Adenosine and angiotensin system interact in the regulation of renal microcirculation in humans

We sought to evaluate the possible interaction be tween the adenosine and a ngiotensin systems in the regulation of renal microcirculation in humans. T wenty normotensive patients entered the study. Ten patients (group 1) were pretreated with 50 mg of captopril, an inhibitor of angiotensin-converting enzyme, whereas 10 patients (group 2) were pretreated with placebo. increme ntal doses of adenosine (from 10(-5) to 1 mg) were injected into a renal ar tery to all patients at 5-min intervals, Adenosine injection reduced mean r enal blood flow velocity in both groups (from 17.3 +/- 2.8 and 16.7 +/- 2 c m/s to 5.1 +/- 1.1 and 3.8 +/- 0.8 cm/s, in groups 1 and 2, respectively). The decrease in flow velocity was immediate after adenosine, and its durati on was proportional to dosage (y = 3.05 x -2.7; R-2 0.46; p < 0.01). Howeve r, group 1 had a slope of regression lower than group 2 (2.37 vs. 3.82 s; p < 0.03). The index of renal resistance (mean arterial pressure/mean blood flow velocity) increased linearly in both groups with adenosine, bur. group 1 showed a lower slope of increment (2.77 vs. 5.57 mm Hg/cm/s; p < 0.01). Adenosine administration induced a marked and transient increase in human r enal resistance. This vasoconstrictive effect of adenosine was blunted by c aptopril pretreatment.