Elevated plasma endothelin‐1 level in streptozotocin‐induced diabetic rats and responsiveness of the mesenteric arterial bed to endothelin‐1

Both the plasma endothelin-1 (ET-1) levels and the plasma glucose levels were markedly elevated in streptozotocin (STZ)-induced diabetic rats. 2. The maximum contractile response of the mesenteric arterial bed to ET-1 was significantly reduced, and the vasodilatation induced by the ET(B)-receptor agonist IRL-1620 in the mesenteric arterial bed was significantly reduced in STZ-induced diabetic rats. 3. ET-1 (10(-8) M) caused a transient vasodilatation followed by a marked vasoconstriction in methoxamine-preconstricted mesenteric arterial beds. The ET-1-induced vasodilatation was significantly larger in beds from diabetic rats than in those from age-matched controls. By contrast, the ET-1-induced vasoconstriction was significantly smaller in STZ-induced diabetic rats than in the controls. 4. Both removal of the endothelium with Triton X-100 and preincubation with BQ-788 (10(-6) M) (ET(B)-receptor antagonist) abolished the ET-1-induced vasodilatation. Preincubation with BQ-485 (10(-6) M) or BQ-123 (3 x 10(-6)) (ET(A)-receptor antagonist) significantly augmented the ET-1-induced vasodilatation in control mesenteric arterial beds, but not that in beds from diabetic rats. 5. These results demonstrate that marked increases not only in plasma glucose, but also in plasma ET-1 occur in STZ-induced diabetic rats. We suggest that the decreased contractile response and the increased vasodilator response of the mesenteric arterial bed to ET-1 may both be due to desensitization of ET(A) receptors, though ET(B) receptors may also be desensitized. This desensitization may result from the elevation of the plasma ET-1 levels seen in STZ-induced diabetic rats.