Abstract

Specific dopaminergic receptors, distinct from the classic alpha and beta-adrenergic receptors, are found in the central and peripheral nervous system and in some non-neuronal tissues. Two types of dopaminergic receptors have different functions and different second messengers. Dopamine is a potent agonist for both types of receptors; the action of dopamine is antagonized by phenothiazines and thioxanthines. The Dj receptor mediates sodilation in the renal, mesenteric, coronary and cerebral territories. Fenoldopam is an investigational selective agonist of the Dj receptor. The D2 receptor inhibits the transmission of nerve impulses in the sympathetic ganglia, inhibits the release of NE from the sympathetic nerve endings by acting on the presynaptic membrane (ura 70-2), inhibits the release of prolactin from the pituitary gland and causes vomiting. Selective D2 receptor agonists include: bromocriptine, lergotril and apomorphine, while butyrophenones such as haloperidol (active in the central nervous system), domperidone (does not cross the blood-brain barrier easily) and sulpiride (a benzamide) are relatively selective D2 receptor antagonists.