Abstract 307: Enhancement of Cerebrovascular Relaxation by Angiotensin II Type 2 Receptor Agonist, C21, is Lost in Type 2 Diabetes
Background: Angiotensin type 1 receptor (AT1R) blockers provide vascular protection and improve stroke outcomes in young otherwise healthy animals. These effects are believed to be mediated by the indirect stimulation of AT2R signaling. The AT2R agonist, compound 21 (C21), improves endothelial function in peripheral vascular beds but its effect on cerebral endothelial function remains unknown. It is important to determine the vascular effects of C21 in diabetes, a comorbid condition which is known to worsen stroke outcomes.
Methods: Endothelium-dependent relaxation was assessed in male Wistar and Type 2 diabetic Goto-Kakizaki (GK) rats (n=3-6) by measuring acetylcholine (ACh, 1 nM - 5 μm) induced dilatory response in basilar arteries. In a subset of experiments C21 dose response curves were generated (0.1 nM - 1 μM) or vessels were pre-incubated with 100 nM C21 ± 1 μM PD123319 (AT2R blocker) for 30 min prior to Ach dose response curves. Area under the curve (AUC) and half maximal effective concentration (EC50 nM) were calculated as indices of total relaxation and receptor sensitivity, respectively. Angiotensin receptors expression was measured by immunoblotting of brain homogenates.
Results: AT2R agonist C21 dose response curves showed no basilar reactivity in either control or diabetic animals. Pre-incubation with C21 enhanced relaxation to Ach in control animals (vehicle 146.7 ± 3.9 vs C21 pretreatment 229.6 ± 11.6), which was abolished by the blockade of AT2R (176.9 ± 25.5, p=0.007). Similarly, C21 improved sensitivity in control animals (vehicle 110.5 ± 32 vs C21 pretreatment 11.9 ± 2) which was abolished in the presence of PD123319 (93.8 ± 31, p=0.04). Basilar artery relaxation (AUC) was impaired in diabetic GK rats (93.9 ± 1.8%) as compared to controls (146.7 ± 3.9%) and C21 had no effect (98 ± 8.9%) indicating a disease and treatment interaction (p<0.001). Normalized AT1R expression levels were 1 ± 0.04 and 0.98 ± 0.05 in control vs diabetic rats and respective AT2R levels were 1 ± 0.1 and 0.84 ± 0.09.
Conclusion: C21 improves vascular relaxation in control but not in diabetic rats in an AT2R-dependent manner. Underlying mechanisms blunting response to C21 need to be further investigated and may impact the subsequent development of C21 as a treatment for stroke.
Author Disclosures: A.Y. Fouda: None. T. Hardigan: None. S. Soliman: None. B. Pillai: None. A. Ergul: B. Research Grant (includes principal investigator, collaborator, or consultant and pending grants as well as grants already received); Modest; Veterans administration merit review BX000347 and 1R01NS083559-01A1. S. Fagan: B. Research Grant (includes principal investigator, collaborator, or consultant and pending grants as well as grants already received); Modest; Veterans Affairs Merit Review (BX000891) & RO1-NS063965.
- © 2014 by American Heart Association, Inc.