Endothelins (ETs) are a family of vasoactive peptides that have mitogenic properties and have also been associated with altered long-term nuclear signaling. We have previously shown that mRNA levels for ET-1, ET-3, and their receptors are upregulated under hyperhexosemic conditions. In this study, an endothelin antagonist was used to assess the effects of endothelin blockage on the production of two basement membrane transcripts, fibronectin and collagen alpha1 (IV). The microvascular basement membranes were analyzed using ultrastructural morphometry. Streptozotocin-induced diabetic rats, galactose-fed rats (30% galactose in diet), and nondiabetic, non-galactose-fed control rats were studied after 1-month and 6-month follow-up. Simultaneously, similar animal groups were treated with a general ET receptor blocker (bosentan, 100 mg x kg(-1) x day(-1)) and investigated. Semiquantitative reverse transcription-polymerase chain reaction for fibronectin and collagen alpha1 (IV) was conducted after 1 month of follow-up with comparison to beta-actin housekeeping gene using slot blot hybridization and densitometry. Basement membrane thickness was assessed after 6 months of follow-up in diabetic rats, using the orthogonal intercept method. After 1 month of follow-up, increased fibronectin and collagen alpha1 (IV) mRNA were present in the retina of diabetic and galactosemic animals, and the bosentan-treated groups exhibited mRNA levels similar to the control animals. After 6 months of follow-up, diabetes and galactose feeding induced basement membrane thickening, which was partially prevented by bosentan treatment. The above findings indicate that increased production of extracellular matrix proteins leading to thickening of microvascular basement membrane, secondary to hyperhexosemia, may be mediated via augmented ET production.

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