Chronic food-restriction alters the expression of somatostatin and growth hormone-releasing hormone in the ovariectomised ewe

Changes in the secretion of GH induced by long-term alterations in nutritio nal status are thought to result from alterations in somatostatin (SRIF) an d growth hormone-releasing hormone (GHRH) at the level of the hypothalamus. To date however, the effect of nutrition on the gene expression of SRIF an d 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 ef fect of under-nutrition on the expression of SRIF and GHRH in the hypothala mus of sheep. Ovariectomised ewes were randomly divided into mio groups and either fed an ad lib diet (n = 6) or a restricted diet of 500 g lucerne ch aff per day (food-restricted; n = 5) for 7 months. lit situ hybridisation w as used to study hypothalamic gene expression for GHRH, SRIF and galanin (G AL). The food-restricted animals had elevated plasma concentrations of GH; this was associated with an increase in GHRH mRNA levels in the arcuate nuc leus (ARC) and reduced SRIF in the rostral periventricular nucleus and vent romedial hypothalamic nucleus. The level of gene expression of GAL in the A RC and SRIF in the caudal periventricular nucleus was similar in ad lib and food-restricted animals. In conclusion, the effect of chronic food-restric tion on the secretion of GH reflects increased GHRH and reduced SRIF synthe sis in the hypothalamus.