Abstract: Objective To investigate the inhibitory effect of low- intensity pulsed ultrasound (LIPUS) on apoptosis of splenic lymphocytes in rats with sepsis and explore its possible mechanism. Methods Seventy-eight female SD rats were randomly divided into LIPUS group, cecal ligation and puncture (CLP) group and sham-operated group (Sham) (n=26), and in the former two groups, rat model of sepsis were established by CLP. Immediately after the operation, the rats in LIPUS group received pulsed ultrasound therapy with an ultrasound intensity of 200 mW/cm2, irradiation time of 20 min, and frequency of 0.37 MHz. The survival of the rats in each group was observed within 72 h after CLP. The changes in splenic lymphocyte counts were observed using HE staining, and apoptosis of the splenic lymphocytes was detected using TUNEL assay and flow cytometry. The expression levels of Bcl-2, Bcl2-associated X protein (Bax) and caspase-3 were detected by immunohistochemistry, Western blotting and RT-qPCR. Results All the rats in the sham-operated group survived for over 72 h. The survival rates of the rats was significantly higher in LIPUS group than in CLP group (P<0.05). Compared with those in CLP group, the apoptosis rate of the splenic lymphocytes in LIPUS group was significantly decreased (P<0.05), the protein and mRNA expression levels of Bcl-2 were increased (P<0.05), and the protein and mRNA expression levels of Bax and caspase-3 were decreased (P<0.05). Conclusions LIPUS inhibits apoptosis of splenic lymphocytes in septic SD rats possibly by regulating the key molecules in the mitochondrial pathway, thereby improving the survival rate and prolonging the survival time of the rats.

Key words: low-intensity pulsed ultrasound; sepsis; apoptosis; mitochondrial pathway