April 2009
Volume 50, Issue 13
ARVO Annual Meeting Abstract  |   April 2009
L-Glutamic Acid Causes Relaxation of Porcine Retinal Arterioles Through a Nmda Receptor Dependent Mechanism
Author Affiliations & Notes
  • K. Holmgaard
    Ophthalmology, Aarhus Univ Hospital, Aarhus, Denmark
  • T. Bek
    Ophthalmology, Aarhus Univ Hospital, Aarhus, Denmark
  • Footnotes
    Commercial Relationships  K. Holmgaard, None; T. Bek, None.
  • Footnotes
    Support  None.
Investigative Ophthalmology & Visual Science April 2009, Vol.50, 392. doi:
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      K. Holmgaard, T. Bek; L-Glutamic Acid Causes Relaxation of Porcine Retinal Arterioles Through a Nmda Receptor Dependent Mechanism. Invest. Ophthalmol. Vis. Sci. 2009;50(13):392.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose: : Previous studies have shown that the glutamate agonist N-metyl-D-aspartic acid, NMDA, induces a dose-dependent vasorelaxation of pre-constricted porcine retinal arterioles when surrounded by the perivascular retina. However, it is unknown whether other than NMDA glutamate receptors are involved in this vasorelaxation.

Methods: : Porcine retinal arterioles with preserved perivascular retinal tissue were mounted in a wire myograph for isometric force measurements. After constriction of the arterioles with U46619, a thromboxane analogue, the vasodilating effects of L-glutamic acid combined with antagonists to respectively the NMDA-, metabotropic, and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-/kinate glutamat receptors were studied. In each experiment the perivascular retinal tissue was removed, and the experiment was repeated on the isolated arteriole.

Results: : L-glutamic acid induced a dose-dependent vasorelaxation, p<0.001 repeated measures ANOVA, (EC50=118.62 µM), which disappeared when the perivascular retina was removed. The NMDA receptor blocker, DL-APV, caused a significant reduction of L-glutamic acid induced vasorelaxation (p=0.033 and 0.048 at 10-3 and 3 x 10-3 M concentrations, respectively), whereas no effect on the glutamate induced vasorelaxation was induced by neither the metabotropic antagonist MCPG (p≥0.1) nor the AMPA / kinate receptor antagonist CNQX (p≥0.11).

Conclusions: : The findings suggest that the vasorelaxing effect of L-glutamic acid on pre-constricted porcine retinal arterioles in vitro depends on the perivascular retinal tissue and is mediated through a direct action on the glutamate NMDA receptor, but not metabotropic or AMPA/kinate receptors.The findings contributes to the understanding of the tone regulation of retinal arterioles and may potentially help identifying mechanisms for controlling perfusion disturbances in retinal vascular disease.

Keywords: retina: neurochemistry • blood supply • glia 

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