Chronic administration of ghrelin regulates plasma glucose and normalizes insulin levels following fasting hyperglycemia and hyperinsulinemia
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© 2015 Elsevier Inc. Ghrelin is an endogenous ligand for the growth hormone secretagogue receptor. The majority of the previous studies have shown that the short-term ghrelin treatment induces hyperglycemia and hypoinsulinemia in healthy humans and rodents. However, the results obtained from long-term treatment with ghrelin are not clear enough. In this study, we assessed acute (1. day) and chronic (21. days) effects of intraperitoneally administered ghrelin (at different doses of 1, 10 and 20. μg/kg) during a 12-h fasting period in rats using glucose oxidase method and direct sandwich ELISA (the Enzyme-Linked Immunosorbent Assay) and then compared the effects of exogenous ghrelin on blood glucose and insulin levels on day 21 with those on day 1. The results showed that acute ghrelin administration markedly increased fasting plasma glucose at doses of 1 and 10. μg/kg as well as insulin levels at 1. μg/kg in comparison to control values. Ghrelin (at 1. μg/kg) altered plasma glucose but not insulin levels on the 21st day compared to control values. In addition, the comparison of the influence of ghrelin administration on plasma glucose and insulin levels on day 21 with those on the first day revealed that the chronic administration of ghrelin notably decreased plasma glucose and insulin levels relative to the acute ghrelin treatment. These findings indicate that hyperglycemia and hyperinsulinemia caused by the exogenous ghrelin during acute treatment are temporary and prolonged treatment with ghrelin regulates plasma glucose and restores insulin to normal levels, suggesting a possible role for ghrelin in improving insulin resistance.