Ghrelin is a novel polypeptide identified in rat stomach, and it increases GH release, gastric motility, and appetite and modulates many other organ functions. It has been reported that ghrelin may be released from a variety of other tissues, but the absolute contribution of the splanchnic bed remains to be defined. We quantified the splanchnic output of ghrelin in 22 healthy people after an overnight fast, with indwelling catheters in the femoral artery and hepatic vein. Splanchnic ghrelin output was calculated by multiplying veno-arterial difference in ghrelin concentration with splanchnic plasma flow (measured by indicator dye dilution technique). Plasma ghrelin was measured using (125)I-labeled ghrelin and rabbit polyclonal antibody raised against octanoylated human ghrelin. Ghrelin concentrations in the artery and in the hepatic veins were 960 +/- 82 pg/ml and 1102 +/- 90 pg/ml (P < 0.001), respectively. The veno-arterial concentration difference was 143 +/- 38 pg/ml, amounting to 15% of the arterial concentration. The splanchnic output of ghrelin was 141 +/- 43 ng/min (P < 0.003). Assuming that the half-life of ghrelin is less than 60 min, the splanchnic output would explain the entire amount of circulating ghrelin in the postabsorptive state. We conclude that a substantial amount of ghrelin is being released from the splanchnic bed in the postabsorptive state in healthy human subjects and that splanchnic bed is the major source of circulating ghrelin in humans.