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K. H. Holmgaard, C. Aalkjær, J. D. C. Lambert, T. Bek; ATP-Induced Relaxation of Porcine Retinal Arterioles Is Mediated via an Adenosine Receptor and Is Dependent on the Perivascular Retinal Tissue. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2275.
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Disturbances in the tone regulation of retinal arterioles are involved in the pathophysiology of a variety of sight-threatening retinal diseases. It has been suggested that ATP, adenosine, and the cyclooxygenase (COX) enzyme may be involved in the pathogenesis of these disease states. Studies of the regulation of retinal vascular tone have previously been performed on isolated arterioles, but recent evidence suggests that the perivascular tissue also plays a role for the regulation of tone. However, whether the effects of ATP and adenosine depend on the presence of the perivascular tissue is presently unknown.
Porcine retinal arterioles were mounted in a wire myograph for isometric force measurements. After constriction of the vessel with the prostaglandin analogue U46619 the effect of the non-specific adenosine receptor antagonist, 8-PSPT on ATP- and adenosine-induced vasorelaxation, and the effect of the ecto-nucleotidase inhibitor, AOPCP on ATP-induced vasorelaxation, was studied. The experiments were performed on arterioles with preserved perivascular tissue, as well as on isolated retinal arterioles. Finally, the experiments were repeated in the presence of the COX inhibitor, ibuprofen.
Both adenosine and ATP caused a concentration-dependent relaxation of porcine retinal arterioles. Following removal of the perivascular retinal tissue, the potency of adenosine was reduced, whereas the response to ATP was nearly abolished. The effects of both compounds were antagonized competitively by 8-PSPT. Moreover, blocking the hydrolysis of ATP with AOPCP abolished its vasorelaxing action. Ibuprofen had no effect on the vasorelaxing effect of adenosine.
The vasorelaxing effect of adenosine in porcine retinal arterioles is reduced and the effect of ATP is nearly abolished after removal of the perivascular retinal tissue. The results suggest that ATP-induced relaxation of porcine retinal arterioles depends on the perivascular retina and an adenosine receptor.
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