Pharmacologic Treatment of Schizophrenia Beyond Dopamine Receptor Blockade-Has Its Time Come Yet?

This Viewpoint describes the need for novel mechanism of action agents for schizophrenia to extend therapeutic options and improve outcomes.

[Effect of prokinetic drugs inhibiting dopaminergic system on gallbladder motility in subjects with duodenal ulcer]

The purpose of this study was to determine the effect prokinetic drugs inhibiting dopaminergic receptors on gallbladder volume in normal conditions. The study comprised 90 males, aged 20-26 years with duodenal ulcer disease in remission alloted into 3 groups, 30 subject each. The gallbladder volume was determined in group I after placebo or 10 and 20 mg or metoclopramide administration; in group II: placebo or 10 and 20 mg of domperidone and in group III after placebo or 50 and 100 mg of sulphiride administration. Gallbladder motility was assessed ultrasonographically from 15 minutes to 2 hours since placebo or drug administration. The effect of the studied prokinetic drugs in fasting on gallbladder motility was differentiated after metoclopramide no significant changes in gallbladder volume were observed; after domperidone in the dose of 20 mg a slight decrease of gallbladder volume was found, whereas after sulphiryde statistically significant decrease was detected.

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.

Dopamine and dopamine receptor agonists in cardiovascular therapy

Dopamine (DA)--previously regarded simply as the precursor of norepinephrine--is now known to have its own unique effects on cardiovascular regulation which are mediated, in part, by activating specific DA receptors. DA has long been used in the treatment of shock and heart failure. In recent years it has been used at low infusion rates for its renal effects, in combination with other more specific inotropic or pressor agents. Lack of oral bioavailability has limited its use in long-term therapy, however; levodopa and dopa conjugates which are orally absorbed and metabolized to the active form are under investigation. The novel DA1 receptor agonist fenoldopam is claiming a role in the management of hypertension, heart failure, and the preservation of renal function. DA2 receptor agonists are also being evaluated as potential antihypertensive agents.