Hypertensive retinopathy in a rat model: modulation by an endothelin–receptor antagonist

Abstract

Abstract: : Purpose: Hypertensive retinopathy manifests as progressive arteriolar and capillary bed damage and basement membrane (BM) thickening in the retinal microvasculature in response to aberrant blood flow. The current study sought to evaluate if dysfunction of the vasoactive endothelin–1 (ET–1) system is involved in the pathogenesis of hypertension–induced retinopathy. Methods:The non–selective endothelin–receptor antagonist Bosentan (100 mg/kg/day) was administered to 10 week old spontaneously hypertensive rats (SHR). Animals were studied at 20 weeks (adult) and 21 months (aged) and comparisons made to untreated SHRs and normotensive Wistar Kyoto (WKY) rats. Retinal mRNA expression of BM proteins laminin ß1, collagen IV and fibronectin was quantified using real–time PCR. Following the isolation of the retinal vascular tree using trypsin digestion, retinal arteriole and capillary bed damage was assessed using qualitative and quantitative microscopy. Results:Laminin ß1 and fibronectin expression in adult and aged rats was greater in SHR (p<0.001) compared to WKY control. Treatment with Bosentan abolished these responses in the SHR groups, did not change WKY expression and markedly attenuated responses in aged SHRs (p<0.001). Collagen IV expression was higher in adult and aged SHRs (p<0.001) compared to WKY. Bosentan increased collagen IV expression in adult rats of both strains, but reduced expression in aged SHRs. Laminin ß1, fibronectin and collagen IV expression declined with age in both SHR and WKY rats (p<0.001). Pathological changes including microaneurysm–like lesions, arteriolar damage, vascular smooth muscle loss and hypercellularity were observed in many aged SHRs, while no such lesions were observed in WKY rats or Bosentan treated groups. Retinal vascular tree quantification revealed acellular capillary number and vascular density in aged rats to be highest in WKY (p<0.01), with no differences observed in the adult group. Bosentan had no effect in either strain. There were no quantifiable differences in overall artery or arteriolar diameter in any experimental group. Conclusions:These results indicate an ET–1–mediated increased basement membrane thickening in the development of hypertensive retinopathy. Variable mRNA expression levels of BM components suggest ET–mediated actions may alter with disease progression. They also suggest a potential adaptive mechanism occurring in the SHR model in response to hypertension, and age–related adaptation in the WKY.

Keywords: retinal degenerations: cell biology • pathology: experimental • hypoxia