Abstract
The present experiments in mice were performed to determine the steady-state effects of exogenous adenosine on the vascular resistance of the whole kidney, of superficial blood vessels, and of afferent arterioles. The steady-state effect of an intravenous infusion of adenosine (5, 10, and 20 μg/min) in wild-type mice was vasodilatation as evidenced by significant reductions of renal and superficial vascular resistance. Resistance decreases were augmented in adenosine 1 receptor (A1AR) –/– mice. Renal vasodilatation by the A2aAR agonist CGS 21680A [2-p-(2-carboxyethyl)phenethyl-amino-5′-N-ethylcarboxamido-adenosine hydrochloride] (0.25, 0.5, and 1 μg/kg/min) and inhibition of adenosine-induced relaxation by the A2aAR antagonist ZM-241385 [4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-yl-amino]ethyl)phenol] (20 mg/kg) suggests that the reduction of renovascular resistance was largely mediated by A2aAR. After treatment with Nω-nitro-l-arginine methyl ester (l-NAME) adenosine was unable to alter superficial blood flow and resistance significantly indicating that adenosine-induced dilatation is NO-dependent. Absence of a dilatory effect in endothelial nitric-oxide synthase (NOS) –/– mice suggests endothelial NOS as the source of NO. When infused into the subcapsular interstitium, adenosine reduced superficial blood flow through A1AR activation. Adenosine (10–7 M) constricted isolated perfused afferent arterioles when added to the bath but not when added to the luminal perfusate. Luminal adenosine caused vasoconstriction in the presence of l-NAME or the A2AR antagonist 3,7-dimethyl-1-(2-propynyl)xanthine. Our data show that global elevation of renal adenosine causes steady-state vasorelaxation resulting from adenosine 2 receptor (A2AR)-mediated generation of NO. In contrast, selective augmentation of adenosine around afferent arterioles causes persistent vasoconstriction, indicating A1AR dominance. Thus, adenosine is a renal constrictor only when it can interact with afferent arteriolar A1AR without affecting the bulk of renal A2AR at the same time.
Footnotes
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This work was supported by the Intramural Research Program of the National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health. P.B.H. and S.H. were recipients of Visiting Fellowships of National Institute of Diabetes and Digestive and Kidney Diseases.
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P.B.H. and S.H. contributed equally to this work.
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doi:10.1124/jpet.105.091017.
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ABBREVIATIONS: A1AR, adenosine 1 receptor; PCR, polymerase chain reaction; eNOS, endothelial nitric-oxide synthase; RBF, renal blood flow; SBF, superficial blood flow; CHA, N6-cyclohexyladenosine; l-NAME, Nω-nitro-l-arginine methyl ester; ZM-241385, 4-(2-[7-amino-2-(2-furyl) [1,2,4]triazolo [2,3-a][1,3,5]triazin-5-yl-amino]ethyl)phenol; CGS 21860, 2-p-(2-carboxyethyl)phenethyl-amino-5′-N-ethylcarboxamido-adenosine hydrochloride; RVR, renal vascular resistance; SVR, superficial vascular resistance; A2AR, adenosine 2 receptor; DMPX, 3,7-dimethyl-1-(2-propynyl)xanthine; ANOVA, analysis of variance; NOS, nitric-oxide synthase.
- Received June 14, 2005.
- Accepted August 19, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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