Identification and Preliminary Characterization of Luteotropic Activity in the Rabbit Placenta1

Abstract

The corpus luteum of the rabbit requires estradiol (E2) and the conceptus to maintain progesterone (P4) during the second half of pregnancy. The factor produced by the fetal placenta that is responsible for maintaining P4 production has not yet been identified. Therefore, the goal of these experiments was to determine whether the rabbit placenta contained luteotropic activity and to begin preliminary characterization of this factor. A bioassay system utilizing corpora lutea explants incubated with placental extracts and other treatments was developed and validated. Neither pooled placental extracts (200 micrograms) nor E2 alone affected P4 production (p > 0.05). However, the combination of placental extracts plus E2 significantly stimulated P4 production approximately 1.5-fold (p < 0.05). Skeletal muscle (200 micrograms) + E2 also had no effect on P4 production, indicating that the effect of placental extracts was tissue-specific. Carboxymethyl-cellulose ion-exchange chromatography of placental extracts yielded four separate fractions, which were examined individually at three doses for activity in the bioassay system. The first and most acidic fraction (Fraction 1) significantly stimulated P4 production at 10 and 100 micrograms when incubated in combination with E2 (p < 0.05). Both heat and trypsin treatment abolished the ability of placental Fraction 1 to stimulate P4 production in the presence of E2. Size fractionation of Fraction 1 using dialysis membranes with 3500, 6000-8000, and 12,000-14,000 molecular weight cutoff points had no effect on bioactivity of Fraction 1. These results indicate that the rabbit placenta contains a potential luteotropin with the characteristics of an acidic, heat-sensitive protein greater than 12,000-14,000 in molecular weight.

History of Maternal Recognition of Pregnancy

“…A putative 6-8 kDa placental luteotrophic factor also has been reported to enhance P4 production by cultured luteal cells alone or in conjunction with E2 (Gadsby 1989 ). Further, a 12-14 kDa rabbit placental luteotropin that is acidic and trypsin and heat sensitive also has been reported (Marcinkiewiz et al 1992 ;Marcinkiewicz and Bahr 1993 ). This factor stimulated the production of P4 by luteal explants in the presence of E2; however, 200 μg/ml of conceptus protein was necessary to achieve a modest increase in P4 production.…”

Aglepristone Use for Termination of Pregnancy in Rabbits

“…Bu özelliğinden dolayı tavşanlarda gebeliğin medikal olarak sonlandırılmasında başarılı bir şekilde kullanılmaktadır. Ayrıca istenmeyen gebeliklerde aglepriston kullanımı operatif ve postoperatif komplikasyonların olmaması ile avantaj sağlamaktadır [26]. Tavşanlarda blastositin uterusa implantasyonu çiftleşmeden sonraki ilk haftanın sonunda oluşmaktadır.…”

“…Çalışmalar sonucunda konseptusun gebeliğin 12. gününden önce uzaklaştırılması P4 konsantrasyonunda kademeli bir düşüş oluşturduğu tespit edilmiştir [26]. Tavşanlarda aglepriston uygulaması ile gebelik sonlandırılması üzerine yapılan bir çalışmada serum P4 konsantrasyonunun yavaş bir şekilde azaldığı ve gebeliğin 15. gününde bazal düzeye indiği rapor edilmiştir [28].…”

“…Korpus luteumun fonksiyonunun sürmesi için konseptusun gerekli olduğu bilinmektedir. Dolayısı ile konseptusun gebeliğin ikinci yarısında uzaklaştırılması serum progesteron konsantrasyonunda hızlı bir düşüş oluşturmaktadır [26]. Aglepriston ile orta dönem gebeliğin sonlandırılması üzerine yapılan bir çalışmada uygulama grubundaki tavşanların serum P4 konsantrasyonlarının gebeliğin 22. gününden sonra kontrol grubuna göre daha düşük seyrettiği görülmüştür [29].…”

Placental lactogen-like proteins in the rabbit placenta

“…These different components probably affect different populations of luteal cells (Hoyer et al 1986). With regard to the origin and nature of the conceptus luteotropin, it has been shown that it is synthesized by the placenta as an acidic polypeptide of larger than 14 kDa (Gadsby and Lancaster 1989;Weerasinghe and Gadsby 1990;Marcinkiewicz and Bahr 1993).…”