Subject: Re: Caffene and headaches

From: [email-masked] (Lyn Frumkin)
Date: 30 Oct 1994 20:52:17 GMT

John C. Moran ([email-masked]) 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