Apelin in goldfish (Carassius auratus): Cloning, distribution and role in appetite regulation

Apelin is a recently discovered peptide produced by several tissues including brain and adipose tissue. In mammals and zebrafish, apelin regulates cardiovascular functions. Recent evidence in mammals suggest that apelin might also regulate food intake. In this study, we cloned a cDNA encoding apelin and examined apelin mRNA distribution within the brain and in peripheral tissues. We also assessed the effects of fasting on apelin brain mRNA abundance. Apelin mRNA was expressed throughout the brain as well as in several peripheral tissues including brain, spleen, heart and fat. Apelin mRNA abundance in both hypothalamus and telencephalon was significant higher in fasted fish than in fed fish. In order to further characterize apelin in goldfish, we assessed the effects of central (intracerebroventricular, icv) and peripheral (intraperitoneal, ip) injections of apelin-13 on food intake in goldfish. Apelin injected ip at a dose of 100 ng/g or icv at a dose of 10 ng/g induced a significant increase in food intake compared to saline-injected fish. Our results suggest that apelin acts as an orexigenic factor in goldfish. Its widespread distribution in the brain and the periphery also suggests that apelin might have multiple physiological regulating roles in fish.