Late dual endothelin receptor blockade with bosentan restores impaired cerebrovascular function in diabetes

Abstract

Aims: Up-regulation of the endothelin (ET) system in type-2 diabetes increases contraction and decreases relaxation in basilar artery. We showed that 1) ET-receptor antagonism prevents diabetes-mediated cerebrovascular dysfunction; and 2) glycemic control prevents activation of the ET-system in diabetes. Here, our goal is to determine whether and to what extent glycemic control or ET-receptor antagonism reverses established cerebrovascular dysfunction in diabetes.

Main methods: Non-obese type-2 diabetic Goto-Kakizaki rats were administered either vehicle, metformin (300 mg/kg/day) or dual ET-receptor antagonist bosentan (100mg/kg) for 4-weeks starting at 18-weeks after established cerebrovascular dysfunction (n=5-6/group). Control group included vehicle-treated aged-matched Wistar rats. Blood glucose and pressure were monitored weekly. At termination, basilar arteries were collected and cumulative dose-response curves to ET-1 (0.1-500 nM), 5-HT (1-1000 nM) and acetylcholine (Ach, 0.1 nM-5 μM) were studied by wire myograph. Middle cerebral artery (MCA) myogenic reactivity and tone were measured using pressurized arteriograph.

Key findings: There was no difference in ET-1 and 5-HT-mediated constrictions. Endothelium-dependent relaxation was impaired in diabetes. Bosentan improved sensitivity to Ach as well as the maximum relaxation. Myogenic-tone is decreased over the course of the disease. Both treatments improved the ability of MCAs to develop tone at 80 mm Hg and only bosentan improved the tone at higher pressures.

Significance: These results suggest that contractile response is not affected by glycemic control or ET-receptor antagonism. Meanwhile, dual ET-receptor blockade is effective in partially improving endothelium-dependent relaxation and myogenic response in a blood pressure-independent manner even after established cerebrovascular dysfunction and offers therapeutic potential.

Keywords: Basilar artery; Endothelial function; Endothelin; Middle cerebral artery; Myogenic tone.

Figure 1

Effect of glycemic control and endothelin receptor antagonism on ET-1-induced isometric contractions in basilar arteries in diabetes. (A) Dose-response curves to ET-1 in control (C), diabetes (D), diabetes+bosentan (D+B) and diabetes+metformin (D+M) groups were similar. There was no difference in maximum response (B) or sensitivity (C) to ET-1 among the groups. Contractile response was expressed as %KCl response and results are given as mean±SEM, n=5- 6/group.

Figure 2

Effect of glycemic control and endothelin receptor antagonism on endothelium-dependent vasorelaxation in basilar arteries in diabetes. (A) Dose-response curves to Ach in ET-1-preconstricted vessels showed severely impaired vasorelaxation in diabetic animals. (B) Maximum relaxation to Ach (R_max) was significantly lower in diabetic animals. While metformin had no effect on R_max, bosentan improved it. (C) Sensitivity to Ach was decreased in diabetes as indicated by greater EC₅₀ values. Bosentan improved sensitivity. Since the metformin dose response curve was flat, EC₅₀ was not determined (ND) for this group. Results are given as mean±SEM, n=5–6/group. ^#p<0.001, *p<0.05 vs C, **p<0.05 vs D+M.

Figure 3

Effect of glycemic control and endothelin receptor antagonism on pressure-induced myogenic tone of isolated MCAs. (A) Myogenic tone at 80 and 120 mm-Hg was lower in diabetic animals and bosentan improved tone development. (B) MCA myogenic tone was decreased during the disease progression in diabetes and only bosentan improved tone at higher pressure points. Mean ± SEM, n=5–6, *p<0.05 vs control, **p<0.05 vs D, ^#p<0.05 vs 10 w, ^##p<0.05 vs 22w D.