Antiemetics receptor specificity

Dopamine is a major neurotransmitter which acts on multiple receptors. It can activate both a and 3 adrenoceptors in addition to acting on specific dopamine receptors. These are widely distributed throughout the CNS and are also present in the renal tubules and renal and mesentric blood vessels, and many dopaminergic drugs are used in the treatment of Parkinson s disease, psychiatric disorders, as antiemetics, and for renal protection. Neuroleptic drugs, such as haloperidol and droperidol, are dopamine receptor antagonists. 

FIGURE 18.4 Pharmacologist s view of emetic stimuli. Myriad signaling pathways lead from the periphery to the emetic center. Stimulants of these pathways are noted in italics. These pathways involve specific neurotransmitters and their receptors (bold text). Receptors are shown for dopamine, D acetylcholine (muscarinic), M histamine, H and 5-hydroxytryptamine, 5-HT. Some of these receptor types also may mediate signaling in the emetic center. This knowledge offers a rationale for current antiemetic therapy. 

As discussed earlier, anandamide but not 2-AG can bind vanilloid VRl receptors whose activation can lead to emetic/antiemetic effects, a property which anandamide shares. Though the tissue levels of both anandamide and 2-AG can be simultaneously altered by drug administration or in pathological states, there is also strong evidence that the release of 2-AG can be independently modified, which can be region specific (Pertwee and Ross, 2002). 

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