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

published July 14, 2009; doi: 10.1 152/ajpendo.00205.2009.-Ghrelin is a stomach-derived peptide that has growth hormone-stimulating and orexigenic activities. Although there have been several reports of ghrelinoma cases, only a few cases have elevated circulating ghrelin levels, hampering the investigation of pathophysiological features of ghrelinoma and chronic effects of ghrelin excess. Furthermore, standard transgenic technique has resulted in desacyl ghrelin production only because of the limited tissue expression of ghrelin O-acyltransferase, which mediates acylation of ghrelin. Accordingly, we attempted to create ghrelin promoter SV4O T-antigen transgenic (OPTag Tg) mice, in which ghrelin-producing cells continued to proliferate and finally developed into ghrelinoma. Adult OP-Tag Tg mice showed elevated plasma ghrelin levels with preserved physiological regulation. Adult OP-Tag Tg mice with increased plasma ghrelin levels exhibited elevated IOF-I levels despite poor nutrition. Although basal growth hormone levels were not changed, those after growth hormone-releasing hormone injection tended to be higher. These results indicate that chronic elevation of ghrelin activates OH-IOF-I axis. In addition, OP-Tag Tg mice demonstrated glucose intolerance. Insulin secretion by glucose tolerance tests was significantly attenuated in OP-Tag Tg, whereas insulin sensitivity determined by insulin tolerance tests was preserved, indicating that chronic elevation of ghrelin suppresses insulin secretion and leads to glucose intorelance. Thus, we successfully generated a Tg model of ghrelinoma, which is a good tool to investigate chronic effects of ghrelin excess. Moreover, their characteristic features could be a hint on ghrelinoma. [ABSTRACT FROM AUTHOR]