Chronic Infusion Of ANG Research Articles

Abstract P324: Role of GABAergic Signaling in AgRP Neurons in the Dipsogenic and Metabolic Responses to Brain Angiotensin

Obesity is a major risk factor for development of hypertension, and evidence supports a role for the suppression of resting metabolic rate (RMR) in the development and maintenance of obesity. Angiotensin II (ANG) AT1A receptors, localized to cells expressing the leptin receptor and Agouti-related peptide (AgRP) within the arcuate nucleus of the hypothalamus (ARC), are involved in transcriptional control of AgRP and γ-aminobutyric acid (GABA) synthetic genes ( Gad65 , Gad67 , Slc32a1 ) within the ARC, as well as the integrative control of thermogenic sympathetic nerve activity (SNA) and RMR responses in vivo to various stimuli including leptin and high fat diet. These data led us to hypothesize that AT1A functions to suppress GABA signaling in AgRP neurons, ultimately to disinhibit SNA and RMR. Treatment of cultured mouse hypothalamic N43/5 cells (which express endogenous Agtr1a , AgRP and Gad67 ) with 100 nM ANG for 1 hour (n=6) resulted in reduced AgRP (0.57-fold of control, p=0.03) and Gad67 (0.72-fold of control, p=0.09) mRNA. Mice with targeted disruption of Slc32a1 (vesicular GABA transporter; VGAT) in AgRP neurons (VGAT AgRP-KO mice) were generated on a mixed background. Compared to littermates (male n=9-17, female n=7-8), VGAT AgRP-KO mice (male n=8-13, female n=2-3) at 8 weeks of age exhibited normal body mass (genotype p=ns, sex p<0.05, interaction p=ns), no changes in food intake (genotype p=ns, sex p=ns, interaction p=ns), but a sex-dependent genotype effect on fluid intake was observed (male con 4.5±0.3 vs KO 5.1±0.4; fem con 5.1±0.4 vs KO 3.7±0.6 mL/d; interaction p<0.05). A preliminary study of male mice instrumented for chronic infusion of ANG (5 ng/hr, 21 days icv) was also performed. This caused modest increases in drinking (con+aCSF n=7, 3.3±0.8, con+ANG n=4, 5.2±1.0, KO+ANG n=3, 7.9±1.1 mL/d, p<0.05) but no change in energy efficiency (11.2±2.9, 11.3±3.5, 10.1±4.1 mg/kcal), indicating no change in energy expenditure, possibly due to the mixed background of this strain. We conclude that ANG acts at AgRP cells of the ARC to suppress GABA and AgRP signaling, and this contributes to energy and fluid homeostasis in a complex, strain- and sex-dependent manner.

Angiotensin-(1–7) attenuates hypertension in exercise-trained renal hypertensive rats

Angiotensin-(1-7) [ANG-(1-7)] plays a counterregulatory role to angiotensin II in the renin-angiotensin system. In trained spontaneous hypertensive rats, Mas expression and protein are upregulated in ventricular tissue. Therefore, we examined the role of ANG-(1-7) on cardiac hemodynamics, cardiac functions, and cardiac remodeling in trained two-kidney one-clip hypertensive (2K1C) rats. For this purpose, rats were divided into sedentary and trained groups. Each group consists of sham and 2K1C rats with and without ANG-(1-7) infusion. Swimming training was performed for 1 h/day, 5 days/wk for 4 wk following 1 wk of swimming training for acclimatization. 2K1C rats showed moderate hypertension and left ventricular hypertrophy without changing left ventricular function. Chronic infusion of ANG-(1-7) attenuated hypertension and cardiac hypertrophy only in trained 2K1C rats but not in sedentary 2K1C rats. Chronic ANG-(1-7) treatment significantly attenuated increases in myocyte diameter and cardiac fibrosis induced by hypertension in only trained 2K1C rats. The Mas receptor, ANG II type 2 receptor protein, and endothelial nitric oxide synthase phosphorylation in ventricles were upregulated in trained 2K1C rats. In conclusion, chronic infusion of ANG-(1-7) attenuates hypertension in trained 2K1C rats.

Acute and chronic angiotensin-(1–7) restores vasodilation and reduces oxidative stress in mesenteric arteries of salt-fed rats

This study determined the effect of ANG-(1-7) on salt-induced suppression of endothelium-dependent vasodilatation in the mesenteric arteries of male Sprague-Dawley rats. Chronic intravenous infusion of ANG-(1-7), oral administration of the nonpeptide mas receptor agonist AVE-0991, and acute preincubation of the arteries with ANG-(1-7) and AVE-0991 all restored vasodilator responses to both ACh and histamine that were absent in the arteries of rats fed a high-salt (4% NaCl) diet. The protective effects of ANG-(1-7) and AVE-0991 were inhibited by acute or chronic administration of the mas receptor antagonist A-779, the ANG II type 2 (AT(2)) receptor blocker PD-123319, or N-nitro-l-arginine methyl ester, but not the ANG II type 1 receptor antagonist losartan. Preincubation with the antioxidant tempol or the nitric oxide (NO) donor diethylenetriamine NONOate and acute and chronic administration of the AT(2) receptor agonist CGP-42112 mimicked the protective effect of ANG-(1-7) to restore vascular relaxation. Acute preincubation with ANG-(1-7) and chronic infusion of ANG-(1-7) ameliorated the elevated superoxide levels in rats fed a high-salt diet, but the expression of Cu/Zn SOD and Mn SOD enzyme proteins in the vessel wall was unaffected by ANG-(1-7) infusion. These results indicate that both acute and chronic systemic administration of ANG-(1-7) or AVE-0991 restore endothelium-dependent vascular relaxation in salt-fed Sprague-Dawley rats by reducing vascular oxidant stress and enhancing NO availability via mas and AT(2) receptors. These findings suggest a therapeutic potential for mas/AT(2) receptor activation in preventing the vascular oxidant stress and endothelial dysfunction associated with elevated dietary salt intake.