PLASMA ANGIOTENSINS AND HUMAN FOREARM CIRCULATION - EFFECTS OF SYMPATHOADRENAL ACTIVATION

Complex interactions appear to exist between the renin-angiotensin sys tem and sympathetic neurotransmission, and sympathetic activity may in fluence local angiotensin in formation. Arterial and forearm venous pl asma levels of angiotensin I and II were therefore studied in 11 healt hy males at rest, during sympathetic activation elicited by mental str ess, and during adrenaline induced vasodilation. Specific assays for a ngiotensin-(1-8) octapeptide and for angiotensin-(1-10) decapeptide (i .e. angiotensin II and I, respectively), were used. Special precaution s to minimize ex vivo formation and/or degradation of angiotensins wer e employed. Mental stress increased regional noradrenaline overflow th ree-fold. with a concomitant three-fold increase in forearm blood flow . whereas intravenous adrenaline infusion increased forearm blood flow twofold and noradrenaline overflow four-fold. There was a constant po sitive veno-arterial concentration difference for angiotensin I under all conditions tested, compatible with local angiotensin I formation. We found no veno-arterial concentration difference for angiotensin ii or regional net angiotensin II overflow under the conditions tested. T hese results in the forearm circulation support previous animal experi mental evidence in skeletal muscle and provide no evidence in favour o f a de novo formation of angiotensin Ii in skeletal muscle in vivo dur ing basal conditions. Furthermore, sympathetic nerve stimulation does nor seem to enhance angiotensin ii generation importantly in this vasc ular bed.