Effects of acute ethionine injection on plasma ghrelin and obestatin levels in trained male rats

Abstract

Ghrelin and obestatin are orexigenic and anorexigenic peptides, respectively, that are secreted from the stomach mucosa into the circulation. These peptides have opposing actions on food intake, weight gain, and adiposity. It is thought that ghrelin is sensitive to a negative energy environment and also plays a considerable role in short- and long-term energy balance and glucose homeostasis. It has been suggested that the levels of ghrelin and obestatin are upregulated by fasting, hypoglycemic status, and a physical-exercise–induced energy deficit. Ethionine (ETH), the ethyl analogue of methionine, has been shown to increase food intake, decrease adenosine triphosphate (ATP) and glycogen levels, and inhibit protein synthesis in the liver. The purpose of this study was to examine the effect of a single dose of ETH (0.7 mg/g of body weight) injection on resting plasma total ghrelin and obestatin concentrations in male trained rats. Thirty-two adult Wistar male rats weighing 180 to 200 g were randomly assigned to control (n = 16) and training (n =16) groups. The training group was exercised for 10 weeks (25 m/min, 0% grade, 60 minutes, and 5 d/wk). Seventy-two hours after the last exercise session, rats were injected with either saline (NaCl) or ETH and then killed. Ethionine compared with a NaCl injection resulted in significant ( P < .013) reductions in resting hepatic ATP and glycogen levels, and in a significant ( P < .001) increase in concentrations of plasma total ghrelin but not obestatin. The results indicate that ETH-induced liver ATP and glycogen deficiency could exert a powerful regulatory influence on plasma total ghrelin, but this is not the case for obestatin. Findings demonstrate the short-term energy-regulating capacity of ghrelin.