Centrally applied ghrelin affects feeding dynamics in male rats

Ghrelin is 28-amino acid peptide, which is produced mainly in the stomach. Since plasma ghrelin are strictly dependent on food intake, this hormone has significant effects on appetite and energy balance. The aim of this investigation was to examine the effects of centrally applied ghrelin on feeding dynamism by measuring the approaches to food container and the amount of food and water intake within 2 hours immediately after ghrelin or PBS injections. Body weight was obtained daily, while ending retroperitoneal (RP) and epididymal (EPI) white adipose tissue (WAT) contents as well as blood levels of leptin and insulin were measured. Five injections of rat ghrelin or PBS (n = 8 per group) were administered once per day (1 microg = 0.15 nmol of ghrelin in 5 microL of PBS), into lateral cerebral ventricle (ICV) of free feeding adult male rats. Results showed that in the first and the second 30-min intervals number of approaches to food container were significantly increased already after the 2(nd) ICV ghrelin application (p < 0.05), by 50% and 67% respectively, in comparison with control rats. Centrally applied ghrelin increased body weight after the 2(nd) injection till the end of treatment (p < 0.05), which was followed by increased food and water intake (p < 0.05). At the end of treatment, RP and EPI WAT contents were increased (by 221%, p < 0.01 and 82%, p < 0.05, respectively). Serum insulin levels were elevated (by 41%, p < 0.05) while serum leptin levels were decreased (by 75%, p < 0.05). These data and the available literature strongly support the opinion that repetitive subnanomolar doses of central ghrelin administration play essential role in food initiation and feeding dynamics in freely feeding adult male rats.