What are the functions of dopamine in the human body across different age groups and demographics?

Dopamine Functions in the Human Body

Dopamine serves as both a critical neurotransmitter in the central nervous system—regulating motor control, reward processing, executive function, and emotional regulation—and as a peripheral hormone controlling renal sodium excretion and cardiovascular hemodynamics. 1, 2

Central Nervous System Functions

Motor Control and Movement Regulation

• Dopamine in the nigrostriatal pathway (substantia nigra to corpus striatum) is essential for coordinated movement, with motor symptoms appearing only after 40-50% of dopaminergic neurons are lost, explaining Parkinson's disease pathophysiology 1
• The indirect movement pathway involves D2 receptor inhibition in the striatum, where dopamine reduces movement suppression by inhibiting these receptors 1
• Dopamine dysfunction in motor pathways underlies the core deficits in Parkinson's disease 3, 4

Reward, Motivation, and Addiction

• The mesolimbic pathway (ventral tegmental area to nucleus accumbens) mediates reward anticipation, evaluation, and learning—the fundamental mechanism underlying addiction and motivational disorders 1
• Dopamine is closely linked to reward, reinforcement, and the development of substance abuse disorders 4
• Obesity results in decreased striatal D2 receptor density, potentially causing compensatory increases in dopamine neurotransmission that perpetuate excessive food intake 1

Executive Function and Cognition

• The mesocortical pathway (ventral tegmental area to prefrontal cortex) controls planning, impulse control, working memory, and attention—deficits that define ADHD 1
• Dopamine D1 receptors play a prominent role in mediating synaptic plasticity, spatial learning and memory, reversal learning, extinction learning, and incentive learning 5
• Dopamine is involved in learning, working memory, cognition, and emotion regulation across multiple brain regions 3, 2

Psychiatric Disorder Pathophysiology

• Antipsychotic efficacy in schizophrenia is mediated through antagonism of dopamine D2 and serotonin 5-HT2A receptors 1
• Stimulants enhance dopamine and norepinephrine in frontal lobe pathways, ameliorating deficits in inhibitory control and working memory in ADHD 1
• Dopamine plays a fundamental role in stereotypic behaviors with direct relevance to obsessive-compulsive disorder 1
• Neuroleptic malignant syndrome results from lack of dopaminergic activity in the CNS, presenting with mental status changes, fever, rigidity, and autonomic dysfunction 1

Cellular Mechanisms

• Dopamine modulates long-term potentiation (LTP) and long-term depression (LTD) in cortical and subcortical areas, affecting synaptic plasticity 3
• Dopamine effects on dendritic spines place this molecule at the interface between motor and cognitive systems 3
• Dopamine acts as a neurotransmitter whose accumulation outside vesicles induces autophagy and cell degeneration 6
• Five dopamine receptor subtypes (DRD1-DRD5) mediate dopamine's diverse functions, with DRD5 activation inducing autophagic cell death in cancer cells and DRD3 activation inducing autophagy while maintaining protein synthesis 6

Peripheral Functions

Renal and Cardiovascular Effects

• Renal dopamine regulates sodium excretion and electrolyte balance, with defective renal dopamine production or receptor function contributing to various forms of hypertension 2
• Dopamine receptors exist in kidney, pancreas, lungs, and blood vessels outside the central nervous system 2
• At low doses (1-2 mcg/kg/min), dopamine predominantly causes dopaminergic receptor stimulation with renal and mesenteric vasodilation 6, 7

Hemodynamic Support in Critical Illness

• At intermediate doses (5-10 mcg/kg/min), dopamine produces β-adrenergic effects with enhanced chronotropy and inotropy 6, 7
• At higher doses (>10 mcg/kg/min), dopamine causes α-adrenergic vasoconstriction 6, 7
• Dopamine is used to treat shock unresponsive to fluids when systemic vascular resistance is low, typically at 2-20 mcg/kg/min 6, 7
• Critical caveat: Low-dose dopamine infusion does not improve renal function despite historical recommendations 6
• Infusion rates >20 mcg/kg/min may result in excessive vasoconstriction or arrhythmias 6, 7

Hormonal Effects

• Dopamine decreases serum concentrations of all anterior pituitary hormones (prolactin, thyrotrophic releasing hormone, growth hormone, and luteinizing hormone) via D receptors in the anterior pituitary and hypothalamic median eminence 6
• Dopamine can induce or aggravate low-T syndrome by suppressing thyroid stimulating hormone secretion and decreasing thyroxin and tri-iodo-thyroxin levels 6
• Dopamine suppresses serum dehydroepiandrosterone sulphate through low prolactin or thyroid hormone levels 6

Immune System Effects

• Dopamine decreases prolactin levels, triggering transient T cell hyporesponsiveness and potentially reducing lymphocyte count 6
• Dopamine may inhibit lymphocyte transformation by mitogens 6

Age-Specific Considerations

Pediatric Populations

• In infants with marked circulatory instability and decompensated shock, epinephrine or norepinephrine may be preferable to dopamine 6, 7
• β-adrenergic effects of dopamine may be reduced in infants and patients with chronic congestive heart failure 6
• In single ventricle postoperative cardiac patients, dopamine increased oxygen consumption without improving blood pressure or cardiac output 6
• For pediatric hypotension refractory to volume replacement, dopamine can be administered at 2-20 mcg/kg/min with continuous hemodynamic monitoring 7

Clinical Monitoring Requirements

• Continuous monitoring of blood pressure, heart rate, and ECG is essential during dopamine administration 7
• Arterial line placement facilitates titration, especially at higher doses 7
• Monitor for extravasation, which causes severe tissue injury; treat with phentolamine (0.1-0.2 mg/kg up to 10 mg diluted in 10 mL saline) injected intradermally at the site 7
• Protect dopamine solutions from light to avoid breakdown 7

Common Pitfalls

• Do not use low-dose dopamine for "renal protection"—this practice lacks evidence and should be abandoned 6
• Avoid excessive doses (>20 mcg/kg/min) due to risk of excessive vasoconstriction and arrhythmias 6, 7
• In critically ill infants, consider epinephrine or norepinephrine first rather than dopamine 6, 7
• Monitor for metabolic effects including hyperglycemia, increased lactate, and hypokalemia with all catecholamines 6
• Be aware of immune suppression effects in critically ill patients receiving dopamine 6