Effect of food restriction on ghrelin in adult male rats and its relation to male reproductive hormones

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Abstract
Ghrelin is an endogenous ligand for growth hormone secretagogue (GHS) receptor (GHS-R). It has recently emerged as an orexigenic food intake controlling signal acting upon hypothalamic centres. To study the effect of food restriction on ghrelin level and its relation to male reproductive hormones, 32 adult male albino rats divided into two groups: Group I (8 rats as a control group) fed ad libitum for 21 days and 24 rats as Group II (food-restricted group) fed 30% of ad libitum intake of food consumed by the control group. Rats were weighed every 3 days. Group II rats were further subdivided into three subgroups: IIa, IIb and IIc that were killed at days 8, 16 and 21 from the start of food restriction respectively. Ghrelin level was assayed by ELISA technique in serum samples and tissue homogenates prepared from the stomach and hypothalamus. In addition, male reproductive hormones: testosterone, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were assayed in serum by chemiluminescence. Mean body weight of food restricted rats was observed to decrease during the period of the experiment. Food restriction produced a significant increase of serum ghrelin and a significant decrease of both gastric and hypothalamic ghrelin in group II when compared with group I. The changes in ghrelin level varied with the duration of food restriction. Significant inverse correlation was found between serum ghrelin and each of gastric and hypothalamic ghrelin in group II. A significant decrease of testosterone, FSH and LH were found in food restricted rats compared with controls. The decrease was significantly related to the duration of food restriction. Significant inverse correlation was detected between serum ghrelin and each of the male reproductive hormones in food restricted group II rats. Thus ghrelin could be one of the hormones responsible for the suppression of male reproductive axis in case of negative energy balance.