Search

Activation of angiotensinergic pathways and central aldosterone (aldo)-MR-ENaC-endogenous ouabain (EO)-AT 1 R pathway play a critical role in Ang II associated hypertension. The SFO contains both MR and AT 1 R and can relay the signals of circulating Ang II to downstream nuclei such as the PVN, SON and RVLM. We evaluated the effect of knockdown of MR and AT 1 R specific in the SFO on reactive oxygen species (ROS) production in downstream nuclei. Wistar rats were intra SFO infused with AAV-MR- or AT 1a R-siRNA and after 7 days received a sc infusion of Ang II at 500 ng/min/kg for 2 weeks. MR and AT 1 R expression were measured by real-time qPCR and western blotting. ROS was assessed by DHE staining. Ang II increased AT 1 R mRNA expression in the SFO. Both MR- and AT 1 R-siRNA in the SFO prevented this increase. Ang II decreased MR mRNA but increased protein expression in the SFO. Both MR- and AT 1 R-siRNA further decreased MR mRNA expression. Ang II significantly increased ROS in the SFO, magno- and parvocellular parts of the PVN, SON and RVLM. Both MR- and AT 1 R-siRNA in the SFO prevented ROS increases in the PVN and RVLM. In contrast, MR- but not AT 1 R-siRNA in the SFO prevented the Ang II-induced ROS in the SON. Both MR- and AT 1 R-siRNA in the SFO prevented most of the Ang II-induced hypertension. These results suggest that aldo-MR signaling in the SFO is needed for the activation of Ang II-AT 1 R signaling from the SFO to the PVN and RVLM. Considering that only MR-siRNA in the SFO prevents circulating Ang II induced ROS in the SON, activation of aldo-MR signaling from the SFO to the SON may via EO enhance AT 1 R dependent activation of pre-sympathetic neurons in the PVN, and thereby to Ang II-hypertension.

Circulating Ang II increases BP through both peripheral and central mechanisms. Activation of both AT 1 R and MR in the CNS plays a critical role in Ang II-induced hypertension. The subfornical organ (SFO) contains both MR and AT 1 R and can relay the signals of circulating Ang II to downstream nuclei such as the PVN. In this study, we evaluated the effect of intra-SFO infusion of AAV-MR-siRNA or AAV-AT 1a R-siRNA on MR or AT 1 R mRNA expression in the SFO and PVN and Ang II induced hypertension as assessed by telemetry. Two week sc infusion of Ang II at 500 ng/kg/min in Wistar rats on regular salt diet increased BP by 60~65 mmHg. This pressor effect of Ang II was largely prevented by AAV-MR-siRNA or AAV-AT 1 R-siRNA in the SFO (Figure). Ang II increased AT 1 R mRNA expression (1.7± 0.4 vs 0.8 ± 0.04 х10 -1 , p1 R-siRNA in the SFO prevented this increase (1.1 ± 0.2х10 -1 and 1.0± 0.3х10 -1 ). In contrast, Ang II decreased MR mRNA expression (3.2 ± 0.2 vs. 4.1 ± 0.2х10 -2 , p1 R-siRNA further decreased MR mRNA expression (2.7 ± 0.2 х10 -2 and 2.3 ± 0.3 х10 -2 ). In the PVN, Ang II increased AT 1 R mRNA by ~100% and MR mRNA by ~20%. Only AT 1 R-siRNA in the SFO prevented these increases in the PVN. AAV mediated eGFP fluorescence expression was observed in the SFO but not the PVN. These results suggest that circulating Ang II differentially regulates MR and AT 1 R expression in the SFO. Prevention of Ang II induced AT 1 R up-regulation by knockdown of either AT 1 R or MR suggests a MR dependent regulation of AT 1 R in the SFO. MR-AT 1 R signaling in the SFO appears to play a major role in Ang II-induced hypertension in rats. * p

Circulating Ang II activates an aldosterone-MR-AT 1 R pathway in the hypothalamus. To obtain insights into the actual aldosterone-MR- AT 1 R neuronal pathway, the present study examined whether intra-PVN infusion of AAV-AT 1a R-siRNA or AAV-MR-siRNA prevents the Ang II induced increases in AT 1 R and MR expression and BP. Two weeks sc infusion of Ang II at 500ng/kg/min in Wistar rats on regular salt diet increased BP by telemetry by 66 ± 3 mm Hg, and AT 1 R and MR protein in the SFO, SON and PVN. Intra-PVN AT 1a R-siRNA decreased AT 1 R but not MR expression in the PVN by sc Ang II, and MR-siRNA decreased MR but not AT 1 R expression in the PVN. AT 1 R and MR expression in both SFO and SON were not significantly changed by the two AAV-siRNA. Specific knockdown of AT 1 R or MR in the PVN by AAV-siRNA prevented ~80% of the increase in BP induced by sc Ang II. These results suggest that circulating Ang II up-regulates brain Ang II and aldosterone and increases MR and AT 1 R in the SFO, SON and PVN. Prevention of Ang II induced increases in MR but not AT 1 R by knockdown of MR and vice versa suggests an independent regulation of MR and AT 1 R in the PVN. Both AT 1 R and MR in the PVN play a critical role in Ang II-induced hypertension in rats. * p

Central blockade of mineralocorticoid receptor (MR) prevents aldosterone (aldo)-salt induced hypertension. We examined the role of the subfornical organ (SFO), aldo synthesized locally in the brain, and MR specifically in the paraventricular nucleus (PVN) in aldo-salt hypertension. Wistar rats with telemetry probes were treated with chronic intra-cerebroventricular infusion of aldo synthase (AS) inhibitor FAD286 (25 μg/day), MR blocker eplerenone (5 μg/day) or vehicle. After 2 days, subcutaneous (sc) aldo infusion (1 μg/h) was started and saline was provided as drinking water. In a second set of rats with telemetry, electrolytic or sham lesions of the SFO, or bilateral intra-PVN infusion of AAV-MR-siRNA or AAV-SCM-siRNA (1 μl of 5x10 10 genomic particles/ml) at 100ng/min were performed, and sc aldo infusion started 1 week later. AAV-MR-siRNA decreased MR mRNA and protein expression in the PVN by ~60 and 30%, but had no effects on MR expression in other nuclei such as the SFO and SON. SFO lesion, blockade of brain AS or MR, or knockdown of MR in the PVN attenuated aldo-salt hypertension by ~60%. Data=means± SE (n=5-9/group). *p These results suggest that an increase in circulating aldosterone may via MR and AT 1 R in the SFO increase local aldosterone production in hypothalamic nuclei such as the SON and PVN, and via MR in the PVN activate a central aldosterone-MR-AT 1 R neuro-modulatory pathway, which plays a major role in the progressive hypertension. (Supported by grant # FRN:MOP-74432 from the Canadian Institutes of Health Research)