Dopamine: pharmacologic and therapeutic aspects.

Dopamine is a biogenic amine synthesized in the hypothalamus, in the arcuate nucleus, the caudad, and various areas of the central and peripheral nervous system. It has been widely established that dopamine and its agonists play an important role in cardiovascular, renal, hormonal, and central nervous system regulation through stimulation of alpha and beta adrenergic and dopaminergic receptors. There are several agonists of dopamine-2 (DA 2 ) dopaminergic receptors, such as bromocriptine, pergolide, lisuride, quinpirole, and carmoxirole, which inhibit norepinephrine release and produce a decrease in arterial blood pressure; in some cases, bromocriptine and pergolide also reduce heart rate. From a therapeutic point of view, the above-mentioned agonists are used for treating Parkinson's disease, acting over DA 2 dopaminergic receptors of the nigrostriatal system. Bromocriptine and the other dopaminergic agonists mentioned act over DA 2 receptors of the tuberoinfundibular system, inhibiting prolactin release and decreasing hyperprolactinemia and tumor size. Among DA 1 receptor agonists, we can mention fenoldopam, piribedil, ibopamine, SKF 3893, and apomorphine (nonspecific). Activation of these receptors decreases peripheral resistance, inducing lowering of arterial blood pressure and increases in heart rate, sympathetic tone, and activity of the renin aldosterone system. Among DA 2 receptor antagonists, we can mention metoclopramide, domperidone, sulpiride, and haloperidol. From a therapeutic point of view, metoclopramide and domperidone are used in gastric motility disorders, and haloperidol is used in psychotic alterations. Antagonists of DA 1 receptors are SCH23390 and clozapine. Clozapine is used for treating schizophrenia.