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B. T. Martin, S. C. Mema, Y. Sauve, S. Harvey; Functional Roles for Growth Hormone in the Mouse Retina. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2004.
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Growth hormone (GH) is traditionally considered to be an endocrine responsible for linear growth and metabolism. However, the recent discovery of locally produced GH and its receptor (GHR) in the retina of both chickens and rats suggests GH may also be an autocrine or paracrine factor with functional roles in vision. To test this hypothesis, we determined GH and GHR localization in the retina of mice, and assessed the effect of exogenous GH on retina function by recording the electroretinogram (ERG).
Retina homogenates from adult mice were subjected to reverse-transcription PCR, with primers designed to amplify the intracellular region of the GHR. Tissue sections of the adult mouse eye were also studied by GH and GHR fluorescence immunocytochemistry and by in situ hybridization using a probe complementary to full length GH mRNA. For functional studies, 1 µL of 0.5 µg/µL recombinant mouse GH (or its vehicle) was injected intravitreally, while precluding lens damage. After 2 hours of dark adaptation, scotopic and photopic intensity responses were recorded.
Retina homogenates contained GHR transcripts identical in size to those found in the liver, an acknowledged GH target site. Retina tissue sections revealed widespread GHR-immunoreactivity, which was particularly abundant in the ganglion cell layer, as was the localization of GH immunoreactivity and GH mRNA. Functionally, the maximum amplitude of the scotopic b-wave declined by 33% (83.5 µV versus 124.5 µV) 2 hours after intravitreal GH injection compared to vehicle. Similar, although smaller, reductions also occurred for maximal scotopic a-wave (by 14%) and photopic b-wave (by 21%) amplitudes. Photopic a-wave and photopic negative response maximal amplitudes were unaffected.
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