Renal vascular reactivity was studied in rats with acute renal failure (ARF) to investigate whether changes in sensitivity to the renal haemodynamic effects of adenosine can explain why adenosine plays a significant role in some but not all forms of ARF. Experiments involved rats with glycerol-induced ARF in which adenosine antagonists have been shown previously to have beneficial effects and rats with HgCl2-induced ARF which was not ameliorated by treatment with the selective A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine (0.1 mg/kg). Close renal arterial injections of adenosine (0.1-10 micrograms) or noradrenaline (0.003-0.1 microgram) produced falls in renal blood flow in rats with HgCl2-induced ARF which were not statistically different from controls. Adenosine evoked falls in renal blood flow in rats with glycerol-induced ARF which were significantly greater 16 and 48 h, but not 30 min after glycerol injection. The enhanced responsiveness to adenosine's renal constrictor effects was most pronounced 48 h following glycerol injection when, for example, a dose of 10 micrograms produced a fall of 60 +/- (SEM) 5% (n = 8) in renal blood flow in comparison to a fall of 27 +/- 5% (n = 8) in controls. By contrast to the renal vascular response to adenosine, the falls in renal blood flow induced by noradrenaline in rats 48 h following glycerol injection were not statistically different from the decreases in renal blood flow recorded in control animals.(ABSTRACT TRUNCATED AT 250 WORDS)