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Adenosine (symbol A) is an ... Caffeine's principal mode of action is as an antagonist of adenosine receptors in the brain. [12] Methylxanthines (e.g. caffeine found ...
Caffeine keeps you awake by blocking adenosine receptors. Each type of adenosine receptor has different functions, although with some overlap. [3] For instance, both A 1 receptors and A 2A play roles in the heart, regulating myocardial oxygen consumption and coronary blood flow, while the A 2A receptor also has broader anti-inflammatory effects throughout the body. [4]
Adenosine is a neuromodulator that is responsible for motor function, mood, memory, and learning. Its main purpose is the coordination of responses to different neurotransmitters. [5] Adenosine plays many important roles in biological systems, for example in the central nervous-, cardiovascular-, hepatic-, renal- and respiratory system.
The P2RY1 receptor is responsible for shape change in platelets, increased intracellular calcium levels and transient platelet aggregation, while the P2Y12 receptor is responsible for sustained platelet aggregation through the inhibition of adenylate cyclase and a corresponding decrease in cyclic adenosine monophosphate (cAMP) levels.
Fatigue and sedation after heavy exertion can be caused by excess adenosine in the cells which signals muscle fiber to feel fatigued. In the brain, excess adenosine decreases alertness and causes sleepiness. In this way, adenosine may play a role in fatigue from MADD. [4] Recovery from over-exertion can be hours, days or even months.
In the brain, serotonin is a neurotransmitter and regulates arousal, behavior, sleep, and mood, among other things. [9] During prolonged exercise where central nervous system fatigue is present, serotonin levels in the brain are higher than normal physiological conditions; these higher levels can increase perceptions of effort and peripheral muscle fatigue. [9]
This makes adenosine a useful medication for treating and diagnosing tachyarrhythmias, or excessively fast heart rates. This effect on the A 1 receptor also explains why there is a brief moment of cardiac standstill when adenosine is administered as a rapid IV push during cardiac resuscitation.
The adenosine A2A receptor has also been shown to play a regulatory role in the adaptive immune system. In this role, it functions similarly to programmed cell death-1 (PD-1) and cytotoxic t-lymphocyte associated protein-4 ( CTLA-4 ) receptors, namely to suppress immunologic response and prevent associated tissue damage.