Xanthine Stimulants

methylxanthines

a family of related chemicals including caffeine, theophylline, and theobromine, that act as CNS stimulants and adenosine receptor antagonists

adenosine

an endogenous nucleoside that plays a role in energy transfer (ATP = energy, cAMP = second messenger) and acts as a neuromodulator in the CNS, generally having inhibitory effects

adenosine receptors

metabotropic receptors (A1, A2A, A2B, A3) in the CNS that bind to adenosine, mediating various physiological effects. some are inhibitory (A1, A3) and some are excitatory (A2A, A2B)

caffeinism

a condition resulting from excessive caffeine intake, characterized by symptoms such as agitation, anxiety, insomnia, and rapid heartbeat

caffeine (1,3,7 - trimethyxanthine)

found in coffee, energy drinks, etc.

theophylline (1,3 - dimethylxanthine)

found in non-herbal tea (in small amounts)

theobromine (3,7 - dimethylxanthine)

found in chocolate

peak blood caffeine levels

after coffee/tea within 30 min (99% uptake by 45 mins)

peak levels after cola/chocolate

at 1.5 to 2 hours

elimination

primarily via liver metabolism (cytochrome P450 enzymes, particularly CYP1A2)

CYP1A2 gene variations

1A form = rapid metabolism, 1F form = slow metabolism (greater effects and more adverse effects due to accumulation)

metabolic rate influenced by

alcohol, grapefruit juice, nonsmoking status, oral contraceptives, pregnancy

effects in PNS

vasodilation, increased blood flow and heart rate, skeletal muscle strenghtening, relaxation of ANS-controlled muscles, bronchodilation and increased breathing rate/depth

effects in CNS

vasoconstriction (relief of headaches in people with high blood pressure and migraine symptoms by blocking adenosine)

subjective effects (low doses 20-200 mg)

feelings of well-being, alertness, energy, motivation for repetitive work, self-confidence (more likely in non-users or deprived users)

effects on sleep (300 mg caffeine)

increases time to fall asleep (18m to 66m), decreases total sleep time (7h55m to 5h50m), decreases acoustic arousal threshold

FDA regulations and caffeine

FDA regulations require only nutrients be listed and caffeine is not considered a nutrient

consumption stats (caffeine)

approx. 80% of the world and 90% of North America

sources of caffeine ranked

1. coffee (~64%)

2. colas (~18%)

3. tea (~16%)

4. energy drinks (~1-3%)

absorption

oral ingestion → bloodstream from the digestive tract → walls of the stomach and small intestine

theophylline

used to clinically treat asthma, smooth muscle relaxation results in dilation of the bronchi of the lungs