Ghrelin in the summer flounder: Immunolocalization to the gastric glands and action on plasma cortisol levels

We searched for evidence of the hormone ghrelin in the stomach of a juvenile, marine teleost, the summer flounder. Using antiserum against the conserved core of the ghrelin peptide, immunoreactivity was observed in the simple, branching epithelium that comprises the gastric glands. The immunoreaction was especially strong in the glandular epithelium located deep in the tissue. Next, we assessed a possible connection between ghrelin and the hypothalamic–pituitary–interrenal axis through a series of three injection experiments in which acylated or non-acylated (des-acyl) ghrelin was injected into the peritoneum of summer flounder (Paralichthys dentatus). A significant increase in plasma cortisol relative to saline-injected controls was observed for the acylated form at a dose of 1000 ng g− 1 of body mass in one of the experiments. In another, there was a trend for des-acyl ghrelin at 1000 ng g− 1 of body mass to increase plasma cortisol. Taken together, this study provides evidence that gastric glands in the stomach of summer flounder are a site of ghrelin production and that peripherally administered ghrelin can stimulate the cortisol axis in a teleost.