Published online Oct 7, 2014. doi: 10.3748/wjg.v20.i37.13521
Revised: March 10, 2014
Accepted: May 28, 2014
Published online: October 7, 2014
AIM: To investigate the role of epidermal growth factor (EGF) in visceral hypersensitivity and its effect on the serotonin transporter (SERT).
METHODS: A rat model for visceral hypersensitivity was established by intra-colonic infusion of 0.5% acetic acid in 10-d-old Sprague-Dawley rats. The visceral sensitivity was assessed by observing the abdominal withdrawal reflex and recording electromyographic activity of the external oblique muscle in response to colorectal distension. An enzyme-linked immunosorbent assay was used to measure the EGF levels in plasma and colonic tissues. SERT mRNA expression was detected by real-time PCR while protein level was determined by Western blot. The correlation between EGF and SERT levels in colon tissues was analyzed by Pearson’s correlation analysis. SERT function was examined by tritiated serotonin (5-HT) uptake experiments. Rat intestinal epithelial cells (IEC-6) were used to examine the EGF regulatory effect on SERT expression and function via the EGF receptor (EGFR).
RESULTS: EGF levels were significantly lower in the rats with visceral hypersensitivity as measured in plasma (2.639 ± 0.107 ng/mL vs 4.066 ± 0.573 ng/mL, P < 0.01) and in colonic tissue (3.244 ± 0.135 ng/100 mg vs 3.582 ± 0.197 ng/100 mg colon tissue, P < 0.01) compared with controls. Moreover, the EGF levels were positively correlated with SERT levels (r = 0.820, P < 0.01). EGF displayed dose- and time-dependent increased SERT gene expressions in IEC-6 cells. An EGFR kinase inhibitor inhibited the effect of EGF on SERT gene upregulation. SERT activity was enhanced following treatment with EGF (592.908 ± 31.515 fmol/min per milligram vs 316.789 ± 85.652 fmol/min per milligram protein, P < 0.05) and blocked by the EGFR kinase inhibitor in IEC-6 cells (590.274 ± 25.954 fmol/min per milligram vs 367.834 ± 120.307 fmol/min per milligram protein, P < 0.05).
CONCLUSION: A decrease in EGF levels may contribute to the formation of visceral hypersensitivity through downregulation of SERT-mediated 5-HT uptake into enterocytes.
Core tip: Results of this study show that visceral hypersensitivity results in a decrease in the plasma and colon tissue levels of epidermal growth factor (EGF). Moreover, the EGF levels were positively correlated with serotonin transporter (SERT) levels. SERT gene expression and protein activity were upregulated in a dose- and time-dependent manner by EGF, and an inhibitor of the EGF receptor kinase blocked SERT gene expression and activity in an intestinal epithelial cell line. The data suggest that decreased EGF levels may contribute to the formation of visceral hypersensitivity through downregulation of SERT activity.