Mechanisms underlying the attenuation of endothelium-dependent vasodilatation in the mesenteric arterial bed of the streptozotocin-induced diabetic rat

1. Experiments were designed to investigate the mechanisms underlying the diabetes-related impairment of the vasodilatations of the perfused mesenteric arterial bed induced by acetylcholine (ACh) and K⁺. 2. In streptozotocin (STZ)-diabetic rats, the ACh-induced endothelium-dependent vasodilatation was attenuated. The dose-response curves for ACh in control and diabetic rats were each shifted to the right by N(G)-nitro-L-arginine (L-NOARG) and by isotonic high K⁺ (60 mM). The ACh dose-response curves under isotonic high K⁺ were not different between control and diabetic rats. 3. We also examined the vasodilatation induced by K⁺, which is a putative endothelium-derived hyperpolarizing factor (EDHF). The mesenteric vasodilatation induced by a single administration of K⁺ was greatly impaired in STZ-induced diabetic rats. Treatment with charybdotoxin plus apamin abolished the ACh-induced vasodilatation but enhanced the K⁺-induced response in controls and diabetic rats. After pretreatment with ouabain plus BaCl₂, the ACh-induced vasodilatation was significantly impaired and the K⁺-induced relaxation was abolished in both control and diabetic rats. 4. The impairment of the endothelium-dependent vasodilatation of the mesenteric arterial bed seen in STZ-induced diabetic rats may be largely due to a defective vascular response to EDHF. It is further suggested that K⁺ is one of the endothelium-derived hyperpolarizing factors and that the vasodilatation response to K⁺ is impaired in the mesenteric arterial bed from diabetic rats.