ABSTRACT
Steroid hormones have the potential to regulate at the transcriptional level the expression of a number of proteins involved in the control of uterine activity. Progesterone and estrogens are the major steroid hormones whose production is massively enhanced during pregnancy. The average myometrial concentrations of steroids were in the same range as the values found in plasma, but were also fourfold less elevated than those assayed in the placenta. Increased synthesis of prostaglandins by uterine tissues and fetal membranes play a major role in the initiation and maintenance of labor. Several experiments suggest that besides their effects on cell surface receptor number, steroid changes in late gestation could also modulate postreceptor mechanisms related to intracellular signaling. Oxytocinergic systems, comprising both the biologically active peptide and its specific receptors, may serve as a good system to compare direct transcriptional regulation with indirect effects of steroid hormones during parturition.
