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Effect of coffee on blood pressure

PATHOPHYSIOLOGY

Caffeine has many effects in the body The three most commonly documented effectsare !"# adenosine receptor anta$onism% ! phosphodiesterase inhibition% and !'#enhanced intracellular calcium le(els Adenosine receptor anta$onism leads to(asoconstriction% hypertension% tremor% and a$itation These effects are fre)uentlyseen in caffeine o(erdose These effects are the re(erse of those seen *ith adenosinea$onist acti(ity% such as arterial (asodilation% inhibition of catecholamine release% andslo*in$ of cardiac pacema+er cells

Caffeine inhibits phosphodiesterases% causin$ increased le(els of cyclic A,P% *hichresults in increased le(els of catecholamines ,uscle contractility is enhanced throu$hincreased intracellular calcium le(els and increased permeability of the sarcoplasmicreticulum to calcium Stimulation of $astric acid and intestinal secretions andlo*erin$ of lo*er esopha$eal sphincter tone by caffeine commonly result in diarrheaand abdominal crampin$

-eneficial effects of caffeine include bronchodilation and (asodilation in thetreatment of apnea in premature infants Althou$h caffeine.induced (asodilation maylo*er blood pressure% caffeine.induced medullary stimulation and increasedcatecholamine release offset this effect

Phenylpropanolamine and ephedrine act primarily (ia increased / " . and / &.adrener$icreceptor a$onist acti(ity and enhanced release of catecholaminesPhenylpropanolamine is as potent as ephedrine but causes less central ner(ous system!C0S# stimulation Phenylephrine is a selecti(e 1 " .adrener$ic receptor a$onist It is aderi(ati(e of epinephrine and produces similar therapeutic and ad(erse effectsPeripheral (asoconstriction and tachycardia are the most common ad(erse effectsTable '23' compares the 1. and /.adrener$ic receptor acti(ity and C0S stimulation of caffeine and other nonprescription sympathomimetics Chronic misuse of these a$entsmay lead to cardio(ascular abnormalities% such as (asculitis% stro+e syndrome%cardiomyopathy% hypertension% and dysrhythmias

Table 36-3 -- Actions of Selected Sympathomimetic Agents at PeripheralAdrenergic Receptors in the Central Nervous System

SubstanceAlpha-AdrenergicResponse

eta-AdrenergicResponse

CNSStimulation

Amphetamine 44 44 444

Caffeine 44 4 4

Ephedrine 44 444 44

Phenylephrine 4444 5 4

Phenylpropanolamine 444 4 444

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SubstanceAlpha-AdrenergicResponse

eta-AdrenergicResponse

CNSStimulation

4% *ee+ acti(ity

4444% stron$est acti(ity

Oral preparations of these dru$s are the most common forms a(ailable% but each of these a$ents may also be used intra(enously Phenylephrine is also a(ailable as anonprescription inhaler Phenylpropanolamine and caffeine may be sold on the streetfalsely as cocaine or amphetamines In these cases% the a$ents may be snorted%in$ested% or ta+en intra(enously

CLI0ICAL P6ESE0TATIO0

All the nonprescription sympathomimetics !i e % caffeine% ephedrine% phenylpropanolamine% and phenylephrine# share some similar clinical features *henta+en in e7cessi(e amounts Common symptoms include nausea% (omitin$% diarrhea%abdominal pain% tremors% an7iety% a$itation% and headaches Less common but morese(ere symptoms include delirium% sei8ures% hypertensi(e crisis% intracerebralhemorrha$e% and myocardial infarction 9ebate still e7ists as to *hether or not asin$le dose of caffeine or phenylpropanolamine can result in clinically si$nificanthypertension Ho*e(er% hypertensi(e crisis is documented in si$nificant acuteo(erdoses Phenylpropanolamine differs from caffeine in that phenylpropanolamine.induced hypertension is associated *ith a refle7 bradycardia Caffeine o(erdose ismost commonly associated *ith tachycardia Althou$h se(ere to7icity and death may

be caused by any of these a$ents in an o(erdose situation% ephedrine% phenylpropanolamine% and phenylephrine appear to ha(e more reportedcardio(ascular complications than caffeine

Althou$h hyperthermia is fre)uently seen *ith se(ere o(erdose of the psychostimulants !amphetamines% methamphetamines% and cocaine#% it is rarely seenin caffeine o(erdoses Sympathomimetic o(erdoses% ho*e(er% can cause se(erehyperthermia that may be lethal if untreated The hyperthermia is thou$ht to be due toacti(ation of specific dopamine receptors Increased motor acti(ity and stimulant.

induced sei8ures are also possible causes of hyperthermia after sympathomimetico(erdose