Mineralocorticoid and AT1 receptors in the paraventricular nucleus contribute to sympathetic hyperactivity and cardiac dysfunction in rats post myocardial infarct

Abstract

Intracerebroventricular infusion of a mineralocorticoid receptor (MR) or angiotensin II type 1 receptor (AT1R) blocker in rats attenuates sympathetic hyperactivity and progressive left ventricular (LV) dysfunction post myocardial infarction (MI). The present study examined whether knockdown of MRs or AT1Rs specifically in the paraventricular nucleus (PVN) contributes to these effects, and compared cardiac effects with those of systemic treatment with the β1-adrenergic receptor blocker metoprolol. The PVN of rats was infused with adeno-associated virus carrying small interfering RNA against either MR (AAV-MR-siRNA) or AT1R (AAV-AT1R-siRNA), or as control scrambled siRNA. At 4 weeks post MI, AT1R but not MR expression was increased in the PVN, excitatory renal sympathetic nerve activity and pressor responses to air stress were enhanced, and arterial baroreflex function was impaired; LV end-diastolic pressure (LVEDP) was increased and LV peak systolic pressure (LVPSP), ejection fraction (EF) and dP/dtmax decreased. AAV-MR-siRNA and AAV-AT1R-siRNA both normalized AT1R expression in the PVN, similarly ameliorated sympathetic and pressor responses to air stress, largely prevented baroreflex desensitization, and improved LVEDP, EF and dP/dtmax as well as cardiac interstitial (but not perivascular) fibrosis. In a second set of rats, metoprolol at 70 or 250 mg kg(-1) day(-1) in the drinking water for 4 weeks post MI did not improve LV function except for a decrease in LVEDP at the lower dose. These results suggest that in rats MR-dependent upregulation of AT1Rs in the PVN contributes to sympathetic hyperactivity, and LV dysfunction and remodelling post MI. In rats, normalizing MR-AT1R signalling in the PVN is a more effective strategy to improve LV dysfunction post MI than systemic β1 blockade.

Figure 1

GFP fluorescence in the PVN after intra-PVN AAV infusion in rat post MI Representative image of eGFP fluorescence in the PVN. eGFP expression was evaluated in brain sections of a rat infused in the PVN with AAV-AT_1aR-siRNA at 25 × 10⁷ genomic particles. Red arrows indicate the PVN and white arrows point to the SON.

Figure 2

MR and AT₁R mRNA expression MR and AT₁R mRNA expression at 4 weeks post MI in the PVN (A and B) and RVLM (C and D) in sham rats and rats treated post MI with intra-PVN infusion of scrambled (SCM)-siRNA, MR-siRNA or AT₁R-siRNA. Data are means ± SEM. Some RVLM samples from the AT₁R-siRNA group were lost, and not enough data are available for this group. PVN (n = 7–8 per group): for AT₁R, F = 16.7, P < 0.0001; for MR, F = 10.5, P < 0.0001. RVLM (n = 4–7 per group): for AT₁R, F = 13.4, P < 0.001; for MR, F = 4.59, P < 0.05. *P < 0.05 vs. others; ^aP < 0.05 vs. MI + MR-siRNA.

Figure 3

Responses to air stress Increases in MAP, RSNA and HR in response to air stress at 4 weeks post MI in sham rats and rats treated post MI with intra-PVN infusion of scrambled (SCM)-siRNA, MR-siRNA or AT₁R-siRNA. Data are means ± SEM (n = 7–10 per group). For MAP, F = 12.7, P < 0.00001; for RSNA, F = 7.5, P < 0.001; for HR, F = 8.1, P < 0.001. *P < 0.05 vs. sham; ^aP < 0.05 vs. MI + SCM-siRNA.

Figure 4

Arterial baroreflex Arterial baroreflex control of RSNA (upper panel) and HR (lower panel) analysed as a logistic model at 4 weeks post MI in sham rats and rats treated post MI with intra-PVN infusion of scrambled (SCM)-siRNA, MR-siRNA or AT₁R-siRNA. For statistics and n, see Table 1.

Figure 5

LV dimensions and ejection fraction LV diastolic and systolic dimensions, and ejection fraction measured by echocardiography at 4 weeks post MI in sham rats and rats treated post MI with intra-PVN infusion of scrambled (SCM)-siRNA, MR-siRNA or AT₁R-siRNA. Data are means ± SEM (n = 7–9 per group). For the LV diastolic dimension, F = 9.02, P < 0.001; for the LV systolic dimension, F = 20.6, P < 0.0001; for ejection fraction, F = 26.1, P < 0.0001. *P < 0.05 vs. sham; ^aP < 0.05 vs. MI + SCM-siRNA.

Figure 6

LV function LV function measured by Millar catheter at 4 weeks post MI in sham rats and rats treated post MI with intra-PVN infusion of scrambled (SCM)-siRNA, MR-siRNA or AT₁R-siRNA. Data are means ± SEM (n = 7–10 per group). For LVEDP, F = 11.9, P < 0.0001; for LVPSP, F = 6.69, P < 0.002; For dP/dt_max, F = 34.6, P < 0.0001. *P < 0.05 vs. sham; ^aP < 0.05 vs. MI + SCM-siRNA.

Figure 7

Fibrosis in peri-infarct area Representative images of interstitial fibrosis in the peri-infarct area of the LV at 4 weeks post MI in rats treated post MI with intra-PVN infusion of scrambled (SCM)-siRNA, MR-siRNA or AT₁R-siRNA.

Figure 8

Perivascular fibrosis Representative images of perivascular fibrosis in the LV at 4 weeks post MI of sham rats or rats treated post MI with intra-PVN infusion of scrambled (SCM)-siRNA, MR-siRNA or AT₁R-siRNA.

Figure 9

Cardiac fibrosis Interstitial fibrosis in peri-infarct area of the LV, septum and RV, and perivascular fibrosis in LV at 4 weeks post MI of sham rats and rats treated post MI with intra-PVN infusion of scrambled (SCM)-siRNA, MR-siRNA or AT₁R-siRNA. Data are means ± SEM (n = 5–7 per group). For peri-infarct, F = 19.3, P < 0.0001; for perivascular, F = 4.73, P < 0.01; for septum, F = 11.8, P < 0.0001; for RV, F = 4.1, P < 0.02. *P < 0.05 vs. sham; ^aP < 0.05 vs. MI + SCM-siRNA.