The effect of adrenalectomy on ghrelin secretion and orexigenic action

Ghrelin is an orexigenic peptide made both in the periphery and in the central nervous system. Relatively little is known about the factors that regulate ghrelin secretion. Because both ghrelin and glucocorticoids are increased during fasting, we hypothesised that ghrelin secretion from the stomach is stimulated by glucocorticoids. Plasma ghrelin concentrations were determined by radioimmunoassay in fed and fasted adrenalectomised (ADX) and sham-operated rats. Fasting plasma ghrelin concentrations were significantly increased in ADX relative to sham rats and were normalised by glucocorticoid replacement. Several lines of evidence suggest that the orexigenic action of ghrelin is mediated through neuropeptide Y (NPY)/agouti-related peptide (AgRP) neurones. Because ADX reduces the orexigenic actions of NPY and AgRP, we hypothesised that ADX would also reduce the orexigenic action of ghrelin. Food intake was assessed in ADX and sham rats following an intra-third-ventricular injection of either saline or ghrelin (1, 5 or 10 microg in 2 microl). ADX rats were equally sensitive to the orexigenic action of ghrelin compared to sham rats. Given that ghrelin has been shown to stimulate glucocorticoid secretion, the current data imply the existence of a regulatory feedback loop whereby glucocorticoids inhibit further ghrelin secretion. The results also suggest that, unlike the orexigenic effects of NPY and AgRP, the ability of ghrelin to stimulate food intake is maintained in ADX rats.