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Submitted on April 25, 2003
Accepted on July 28, 2003
1 Department of Physiology, Department of Morphological Science, Department of Medicine-Molecular Endocrinology Section, University of Santiago de Compostela, School of Medicine, 15705 Santiago de Compostela, Spain
* To whom correspondence should be addressed. E-mail: fscadigo{at}usc.es.
Ghrelin, a 28 amino acid acylated peptide, strongly stimulates GH release and food intake. In the present study, we find that ghrelin is expressed in somatotrophs, lactotrophs and thyrotrophs, but not in corticotrophs or gonadotrophs of rat pituitary.
Persistent expression of the ghrelin gene is found during postnatal development in male and female rats, although the levels significantly decrease in both cases from pituitaries of 20-day-old rats onwards, while at 60-day-old the levels were higher in male than in female rats. This sexually dimorphic pattern appears to be mediated by estrogens, since ovariectomy, but not orchidectomy, increases pituitary ghrelin mRNA levels. Taking into account that somatotroph cell function is markedly influenced by thyroid hormones, glucocorticoids, GH and metabolic status, we also assess such influence. We find that ghrelin mRNA levels decrease in hypothyroid and in glucocorticoid treated rats; increase in GH-deficient rats (dwarf rats) and remain unaffected by food-deprivation.
In conclusion, we have defined the specific cell types that express ghrelin in the rat AP gland. These data provide direct morphological evidence that ghrelin may well be acting in a paracrine-like fashion in the regulation of AP cell function. In addition, we clearly demonstrate that pituitary ghrelin mRNA levels are age- and gender-dependent. Finally we show that pituitary ghrelin mRNA levels are influenced by alteration on thyroid hormone, glucocorticoids and GH levels, but not by fasting, which indicates that the regulation of ghrelin gene-expression is tissue-specific.
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