Part of the complexity of hormone and neuropeptide function is that the same chemical produced by different cells/tissues can have different effects on the body.  A good example of this is the hormone oxytocin.  It has been known for a long time that oxytocin acts as a classical 'maternal' hormone that is secreted into the blood to cause contraction of the uterus during birth and regulate milk production in nursing mothers.  However, we now know that oxytocin also acts as a signalling molecule within the brain and exerts 'prosocial' effects, such as reducing aggression, anxiety and depression.