Comparison of the effects of estrogen alone (E2) and estrogen plus progesterone (E2 + P4) on the expression of contraction-associated proteins, as determined by quantitative reverse transcriptase–polymerase chain reaction (qPCR). CNN1 indicates calponin 1; MYL6B, myosin light chain 6B; MYLIP, myosin regulatory light chain interacting protein; MYLK, myosin light chain kinase; TPM1, tropomyosin 1α; SMTN, smoothelin. Each value is the mean ± standard error (SE) of triplicate determinations. With the exception of MYLK, E2 + P4 treatment caused a significant (P ≤ 0.05) reduction in expression of the genes indicated.