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RhoA/Rho-Kinase Cascade Is Involved in Oxytocin-Induced Rat Uterine Contraction

Osaka University Graduate School of Medicine, Department of Obstetrics and Gynecology, Suita, Osaka 565-0871, Japan

Address all correspondence and requests for reprints to: Masahiro Tahara, Osaka University Graduate School of Medicine, Department of Obstetrics and Gynecology, 2-2 Yamadaoka, Suita, Osaka, 565-0871, Japan. E-mail: . taharam{at}gyne.med.osaka-u.ac.jp

The RhoA/Rho-kinase cascade is involved in various cellular functions, including migration, proliferation, and smooth muscle contraction. We examined the potential role of this pathway in oxytocin-induced uterine contraction. The specific Rho-kinase inhibitor Y-27632 inhibited oxytocin-induced rat uterine contraction on d 21 of pregnancy in a concentration-dependent manner, whereas the extent of this inhibition was reduced in the nonpregnant uterus. Y-27632 had no effect on oxytocin-induced intracellular Ca²⁺ mobilization in myometrial cells. Immunoblot analysis showed that oxytocin increased the level of myosin light chain phosphorylation, and this increase was attenuated by Y-27632. Oxytocin increased the phosphorylation of myosin-binding subunit of myosin phosphatase, one of the major substrates of Rho-kinase, and this increase was reduced by Y-27632. The expression of Rho-kinase protein was shown to increase in the uterus during pregnancy compared with the nonpregnant uterus, whereas the expression of RhoA protein remained at the same level during pregnancy. RT-PCR and Northern blot analysis showed that the expression of Rho-kinase was up-regulated at the transcriptional level during pregnancy. These results suggest that the RhoA/Rho-kinase pathway may have an important role in oxytocin-induced uterine contraction, and that up-regulation of Rho-kinase is involved in the mechanism underlying the increased contractility of the pregnant myometrium.

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