP were significantly [P < 0.001] higher in the trained rats in comparison to the control rats. Also there was a significant and positive correlation between Soleus AGRP and plasma AGRP. It can be speculated that negative energy balance as well as local hyperphagia in muscle, induced by exercise produces satiety, signals the hypothalamus, which therefore increases release of AGRP facilitating energy recovery. This mechanism may be involved in glycogen supercompensation as well