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Maternal Recognition of Pregnancy

Maternal Recognition of Pregnancy. During early pregnancy, the blastocyst must signal its presence to the maternal system to stimulate CL maintenance for establishment of pregnancy. The term “Maternal Recognition of Pregnancy” (first coined by Short in 1969)

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Maternal Recognition of Pregnancy

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  1. Maternal Recognition of Pregnancy During early pregnancy, the blastocyst must signal its presence to the maternal system to stimulate CL maintenance for establishment of pregnancy. The term “Maternal Recognition of Pregnancy” (first coined by Short in 1969) is usually associated with prevention of CL regression when applied to domestic species. However, the definition is inappropriate for marsupials and other Eutherian species such as the dog and ferret. Maternal Recognition of Pregnancy can be defined simply as a functional relationship between the uterus, CL and embryo itself. In most eutherian mammals, maternal recognition of pregnancy is established when the length of the estrous cycle exceeds that of the normal cycle. The signal which originates from the pre-attached blastocyst acts either directly at the endometrial level (gilt, mare, cow, ewe) or indirectly at the ovarian level (human) to block the action of prostaglandin F2a (PGF2a).

  2. Function of the Corpus Luteum Ludwig Frankel pioneered the role of the corpus luteum in pregnancy maintenance when he demonstrated that removal of the CL (ovariectomy) from a pregnant rabbit terminated pregnancy. Gilt - Cow - Ewe - Mare - Woman - Ovariectomy at any stage of gestation will terminate pregnancy. However, Dziuk demonstrated that if CL were removed slowly, one CL could support pregnancy. Ovariectomy up to 210 days of gestation will terminate pregnancy. After 210 days no effect - adrenal and placenta are sources of progesterone. Ovariectomy up to 50 days of gestation will terminate pregnancy. CL normally regress approximately Day 150 of gestation No effect after Day 24.

  3. Pituitary Support of CL Function Gilt: There is necessity of secretion of a pituitary luteotrophin (LH) apparent in the hypophysectomized-hysterectomized gilt. However, it is not necessary until after Day 12 of the cycle. Prolactin can serve as a luteotrophin after Day 70 of gestation. Ewe: The presence of the pituitary gland is essential from maintenance of pregnancy in the ewe during the first 50 days of gestation. Hypophysectomy before Day 50 causes regression of the CL and abortion. After Day 50 there is no effect.

  4. WRONG Comparative Placentation, Ed Steven,1975, p 192

  5. It is clear that the first signal from the blastocyst is the release of hCG. The syncytiotrophoblast is the major source of hCG. Hearn, J. Reprod Fert 76:806

  6. hCG consists of two nonidentical glycosylated subunits (a & b). Production of the two subunits can vary throughout pregnancy. a = similar to a chain of FSH, LH etc b = biologically active chain Peaks during first trimester Human Placental Lactogen - 90 % homology with growth hormone Single nonglycosylated chain Peaks near term Luteal function is needed only for the first 6-7 weeks of gestation. After this period, the placenta produces enough progesterone to maintain pregnancy. Hormonal Control of Reproduction, Austin & Short, p 182

  7. Human Pregnancy Early Pregnancy Factor Pregnancy Specific B Glycoprotein - 29% CHO Function: Immunosuppression Placental Associated Protein - similar of a2 macrogolubin - Only present in plasma during pregnancy. Inhibitor of leukocyte elastase - breaks down basement membranes. Prevents maternal proteolytic attack. Low levels usually indicate pregnancy failure (2 wk prior) Placental Protein-5 - Antiplasmin and antitrypsin activity - may serve as a coagulation inhibitor Physiology of Reproduction, Ed. Knobil & Neill, p 1996

  8. Approximately 2 days before they can ovulate 30-32 days 18-22 days 4 day cycle 10-14 days 22 days Delayed implantation Marshalls Physiology of Reproduction, p460

  9. Rat In the rat, the corpus luteum is formed on the morning of estrus in response to the LH surge released the previous day. However, unlike most other mammals, the newly formed CL secretes progesterone for only 2 days after formation. Rodent corpora lutea can be maintained (psuedopregncncy) by coital stimulation for 10-12 days Hormonal Control of Reproduction, Austin & Short, p 182

  10. Mating in the rat induces two daily surges of prolactin, one at the end of the light period (diurnal) and the other at the end of the dark period (nocturnal). These surges are last seen on Day 9 (diurnal) and 10 (nocturnal) of pregnancy. On Day 9, placental lactogen is secreted by the placenta which peaks on Day 12. The prolactin surges do not require ovarian steroids. These surges will endure for up to 14 days. A luteotrophic hormone of placental origin terminates the surges of prolactin, while a shifting of the ratio of estradiol to progesterone at the end to the pseudopregnancy terminates the prolactin surges in nonpregnant animals.

  11. Soares et al. 1998, Biol Reprod 58: 273

  12. Soares et al. 1998, Biol Reprod 58: 273

  13. The decidual and placental tissue of the rat secretes a luteotropin Placental Lactogen to maintain luteal secretion of progesterone. Placental lactogen or the decidual luteotrophin may maintain estradiol synthesis by the corpus luteum which has an effect on progesterone synthesis through the steroidogenic pathway Placental Lactogen produced by giant cells - is related to Prolactin and Growth Hormone. mPL-I - Glycoprotein, detected Day 6 peak Day 10. mPL-II - Gycoprotein, detected Day 10 increases till term. Regulated by fetal genotype, growth hormone, nutritional status Receptors in ovary & liver Both Lactogenic in mammary gland

  14. Soares et al. 1998, Biol Reprod 58: 273

  15. Systemic Versus Local Utero-ovarian Pathway for PGF2a Induced Luteolysis In the absence of pregnancy, the uterus produces a luteolysin which passes to the ovaries and causes regression of the corpus luteum, thereby ending the estrous cycle. A number of studies have demonstrated the luteolytic properties of prostaglandin F2a and proposed that it is the uterine luteolysin. Blood vessesls of the female reproductive tract form a unique network with a large common contact area between veins and arteries in most domestic farm species. For many substances, a local transfer from veins to arteries, thus short-circuiting the peripheral blood circulation, has been demonstrated. This maybe critical since much of the uterine PGF2a can be cleared from the circulation by metabolism to 15-keto-13, 14 dihydroprostaglandin F2a metabolite in one passage through the lungs (cow, ewe).

  16. Uterine PGF2a can the reach the corpus luteum by three possible pathways 1. Systemic utero-ovarian (passage through lungs) 2. Local utero-ovarian (ovarian artery and uterine vein) 3. Local uterine lymphatic vessels

  17. Why must the equine embryo migrate between the uterine horns? Veterinary Scope 1, 1976

  18. Veterinary Scope 1, 1976

  19. Veterinary Scope 1, 1976

  20. Bovine Uteroovarian Vasculature Veterinary Scope 1, 1976

  21. Veterinary Scope 1, 1976

  22. Maternal Recognition of Pregnancy in the Gilt In the cyclic gilt, luteal regression begins on about day 15 with plasma progesterone concentrations declining to basal levels (1 ng/ml or less) by day 17 to 18. Bilateral hysterectomy before day 16 results in prolonged luteal function for periods equal to or longer than 114 days. However, unilateral pregnancy fails in pigs by 21 days in the presence of a non-gravid uterine horn. One fourth of the one uterine horn approached the minimal quantity of uterine tissue necessary for bilateral luteal regression in the pig. The results of studies indicating that concetuses must be present in both uterine horns (2 per horn) for pregnancy to be established indicate a combined and local uterro-ovarian pathway. In swine, PGF2a is converted into an inactive metabolite, 15 keto - 13, 14 dihydro-prostaglandin F2a, by the lungs as it is in other species. However, only 18% of the PGF2a released is metabolized in one passage through the lungs in comparison to 99% in the lungs of the ewe. Therefore active PGF2a can reach the contralateral ovary by a systemic route in the pig thereby causing luteolysis on both ovaries.

  23. PGF2a is luteolytic in the pig when given after Day 12 of the cycle or pregnancy. The CL of the pig may remain refractory to PGF2a until LH begins to dissociate from the luteal cell receptors. It is thought that conformational changes within the luteal cells facilitate PGF2a binding. The PGF2a alters adenylate cyclase system to inhibit progesterone secretion and activate lysosomal enzymes to cause morphological regression of the luteal cells. Maternal Recognition of pregnancy occurs on about Day 12 in the pig. Flushing of embryos from the uterine horns after Day 12 results in an extension of the diestrous period. Conceptus estrogen synthesis (estrone, estradiol-17b and estriol), as well as possible effects of catechol estrogens, on Day 12 coincident with rapid elongation of the blastocyst is the maternal recognition signal. This production of estrogen is reinforced by a second period of synthesis and release between Day 15 to 18 which sustains pregnancy till term. Injection of exogenous estrogen on Day 11 and 14 through 16 will stimulate pseudopregnancy (prolonged CL function in the absence of any embryo) for an equivalent or slightly longer period than pregnancy.

  24. Control of luteolysis or timing is regulated by progesterone stimulation and the down-regulation of progesterone receptor in the uterine surface epithelium and glands.

  25. P4 (ng/ml) PGF2a (1000 pg/ml) P4 (ng/ml) P4 (ng/ml) PGF2a (1000 pg/ml) 18 2 1.5 12 1 .5 6 P4 (ng/ml) 3 12 8 2 4 1

  26. COX-2 Gene Expression During Estrous Cycle and Early Pregnancy b b Fold Difference in Gene Expression Day Effect (P < .0001) b a a a Day Days with differ superscripts differ significantly (P < 0.05)

  27. NF-kB Pathway

  28. Note the loss of progesterone receptor from the surface and glandular epithelium on Day 10 Progesterone receptor on Day 0 of the estrous cycle of the pig

  29. IL-1b IL-1R IL-1RAP Inducible Kinase Ubiquitination and Degradation Phosphorylation of IkB IkBa IKKg IKKa IKKb P50 Nucleus IkBa P65 NF-kB P50 Translocation to Nucleus P65 Transcription NF-kB responsive genes PR

  30. IL-1b IL-1RAP IL-1R Estrogen Inducible Kinase Ubiquitination and Degradation Phosphorylation of IkB IkBa IKKg IKKa IKKb P50 Nucleus IkBa IL-8 TNF-a LIF KGF COX-2 Integrins P65 NF-kB ER P50 Translocation to Nucleus P65 Transcription NF-kB responsive genes

  31. Conceptus estrogen production appears to reduce the levels of PGF2a in the uter-oovarian vein in pregnant animals in comparison to nonpregnant gilts. However, the levels of PGF2a found in the uterine lumen during Days 12 through 18 are extremely elevated in pregnant compared to nonpregnant gilts Pregnant Nonpregnant Bazer et al. 1982, Control of Reproduction in the Pig, p227

  32. There are two periods of estrogen release by the conceptuses in the pig. A sharp but short release on Day 12, followed by a more sustained increase from Day 15 to 30.

  33. Loss of progesterone receptor in the uterine epithelium allow an increase in the presence of estrogen receptor.

  34. How is the release of a large quantity of estrogen prevented from having a systemic effect like stimulating uterine myometrial contractions?

  35. Geisert et al. 1990, J. Reprod Fert Suppl. 40:293

  36. The Theory of Maternal Recognition of Pregnancy in the Pig was First Proposed by Bazer and Thatcher (1977) In nonpregnant pigs, progesterone enhances and/or induces PGF2a synthesis by the uterine endometrium and secretion is associated with the elevated plasma estradiol concentrations (ovarian) between Day 12 and 18 of the cycle. Secretion of PGF2a in mid-luteal phase is primarily in an endocrine direction (uterine capillaries). The increased levels of PGF2a lead to luteolysis. In pregnant pigs, progesterone stimulates PGF2a in the endometrium as in nonpregnant pigs. However, estrogen production by pig conceptuses (local uterine effect) alters direction of PGF2a movement so that it remains in the uterine lumen (exocrine secretion). Maintenance of PGF2a in exocrine direction would prevent PGF2a from entering the uterine venous drainage. Therefore, PGF2a synthesis is not inhibited but compartmentalized. It is also significant that histotroph (protein in lumen) is also maintained in an exocrine direction.

  37. Immunocytochemical staining for uteroferrin in the porcine endometrium Day 15 of the estrous cycle Note presence of stain in the stroma and not in the uterine lumen. This is an example of endocrine secretion! Note presence of staining in the lumen of glands. This is an example of exocrine secretion! Day 15 of pregnancy Chen et al. 1975, Biol Reprod 13:304

  38. Pig Conceptuses Protein Secretion Day 10.5 Day 11.5 Retinoic Binding Protein Interferon-g Godkin et al. 1982, Biol Reprod 27:977

  39. Endometrial fluorescence following systemic treatment of gilts with Evans Blue Day 12 of Pregnancy Day 15 of Cycle Day 15 of Pregnancy There are distinct changes in bloodflow during early pregnancy. Keys et al, 1986, Biol Reprod 34:405

  40. IGF-I IGF-BP Geisert and Yelich, 1997, J. Reprod Fert Suppl. 52:133

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