Objective To evaluate the facilitating effect of angiotensin II on sympathetic neurotransmission to quantitatively compare the sympatho-inhibitory potencies of the selective AT(1)-receptor antagonists losartan, irbesartan and telmisartan in the isolated rabbit thoracic aorta. Design To investigate the influence of pharmacological compounds on pre-junctional sympathetic transmission, the quantification of sympathetic transmitter release is the most straightforward approach. Methods To investigate the sympatholytic properties of AT(1)-blockers, we studied their effects on the enhancement by angiotensin 11 of electrical field stimulation (EFS)-evoked (2 Hz) sympathetic transmission in a modified spillover model. Results Angiotensin 11 (0.01 nmol/l-0.1 mumol/1) caused a concentration-dependent enhancement of EFS-evoked noradrenaline release (control versus concentrations 0.1 nmol/l-0.1 mumol/l, P irbesartan losartan (where > signifies P irbesartan = losartan. These differences may be explained by differences in affinity for the pre-synaptic AT(1)-receptor. (C) 2002 Lippincott Williams Wilkins