17β-Estradiol Induces Gastrointestinal Motility Disorder by Decreasing CPI-17 Phosphorylation Via Changes in Rho-Family G-Protein Rnd Expression in Small Intestine

In the present study, we investigated the long-term effects of 17 beta-estradiol on the motility of small intestine in in vitro organ culture and in vivo treatment studies. When rat ileal circular smooth muscle tissues were cultured with 17 beta-estradiol (0.1 and 1 mu M) for 5 days, carbachol-induced contraction was inhibited. In ileal tissue isolated from ovariectomized rat treated with 17 beta-estradiol (200 mu g/kg/day s.c. for 3 days), carbachol-induced contraction was also impaired. Both in vitro and in vivo, 17 beta-estradiol treatment upregulated heat shock protein 27 (HSP27) expression, indicating the activation of estrogen receptor in the intestinal smooth muscle. 17 beta-estradiol did not change protein expression levels of RhoA and RhoA-associated coiled coil-forming serine/threonine kinases (ROCKS); however, it upregulated Rnd2 and Rnd3, Rho-family G-proteins that counteract the functions of RhoA, both in vitro and in vivo. In organ Culture., treatment of ileal tissue with 17 beta-estradiol greatly suppressed the carbachol-induced increase in phosphorylation at Thr38 in CPI-17 without altering total CPI-17 protein expression. These results suggest that 17 beta-estradiol upregulates Rnd expression to inhibit the RhoA-mediated Ca2+ sensitization of contractile mechanisms, which arc mediated by CPI-17 phosphorylation in ileal smooth muscle. This mechanism may contribute to the intestinal motility disorder occurring in gender-dependent bowel diseases.