Complex sentence: Ghrelin and synthetic ghrelin mimetics (the growth hormone secretagogues) increase food intake and increase fat mass by triggering receptors inn the arcuate nucleus that include the orexigenic neuropeptide Y (NPY) neurons.
Split into simpler sentences: Ghrelin and synthetic ghrelin mimetics (the growth hormone secretagogues) increase food intake and increase fat mass by an action exerted at the level of the hypothalamus. They activate cells in the arcuate nucleus that include the orexigenic neuropeptide Y (NPY) neurons.