Janet Barrett

Evidence for homology between ovine and human placental lactogens

The biological and immunological properties of highly purified ovine placental lactogen (oPL) and human placental lactogen (hPL) have been compared. Like hPL and ovine prolactin (oPR). oPL stimulates lactation in vivo and in vitro and binds to prolactin receptors from mammary tissue. Like hPL and ovine growth hormone (oGH), oPL binds to growth hormone receptors from liver. OPL of equivalent activity to hPL in the prolactin receptor assay is approximately 20 times more active than hPL (but 5 times less active than oGH) in the growth hormone receptor assay. Immunologically, oPL cross-reacts with oGH but not with hPL. The striking homologies between oPL, and hPL indicate that sheep is an excellent animal model in which to study placental lactogen physiology.

Development of the sheep as an animal model to study placental lactogen physiology

Ovine placental lactogen, purified from term sheep cotyledons, has been found to have chemical and biologic properties similar to those of human placental lactogen, ovine growth hormone, and ovine prolactin. OPL stimulates lactation in vivo and in vitro and binds to prolactin and growth hormone membrane receptors. Its binding to growth hormone receptors is approximately 20 times greater than that of hPL, suggesting that its somatotrophic potency is greater than that of hPL. Preliminary in vivo studies in the sheep indicate that oPL affects maternal carbohydrate, lipid, and protein metabolism and that its effects are, in part, similar to those of hPL and growth hormone.

Synthesis of Prolactin by Human Decidua in Vitro

To determine whether human decidua and/or chorion synthesizes and secretes prolactin, explants of decidua obtained at Caesarian section and explants of chorion from the membranes separating dizygotic twins were cultured for periods of up to 6 days. The decidual explants released 366 +/- 37 ng prolactin/100 mg tissue (mean +/- S.D.) during each day in culture and incorporated 3H-labelled amino acids into immunoprecipitable prolactin. In the radioimmunoassay for prolactin, serial dilutions of incubation medium displaced 125I-labelled prolactin parallel to the displacement by pituitary prolactin and the prolactin in the medium eluted from Sephadex G-150 in a position indentical to that of pituitary prolactin. Chorionic explants released prolactin into the incubation medium during day 1 of culture only and did not incorporate 3H-labelled amino acids into prolactin. These results demonstrate that prolactin is synthesized by the decidua and not by the chorion and suggest that the decidua is the source of prolactin in amniotic fluid.

Prolactin Synthesis by Human Chorion-Decidual Tissue: A Possible Source of Prolactin in the Amniotic Fluid

Explants of human chorion-decidual tissue obtained at delivery from normal, full-term pregnancies synthesize and secrete prolactin. This hormone is indistinguishable from pituitary prolactin by chromatographic, electrophoretic, immunologic, and receptor assay techniques. These results suggest that chorion-decidua may be the source of the large quantities of prolactin in amniotic fluid.