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X. Zhu, M. Feldkaemper, A.J. Fischer, J. Wallman; Wearing Positive vs. Negative Spectacle Lenses Has Opposite Effects on Glucagon Concentration in the Suprachoroidal Fluid of Chicks . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1138.
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© ARVO (1962-2015); The Authors (2016-present)
Chick eyes compensate rapidly for both positive and negative lens–wear by opposite changes in choroidal thickness and in the rate of ocular elongation. Recent evidence points to glucagon as a possible signal for the direction of compensation: (a) glucagonergic amacrine cells show opposite modulation of immediate early gene expression to wearing positive and negative lenses (Fischer et al., 1999); (b) glucagon and its antagonist modulate both choroidal thickness and ocular elongation (Zhu et al., ARVO 2001; Feldkaemper and Schaeffel, 2002; Vessey et al., 2005). We now have measured glucagon concentration in the suprachoroidal fluid during lens–wear and have assayed the choroid for mRNA of glucagon precursors and receptors.
One–week–old chicks wore a +8 or –8 D lens over one eye for 3 days, after which the eyes were enucleated, 5–40 µl of suprachoroidal fluid was drawn from the space between the choroid and sclera, and glucagon concentration was measured by radioimmunoassay (Euro–Diagnostica). Proglucagon mRNA and glucagon receptor mRNA were measured by RT–PCR, followed by subcloning and sequencing.
Glucagon concentration in the suprachoroidal fluid increased in eyes wearing positive lenses, compared to fellow control eyes (Mean ± SEM): 4.3 ± 1.2 vs. 2.8 ± 0.9 nM (mean ratio, 2.3), and decreased in eyes wearing negative lenses: 2.7 ± 0.4 vs. 4.0 ± 0.9 nM (ratio, 0.8). These ratios are significantly different (p<0.01, Mann–Whitney, n=8,9). It is uncertain whether this glucagon is made in the choroid: one of the authors of this abstract (MF) found low levels of proglucagon mRNA in choroid, while another author (AJF) found none, although both agree on the presence of glucagon receptor mRNA in the choroid (reported by Buck et al., 2004).
Glucagon concentration in the suprachoroidal fluid changes in opposite directions when positive or negative lenses are worn. We conjecture that this glucagon may come from the retina or retinal pigment epithelium and act on the choroidal glucagon receptors.
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