FIG. 6.

Metformin (Met) alters GH-dependent pathway and liver metabolites through SHP induction in vivo. A: Male and female wild-type (WT) and SHP-null mice were orally injected with metformin (200 mg/kg body weight) for 6 h and then intraperitoneally treated with GH (2 μg/g body weight) for 1 h in the feeding condition. Tissue extracts were isolated from liver tissue harvested from the mice of the indicated groups and assessed by Western blot analysis with appropriate antibodies. Protein levels were normalized to total form antibodies and/or β-actin levels. All mice were separated into experimental groups (n = 4–6 mice/group). B: WT and SHP-null mice were orally administered with metformin (200 mg/kg body weight) for 6 h and then intraperitoneally treated with GH (2 μg/g body weight) for 3 h in the fed condition. Tissue extracts were isolated from liver tissue harvested from the mice of the indicated groups and assessed by Western blot analysis with appropriate antibodies. Protein levels were normalized to total form and/or β-actin levels. All mice were separated into experimental groups (n = 4–6 mice/group). C: WT and SHP-null mice were measured at the observed time periods after metformin and GH treatment. Metabolites were analyzed with the liquid chromatography-mass spectrometry/mass spectrometry method as described in research design and methods. *P < 0.05, **P < 0.005, and #P < 0.005 compared with untreated control wild-type mice, GH-treated wild-type mice, and GH- and Met-treated wild-type mice. D: Growth hormone upregulates PDK4 gene expression by STAT5 transactivation, whereas metformin, a known activator of SHP via AMPK pathway, represses the GH-STAT5 pathway via downregulation of DNA-binding activity of STAT5 on the PDK4 gene promoter.