Caffeine, role

Adenosine is produced by many tissues, mainly as a byproduct of ATP breakdown. It is released from neurons, glia and other cells, possibly through the operation of the membrane transport system. Its rate of production varies with the functional state of the tissue and it may play a role as an autocrine or paracrine mediator (e.g. controlling blood flow). The uptake of adenosine is blocked by dipyridamole, which has vasodilatory effects. The effects of adenosine are mediated by a group of G protein-coupled receptors (the Gi/o-coupled Ai- and A3 receptors, and the Gs-coupled A2a-/A2B receptors). Ai receptors can mediate vasoconstriction, block of cardiac atrioventricular conduction and reduction of force of contraction, bronchoconstriction, and inhibition of neurotransmitter release. A2 receptors mediate vasodilatation and are involved in the stimulation of nociceptive afferent neurons. A3 receptors mediate the release of mediators from mast cells. Methylxanthines (e.g. caffeine) function as antagonists of Ai and A2 receptors. Adenosine itself is used to terminate supraventricular tachycardia by intravenous bolus injection. 

Beyond Viagra, there are a number of other PDE inhibitors that are used clinically. In fact, the classic drugs papaverine and dipyridamole were used clinically before their effects on PDEs were known. Caffeine and theophylline (a compound found in tea) are also PDE inhibitors. However, all of these drugs most likely have multiple targets, making conclusions regarding the roles of PDEs in processes that are sensitive to these agents difficult to interpret. Certainly, some of their effects are due to their actions on adenosine receptors. 

Garrett BE, Griffiths RR The role of dopamine in the behavioral effects of caffeine in animals and humans. Pharmacol Biochem Behav 57 533—541, 1997... 

In addition the role played by the sorbent on which the chromatography is carried out must not be neglected. For instance, it is only on aluminium oxide layers and not on silica gel that it is possible to detect caffeine and codeine by exposure to chlorine gas and treatment with potassium iodide — ben2idine [37]. The detection limits can also depend on the sorbent used. The detection limit is also a function of the h/ f value. The concentration of substance per chromatogram zone is greater when the migration distance is short than it is for components with high h/ f values. Hence, compounds with low h/ f values are more sensitively detected. 

The role of caffeine in stress and stress reactions has been well documented.206 It affects the neuroendocrine107 and heart rate207 208 responses to stress, as well as the skin conductance response to stressful anagram... 

Sargent, J., and Solbach, P., Stress and headache in the workplace The role of caffeine. Medical Psychotherapy An International Journal 1, 83-86, 1988. 

Virus, R. M., Ticho, S., Pilditch, M. Radulovacki, M. (1990). A comparison of the effects of caffeine, 8-cyclopentyltheophylline, and alloxazine on sleep in rats. Possible roles of central nervous system adenosine receptors. Neuropsychopharmacology 3 (4), 243-9. 

Solids that form specific crystal hydrates sorb small amounts of water to their external surface below a characteristic relative humidity, when initially dried to an anhydrous state. Below this characteristic relative humidity, these materials behave similarly to nonhydrates. Once the characteristic relative humidity is attained, addition of more water to the system will not result in a further increase in relative humidity. Rather, this water will be sorbed so that the anhydrate crystal will be converted to the hydrate. The strength of the water-solid interaction depends on the level of hydrogen bonding possible within the lattice [21,38]. In some hydrates (e.g., caffeine and theophylline) where hydrogen bonding is relatively weak, water molecules can aid in hydrate stabilization primarily due to their space-filling role [21,38]. 

Kotlikoff Susan Wray, I was impressed by your comment that you have no caffeine responses. One of the things that differs between different smooth muscle tissues is the state of expression of RyR2, which is the cardiac isoform that is also found in some smooth muscles, although not all. RyR2 is more sensitive to caffeine than RyR3, which is more ubiquitously expressed and has lower sensitivity. This may be a telling statement about the functional role of the RyR in the tissue that you are looking at. 

The various chemical processes influencing the colour formation in tea have been vigorously investigated. The self-association of black tea polyphenol theaflavin and its com-plexation with caffeine [175], and the role of epicatechin quinone in the synthesis and degradation of theaflavin [176] have been studied in detail. 

The role of caffeine in migraine headaches is due to its vasoconstrictor effects. Caffeine is used in combination with ergotamine for migraine (Sawynok 1995 Sargent et al. 1988). However, discontinuation or missing a dose of caffeine after chronic use can precipitate headaches (Fennelly et al. 1991 Couturier etal. 1992). 

According to the data available in the literature, both nicotine and caffeine reach much higher concentrations in winter than in summer. The ambient temperature probably influences the net amounts of compounds in the particulate phase, through promoting volatilization in the warm season for instance, nicotine was 2.2 times more abundant in winter than in summer. Nonetheless, atmospheric oxidants seem to play a complementary role in fact, with regard to nicotine this hypothesis is in... 

Bioinorganic chemists have been attracted by the complex formations of NHC because the imidazolin-2-ylidene motif is encountered frequently in living organisms. The imidazole moiety is part of the purin bases in both DNA and RNA as well as the amino acid histidine which appears in proteins and enzymes and is in many cases considered to play a decisive role within the catalytically active center. The possible formation of NHC complexes under physiological conditions or in vivo has been addressed by investigation of A-confused caffeine 73 or purine 74 complexes. 

Alcohols are oxidized to aldehydes by the liver enzyme alcohol dehydrogenase, and aldehydes to carboxylic acids by aldehyde dehydrogenase. In mammals, monooxygenases can be induced by plant secondary metabolites such as a-pinene, caffeine, or isobornyl acetate. Reduction is less common and plays a role with ketones that cannot be further oxidized. Hydrolysis, the degradation of a compound with addition of water, is also less common than oxidation. 

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