Effect of food restriction on ghrelin in normal-cycling female rats and in pregnancy

Objective: Ghrelin is a 28-amino-acid acylated peptide that was recently identified as the endogenous ligand for the growth hormone secretagogue receptor. Previous studies have shown that ghrelin potently increases growth hormone release and food intake. The aim of this study was to clarify the physiological implications of ghrelin in the regulation of energy balance, by assessing the effect of undernutrition throughout 21 days in normal-cycling and pregnant rats on ghrelin. Research Methods and Procedures: We have determined ghrelin levels by radioimmunoassay and gastric ghrelin mRNA expression by Northern blot analysis during 21 days of chronic food restriction (30% of ad libitum available diet) in normal-cycling female rats and in pregnancy. Results: Our results show that chronic food restriction led to an increase in plasmatic ghrelin levels in normal-cycling female rats. In pregnancy, ghrelin plasmatic levels were enhanced particularly during the latter part of gestation (19 and 21 days) compared with pregnant rats with free access to food. Gastric ghrelin mRNA expression showed a similar expression pattern, being higher in the food-restricted group than in the group fed ad libitum, in normal-cycling as well as in pregnant rats. Discussion: These observations indicate that ghrelin plasmatic levels and ghrelin gastric mRNA are up-modulated during undernutrition in normal-cycling rats and in pregnancy. These findings suggest that increased ghrelin levels may have a role in mediating the physiological responses to undernutrition and could represent an adaptative response to prevent long-lasting alterations in energy balance and body weight homeostasis.