Dopamine agonists and their role in Parkinson's disease treatment

Dopamine agonists directly activate dopamine receptors, bypassing the presynaptic synthesis of dopamine. There are two main classes of dopamine receptors: the D1 class linked to the enzyme adenyl cyclase and the D2 coupled to G-proteins that inhibit adenyl cyclase. Dopamine agonists are effective as monotherapy in early Parkinson's disease and as an adjunctive treatment to levodopa in the advanced stages of the disease. Dopamine agonists are increasingly used early, particularly in young-onset Parkinson's disease due to their levodopa-sparing effects and putative role as neuroprotective agents. The potential neuroprotective property of agonists has been the focus of research and debate in recent years. This review summarizes the use of dopamine agonists in Parkinson's disease and reviews the laboratory, clinical and functional imaging evidence of neuroprotection in this class of drug and discusses the clinical implications of their use in Parkinson's disease management.