The effect of centrally administered ghrelin on pituitary ACTH cells and circulating ACTH and corticosterone in rats
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Ghrelin is a brain-gut peptide known for its growth hormone (GH)-releasing and appetite-inducing activities. This natural GH secretagogue (GHS) was originally purified from rat stomach, but it is expressed widely in different tissues where it may have endocrine and paracrine effects. The central effects of ghrelin on adrenocorticotropic, hormone (ACTH) cells, ACTH release and subsequent corticosterone release from adrenal glands remains to be clarified. The aim of this study was to specifically determine the morphological features of ACTH-producing pituicytes and blood concentration of ACTH and corticosterone after central administration of ghrelin. Five doses of rat ghrelin or PBS (n = 10 per group) were injected every 24 h (1 mu g of ghrelin in 5 mu L PBS), into the lateral cerebral ventricle of male rats. Results showed that ghrelin increased (p < 0.05) absolute and relative pituitary weights compared to controls (58% and 41% respectively). Morphometric parameters, i.e. the volume of the ACTH cells, nuclear volume, and volume density were all increased (p < 0.05), by 17%, 6% and 13%, respectively, 2 h after the last ghrelin treatment. Ghrelin increased circulating concentrations of ACTH and corticosterone (p < 0.05) by 62% and 66%, respectively. The data provide clear documentation that intracerebroventricular ghrelin stimulates ACTH cell hypertrophy and proliferation, and promotes ACTH and corticosterone release. Determining the role of ghrelin in physiological stress responses and whether control of the peptide's activity would be useful for prevention and/or treatment of stress-induced diseases remain important research goals. (c) 2006 Elsevier Inc. All rights reserved.