Chapter

The Life Cycle of the Corpus Luteum

pp 227-248

Date:

Corpus Luteum Regression and Early Pregnancy Maintenance in Pigs

  • Adam J. ZiecikAffiliated withDepartment of Hormonal Action Mechanisms/Molecular Biology Laboratory, Institute of Animal Reproduction and Food Research of Polish Academy of Sciences Email author 
  • , Emilia PrzygrodzkaAffiliated withDepartment of Hormonal Action Mechanisms/Molecular Biology Laboratory, Institute of Animal Reproduction and Food Research of Polish Academy of Sciences
  • , Monika M. KaczmarekAffiliated withDepartment of Hormonal Action Mechanisms/Molecular Biology Laboratory, Institute of Animal Reproduction and Food Research of Polish Academy of Sciences

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Abstract

Development of the porcine corpus luteum (CL) requires the initial preovulatory LH surge and support of many biologically active agents including tonic secretion of LH, ovarian steroids, growth factors, and prostaglandins. A lack of embryo presence in the uterus leads to CL regression, characterized by disrupted progesterone production (functional luteolysis) and further degeneration of luteal and endothelial cells (structural luteolysis) triggered by prostaglandin F2α (PGF2α). The porcine CL expresses abundant levels of PGF2α receptors in the early and mid-luteal phase of the estrous cycle but remains insensitive to a single treatment of exogenous PGF2α until about day 12 of the estrous cycle. The nature of porcine CL resistance to PGF2α remains unknown, and the mechanism of luteolytic sensitivity acquisition involves infiltration of immune cells into the CL. Former theories of luteolysis inhibition and maternal recognition of pregnancy in the pig have proposed that possible mechanism for prevention of luteal regression is connected with a limited PGF2α supply to CL, evoked by its sequestering in the uterus. Later studies besides the increased synthesis of prostaglandin E2 (PGE2) by the conceptus and endometrium revealed simultaneously decreased expression of PGF2α synthesis enzymes. This chapter summarizes available knowledge on the porcine CL maintenance and regression and present our recent studies leading to a novel ‘two signal-switch’ hypothesis, based on the interplay of both PGF2α and PGE2 postreceptor signaling pathways. Several practical aspects of how to prolong and enhance CL function and improve pregnancy maintenance are also discussed.

Keywords

Corpus luteum Luteolytic sensitivity Luteolysis inhibition Pregnancy establishment Embryo signals Prostaglandins Two-switches hypothesis Pig