To establish a tool to study ghrelin production and secretion in vitro, we developed a novel ghrelin-producing cell line, MGN3-1 (mouse ghrelinoma 3-1) cells from a gastric ghrelin-producing cell tumor derived from ghrelin-promoter Simian virus 40-T-antigen transgenic mice. MGN3-1 cells preserve three essential characteristics required for the in vitro tool for ghrelin research. First, MGN3-1 cells produce a substantial amount of ghrelin at levels approximately 5000 times higher than that observed in TT cells. Second, MGN3-1 cell expressed two key enzymes for acyl modification and maturation of ghrelin, namely ghrelin O-acyltransferase for acylation and prohormone convertase 1/3 for maturation and the physiological acyl modification and maturation of ghrelin were confirmed. Third, MGN3-1 cells retain physiological regulation of ghrelin secretion, at least in regard to the suppression by somatostatin and insulin, which is well established in in vivo studies. Thus, MGN3-1 cells are the first cell line derived from a gastric ghrelin-producing cell preserving secretion of substantial amounts of ghrelin under physiological regulation. This cell line will be a useful tool for both studying the production and secretion of ghrelin and screening of ghrelin-modulating drugs.

To understand the physiological role of ghrelin, it is crucial to study both the actions of ghrelin and the regulation of ghrelin secretion. Although ghrelin actions have been extensively revealed, the direct factors regulating ghrelin secretion by ghrelin-producing cells (X/A-like cells), however, is not fully understood. In this study, we examined the effects of peptide hormones and neurotransmitters on in vitro ghrelin secretion by the recently developed ghrelin-producing cell line MGN3-1. Oxytocin and vasopressin significantly stimulated ghrelin secretion by MGN3-1 cells. Because MGN3-1 cells express only oxytocin receptor mRNA, not vasopressin receptor mRNA, oxytocin is the likely regulator, with the effect of vasopressin mediated by a cross-reaction. We also discovered that dopamine stimulates ghrelin secretion from MGN3-1 cells in a similar manner to the previously known ghrelin stimulators, epinephrine and norepinephrine. MGN3-1 cells expressed mRNA encoding dopamine receptors D1a and D2. The dopamine receptor D1 agonist fenoldopam stimulated ghrelin secretion, whereas the D2, D3 agonist bromocriptine did not. Furthermore, the D1 receptor antagonist SKF83566 attenuated the stimulatory effect of dopamine. These results indicate that the stimulatory effect of dopamine on ghrelin secretion is mediated by the D1a receptor. In conclusion, we identified two direct regulators of ghrelin, oxytocin and dopamine. These findings will provide new direction for further studies seeking to further understand the regulation of ghrelin secretion, which will in turn lead to greater understanding of the physiological role of ghrelin. (Endocrinology 152: 2619 -2625, 2011) G hrelin is a stomach-derived 28-amino acid peptide hormone with a unique modification of acylation, first described by Kojima et al. in 1999 (1). To understand better the physiological function of ghrelin, it is crucial to study both ghrelin action and the regulation of ghrelin secretion. The actions of ghrelin have been vigorously investigated by multiple groups, revealing a wide variety of activities, including GH-stimulating (2), orexigenic (3), fat-storing (4), cardiovascular (5), gastroprokinetic (6), and insulin-suppressing (7) activities. In contrast, the regulation of ghrelin secretion from ghrelin-producing cells (X/A-like cells) is not fully understood. Although the results of in vivo studies suggest that plasma ghrelin levels are regulated by acute and chronic energy status (8 -10), the individual factors regulating ghrelin secretion by ghrelin-producing cells (X/A-like cells) remains unclear due to the lack of an appropriate in vitro assay system.Recently we established a ghrelin-producing cell line, MGN (mouse ghrelinoma) 3-1 cells from a gastric ghrelinoma isolated from ghrelin promoter SV40-T antigen transgenic mice (11, 12). The MGN3-1 cell is the first cell line derived from a gastric ghrelin-producing cell that preserves the ability to secrete of substantial amounts of ghrelin under physiological regulation, making this line one of Abbre...

Aging is associated with decreases in food intake and GH secretion, termed the anorexia of aging and somatopause, respectively. The mechanisms underlying these phenomena are not fully understood. Although many approaches have attempted to improve these age-related physiological changes, none have achieved satisfactory results. Ghrelin, a 28-amino-acid acylated peptide, was identified as an endogenous ligand for the GH secretagogue receptor. Ghrelin stimulates GH secretion and food intake in animals and humans. Previous studies have demonstrated that the mean plasma concentrations of ghrelin in normal-weight elderly people were lower than those in younger people. We hypothesized that ghrelin administration might improve the metabolic and physiological changes that accompany the anorexia of aging and somatopause. First, 75-wk-old mice fasted for 72 h, after which they resumed feeding with sc administration of ghrelin (360 microg/kg) twice daily for 4 d. Multiple administrations of ghrelin after a 72-h fast increased food intake and hastened body weight recovery with a high lean body mass ratio. Next, 50-wk-old mice were sc injected with rat ghrelin (40 microg/kg) twice weekly from 50-80 wk of age. Long-term administration of ghrelin kept aged mice with low body weight and low adiposity. These results suggest that ghrelin might be a novel approach for the therapy of age-related metabolic and physiological changes.

Akamizu T. A mouse model of ghrelinoma exhibited activated growth hormone-insulin-like growth factor I axis and glucose intolerance.

Abstract. This report concerns a case of cortisol-producing adrenocortical adenoma without the phenotype of Cushing's syndrome. A left adrenal tumor was incidentally detected in this patient. A diagnosis of adrenal Cushing's syndrome was based on the results of endocrinological and radiological examinations, although she showed none of the physical signs of Cushing's syndrome, glucose intolerance, hypertension or dyslipidermia. After a successful laparoscopic left adrenalectomy, the pathological diagnosis was adrenocortical adenoma. Slow tapering of glucocorticoids was needed to prevent adrenal insufficiency after surgery, and the plasma ACTH level remained high even though the serum cortisol level had reached the upper limit of the normal range. Further examination showed a urinary THF + allo-THF/THE ratio of 0.63, which was lower than that of control (0.90 ± 0.13, mean ± SD). Serum cortisol/cortisone ratios after the cortisone acetate administration were also decreased, and the serum half-life of cortisol was shorter than the normal range which has been reported. These findings indicated a partial defect in 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) activity, which converts cortisone to cortisol. Our case suggests that a change in 11β-HSD1 activity results in inter-individual differences in glucocorticoid efficacy.