Abstract 5256: Increased Endothelin-A Receptor-Protein Expression/Localization and Contractile Response to Endothelin-1 of Coronary Microvasculature From Diabetic Patients
Objectives: Hyperglycemia is a potent stimulus for endothelin-1 (ET-1) production. Increased ET-1 exposure of coronary vasculature and myocytes in diabetics can hamper blood flow delivery to the vulnerable myocardium and exacerbate contractile function. In the present study, we investigated the protein expression/localization of ET-A receptors, the contractile response to ET-1 and the inhibition of ET-A receptors in the human coronary microvasculature in diabetic and case-matched non-diabetic patients.
Methods: Right discarded atrial tissues were harvested pre-CPB from 30 patients with and without diabetics undergoing cardiac surgery. Coronary arterioles (90 – 180 micrometer in diameter) were dissected from the harvested tissue and placed in an organ bath containing Krebs solution. Microvascular constriction was assessed by videomicroscopy in response to ET-1, with and without an endothelin-A (ET-A) receptor antagonist. The expression and localization of ET-A receptors were also examined using immunoblot and confocal immunofluorescence microscopy.
Results: ET-1 caused a dose-dependent contractile response of coronary arterioles from diabetics and non-diabetics. The contractile response of diabetic arterioles to ET-1 (10−9M) was significantly increased compared with those of non-diabetics (15±3% vs. 8±2%, P<0.05). The contractile response of microvessels from diabetics and non-diabetics to ET-1 was significantly inhibited in the presence of the ET-A receptor antagonist BQ123 (10−7M, P<0.05, respectively). The protein expression of ET-A receptors was significantly elevated from 1 fold of non-diabetics to 2.5 folds of diabetics (P<0.01). Immunofluorescent staining displayed stronger ET-A receptors signals of smooth muscle from diabetics than those of non-diabetics.
Conclusion: Hyperglycemia up-regulates ET-A-receptor protein expression/localization and increases the contractile response to ET-1 in the diabetic coronary microvasculature. The contractile response to ET-1 is via activation of ET-A receptors in diabetics since blockade of ET-A receptors prevented ET-1-induced vasoconstriction. These findings support the notion that diabetic patients face an increased ET over-stimulation.