Orexin levels change as animals develop.

Animals with orexin have genes that encode prepro-orexin and and the two orexin receptors.  However, orexin mRNA and protein are not made in developing rats until a day or two before they are normally born (3).  

The amount of mRNA for both the hormones and their receptors increases dramatically in animals after they are born and before they become adults.  

Orexin may be involved in weaning.

Orexin may have a role in developing weaning behavior in young mammals, or weaning may elicit changes in the orexin system that support adult feeding behavior.

Levels of orexin dramatically increase in young kangaroos around the time of weaning (1), and peak levels of orexin axonal fibers occurs in mice around the same time that adult feeding and sleep-wake patterns are developed (3).

Administration of leptin-- levels of which naturally surge in the period several days before weaning-- to newborn rats increased the expression of mRNA for prepro-orexin a few days later (1).  

Orexin may help in pregnancy.

The mRNA for prepro-orexin is expressed to a greater degree in pregnant rats than in nonpregnant rats during the first days of pregnancy (2).  Orexin may play a role in the different metabolic needs during pregnancy in mammals.