Hypothalamic mu-opioid receptors in cardiovascular control: a review

The endogenous opioid system includes three major families of peptides [22]: dynorphins (derived from pre-proenkephalin B); endorphins (derived from pre-proopiomelanocortin) and enkephalins (derived from pre-proenkephalin A). Multiple species of opioid peptides are derived from these major precursors and many of them possess potent cardiovascular properties. Multiple forms of opioid receptors have been defined in the central nervous system. Although the relationship of these receptors to the multiple actions of the opioid systems is not well understood, some predications can be made: in vitro the dynorphin-related peptides bind preferentially to kappa-opioid receptors; the enkephalins bind preferentially to delta and mu-opioid receptors and while beta-endorphin binds to mu- and delta-, but not to kappa-opioid receptors. While little is known on the role of the opioid system in normal cardiovascular regulation, it has become clear that cardiovascular stress situations substantially modify the activity of the endogenous opioid system. This review focuses on the mu-opioid system in the hypothalamus with special emphasis on its potential role in cardiovascular control of both normal and pathophysiologic states.