Coronary vasomotor reactivity to endothelin-1 in the prediabetic metabolic syndrome

Objective: The purpose of the present investigation was to test the hypothesis that coronary vasoconstrictor responses to endothelin-1 are augmented in the prediabetic metabolic syndrome. Methods: ELISA was used to measure plasma endothelin-1 and intracoronary endothelin-1 doseresponse experiments were conducted in vivo on normal control and high-fat-fed prediabetic dogs. Additionally, isolated left circumflex (LCX) coronary arteries and arterioles (<160 μm) were used for in vitro functional studies and molecular analyses (quantitative real-time PCR and Western blotting). Results: Plasma endothelin-1 concentrations were not different between control and prediabetic dogs. Coronary vasoconstriction to endothelin-1 was similar in control and prediabetic dogs, both in vivo and in isolated arterioles. Nonetheless, real-time PCR analysis revealed significant decreases in ET_A receptor transcript levels in LCX coronary arteries and arterioles. Also, Western blotting revealed a significant decrease in ET_A receptor protein in LCX coronary arteries. Conclusions: The findings of the present investigation indicate that although ET_A receptor-signaling is sensitized by induction of the metabolic syndrome, endothelin-mediated coronary vasoconstriction does not significantly contribute to coronary dysfunction at this early stage of prediabetes.