Coordinate regulation of prostaglandin metabolism for induction of parturition in mice.

Prostaglandins are essential for the initiation of parturition in mice. The peak in uterine prostaglandin F(2)(alpha) levels occurs at d 19.0 of gestation, just before the onset of labor. Our studies set out to determine the important regulatory step(s) involved in this increase of prostaglandin F(2)(alpha). We show that cytosolic phospholipase A(2) mRNA, protein, and activity do not significantly vary during mouse gestation. Rather, our studies demonstrate that cyclooxygenase-1 mRNA is abruptly induced at d 15.5 of gestation, but cyclooxygenase-1 protein levels only gradually increase throughout gestation. In contrast, cyclooxygenase-2 protein remains constant during gestation. We find that prostaglandin F synthase protein increases significantly during gestation reaching peak levels between d 15.5 and d 17.5 of gestation. We also find that the level of prostaglandin dehydrogenase, responsible for degradation of prostaglandins, decreases during late gestation. Taken together these results suggest that the regulation of prostaglandin F(2)(alpha) is a complex process involving the coordinate induction of synthetic enzymes along with a decrease in degradative enzymes involved in prostaglandin metabolism.