Preventive and Therapeutic Effects of Sericin-Derived Oligopeptides (SDOs) from Yellow Silk Cocoons on Blood Pressure Lowering in L-NAME-Induced Hypertensive Rats

Our previous research has shown that SDOs derived from yellow silk cocoons have hypotensive effects on rats in chronic toxicity testing. This study investigated the potential preventative and therapeutic benefits of SDOs on hypertensive rats induced by L-NAME. The experiment involved nine rat groups: (1) normal control, (2) normal + 200 $\mathrm{m}\mathrm{g} {\mathrm{k}\mathrm{g}}^{-1}$ BW SDOs, (3) hypertensive (HT) control, (4) HT + 50 $\mathrm{m}\mathrm{g} {\mathrm{k}\mathrm{g}}^{-1}$ BW SDOs, (5) HT + 100 $\mathrm{m}\mathrm{g} {\mathrm{k}\mathrm{g}}^{-1}$ BW SDOs, (6) HT + 200 $\mathrm{m}\mathrm{g} {\mathrm{k}\mathrm{g}}^{-1}$ BW SDOs, (7) HT + enalapril (Ena), (8) HT + soy protein isolate (SPI), and (9) HT + bovine serum albumin (BSA). In the preventative approach, rats received 40 $\mathrm{m}\mathrm{g} {\mathrm{k}\mathrm{g}}^{-1}$ of L-NAME with the studied substances during the four-week investigation. SDOs given at doses of 100 and 200 $\mathrm{m}\mathrm{g} {\mathrm{k}\mathrm{g}}^{-1}$ BW demonstrated a significant decrease in systolic blood pressure (SBP) without affecting heart rate (HR). In therapeutic studies, 40 $\mathrm{m}\mathrm{g} {\mathrm{k}\mathrm{g}}^{-1}$ BW of L-NAME increased SBP in the experimental groups over the first four weeks, resulting in mean SBP values above 150 mmHg. Administering 100 and 200 $\mathrm{m}\mathrm{g} {\mathrm{k}\mathrm{g}}^{-1}$ BW SDOs and 100 $\mathrm{m}\mathrm{g} {\mathrm{k}\mathrm{g}}^{-1}$ BW SPI significantly reduced SBP. However, SDOs at 200 $\mathrm{m}\mathrm{g} {\mathrm{k}\mathrm{g}}^{-1}$ BW exhibited SBP closer to the enalapril group. In functional vascular tests, rats given SDOs at a dose of 200 $\mathrm{m}\mathrm{g} {\mathrm{k}\mathrm{g}}^{-1}$ BW had the highest relaxation and lowest contraction percentages, like the normal control groups. The research found that SDOs may inhibit and manage hypertension in both healthy and hypertensive rats by safeguarding endothelial cells.