Subject: Caffeine and falling blood pressure...?

     A final lab in which we injected rats with caffeine (.1 mg - 10 mg) 
over the course of 4h. Our exp. looked at heart rate nad blood pressure. 
Our heart rate went up dramatically but our blood pressure actually went 
down! 
     My reasons were that the heart rate increased so fast that the cardiac 
output rapidly went up. In addition the extra fluid volume that went along 
with the injections (caffeine dissolved in saline) could initially raise 
the blood pressure.  The body would respond to these changes by releasing 
signaling molecules to dilate the vessels, homeostatically lowering the 
blood pressure.  However, the adenosine receptors on the vessels are 
blocked by caffeine, right? This would inhibit the dilating...I am all 
confused and am trying to come up with an explanation for the lowered blood 
pressure.  It did occur the by far the most at the high doses (4-10 mg) 
which are extremely high doses for a rat.  Any help would be a

Re: Caffeine and falling blood pressure...?