Restoration of cerebral vascular relaxation in renin congenic rats by introgression of the Dahl R renin gene

Abstract

Background: This study determined whether transfer of the renin gene from the Dahl salt-resistant (Dahl R) strain into the Dahl salt-sensitive (SS) genetic background restores the relaxation of middle cerebral arteries (MCAs) to different vasodilator stimuli in S/renRR renin congenic (SS.SR-(D13N1 and Syt2)/Mcwi) (RGRR) rats maintained on low-salt (0.4% NaCl) diet.

Methods: Responses to vasodilator stimuli were evaluated in isolated MCA from SS (Dahl SS/Jr/Hsd/MCWi), RGRR rats, and Dahl R rats.

Results: MCA from SS rats failed to dilate in response to acetylcholine (ACh; 10(-6) mol/l), hypoxia (PO2 reduction to 40-45 mm Hg), and iloprost (10(-11) g/ml). ACh- and hypoxia-induced dilations were present in Dahl R rats and restored in RGRR rats. MCA from RGRR and SS constricted in response to iloprost, whereas MCA from Dahl R rats dilated in response to iloprost. MCA from SS, RGRR, and Dahl R rats exhibited similar dilations in response to cholera toxin (10(-9) g/ml) and dialated in response to the nitric oxide (NO) donor DEA-NONOate (10(-5) mol/l).

Conclusions: (i) Restoration of normal regulation of the renin-angiotensin system restores dilations to ACh and hypoxia that are impaired in SS rats, (ii) prostacyclin signaling is impaired in SS and RGRR rats but intact in Dahl R rats, indicating that alleles other than the renin gene affect vascular relaxation in response to this agonist; and (iii) vascular smooth muscle sensitivity to NO is preserved in SS and RGRR and is not responsible for impaired arterial relaxation in response to ACh in SS rats.

Figure 1

(A) Responses to 10⁻⁶ mol/L acetylcholine (ACh) in MCA from SS, RGRR, and Dahl R rats. Asterisk denotes a significant difference in the response in MCA from SS rats vs. RGRR and Dahl R rats. (B) Effect of the cyclooxygenase (COX) inhibitor indomethacin (Indo) (1O⁻⁶ mol/L), the NOS inhibitor L-NMMA (1O⁻⁴ mol/L) and combined COX and NOS inhibition with Indo +L-NMMA on response to ACh in MCA from RGRR rats (solid bars) and Dahl R rats (open bars) fed low salt diet. Asterisk denotes a significant difference from response in the absence of any inhibitor (P<0.05). (C) Responses to DEA-NONOate (10 μM) in MCA from SS, RGRR, and Dahl R rats fed low salt diet. Asterisk denotes a significant difference from the response in MCA from SS and RGRR rats. All data are presented as mean change (Δ) in diameter (μm) ± SEM from resting control diameter for 6–10 rats/group.

Figure 1

(A) Responses to 10⁻⁶ mol/L acetylcholine (ACh) in MCA from SS, RGRR, and Dahl R rats. Asterisk denotes a significant difference in the response in MCA from SS rats vs. RGRR and Dahl R rats. (B) Effect of the cyclooxygenase (COX) inhibitor indomethacin (Indo) (1O⁻⁶ mol/L), the NOS inhibitor L-NMMA (1O⁻⁴ mol/L) and combined COX and NOS inhibition with Indo +L-NMMA on response to ACh in MCA from RGRR rats (solid bars) and Dahl R rats (open bars) fed low salt diet. Asterisk denotes a significant difference from response in the absence of any inhibitor (P<0.05). (C) Responses to DEA-NONOate (10 μM) in MCA from SS, RGRR, and Dahl R rats fed low salt diet. Asterisk denotes a significant difference from the response in MCA from SS and RGRR rats. All data are presented as mean change (Δ) in diameter (μm) ± SEM from resting control diameter for 6–10 rats/group.

Figure 1

(A) Responses to 10⁻⁶ mol/L acetylcholine (ACh) in MCA from SS, RGRR, and Dahl R rats. Asterisk denotes a significant difference in the response in MCA from SS rats vs. RGRR and Dahl R rats. (B) Effect of the cyclooxygenase (COX) inhibitor indomethacin (Indo) (1O⁻⁶ mol/L), the NOS inhibitor L-NMMA (1O⁻⁴ mol/L) and combined COX and NOS inhibition with Indo +L-NMMA on response to ACh in MCA from RGRR rats (solid bars) and Dahl R rats (open bars) fed low salt diet. Asterisk denotes a significant difference from response in the absence of any inhibitor (P<0.05). (C) Responses to DEA-NONOate (10 μM) in MCA from SS, RGRR, and Dahl R rats fed low salt diet. Asterisk denotes a significant difference from the response in MCA from SS and RGRR rats. All data are presented as mean change (Δ) in diameter (μm) ± SEM from resting control diameter for 6–10 rats/group.

Figure 2

Response of MCA to (A) reduced PO₂ ; *-P<0.05 vs. SS; #-P<0.05 vs. RGRR; (B) iloprost, *-P<0.05 vs. SS; and (C) cholera toxin in MCA from SS and RGRR rats fed low salt diet. Data are presented as mean change (Δ) in diameter (μm) ± SEM for 6–9 rats/group.

Figure 2

Response of MCA to (A) reduced PO₂ ; *-P<0.05 vs. SS; #-P<0.05 vs. RGRR; (B) iloprost, *-P<0.05 vs. SS; and (C) cholera toxin in MCA from SS and RGRR rats fed low salt diet. Data are presented as mean change (Δ) in diameter (μm) ± SEM for 6–9 rats/group.

Figure 2

Response of MCA to (A) reduced PO₂ ; *-P<0.05 vs. SS; #-P<0.05 vs. RGRR; (B) iloprost, *-P<0.05 vs. SS; and (C) cholera toxin in MCA from SS and RGRR rats fed low salt diet. Data are presented as mean change (Δ) in diameter (μm) ± SEM for 6–9 rats/group.

Figure 3

Response to reduced PO₂ in MCA from RGRR (solid bars) and Dahl R rats (open bars) on low salt diet in the presence or absence of the COX inhibitor indomethacin (Indo), the NOS inhibitor L-NMMA, or both inhibitors. Asterisk denotes a significant difference from control values measured in the absence of any inhibitor. Data are presented as mean change (Δ) in diameter (μm) ± SEM for 5–10 rats/group.

Figure 4

Effect of reduced PO₂ on prostacyclin (assessed as 6-keto PGF_1α), thromboxane A₂ (assessed as TXB₂) and PGE₂ production in cerebral arteries of RGRR rats. Data are expressed as mean % of the control (21% O₂) value ± SEM following reduction of O₂ concentration from 21% O₂ to 5% O₂ (3–6 measurements per group).