Maternal recognition of pregnancy

Dr Alok Kumar

Assistant Professor cum Jn. Scientist

Veterinary Gynaecology and Obstetrics

alok9alright@gmail.com

Definition of MRP

• Presence of viable, developing embryo(s), prevents CL from regressing and therefore in polyestrous species inhibits return of estrus. The phenomenon is describes as “Maternal recognition of pregnancy (MRP)” by Short (1969)

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• The critical period for signaling by the conceptus to block luteolysis and allow pregnancy to be established is called Maternal recognition of pregnancy (MRP).

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Luteolysis in cow and ewe

• Frequency of PGF_2α release
• Threshold – 05 pulses/24 hours
• Pregnant ewe – 1.3 pulses/24 hours ( during 14 – 15 days)
• Non pregnant ewe – 7.6 pulses/24 hours

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Days of MRP

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MRP in EWE

• Protein, molecular weight of 19- 24 Kda
• Ovine trophoblast protein (oTP-1)
• Now classified as tau interferon

(oIFN-tau)

• Maximum secretion occurring

between days 10 of gestation

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The antiluteolytic factor produced by the ovine conceptus is characterized by

MRP in cattle

• The antiluteolytic factor produced by the bovine conceptus is characterized by:
• Protein, molecular weight of 24,000 da
• Bovine trophoblast protein (bTP-1)
• Now classified as tau interferon (bIFN-tau)
• Maximum secretion occurring between days 16 and 19 of gestation
• It is first secreted at the time of elongation of the blastocyst
• Continues to be secreted until day 38 of gestation
• EPSI – Endometrial PG synthetase inhibitor – reduced PG production

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Mechanism of MRP in cow and ewe

• IFN-tau secreted by embryo
• silencing the transcription of the estrogen receptor alpha gene in uterine luminal and superficial glandular epithelial
• Reduction of Estrogen-induced expression of oxytocin receptors in these cells.
• Indirectly suppresses the expression of oxytocin receptors in endometrial epithelial cells.
• Oxytocin of luteal and pituitary origin can thus no longer bind to the uterus
• Reduction in the pulsatile secretion of PGF2α

MRP in Goat

• The caprine conceptus secretes a protein originally designated cTP-1

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• Recently named as cIFN-tau

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• secreted between days 16 and 21 of gestation.

MRP pig

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• Spacing and elongation of conceptus
• Production of E₂
• E₂ acts as Luteotrophic factor
• Endocrine – exocrine model of MRP

MRP in pig

• Spacing - Post uterine entry on day 4, embryos start migrating throughout both uterine horns so that by day 12 they have more or less become evenly distributed.

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• porcine conceptus has been shown to convert progesterone to estrone and estradiol-17 beta.

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• The production of estrogens increases with the rapid elongation of the blastocyst, which may reach a length of 80 to 100 cm each between days 12 and 15.

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• Spacing and Elongation - the conceptuses are able to influence locally a large surface of the endometrium

The luteotrophic effects of estrogen include

1. maintenance of LH receptors in the CLs
2. Secretion of prostaglandin E2 to protect the CLs against the luteolytic action of PGF2α
3. Altering the transport of PGF2α from an endocrine (towards the vasculature) to an exocrine (into the uterine lumen) direction
4. PreventingPGF2α from reaching the CLs.

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Estrogen-induced prolactin receptors in the endometrium might facilitate this redirecting.

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The fate of the intrauterine PGF2α - fetal membranes readily metabolizes it to PGFM (15-keto-13, 14-dihydro-PGF2α), which is inactive.

MRP in pig

MRP in Horses

Exact machanism in not yet clear

Involves

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1. Estrogen production

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• Migration of conceptus

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• Suppression of prostaglandin synthatase 2 activity

MRP in Horses

• Suppression of uterine PGF production (till day – 16) includes

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1. conceptus-directed downregulation of endometrial prostaglandin synthase 2 activity
2. a posttranscriptional inhibition of endometrial oxytocin-receptor expression

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• Migration of the spherical conceptus within the uterine lumen until it becomes ‘fixed’ at 16 to 18 days of gestation at the base of the uterine horn.

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• E₂ indirectly influences production of other hormones and substances necessary for MRP

References and suggested reading

• Books
• Reproduction in Farm Animals (E.S.E. Hafez & B. Hafez)
• Veterinary Reproduction and Obstetrics (David E. Noakes)
• Reproductive Technologies in Farm Animals (Ian Gordon)

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Articles

• Short RV. Implantation and the Maternal Recognition of Pregnancy in Foetal Autonomy. London: J & A Churchill; 1969.
• Bazer FW. J Anim Sci and Biotechn. 2013;4:23.
• Stout TAE. Theriogenology. 2016;86:349.