Comparison of angiotensin II-induced blood pressure and structural changes in Fischer 344 and Wistar Kyoto rats.

1. The purpose of the present study was to evaluate the blood pressure (BP) response, the BP and heart rate (HR) components of the startle reaction and the structure of the carotid artery and the aorta during chronic infusion of angiotensin (Ang) II in Fischer 344 (F344) compared with Wistar Kyoto (WKY) rats, two in-bred normotensive contrasted strains. 2. Osmotic mini-pumps filled with saline vehicle or AngII (120 ng/kg per min) were implanted subcutaneously in 8-week-old normotensive rats and infused for 4 weeks in F344 rats (saline, n = 10; AngII, n = 10) and WKY rats (saline, n = 10; AngII, n = 9). Basal BP, HR and the responses to an acoustic startle stimulus (duration 0.7 s, 115 dB) were recorded in conscious rats. The structure of the carotid artery and aorta was determined in 4% formaldehyde-fixed arteries. 3. Compared with WKY rats, vehicle-treated F344 rats had lower bodyweight (BW; 266 +/- 7 vs 299 +/- 9 g; P < 0.05) and heart weight (0.80 +/- 0.02 vs 0.98 +/- 0.04 g; P < 0.05) and higher aortic systolic BP (SBP; 131 +/- 1 vs 123 +/- 5 mmHg; P < 0.001) and diastolic BP (98 +/- 3 vs 89 +/- 2 mmHg; P < 0.001). In F344 rats, compared with the WKY rats, the wall thickness/BW ratio was increased in the carotid artery (156 +/- 9 vs 131 +/- 6 nm/g; P < 0.05) and abdominal aorta (264 +/- 13 vs 217 +/- 12 nm/g; P < 0.05) and decreased in the thoracic aorta (246 +/- 13 vs 275 +/- 8 nm/g; P < 0.05). There was no difference in elastin and collagen density. Angiotensin II differentially enhanced BP in both strains: (SBP: 163 +/- 5 and 132 +/- 4 mmHg in F344 and WKY rats, respectively; P(strain x treatment) < 0.05). Circumferential wall stress was increased in the aorta of F344 rats compared with WKY rats (1176 +/- 39 vs 956 +/- 12 kPa (P < 0.001) and 1107 +/- 42 vs 813 +/- 12 kPa (P < 0.001) in thoracic and abdominal aortas, respectively). The startle response was amplified in F344 rats, with enhanced increases in SBP and pulse pressure (PP) and bradycardia compared with responses of WKY rats (+44 +/- 9 mmHg, +10 +/- 2 mmHg and -40 +/- 17 b.p.m., respectively, in F344 rats vs+28 +/- 4 mmHg, + 4 +/- 2 mmHg and -19 +/- 10 b.p.m. in WKY rats, respectively; P(strain) < 0.05 for BP and PP). The startle response was not affected by AngII. 4. These results indicate a higher BP producing an increase in wall thickness in F344 rats compared with WKY rats. We propose that an increase in sympathetic nervous activity causes these haemodynamic differences, as suggested by the excessive increase in BP during an acoustic startle stimulus. Angiotensin II increased BP in F344 rats, but did not exaggerate the increase in BP during the startle reaction.