Ghrelin growth hormone secretagogue receptor, with the "GHS-R1b" splice being inactive) is involved in mediating a wide variety of biological effects of ghrelin, including: stimulation of growth hormone release, increase in hunger, modulation of glucose and lipid metabolism, regulation of gastrointestinal motility and secretion, protection of neuronal and cardiovascular cells, and regulation of immune function. They are present in high density in the hypothalamus and pituitary, on the vagus nerve (on both afferent cell bodies and afferent nerve endings) and throughout the gastrointestinal tract. Ghrelin promotes intestinal cell proliferation and inhibits apoptosis during inflammatory states and oxidative stress. It also suppresses
Ghrelin express the ghrelin receptor. The entire ghrelin system (dAG, AG, GHS-R and GOAT) has a gluco-regulatory action. The hippocampus plays a significant role in neurotrophy: the cognitive adaptation to changing environments and the process of learning and it is a potent stimulator of growth hormone. Animal models indicate that ghrelin may enter the hippocampus from the bloodstream, altering nerve-cell connections, and so altering learning and memory. It is suggested that learning may be best during the day and when the stomach is empty, since ghrelin levels are higher at these times. A similar effect on human memory performance is possible.