Response of isolated renal artery rings to adenosine and inosine

The responses to adenosine and its analog, inosine, were compared in isolated rings of canine small renal arteries (0.5–1.3 mm o.d.). The rings were not contracted prior to nucleoside administration in order to detect any contraction response due to the nucleoside itself. Relaxation responses were elicited by progressively increasing the nucleoside concentration in the bathing medium. The maximal response (R_max) was expressed as a percentage of the decrease in isometric tension. The ED50 for adenosine and inosine was 0.18 ± .002 μM and 202 ± 44 μM, respectively (P < 0.05) The R_max for inosine was significantly less (P < 0.05) than that for adenosine, with a mean ratio of adenosine R_max inosine R_max of 1.47 ± 0.2. The results of these experiments indicated that adenosine and inosine directly relax isolated small renal arterial rings, although the classic in situ renal response to adenosine is increased resistance. Also, the relaxing action of adenosine, but not inosine, is significantly attenuated by 10 μM aminophylline. Further, renal arterial rings exhibit a greater sensitivity to adenosine than that previously reported for canine coronary artery rings, while the response to inosine is virtually identical.