Adenosine and the vascular tissue renin-angiotensin system in the forearm of essential hypertensive patients

The present study was designed to evaluate whether adenosine can activate a vascular tissue renin-angiotensin system in the forearm of essential hypertensive patients. In a group of 6 patients, we infused adenosine at cumulative increasing doses into the brachial artery and collected simultaneous arterovenous samples for angiotensin II determinations (by radioimmunoassay). Forearm blood flow was evaluated by strain-gauge plethysmography. Adenosine caused a dose-dependent increment in forearm blood flow and in venous angiotensin II, whereas it did not affect arterial angiotensin II. When repeated in the presence of the antagonist, theophylline, the adenosine effect was blunted. Moreover, in the forearm of another group of 6 hypertensives, ischemia was applied for 7 min to induce the production of endogenous adenosine while active renin (by radioimmunometric assay) and angiotensin II were measured. During the reactive hyperemia, venous active renin and angiotensin II increased, while arterial values did not change. This effect was also blunted by theophylline. Taken together these data indicate that either exogenous or endogenous adenosine can activate a vascular tissue renin-angiotensin system in the forearm of essential hypertensive patients