The aim of the present study was to investigate the role of Ca2+-activated Cl- channels in the renal vasoconstriction elicited by angiotensin II (ANG II) and norepinephrine (NE). Renal blood flow (RBF) was measured in vivo using electromagnetic flowmetry. Ratiometric photometry of fura 2 fluorescence was used to estimate intracellular free Ca2+ concentration ([Ca2+]i) in isolated preglomerular vessels from rat kidneys. Renal arterial injection of ANG II (2-4 ng) and NE (20-40 ng) produced a transient decrease in RBF. Administration of ANG II (10-7 M) and NE (5 x 10-6 M) to the isolated preglomerular vessels caused a prompt increase in [Ca2+]i. Renal preinfusion of DIDS (0.6 and 1.25 micromol/min) attenuated the ANG II-induced vasoconstriction to approximately 35% of the control response, whereas the effects of NE were unaltered. Niflumic acid (0.14 and 0.28 micromol/min) and 2-[(2-cyclopentenyl-6,7-dichloro-2,3-dihydro-2-methyl-1-oxo-1H-inden-5-yl)oxy]acetic acid (IAA-94; 0.045 and 0.09 micromol/min) did not affect the vasoconstrictive responses of these compounds. Pretreatment with niflumic acid (50 microM) or IAA-94 (30 microM) for 2 min decreased baseline [Ca2+]i but did not change the magnitude of the [Ca2+]i response to ANG II and NE in the isolated vessels. The present results do not support the hypothesis that Ca2+-activated Cl- channels play a crucial role in the hemodynamic effects of ANG II and NE in rat renal vasculature.