AB - The placenta plays an essential role in fetal growth and the maintenance of pregnancy. Successful development and maturation of the embryo is totally dependent on placental function. The main endocrine participation of the placenta is attributed to placental lactogens (PLs). Progesterone is essential for pregnancy in all mammals and is secreted by the ovary and placenta, depending on the animal species. In the rat, the main source of progesterone throughout pregnancy is the ovary, and 20a- hydroxysteroid dehydrogenase (20a-HSD) is a key enzyme for ovarian progesterone secretion. The primary action of prolactin (PRL) in the maintenance of ovarian progesterone secretion is suppression of the activity of ovarian 20a-HSD. In this review, the sequence homologies between cDNAs for PLs and PRL and the intimate functional relationship between the ovary and placenta are discussed. We postulate the possibility of co-evolution of PLs and ovarian 20a-HSD.
20alpha-HSD has been initially described as a progesterone metabolizing enzyme of the ovary. On a functional level, ovarian 20alpha-HSD is actively involved in the control of progesterone homeostasis in pregnancy of rats and mice. While 20alpha-HSD expression and activity is downregulated in the corpus luteum of pregnancy, 24 hrs prior to parturition ovarian 20alpha-HSD activity is acutely stimulated. Accordingly, in mice with targeted deletion of the 20alpha-HSD gene, progesterone blood concentration remain high throughout pregnancy which results in a delay of 2–4 days in parturition. Indicating that expression of 20alpha-HSD activity is mandatory for the induction of parturition through reduction of progesterone blood concentration. In mice, 20alpha-HSD is also expressed in the adrenals, kidneys, brain, thymus, T cells and bone marrow. Its induction in hematopoietic cells was used as an assay for the identification of T cell derived factor interleukin-3. In addition, the enzyme reduces and inactivates 17-deoxycorticosterone, the precursor of aldosterone and corticosterone.
E. coli transfected with pGEX-4T-3-20?HSD was grown in 2 × YTG medium. 1PTG was added to induce the expression of fusion protein. Twenty micrograms of protein were used as a starting material. GST and rec GST-20?HSD were purified with glutathione beads. To release 20?HSD, the bound GST-20?HSD proteins were digested with thrombin at room temperature for 6 h. The purified rec GST-20?HSD and purified rec 20?HSD proteins ( ?g each) were subjected to SDS-PAGE, transferred to cellulose membranes, and immunodetected with the anti-20?HSD antibody, followed by alkaline phosphatase-conjugated goat anti-rabbit IgG. Left panel, Gel stained for proteins with Coomassie blue. Right panel, Immunoblots. Lane 1, Purified GST; lane 2, purified GST-20?HSD; lane 3, thrombin cleavage for fusion protein bound to glutathione-Sepharose 4B; lane 4, proteins remained absorbed to column after thrombin digestion.