Decidual luteotropin secretion and action: its role in pregnancy maintenance in the rat

Studies of rat decidual luteotropin production and action have revealed that decidual mRNA directs the synthesis of a 28,000 MW protein in a cell-free system which binds to prolactin receptors in luteal cells and appears to represent a prohormone for decidual luteotropin. Hybridization studies indicate that although rat decidual and prolactin-like placental hormones bind to prolactin receptors, they possess little homology to other members of the prolactin family. In addition, results of this investigation have revealed a possible physiological relationship between the mesometrial and the antimesometrial cells of the decidual tissue. The large antimesometrial cells produce decidual luteotropin in which secretion and/or synthesis is inhibited by the neighboring mesometrial cells. Since mesometrial cells possess binding sites for decidual luteotropin, it is possible that decidual luteotropin acts on the mesometrial cell to affect the formation of its own inhibitor. Mesometrial cells are rich in glycogen, whose synthesis is stimulated by prolactin-like hormones in other tissues. Therefore, decidual luteotropin may also act on these cells to enhance glycogen formation. In summary, decidual luteotropin appears to have at least two sites of action--the luteal cell, where it can substitute for prolactin in maintaining progesterone production, and the mesometrial cell, where its role remains to be investigated.