Effects of short-term growth hormone administration on plasma leptin levels in normal and diet-induced obesity rats

Abstract

Obesity has related to the alteration of hormonal profiles, i.e. growth hormone (GH), insulin and leptin. Because of the pleiotropic mechanisms of GH, it plays important roles both in the pathophysiological mechanisms and the therapeutic hormonal supplementation, which probably affected plasma leptin. The present research aimed firstly to demonstrate the effect of short-term GH administration on plasma leptin in 3 conditions; basal, meal-induced and fasting condition, from the rats with different adipose tissue mass. Secondly, to investigate short-term effect of GH on insulin sensitivity and body adiposity in control, diet resistant (DR) and diet-induced obesity (DIO) rats. In this regard, the rats were divided to control and hypercaloric (HC) diet-feeding rats. After 6 weeks of feeding period, HC diet-feeding rats were selected for DR and DIO rats. Exogenous GH (1 mg/kg, twice daily) was injected and compared with saline-treated rats. Short-term GH treatment decreased plasma leptin only in DIO rats that significantly occurred at 32 h after the first GH injection. The leptin response probably depended on the higher body adiposity in DIO rats than that of control and DR rats. For meal-induced plasma leptin, short-term GH treatment had no effect in all rats. For fasting condition, GH treatment attenuated the effect of fasting on plasma leptin in control and DR rats, which had the lower adiposity than that of DIO rats. Insulin resistance (IR) was induced by short-term GH treatment, which demonstrated by the higher fasting insulin and increased surrogate indexes of insulin resistance in DR rats, including the homeostasis model IR and adipose tissue IR. Therefore, we conclude that the effect of short-term GH treatment on plasma leptin might depend on body adiposity and energy status. These findings reveal the evidence of short-term GH treatment on plasma leptin and may suggest the short-term GH treatment as adjunctive therapy in obese stage.