Effects of a selective endothelin a receptor antagonist on the expressions of iNOS and eNOS in the heart of early streptozotocin-induced diabetic rats.

Vascular tone is regulated through the actions of locally produced agents. Among the vasoconstrictors, the most potent agent is endothelin (ET), which exerts its vasoconstrictor actions principally through ET type A (ET(A)) receptors. Of the vasodilators, nitric oxide (NO) seems to be the most important contributor to the acute regulation of vascular tone. Vasculopathy is an important feature of diabetes mellitus (DM). Endogenous ET-mediated vasoconstrictor tone is augmented in diabetic states, and conflicting results persist concerning the NO system in diabetes. The present study investigated the expressions of inducible NO synthases (iNOS) and endothelial NOS (eNOS) in the heart of diabetic animals and the effects of a selective ET(A) receptor antagonist on these alterations. Type I diabetes was induced by intraperitoneal injection of streptozotocin (65 mg/kg) in Sprague-Dawley rats, while control (Con) rats received only citrate buffer. After 1 week, the streptozotocin-administered rats were randomly divided into two groups: the selective ET(A) receptor antagonist-administered group (DM+TA-0201, 1 mg/kg/day, by osmotic minipump for 2 weeks) and the DM+vehicle group (comprising the diabetic rats that received saline). The random blood glucose level was 405 +/- 103 mg/dl in DM animals, and this level was unchanged by ET antagonism. Body weight was more greatly decreased in DM rats than in Con rats, but the left ventricle to body weight ratio was increased in the DM group and was unaffected by ET antagonism. Protein expressions of eNOS and iNOS were assessed in the left ventricular tissues. eNOS expression was significantly increased in DM heart and was greatly inhibited by the treatment with ET antagonist. The expression of iNOS was also increased in early DM heart but was reversed by the ET antagonist. Thus, endothelin antagonism might be beneficial for DM heart by reversing the upregulated eNOS and iNOS expressions.