Abstract

Changes in the secretion of GH induced by long-term alterations in nutritional status are thought to result from alterations in somatostatin (SRIF) and growth hormone-releasing hormone (GHRH) at the level of the hypothalamus. To date however, the effect of nutrition on the gene expression of SRIF and GHRH in a species where GH secretion is increased by food restriction, as is the case for the sheep and human, remains unknown. We determined the effect of under-nutrition on the expression of SRIF and GHRH in the hypothalamus of sheep. Ovariectomised ewes were randomly divided into two groups and either fed an ad lib diet (n=6) or a restricted diet of 500 g lucerne chaff per day (food-restricted; n=5) for 7 months. In situ hybridisation was used to study hypothalamic gene expression for GHRH, SRIF and galanin (GAL). The food-restricted animals had elevated plasma concentrations of GH; this was associated with an increase in GHRH mRNA levels in the arcuate nucleus (ARC) and reduced SRIF in the rostral periventricular nucleus and ventromedial hypothalamic nucleus. The level of gene expression of GAL in the ARC and SRIF in the caudal periventricular nucleus was similar in ad lib and food-restricted animals. In conclusion, the effect of chronic food-restriction on the secretion of GH reflects increased GHRH and reduced SRIF synthesis in the hypothalamus.