Different responses of circulating ghrelin, obestatin levels to fasting, re-feeding and different food compositions, and their local expressions in rats

Obestatin, a sibling of ghrelin derived from preproghrelin, opposes several physiological actions of ghrelin. Our previous study has demonstrated that both plasma ghrelin and obestatin levels were decreased significantly 2h after food intake in human. To further expand current knowledge, we investigated the temporal profiles of their levels in ad libitum fed rats, 48h fasted rats and 48h fasted rats refed 2h with a standard chow, crude fiber, 50% glucose or water, and their expressions in stomach, liver and pancreatic islets immunohistochemically. Plasma ghrelin and obestatin levels were measured by EIA. Plasma leptin, insulin and glucose levels were also evaluated. Both plasma ghrelin and obestatin levels increased significantly in fasted rats compared with ad libitum fed rats. The ingestion of standard chow produced a profound and sustained suppression of ghrelin levels, whereas plasma obestatin levels decreased significantly but recovered quickly. Intake of crude fiber or 50% glucose, however, produced a more profound and sustained suppression of obestatin levels, though they had relatively less impact on ghrelin levels. Plasma glucose was the only independent predictor of ghrelin levels, obestatin levels, and ghrelin to obestatin ratios. Obestatin immunoreactivity was detected in the fundus of stomach, liver and pancreatic islets, with roughly similar patterns of distribution to ghrelin. These data show quantitative and qualitative differences in circulating ghrelin and obestatin responses to the short-term feeding status and nutrient composition, and may support a role for obestatin in regulating metabolism and energy homeostasis.