Abstract P638: Muscadine Grape Seed Extract Improves Glucose Handling in Female but not Male Hypertensive (mRen2)27 Rats

Muscadine grapes ( Vitis rotundifolia ) are enriched in polyphenols and other flavan-3-ols that may potentially convey cardiovascular benefit through the antioxidant properties of these compounds. In the current study, we established the effects of a muscadine grape extract (MGE, Piedmont Research and Development Corp.) on blood pressure and metabolic function in 20 week-old female and male hemizygous (mRen2)27 transgenic rats, an Ang II-AT 1 R-dependent model of hypertension. Littermates were treated with MGE (0.2 mg/mL) in the drinking water for 6 weeks (n = 7; male and n=5; female); controls were given water only (n = 7; male and n = 6; female). Intraperitoneal glucose tolerance test (IPGTT) assessed glucose metabolism and serum levels of glucose and insulin were also determined. There were no significant differences between the control and MGE-treated groups for either sex in systolic blood pressure (males: 168 ± 5 vs. 179 ± 4 mmHg; females: 183 ± 5 vs. 162 ± 11 mmHg) or body weight (males: 513 ± 12 vs. 508 ± 22 g; females: 297 ± 4 vs. 294 ± 89 g). The glucose response (area under the curve - AUC) in the female MGE-treated group was markedly lower compared to the untreated controls; however, MGE elicited no effect on the glucose AUC in males (see figure). Although MGE did not influence serum insulin AUC in males or females, the MGE-treated females exhibited a trend for a lower glucose-insulin index. We conclude that MGE intake improves glucose utilization in adult female hypertensive rats independent of changes in blood pressure or body weight. The mechanism(s) underlying the differential response to MGE between the female and male (mRen2)27 transgenic remain to be established

Abstract P189: Angiotensin II - Endocannabinoid Interactions in the Nucleus of the Solitary Tract are Important for Regulation of Baroreflex Control of Heart Rate

Hypertension resulting from elevated brain angiotensin (Ang) II is associated with impaired functioning of neural reflexes regulating sympathetic and parasympathetic outflow. Restoration of normal baroreflex sensitivity (BRS) for control of heart rate (HR) is achieved in a rat model of Ang II - dependent hypertension [ (mRen2)27 transgenic rats ] by local injection of the cannabinoid CB 1 receptor antagonist rimonabant (SR141716A), a CB 1 receptor antagonist, into the solitary tract nucleus (NTS) of anesthetized rats or by chronic oral rimonabant treatment, which has central and peripheral sites of action. Together with elevated brain dorsal medullary tissue concentrations of 2-arachidonylglycerol present in the (mRen2)27 rats, these findings are consistent with an activated endocannabinoid system contributing to the impaired BRS in these animals. To further explore acute interactions between Ang II - mediated suppression of BRS and the endocannabinoids, Ang II was injected into NTS of anesthetized Sprague-Dawley rats 10 minutes following NTS injection of rimonabant or aCSF (120 nL, bilaterally). In the presence of aCSF, Ang II reduced BRS by ~50% (In msec/mm Hg: 1.14 ± 0.14 before versus 0.53 ± 0.16; n = 7, p < 0.008); this effect was abolished in the presence of rimonabant (In msec/mm Hg: 0.92 ± 0.16 before versus 0.86 ± 0.21; n = 4, p = 0.8). There was no difference in mean arterial pressure or heart rate before or after Ang II treatment in either aCSF or rimonabant groups. Thus, the data support the interpretation that Ang II - mediated attenuation of BRS for control of HR involves release of endocannabinoids. Others report that the pressor actions following acute local injections of Ang II into the hypothalamic paraventricular nucleus are prevented by blockade of CB 1 receptors. We conclude that functional interactions between these two systems occur at multiple brain sites relevant to blood pressure control mechanisms and together the findings support a role for elevated brain endocannabinoids as contributors to the altered reflexes characteristic of Ang II - dependent hypertension. Support: HL-51952, DA-024863 and DA-03690, the Hypertension & Vascular Research Center, Farley[[Unable to Display Character: &#8208;]]Hudson Foundation

Long-term systemic angiotensin II type 1 receptor blockade regulates mRNA expression of dorsomedial medulla renin-angiotensin system components

In Fischer 344 (F344) rats, renin-angiotensin system (RAS) blockade for 1 yr with the angiotensin II type 1 (AT(1)) receptor blocker L-158,809 prevents age-related impairments in metabolic function, similar to transgenic rats with low glial angiotensinogen (Aogen). Brain RAS regulation may contribute to the benefits of long-term systemic AT(1) antagonism. We assessed the mRNA of RAS components in the dorsomedial medulla of F344 rats at 3 (young; n = 8) or 15 mo of age (old; n = 7) and in rats treated from 3 to 15 mo of age with 20 mg/l of the AT(1) receptor antagonist L-158,809 (Old+L; n = 6). Aogen and renin mRNA were lower in the young compared with old group. Angiotensin-converting enzyme (ACE) mRNA was lower in the old and Old+L compared with the young group. ACE2 and neprilysin expression were significantly higher in Old+L compared with young or old rats. AT(1b), AT(2), and Mas receptor mRNA were higher with treatment. Leptin receptor mRNA was lower in the old rats and this was prevented by L-158,809 treatment. Dual-specificity phosphatase 1 (DUSP1) mRNA was highest in the Old+L group. Aggregate correlate summation revealed a positive relationship for Mas receptor mRNA with food intake. The findings provide evidence for regulation of dorsomedial medullary renin and Aogen mRNA during aging. Long-term AT(1) receptor blockade increases the mRNA of the enzymes ACE2 and neprilysin and the MAS receptor, which could potentially shift the balance from ANG II to ANG-(1-7) and prevent age-related declines in the leptin receptor and its signaling pathway.

Chronic immunoneutralization of brain angiotensin-(1-12) lowers blood pressure in transgenic (mRen2)27 hypertensive rats

Angiotensin-(1-12) [ANG-(1-12)] is a newly identified peptide detected in a variety of rat tissues, including the brain. To determine whether brain ANG-(1-12) participates in blood pressure regulation, we treated male adult (mRen2)27 hypertensive rats (24-28 wk of age) with Anti-ANG-(1-12) IgG or Preimmune IgG via an intracerebroventricular cannula for 14 days. Immunoneutralization of brain ANG-(1-12) lowered systolic blood pressure (-43 +/- 8 mmHg on day 3 and -26 +/- 7 mmHg on day 10 from baseline, P < 0.05). Water intake was lower on intracereroventricular day 6 in the Anti-ANG-(1-12) IgG group, accompanied by higher plasma osmolality on day 13, but there were no differences in urine volume, food intake, or body weight during the 2-wk treatment. In Preimmune IgG-treated animals, there were no significant changes in these variables over the 2-wk period. The antihypertensive effects produced by endogenous neutralization of brain ANG-(1-12) suggest that ANG-(1-12) is functionally active in brain pathways regulating blood pressure.

Injections of angiotensin-converting enzyme 2 inhibitor MLN4760 into nucleus tractus solitarii reduce baroreceptor reflex sensitivity for heart rate control in rats

Injections of the angiotensin(1-7) [Ang(1-7)] antagonist [d-Ala7]-Ang(1-7) into the nucleus of the solitary tract (NTS) of Sprague-Dawley rats reduce baroreceptor reflex sensitivity (BRS) for control of heart rate by approximately 40%, whereas injections of the angiotensin II (Ang II) type 1 receptor antagonist candesartan increase BRS by 40% when reflex bradycardia is assessed. The enzyme angiotensin-converting enzyme 2 (ACE2) is known to convert Ang II to Ang(1-7). We report that ACE2 activity, as well as ACE and neprilysin activities, are present in plasma membrane fractions of the dorsomedial medulla of Sprague-Dawley rats. Moreover, we show that BRS for reflex bradycardia is attenuated (1.16 +/- 0.29 ms mmHg-1 before versus 0.33 +/- 0.11 ms mmHg-1 after; P < 0.05; n = 8) 30-60 min following injection of the selective ACE2 inhibitor MLN4760 (12 pmol in 120 nl) into the NTS. These findings support the concept that within the NTS, local synthesis of Ang(1-7) from Ang II is required for normal sensitivity for the baroreflex control of heart rate in response to increases in arterial pressure.

Long-term AT1 receptor blockade improves metabolic function and provides renoprotection in Fischer-344 rats

Fischer-344 (F344) rats exhibit proteinuria and insulin resistance in the absence of hypertension as they age. We determined the effects of long-term (1 yr) treatment with the angiotensin (ANG) II type 1 (AT(1)) receptor blocker L-158,809 on plasma and urinary ANG peptide levels, systolic blood pressure (SBP), and indexes of glucose metabolism in 15-mo-old male F344 rats. Young rats at 3 mo of age (n = 8) were compared with two separate groups of older rats: one control group (n = 7) and one group treated with L-158,809 (n = 6) orally (20 mg/l) for 1 yr. SBP was not different between control and treated rats but was higher in young rats. Serum leptin, insulin, and glucose levels were comparable between treated and young rats, whereas controls had higher glucose and leptin with a similar trend for insulin. Plasma ANG I and ANG II were higher in treated than untreated young or older rats, as evidence of effective AT(1) receptor blockade. Urinary ANG II and ANG-(1-7) were higher in controls compared with young animals, and treated rats failed to show age-related increases. Protein excretion was markedly lower in treated and young rats compared with control rats (young: 8 +/- 2 mg/day vs. control: 129 +/- 51 mg/day vs. treated: 9 +/- 3 mg/day, P < 0.05). Long-term AT(1) receptor blockade improves metabolic parameters and provides renoprotection. Differential regulation of systemic and intrarenal (urinary) ANG systems occurs during blockade, and suppression of the intrarenal system may contribute to reduced proteinuria. Thus, insulin resistance, renal injury, and activation of the intrarenal ANG system during early aging in normotensive animals can be averted by renin-ANG system blockade.

Impaired heart rate baroreflex in older rats: role of endogenous angiotensin-(1-7) at the nucleus tractus solitarii

Age-related baroreflex reductions in function may originate from central neural dysregulation as well as vascular structural/functional changes. We determined the role of 2 angiotensin (Ang) peptides at the nucleus tractus solitarii in age-related baroreflex impairment. Baroreflex sensitivity control of heart rate in response to increases in blood pressure was tested in younger (3 to 5 months) and older (16 to 20 months) anesthetized male Sprague-Dawley rats before and after bilateral solitary tract injections of the Ang II type 1 (AT1) receptor antagonist candesartan (24 pmol) or the Ang-(1-7) antagonist (D-Ala7)-Ang-(1-7) (144 fmol or 24 pmol). Basal reflex sensitivity of older rats was significantly lower than younger rats. In younger rats, the reflex was facilitated by bilateral candesartan injections and attenuated by bilateral (D-Ala7)-Ang-(1-7) injections. In older rats, the reflex was facilitated by AT1 blockade; however, (D-Ala7)-Ang-(1-7) injected into the solitary tract nucleus had no effect. Neprilysin mRNA in the medulla was lower in older rats compared with younger rats, whereas angiotensin-converting enzyme (ACE), ACE2, and mas receptor mRNA levels of older rats did not differ from values of younger rats. Thus, opposing actions of endogenous Ang II and Ang-(1-7) in the solitary tract nucleus contribute to baroreflex function in response to increases in mean arterial pressure of younger rats. The attenuated counterbalancing effect of Ang-(1-7) on baroreflex function is lost in older rats, which may be attributable to diminished production of the peptide from neprilysin.