## Results
### Malondialdehydedehyde Content  
As shown in Table 4, the rats in the control group had the highest MDA contents, and the rats in the normal group had the lowest MDA contents. OPO-H-treated rats had lower MDA contents than OPO-L-treated rats, limonene-treated rats and rats in the control group, but the OPO-H-treated rats had higher MDA contents than captopril-treated rats and rats in the normal group.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Group** & **Serum (\(\mu\)mol/L)** & **Heart (nmol/gprof)** & **Liver (nmol/gprof)** & **Kidney (nmol/gprof)** \\ \hline Normal & 2.23 \(\pm\) 0.49 \({}^{\mathrm{d}}\) & 2.12 \(\pm\) 0.21 \({}^{\mathrm{d}}\) & 0.50 \(\pm\) 0.06 \({}^{\mathrm{d}}\) & 1.35 \(\pm\) 0.15 \({}^{\mathrm{c}}\) \\ Control & 5.89 \(\pm\) 0.31 \({}^{\mathrm{a}}\) & 4.36 \(\pm\) 0.23 \({}^{\mathrm{a}}\) & 1.13 \(\pm\) 0.08 \({}^{\mathrm{a}}\) & 2.66 \(\pm\) 0.17 \({}^{\mathrm{a}}\) \\ Limonene & 5.69 \(\pm\) 0.27 \({}^{\mathrm{a}}\) & 4.33 \(\pm\) 0.12 \({}^{\mathrm{a}}\) & 1.14 \(\pm\) 0.05 \({}^{\mathrm{a}}\) & 2.40 \(\pm\) 0.18 \({}^{\mathrm{a}}\) \\ OPO-L & 4.09 \(\pm\) 0.25 \({}^{\mathrm{b}}\) & 3.75 \(\pm\) 0.14 \({}^{\mathrm{b}}\) & 0.92 \(\pm\) 0.08 \({}^{\mathrm{b}}\) & 1.81 \(\pm\) 0.20 \({}^{\mathrm{b}}\) \\ OPO-H & 3.68 \(\pm\) 0.34 \({}^{\mathrm{c}}\) & 2.98 \(\pm\) 0.27 \({}^{\mathrm{c}}\) & 0.72 \(\pm\) 0.07 \({}^{\mathrm{c}}\) & 1.62 \(\pm\) 0.13 \({}^{\mathrm{bc}}\) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Malondialdehydedehyde (MDA) content in serum, heart, liver and kidney of \(L\)-NNA-induced hypertensive rats.  
Figure 5: Effects of orange peel oil on the SP and DP of \(L\)-NNA-induced hypertensive rats. Notes: SP, systolic pressure; DP, diastolic pressure; OPO-L, orange peel oil low dose, 5 mL/kg bodyweight (bw); OPO-H, orange peel oil high dose, 10 mL/kg bw; captopril, 15.6 mg/kg bw; and limonene, 10 mL/kg bw.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Group** & **Serum (\(\mu\)mol/L)** & **Heart (\(\mu\)mol/gprof)** & **Liver (\(\mu\)mol/gprof)** & **Kidney (\(\mu\)mol/gprof)** \\ \hline Normal & 105.31 \(\pm\) 4.92 \({}^{\mathrm{a}}\) & 15.29 \(\pm\) 1.35 \({}^{\mathrm{a}}\) & 17.11 \(\pm\) 0.46 \({}^{\mathrm{a}}\) & 13.51 \(\pm\) 0.57 \({}^{\mathrm{a}}\) \\ Control & 58.91 \(\pm\) 3.12 \({}^{\mathrm{e}}\) & 7.35 \(\pm\) 0.97 \({}^{\mathrm{e}}\) & 5.83 \(\pm\) 0.34 \({}^{\mathrm{e}}\) & 6.65 \(\pm\) 0.72 \({}^{\mathrm{c}}\) \\ Limonene & 59.03 \(\pm\) 2.70 \({}^{\mathrm{e}}\) & 7.95 \(\pm\) 0.40 \({}^{\mathrm{e}}\) & 5.97 \(\pm\) 1.00 \({}^{\mathrm{e}}\) & 6.44 \(\pm\) 1.85 \({}^{\mathrm{c}}\) \\ OPO-L & 70.99 \(\pm\) 2.54 \({}^{\mathrm{d}}\) & 9.48 \(\pm\) 1.13 \({}^{\mathrm{d}}\) & 9.29 \(\pm\) 0.82 \({}^{\mathrm{d}}\) & 8.16 \(\pm\) 0.28 \({}^{\mathrm{b}}\) \\ OPO-H & 86.35 \(\pm\) 3.48 \({}^{\mathrm{c}}\) & 12.11 \(\pm\) 1.76 \({}^{\mathrm{c}}\) & 11.75 \(\pm\) 0.76 \({}^{\mathrm{c}}\) & 12.03 \(\pm\) 1.34 \({}^{\mathrm{a}}\) \\ Captopril & 97.37 \(\pm\) 3.06 \({}^{\mathrm{b}}\) & 13.54 \(\pm\) 2.02 \({}^{\mathrm{b}}\) & 14.63 \(\pm\) 2.38 \({}^{\mathrm{b}}\) & 13.21 \(\pm\) 2.29 \({}^{\mathrm{a}}\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Nitric oxide (NO) contents in serum, heart, liver and kidney of \(L\)-NNA-induced hypertensive rats.