Skip to main page content
U.S. flag

An official website of the United States government

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2018 Jul 1;315(1):C44-C51.
doi: 10.1152/ajpcell.00024.2018. Epub 2018 Apr 6.

Pharmacological regulation of outflow resistance distal to Schlemm's canal

Fiona McDonnell  1 , W Michael Dismuke  1 , Darryl R Overby  2 , W Daniel Stamer  1   3
Affiliations

Pharmacological regulation of outflow resistance distal to Schlemm's canal

Fiona McDonnell et al. Am J Physiol Cell Physiol. .

Abstract

The trabecular meshwork (TM) and Schlemm's canal generate the majority of outflow resistance; however, the distal regions of the conventional outflow pathway account for 25-50% of total resistance. Sections of distal vessels are surrounded by α-smooth muscle actin-containing cells, indicating that they may be vasoregulated. This study examined the effect of a potent vasodilator, nitric oxide (NO), and its physiological antagonist, endothelin-1 (ET-1), on the regulation of outflow resistance in the distal regions of the conventional outflow pathway. Using a physiological model of the conventional outflow pathway, human and porcine anterior segments were perfused in organ culture under constant flow conditions, while intrachamber pressure was continually monitored. For porcine anterior segments, a stable baseline outflow facility with TM intact was first achieved before anterior segments were removed and a trabeculotomy was performed. For human anterior segments, a trabeculotomy was immediately performed. In human anterior segments, 100 nM ET-1 significantly decreased distal outflow facility from 0.49 ± 0.26 to 0.31 ± 0.18 (mean ± SD) µl·min-1·mmHg, P < 0.01. Perfusion with 100 µM diethylenetriamine-NO in the presence of 1 nM ET-1 immediately reversed ET-1 effects, significantly increasing distal outflow facility to 0.54 ± 0.35 µl·min-1·mmHg, P = 0.01. Similar results were obtained in porcine anterior segment experiments. Therefore, data show a dynamic range of resistance generation by distal vessels in both the human and the porcine conventional outflow pathways. Interestingly, maximal contraction of vessels in the distal outflow tract of trabeculotomized eyes generated resistance very near physiological levels for both species having an intact TM.

Keywords: aqueous humor; distal outflow; glaucoma; outflow physiology.

PubMed Disclaimer

Figures

Fig. 1.
Fig. 1.
Histology showing conventional outflow pathway pre- and post-trabeculotomy in human and porcine eyes. Radial sections (1 µm) from perfusion-fixed human (A) and porcine (B) eyes were taken with the trabecular meshwork (TM) intact and after trabeculotomy. Following trabeculotomy in human eyes, all of the TM and inner wall of Schlemm’s canal were removed, leaving only the outer wall (arrows) and the distal regions present. The images shown were taken from anterior segments from different donors. For porcine eyes, the angular aqueous plexus (AAP) can be seen in both sections (asterisks); however, parts of the AAP are open to the anterior chamber in the post-trabeculotomy section, whereas others are not. CC, collector channel.
Fig. 2.
Fig. 2.
Outflow facility data from perfused human anterior segments. A: perfusion trace summary showing combined outflow facility data from 7 pairs of human anterior segments, normalized to baseline measurements. Endothelin-1 (ET-1; 100 nM) was exchanged into both anterior segments of the pair at ~2 h. Diethylenetriamine-nitric oxide (DETA-NO; 100 µM) was then exchanged into the experimental segment at ~4 h in the presence of ET-1 (1 nM), whereas ET-1 (100 nM) was exchanged into the contralateral segment. Data are presented as mean ± SD (solid lines ± shaded regions). B: box and whisker plot summary of outflow facility data collected at each stage of the human anterior segment perfusion. Data show an average (represented by the + in the box of each data set) facility value of 0.23 ± 0.06 µl·min−1·mmHg in anterior segments with the trabecular meshwork (TM) intact reported in previous studies [Ψthe outflow facility data were obtained from 73 anterior segments that had been perfused and previously published by our laboratory (8, 13, 46, 55, 56)]. Trabeculotomized eyes (TRAB) showed a facility value of 0.49 ± 0.26 µl·min−1·mmHg (control and experimental data). ET-1 treatment decreased facility to 0.31 ± 0.18 µl·min−1·mmHg (control and experimental data), and DETA-NO reversed this decrease in facility, achieving a value of 0.54 ± 0.35 µl·min−1·mmHg (experimental data). The box represents the range of the values from the 25th to the 75th percentile, whereas the error bars show the minimum and maximum values of each data set. The horizontal line in the box represents the median value.
Fig. 3.
Fig. 3.
Outflow facility data from human anterior segments exposed to 1 nM endothelin-1 (ET-1). A: perfusion trace summary showing combined outflow facility data from 3 pairs of human anterior segments, normalized to baseline measurements. ET-1 (100 nM) was exchanged into both anterior segments of the pair at ~2 h. Diethylenetriamine-nitric oxide (DETA-NO; 100 µM) was then exchanged into the experimental segment at ~4 h in the presence of ET-1 (1 nM), whereas ET-1 (1 nM) was exchanged into the contralateral segment. Data are presented as mean ± SD (solid lines ± shaded regions). B: box and whisker plot summarizing the facility values obtained at each stage of the human anterior segment perfusions. Data show an average (represented by the + in the box of each data set) facility value of 0.23 ± 0.06 µl·min−1·mmHg in anterior segments with the trabecular meshwork (TM) intact reported in previous studies [Ψthe outflow facility data were obtained from 73 anterior segments that had been perfused and previously published by our laboratory (8, 13, 46, 55, 56)]. Trabeculotomized eyes (TRAB) showed a facility value of 0.61 ± 0.12 µl·min−1·mmHg (control and experimental data). ET-1 treatment decreased facility to 0.40 ± 0.15 µl·min−1·mmHg (control and experimental data), and DETA-NO reversed this decrease in facility, achieving a value of 0.54 ± 0.15 µl·min−1·mmHg (experimental data). The box represents the range of the values from the 25th to the 75th percentile, whereas the error bars show the minimum and maximum values of each data set. The horizontal line in the box represents the median value.
Fig. 4.
Fig. 4.
Combined and normalized facility data from porcine anterior segment perfusions. A: combined perfusion data showing outflow facility in 8 porcine anterior segment pairs normalized to baseline. Endothelin-1 (ET-1; 100 nM) was exchanged into both anterior segment chambers of the pair at ~2 h. Diethylenetriamine-nitric oxide (DETA-NO; 100 µM) was then exchanged into the experimental chamber at ~4 h in the presence of ET-1 (1 nM), whereas ET-1 (100 nM) was exchanged into the contralateral segment. Data are presented as mean ± SD (solid lines ± shaded regions). B: box and whisker plot showing the facility values collected at each stage of the porcine anterior segment perfusions. Data show a facility value of 0.28 ± 0.13 µl·min−1·mmHg in anterior segments with the trabecular meshwork (TM) intact (control and experimental data). Trabeculotomized eyes (TRAB) showed a facility value of 0.72 ± 0.32 µl·min−1·mmHg (control and experimental data). ET-1 treatment decreased facility to 0.48 ± 0.21 µl·min−1·mmHg (control and experimental data), and DETA-NO reversed this decrease in facility achieving a value of 0.73 ± 0.21 µl·min−1·mmHg (experimental data). The mean is indicated by the cross in the box. The box represents the range of the values from the 25th to the 75th percentile, whereas the error bars show the minimum and maximum values of each data set. The horizontal line in the box represents the median value.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Ashpole NE, Overby DR, Ethier CR, Stamer WD. Shear stress-triggered nitric oxide release from Schlemm’s canal cells. Invest Ophthalmol Vis Sci 55: 8067–8076, 2014. doi:10.1167/iovs.14-14722. - DOI - PMC - PubMed
    1. Ayub H, Khan MI, Micheal S, Akhtar F, Ajmal M, Shafique S, Ali SH, den Hollander AI, Ahmed A, Qamar R. Association of eNOS and HSP70 gene polymorphisms with glaucoma in Pakistani cohorts. Mol Vis 16: 18–25, 2010. - PMC - PubMed
    1. Bentley MD, Hann CR, Fautsch MP. Anatomical variation of human collector channel orifices. Invest Ophthalmol Vis Sci 57: 1153–1159, 2016. doi:10.1167/iovs.15-17753. - DOI - PMC - PubMed
    1. Borghi V, Bastia E, Guzzetta M, Chiroli V, Toris CB, Batugo MR, Carreiro ST, Chong WK, Gale DC, Kucera DJ, Jia L, Prasanna G, Ongini E, Krauss AH, Impagnatiello F. A novel nitric oxide releasing prostaglandin analog, NCX 125, reduces intraocular pressure in rabbit, dog, and primate models of glaucoma. J Ocul Pharmacol Ther 26: 125–132, 2010. doi:10.1089/jop.2009.0120. - DOI - PubMed
    1. Braughler JM, Mittal CK, Murad F. Purification of soluble guanylate cyclase from rat liver. Proc Natl Acad Sci USA 76: 219–222, 1979. doi:10.1073/pnas.76.1.219. - DOI - PMC - PubMed

Publication types