Increased production of reactive oxygen species (ROS) may be involved in the pathophysiology of pressure-overload hypertrophy. We have previously shown that an ROS-generating phagocyte-type NADPH oxidase is expressed in the heart and is involved in the hypertrophic response to subpressor angiotensin II (Ang II) infusion. In this study we compared the response to chronic pressure overload or pressor Ang II infusion in male gp91phox^-/- mice and matched wild-type C57/Bl6J controls. Adult male mice (16-20 g) underwent (a) suprarenal aortic constriction or (b) 1.1 mg kg^-1 day^-1 Ang II or saline infusion via a subcutaneous osmotic minipump. All mice were anaesthetised using 2.5 % isofluorane. The abdominal aorta was constricted with an 8.0 nylon suture tied down onto a 29-gauge needle. Sham animals underwent an identical procedure with the exception of band placement. Perioperative mortality was < 10 % in both groups. Animals were studied a week later (n = 4-6 per group) and were humanely killed according to Home Office guidelines using sodium pentobarbitone (120 mg kg^-1 I.P.). Data are expressed as means ± S.E.M. and statistical analysis was made using Student’s unpaired t test or two-way ANOVA for repeated measures. In all cases P < 0.05 was taken to be significant.

Ang II infusion increased systolic blood pressure in both WT (162.1 ± 9.8 vs. 132.5 ± 2.2 mmHg; P < 0.05) and gp91phox^-/- mice (138.1 ± 6.0 vs. 123.2 ± 3.5 mmHg; P < 0.05).

Heart : body weight ratio was significantly increased by Ang II (~24 %) in WT (4.26 ± 0.1 vs. 3.44 ± 1.0 mg kg^-1; P < 0.05) but not in gp91phox^-/- mice (3.99 ± 0.06 vs. 3.72 ± 0.11 mg kg^-1; P = n.s.). In line with this, Ang II increased cardiac NADPH oxidase activity in WT (70.7 ± 18.6 %, P < 0.05) but not in gp91phox^-/- mice, -17 ± 13 %). In contrast, aortic banding induced similar increases (~25 %) in LV : body weight ratio in WT (3.91 ± 0.13 vs. 3.14 ± 0.11 mg kg^-1; P < 0.05) and gp91phox^-/- mice (4.29 ± 0.05 vs. 3.38 ± 0.11 mg kg^-1; P < 0.05). Surprisingly, NADPH oxidase activity was increased after banding in both WT (38 ± 11% P < 0.05) and gp91phox^-/- hearts (58 ± 10% P < 0.05), and was inhibited by diphenyleneiodonium but not reduced by L-NAME in either group. Aortic banding resulted in an increase in gp91phox mRNA expression by real time PCR in WT hearts (1.9 ± 0.2 vs. 1.3 ± 0.01 arbritary units; P < 0.05).WT and gp91phox^-/- hearts expressed nox 4 mRNA at a similar level, with no significant increases after aortic banding.

These results indicate that whereas a gp91phox-containing NADPH oxidase is essential for the development of Ang II-induced cardiac hypertrophy, this enzyme is not required for the development of pressure overload hypertrophy. The increase in ROS production following pressure overload appears to involve an alternative gp91phox isoform.

All procedures accord with current UK legislation.