Dissociation of Alterations in Levels of Myosin Light Chain Kinase and Cyclic AMP-dependent Protein Kinase in Rabbit Myometrium during Pregnancy

The alteration in levels of myosin light chain kinase and cyclic AMP-dependent protein kinase was studied in rabbit myometrium during pregnancy. The specific activity of myosin light chain kinase was 160.9±2.7, 128.1 ±3.5, and 126.5±4.4% at the 10th, 20th and 28th days after pregnancy, respectively, in comparison with the value seen in samples from non-pregnant rabbits. On the other hand, the specific activity of cyclic AMP-dependent protein kinase gradually decreased to 75.9 ±1.7, 58.7 ±3.5 and 36.9 ±1.9% of that of the control at each time with the increase in the time of gestation. The protein kinase inhibitor was not involved in the decrease in cyclic AMP-dependent protein kinase. These results suggest that the dissociation of the dynamic states of the two enzymes may make it possible for the myometrium to efficiently respond for contraction in the last stage of pregnancy.