Salicylic acid, physiological effects

Chlorogenic acid forms a 1 1 complex with caffeine, which can be crystallized from aqueous alcohol and yields very little free caffeine on extraction with chloroform. Other compounds with which caffeine will complex in this way include isoeugenol, coumarin, indole-acetic acid, and anthocyanidin. The basis for this selection was the requirement for a substituted aromatic ring and a conjugated double bond in forming such a complex. This kind of complex does modify the physiological effects of caffeine.14 Complex formation will also increase the apparent aqueous solubility of caffeine in the presence of alkali benzoates, cinnamates, citrates, and salicylates.9... 

Salicylic acid is mainly responsible for the toxic effects of aspirin, and it has a number of metabolic and physiological effects some of which are interrelated (Fig. 7.58) ... 

Salicylamide reportedly exerts a moderately quicker and deeper analgesic effect than aspirin. Long-term studies on rats revealed no untoward symptomatic or physiological reactions. Its metabolism differs from that of other salicylic compounds, and it is not hydrolyzed to salicylic acid." Its analge.sic and antipyretic activity is probably no greater than that of aspirin, and possibly less. It can be used in place of salicylates, however, and is particularly useful for patients with a demonstrated sensitivity to salicylates. It is excreted much more rapidly than other salicylates, which probably accounts for its lower toxicity and. thus, does not permit high blixHl levels. 

Michotte has suggested that biolt ical oxidation processes in mesenchymal tissues require a balance of C -hydroxysteroids and adrenergic substances, and this is disturbed in rheumatic diseases owing to the failure of the adrenergic component. It is alleged that pyrocatechoic acid (V) may replace this component, restore the physiological imbalance and, consequently, suppress the inflammatory reaction. Adams and Cobb found that neither pyrocatechoic acid nor its diacetyl derivative administered orally inhibits ultra-violet erythema in the guinea-pig. The former compound, administered subcutaneously, reduces vascular permeability in the mouse peritoneum, but the effect is less than that of salicylic acid . Other dihydroxybenzoic acids tested are not active in this system . 

Aspirin (acetylsalicylic acid) and other salicylates are still a common cause of human poisoning, both therapeutic and suicidal, and account for a significant number of deaths each year. Although the toxic effects have a biochemical basis, some of the effects caused are clearly physiological, and consequently, it has been used as an example in this category. 

Probenecid and salicylate decrease urate binding to serum proteins. However, since reabsorption of uric acid is thought to be almost complete at physiologic filtered loads, small changes in filtered urate load should have little or no effect on urate excretion. 

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