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OBJECTIVE: To explore the influences of micro ribonucleic acid (miR)-34a on liver function and hepatocyte proliferation during hepatocyte regeneration in rats and its mechanism. MATERIALS AND METHODS: A total of 80 Sprague-Dawley rats were randomly divided into 4 groups: Sham-2 d group (2 days after hepatectomy), Sham-10 d group (10 days after hepatectomy), miR-34a siRNA-2d group (miR- 34a knockdown + 2 days after hepatectomy) and miR-34a siRNA-10 d group (miR-34a knockdown + 10 days after hepatectomy), with 20 rats in each group. Serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) were detected at 2 d and 10 d after the operation. The rat liver was harvested for calculating the liver/body weight ratio. In addition, the deoxyribonucleic acid (DNA) content in rat hepatocytes was detected via Feulgen staining. The pathological changes in rat liver were detected via hematoxylin- eosin (H&E) staining. Moreover, the hepatocyte apoptosis in each group was detected via terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. Expression levels of proliferating cell nuclear antigen (PCNA), Notch1 intracellular domain (NICD), and hypoxia-inducible factor-1α (HIF-1α) in liver tissues of each group were detected via immunohistochemistry and Western blotting. RESULTS: No significant differences in the liver/body weight ratio, serum levels of ALT, AST, LDH, pathological structure of the liver, hepatocyte apoptosis level, and PCNA expression in hepatocytes were found between miR-34a siRNA-2 d group and Sham-2 d group. However, the expression levels of NICD and HIF-1α in the liver significantly increased in miR-34a siRNA- 2 d group compared with those in Sham-2 d group (p<0.05). On the contrary, compared with those in Sham-10 d group, the liver function and hepatocyte regeneration level significantly increased in miR-34a siRNA-10 d group. Increased liver/body weight ratio, remarkable decline in serum levels of ALT, AST, and LDH, significant alleviation of pathological injury of liver tissues, decreased the apoptosis level and upregulated PCNA protein were observed in miR-34a siRNA- 10 d group than those of Sham-10 d group. The Notch/HIF-1α signaling pathway was also significantly activated. CONCLUSIONS: MiR-34a knockdown can significantly enhance the liver function and hepatocyte regeneration ability in rats at 10 d after hepatectomy through activating the Notch/HIF-1α signaling pathway. [ABSTRACT FROM AUTHOR]