Since the 1980’s a number of so-called ‘appetite regulating’ peptides (ARP) have been discovered within the hypothalamus and the roles that these play in the regulation of feeding and energy expenditure is well documented. As a general rule, those peptides that stimulate food intake also reduce reproductive function and vice versa. This has been demonstrated in various species and may be an adaptive measure that evolved to allow direction of energy towards either accumulation of energy or reproduction. Neuropeptide Y (NPY) is an orexigen produced in the arcuate nucleus and it negatively regulates reproduction. In sheep, the effect to suppress reproductive function is effected via the Y2 receptor, whereas the Y1 receptor mediates orexigenic effects. The pro-opiomelanocortin (POMC) cells of the arcuate nucleus produce melanocortins which suppress appetite. Central administration of with the anorexigenic melanocortin, α-melanocyte stimulating hormone (α-MSH) stimulates gonadotropin secretion. Within the arcuate nucleus, the NPY cells and the POMC cells connect to the kisspeptin cells and this may explain how ARP impact on reproductive function. Cells in the dorsomedial nucleus of the hypothalamus produce gonadotropin inhibitory hormone (GnIH), which project to the ARP cells of the lateral hypothalamus as well as the gonadotropin releasing hormone (GnRH) cells. Accordingly, this peptide suppresses reproductive function and stimulates food intake. Circulating factors such as leptin and ghrelin also have effects on the reproductive axis, the former being stimulatory and the latter being inhibitory. These data explain some effects of body weight on reproduction because relative adiposity dictates levels of ARP expression. There is also an indication that potential ARP-based therapeutics may impact on reproductive function.