From lrfrum@hardy.u.washington.edu Mon Nov 7 20:35:51 EST 1994
Article: 86812 of sci.med
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From: lrfrum@hardy.u.washington.edu (Lyn Frumkin)
Newsgroups: sci.med
Subject: Re: Caffene and headaches
Date: 30 Oct 1994 20:52:17 GMT
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John C. Moran (jcm@crl.com) wrote:
: But doesn't caffeine also raise blood pressure? How is this consistent
: with dilating coronary and pulmonary vessels?
Caffeine typically does not affect blood pressure in the average person.
Administration of 250-350mg of caffeine to persons who do not normally
drink caffeine can produce small, transient increases in blood pressure
[see Myers, M. Effect of caffeine on blood pressure. Archives of Internal
Medicine, 148, 1189-93, 1988]. It is not clear to me why caffeine is
thought to have different actions on different vessel systems; some
authors suggest that such actions are not direct but the result of
caffienes effects on the brainstem [Goodman & Gilmans Pharmacological
Basis of therapeutics, Pergamon Press, NY, p.620]. Despite caffeines role
in anatagnizing adenosine-related cerebral vasodilation [and thus
presumably helping migraine], its role in the coronary system may be more
varied. Goodman and Gilman suggest that " the actions ..[of
methylxanthines] ... on the circulatory system are complex and sometimes
antagonistic.... largely dependant upon conditions at time of
administration, dose used, and history of [the patient] .... in addition
to effects on the vagal centers in the brainstem, there are an array of
more or less direct actions on vascular and cardiac tissue in
combination with peripheral actions mediated by catecholamines [and
possibly] the renin-angiotensin system. The observation of a single
function such as blood pressure is deceiving because the drugs may act on
a variety of circulatory factors in such a way that the blood pressure
may remain essentialy unchanged".
Although the relationship of caffeine to blood pressure seems to be
purely empiric, there are other theories [including contradictory
ones] besides the one above to explain the action of xanthines on
the circulatory system.
Lyn Frumkin, MD, PhD
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