[Enhanced alpha adrenoreceptor-mediated vasoconstrictor component in essential hypertension].

Changes in forearm blood flow in response to infusions of the postsynaptic alpha blocking agent prozosin (0.5 microgram/min/100 ml forearm tissue) and of the nonspecific vasodilating drug sodium nitroprusside (0.6 microgram/min/100 ml forearm tissue) into the brachial artery were assessed in 24 patients with essential hypertension (EHT) and in 16 age-matched normotensive subjects (NT). Under basal conditions forearm blood flow was higher in EHT (4.0 +/- 0,2 vs. 2.6 +/- 0.3 ml/min/100 ml forearm tissue, p less than 0.001). Forearm blood flow response to prazosin was greater in EHT than in NT (7.7 +/- 0.8 vs. 2.6 +/- 0.3, p less than 0.001) while sodium nitroprusside responses were similar in EHT and NT (13.8 +/- 0.8 vs 13.0 +/- 0.8 vs. 13.0 +/- 0.1, n.s.). These results indicate an enhanced alpha adrenoceptor-mediated vasoconstrictor component in EHT and help to explain the effectiveness of antihypertensive drugs which interfere with sympathetic control of vascular resistance.