Microcirculatory responses to adenosine in the newborn pig retina.

J M Gidday, T S Park

Index: Pediatr. Res. 33(6) , 620-7, (1993)

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Abstract

The reactivity of retinal arterioles and venules to exogenous and endogenous adenosine was investigated in the newborn piglet eye in vivo. The retinal microcirculation of isoflurane-anesthetized newborn pigs was observed at 310x using videomicroscopy, and changes in the diameter of arterioles (50-100 microns in diameter) and venules (150-250 microns in diameter) occurring in response to intravitreal topical microsuffusions of various adenosinergic compounds were determined. Dose-dependent dilations of the arterioles and venules resulted from intravitreal adenosine (0.2-200 nmol) and three of its agonists: 5'-N-ethylcarboxyamidoadenosine (0.2-20 pmol), 2-chloroadenosine (0.2 pmol-2 nmol), and N6-cyclohexyladenosine (0.2 and 2.0 nmol). The resulting order of vasodilatative potency, wherein 5'-N-ethylcarboxyamidoadenosine >> 2-chloroadenosine > adenosine = N6-cyclohexyladenosine, is indicative of A2 adenosine receptor-mediated vasodilation. Significant arteriolar dilations [24 +/- 4% (p = 0.0012) and 35 +/- 5% (p = 0.0008), respectively] also resulted from intravitreal application of 0.2 nmol of iodotubercidin, an adenosine kinase inhibitor, and 0.1 nmol of nitrobenzylthioinosine, an inhibitor of adenosine reuptake/transport. The dilation induced by nitrobenzylthioinosine was blocked (p < 0.0004) by coadministration of the relatively specific A2 adenosine receptor antagonist 1,3-dipropyl-7-methylxanthine (1 nmol), confirming that nitrobenzylthioinosine induced dilation via potentiation of endogenous adenosine. Administration of 1,3-dipropyl-7-methylxanthine alone did not significantly affect arteriolar or venular diameters, suggesting that endogenous adenosine does not contribute to the maintenance of basal tone.(ABSTRACT TRUNCATED AT 250 WORDS)