In rats with streptozotocin (STZ)-induced diabetes, the renal vasoconstrictor effect of adenosine is enhanced. We investigated the role of nitric oxide (NO) in the renal vascular response to exogenous and endogenous adenosine in control and STZ diabetic rats. Exogenous adenosine (0.01-100 nmol) injected into the abdominal aorta decreased renal blood flow (RBF) in a dose-dependent manner to a much greater extent in STZ rats than in control rats (P < 0.001). Inhibition of NO synthesis with N-nitro-L-arginine (L-NNA, 30 µmol/kg iv) and with renal perfusion pressure controlled potentiated the adenosine-induced renal vasoconstriction to a significantly greater extent in control rats than in STZ rats. In control rats, L-NNA shifted the dose-response curve of exogenous adenosine-induced RBF reductions to the left by a factor of 32 [half-maximal effective dose (ED₅₀), from 5.5 to 0.17 nmol adenosine, n = 6] and in STZ rats only by a factor of 4.6 (ED₅₀, from 0.32 to 0.07 nmol adenosine, n = 6). The renal response to endogenous adenosine was assessed by the magnitude of the postocclusive reduction of RBF (POR) after a 30-s renal artery occlusion. POR was markedly enhanced in STZ rats (67.8 ± 3.8%, P < 0.001) compared with control rats (38.8 ± 4.3%). L-NNA markedly enhanced POR in control rats but did not increase POR in STZ rats. These findings demonstrate a greater potentiation of the adenosine-induced renal vasoconstriction in the presence of L-NNA infusion in control rats compared with STZ rats. We conclude that the increased vasoconstrictor sensitivity of the diabetic renal vasculature to adenosine is caused by a defective NO-dependent renal vasodilation of the afferent arteriole in diabetic rats.

renal hemodynamics; experimental insulin-dependent diabetes mellitus; nitric oxide-dependent renal vasodilation; diabetic dysfunctional vasoregulation; renal ischemia

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