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

Feb 28, 2002Endocrinology

RhoA/Rho-kinase pathway may help oxytocin cause uterine contractions in rats

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Abstract

The Rho-kinase inhibitor Y-27632 inhibited oxytocin-induced rat uterine contraction on day 21 of pregnancy in a concentration-dependent manner.

Y-27632's inhibition of uterine contraction was less effective in the nonpregnant uterus.
Y-27632 did not affect oxytocin-induced intracellular calcium mobilization in myometrial cells.
Oxytocin increased phosphorylation of myosin light chain, which was reduced by Y-27632.
Phosphorylation of the myosin-binding subunit of myosin phosphatase was also increased by oxytocin and attenuated by Y-27632.
Rho-kinase protein expression increased in the uterus during pregnancy, while RhoA protein levels remained unchanged.
Rho-kinase expression was up-regulated at the transcriptional level during pregnancy.

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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 Ca(2+) 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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RhoA/Rho-Kinase Cascade Is Involved in Oxytocin-Induced Rat Uterine Contraction

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