Dopamine agonist - Dopamine Insomnia

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A dopamine receptor agonist is a compound that activates dopamine receptors. Dopamine receptor agonists activate signaling pathways through trimeric G-proteins and ?-arrestins, ultimately leading to changes in gene transcription.

Today, for several dopamine receptor subtypes (D1, D2, D3) agonists are known, that differentially address these signalling pathways. They are called biased agonists.

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Uses

Some medical drugs act as dopamine agonists and can treat hypodopaminergic (low dopamine) conditions; they are typically used for treating Parkinson's disease, attention deficit/hyperactivity disorder (in the form of stimulants) and certain pituitary tumors (prolactinoma), and may be useful for restless legs syndrome (RLS). Both Requip (Ropinirole) and Mirapex (Pramipexole) are FDA-approved for the treatment of RLS. There is also an ongoing clinical trial to test the effectiveness of the dopamine agonist Requip (ropinirole) in reversing the symptoms of SSRI-induced sexual dysfunction. Additionally, a systematic review and meta-analysis concluded that prophylactic treatment with cabergoline reduces the incidence, but not the severity, of ovarian hyperstimulation syndrome (OHSS), without compromising pregnancy outcomes, in females undergoing stimulated cycles of in vitro fertilization (IVF).

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Side-effects

Some of the common side effects of dopamine agonists include:

• Euphoria
• Pericardial effusion
• Fibrous thickening of lining that covers some of the internal organs including the heart or the lungs (fibrotic reaction)
• Hallucinations
• Causing or worsening psychosis
• Orthostatic hypotension
• Increased orgasmic intensity
• Weight loss
• Anorexia (symptom)
• Nausea and possible vomiting
• Insomnia
• Unusual tiredness or weakness
• Dizziness
• Drowsiness
• Possible Narcolepsy manifestations (Sleep attacks)
• Lightheadedness
• Raynaud's phenomenon (common side effect of ergot derivatives)
• Syncope
• Twitching, twisting, or other unusual body movements
• Pathological addiction (gambling, shopping, internet pornography, hyper-sexuality) - specifically D₃-preferring agonists

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Examples

Examples of dopamine agonists include:

Partial agonist

• Aripiprazole (Partial agonist of the D₂ family receptors - Trade name "Abilify" in the United States; atypical antipsychotic)
• Phencyclidine (a.k.a. PCP; partial agonist. Psychoactivity mainly due to NMDA antagonism)
• Quinpirole (Partial agonist of the D₂ and D₃ family of receptors)
• Salvinorin A (chief active constituent of the psychedelic herb salvia divinorum, the psychoactivity of which is mainly due to Kappa-opioid receptor agonism; partial agonist at the D₂ with an Intrinsic activity of 40-60%, binding affinity of K_i=5-10nM and EC₅₀=50-90nM)

Agonists of full/unknown efficacy

• Apomorphine (Apokyn - used to treat Parkinson's disease/Restless leg syndrome) - G-protein bias at the D1 receptor.
• Bromocriptine (Parlodel - used to treat Parkinson's disease/Restless leg syndrome)
• Cabergoline (Dostinex - used to treat Parkinson's disease/Restless leg syndrome)
• Ciladopa (used to treat Parkinson's disease/Restless leg syndrome)
• Dihydrexidine (used to treat Parkinson's disease/Restless leg syndrome)
• Dinapsoline (used to treat Parkinson's disease/Restless leg syndrome)
• Doxanthrine (used to treat Parkinson's disease/Restless leg syndrome)
• Epicriptine (used to treat Parkinson's disease/Restless leg syndrome)
• Lisuride (used to treat Parkinson's disease/Restless leg syndrome)
• Pergolide (used to treat Parkinson's disease/Restless leg syndrome) - previously available as Permax, but removed from the market in the USA March 29, 2007.
• Piribedil (Pronoran and Trivastal - used to treat Parkinson's disease/Restless leg syndrome)
• Pramipexole (Mirapex and Sifrol - used to treat Parkinson's disease/Restless leg syndrome)
• Propylnorapomorphine (used to treat Parkinson's disease/Restless leg syndrome)
• Quinagolide (Norprolac - used to treat Parkinson's disease/Restless leg syndrome)
• Ropinirole (Requip - used to treat Parkinson's disease/Restless leg syndrome)
• Rotigotine (Neupro - used to treat Parkinson's disease/Restless leg syndrome)
• Roxindole (used to treat Parkinson's disease/Restless leg syndrome)
• Sumanirole (used to treat Parkinson's disease/Restless leg syndrome)

Some, such as fenoldopam, are selective for dopamine receptor D1.

Indirect agonists

There are two classes of drugs that act as indirect agonists of dopamine receptors: dopamine reuptake inhibitors and dopamine releasing agents.

The most commonly prescribed indirect agonists of dopamine receptors include:

• Amphetamine and/or dextroamphetamine (used to treat attention deficit hyperactivity disorder, narcolepsy, and obesity)
• Bupropion (used to facilitate smoking cessation and treat nicotine addiction and clinical depression)
• Lisdexamfetamine (used to treat attention deficit hyperactivity disorder and binge eating disorder)
• Methylphenidate or dexmethylphenidate (used to treat attention deficit hyperactivity disorder and narcolepsy)

Other examples include:

• Cathinone (no medical uses)
• Cocaine (no medical uses as a central nervous system stimulant)
• Methamphetamine (used in rare circumstances to treat attention deficit hyperactivity disorder and obesity)
• Phenethylamine (endogenous trace amine with no medical uses)
• p-Tyramine (endogenous trace amine with no medical uses)

Source of the article : Wikipedia