Acute Effects of Caffeine

Smith, B., Rafferty, J., Lindgren, K., Smith, D. and Nespor, A., Chronic and acute effects of caffeine Testing a biobehavorial model. Physiol Behav, 51, 131-137, 1991. 

Elkins, R., Rapoport, J. and Zahn, T., Acute effects of caffeine in prepubertal... 

Van Soeren, M., Mohr, T., Kjaer, M. and Graham, T., Acute effects of caffeine ingestion at rest in humans with impaired epinephrine responses. J Appl Physiol 80(3), 999 1005, 1996. 

Lorist MM, Snel J, Kok A, Mulder G. (1996). Acute effects of caffeine on selective attention and visual search processes. Psychophysiology. 33(4) 354-61. 

The acute effects of caffeine include diuresis, stimulation of the heart and CNS, relaxation of smooth muscles, and stimulation of gastric acid. 

There does, however, appear to be a ceiling on the acute dosage of caffeine that will enhance reaction time. At relatively low doses given prior to simple tasks or highly practiced complex tasks, the drug does enhance RT.41 104-117-143-144 However, these results may not apply to more complex tasks that have not been extensively practiced. For example, Lieberman79 found that 64 mg of caffeine decreased RT on a simple visual task in which the subject had to identify an object. However, the same dose of caffeine had no effect on RT when the subject had to choose objects in a more complex task. In fact, caffeine has been found to have detrimental effects on reaction times in some complex tasks.51 104 145 Again, there appears to be an inverted-U relationship between overall arousal — induced by the combination of caffeine and other arousal factors — and performance on reaction time tasks. 

Zahn, T. and Rapoport, J., Autonomic nervous system effects of acute doses of caffeine in caffeine users and abstainers. Int J Psychophslol 5, 33-41, 1987. 

Massey, L. K., Hollingberry, P. W., Acute effects of dietary caffeine and sucrose on urinary mineral excretion of healthy adolescents, Nutrition Research, 8, 1005, 1988. 

James JE. (1998). Acute and chronic effects of caffeine on performance, mood, headache, and sleep. Neuropsychobiology. 38(1) 32-41. 

Nehlig A, Lucignani G, Kadekaro M, Porrino U, Sokoloff L. (1984). Effects of acute administration of caffeine on local cerebral glucose utilization in the rat. EurJ Pharmacol. 101(1-2) 91-100. 

Acute Toxic Effects of Caffeine Chronic Effects of Caffeine Use Therapeutic Uses of Caffeine Conclusions Summary... 

The CNS-stimulation action of caffeine elevates mood. This effect was documented in a quote from the will of Dr. William Dunlap, who died in 1848 1 leave John Caddie a silver teapot, to the end that he may drink tea therefrom to comfort him under the affliction of a slatternly wife (Gilbert, 1976, p. 77). The acute mood-elevating effects of caffeine account for much of the popularity that coffee and tea have as morning wake-up beverages. It also has been speculated that many people who are afflicted with significant depression medicate themselves by using caffeine products. 

T Caffeine s acute effects of mood elevation and overall improvement in task performance seem to be reinforcing to humans. 

These studies, and many others, conclude that the acute locomotor stimulant effects of caffeine in animal models are mediated in part by dopaminergic systems and dopamine receptors. Recent studies suggest that tolerance to the locomotor stimulant effects of chronic caffeine may also be related to specific changes in dopaminergic function (128). Thus, in spite of the fact that methylxanthines are structurally different from other psychostimulants, and do not directly affect dopamine transporters or receptors, in fact their stimulant action is derived from effects on central dopamine pathways. 

The results of the dexamethasone suppression test can be falsified by the acute ingestion of caffeine but chronic caffeine use does not appear to have an effect. 

Studies on the effects of caffeine on blood pressure indicate that caffeine causes an acute rise in blood pressure, usually occurring 30 minutes to 4 hours after ingestion (Nurminen et al. 1999). The blood-pressure raising effects may be more pronounced in persons with high blood pressure (Nurminen et al. 1999). With routine consumption of caffeine, most individuals develop tolerance to the blood-pressure raising effects, while some do not (James 1994 Lovallo et al. 2004). Studies on the effects of caffeine or coffee on blood pressure have mixed results. Some studies show a mild elevation of blood pressure after caffeine consumption (James 2004), while others show no effect or a habituation to the effect. In addition, the effects of coffee on blood pressure may be different than those of caffeine, since coffee contains other compounds, such... 

The acute oral LD50 (dose sufficient to kill one-half of the population of tested subjects) of caffeine is more than 200 mg kg in rats, 230 mg kg in hamsters and guinea pigs, 246mgkg in rabbits, and 127mgkg in mice. The sensitivity of rats to the lethal effects of caffeine increases with age, and higher toxicity is observed in male than in female rats. 

Pentoxifylline is stmcturaHy related to other methylxanthine derivatives such as caffeine [58-02-2] (1,3,7-trimethylxanthine), theobromine [83-67-0] (3,7-dimethylxanthine), and theophylline [58-55-9] (3,7-dihydro-1,3-dimethyl-1 H-piirine-2,6-dione or 1,3-dimethylxanthine), which also show radioprotective activity in some instances, suggesting that methylxanthines as a dmg class may radioprotect through a common mechanism (see Alkaloids). In a retrospective analysis of cervical and endometrial cancer patients receiving primary or adjuvant XRT, no association between caffeine consumption and incidence of acute radiation effects has been found. However, there was a decreased incidence of severe late radiation injury in cervical cancer patients who consumed higher levels of caffeine at the time of thek XRT (121). The observed lack of correlation between caffeine consumption and acute radiation effects is consistent with laboratory investigations using pentoxifylline. 

Human functioning the dual-interaction model. (From Smith, B.D., Effects of acute and habitual caffeine ingestion in physiology and behavior Tests of a biobehavioral arousal theory. Special issue Caffeine Research, Pharmacopsychoecologia, 7(2), 151-167, 1994. With permission.)... 

Moderate levels of chronic use of caffeine and other arousal agents tend to reduce the effects of acute exposure. However, higher chronic levels can exacerbate the impact of acute exposure. 

The individual s average habitual exposure to caffeine moderates the effect of acute exposure on both physiological and psychological functioning. 

As we noted earlier, caffeine affects not only arousal, but also other behavioral influences such as attentional focus. However, it now appears that these other effects may be secondary to the impact of the drug on arousal and that a multi-factorial model incorporating the inverted-U function may best describe that relationship. Most results in the literature to date are supportive of the biobehavioral model proposed here. However, research on the psychological effects of acute and habitual caffeine... 

---