�Lecture – 03��Applied endocrinology of pregnancy�

Endocrinological structures during pregnancy

• Carpus luteum
• Placenta

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• Both structures act as temporary endocrine organ.
• Perform steroidogenic activity
• Steroidogenic activity of placenta is observed in majority of mammals except DOG

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Hormones of pregnancy

• Mare and Ewe derives their progesterone from placenta at later half of pregnancy known as luteo-placental shift

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• Serum progesterone level remains constant throughout pregnancy in cow and ewe but in Sow, its high level is observed during early stage of pregnancy

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1. Progesterone

• Principal hormone for pregnancy maintenance
• During initial stage of pregnancy, functional CL releases progesterone
• CL persist throughout pregnancy in all species except in mare
• Cow, Doe and Sow – primary source of progesterone is CL

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Role of progesterone during pregnancy

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It controls various essential functions during gestation period

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• Endometrial differentiation
• Myometrial quiescence
• Closure of the cervix
• Local immunotolerance in the pregnant uterus

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2. Placental estrogens

• Estradiol-17β is the most relevant form of estrogen found in dam blood
• In sheep and cattle Estrone and sulphonated form of estrogen remains high during gestation period
• Ruminanats and camelids, the maternal estrogen rises at uniform rate
• Sudden peak of estrogen during mid gestation is physiological in Equines
• Species specific placental estrogens in equines is termed as equilin and equilenin

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Placental synthesis of estrogens

• Bovine placenta synthesizes estrogen from cholesterol (precursor)
• Equine placentae can not synthesize estrogen like bovine, due to its dependency on fetal gonads for C₁₉ precursor
• Steroidogenesis associated with pregnancy in horse is a dependent process involving placenta and fetus which led to the terminology - feto-placental unit

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Functions of placental estrogens

Ruminants including the role of placental estrogens

• Preparation of the birth canal for

parturition

• Myometrial excitability at advance stage
• Mammary gland development during late

gestation

Maternal estrogen levels start to increase significantly between days 120-150.

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In ruminants sulphonated estrogen level remains higher throughout pregnancy exept immediate pre or intrapartal period

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Androgens

C₁₉ steroids

• Androstenedione
• Dehydroepiandrosterone (DHEA)
• Sulfonated DHEA (DHEAS)

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C₁₉ steroids act as precursors for the synthesis of bioactive androgens

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C₁₉ steroids serves as precursor for placental estrogen synthesis in equines

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Pregnancy-associated prolactin and growth hormones

In rodents and ruminants these substances named as

• Placental lactogen (PL)
• PRL-like proteins (PLPs)
• PRL-related proteins (PRPs)
• Proliferin (PLF).

Functions

In ruminants associated with

• Development of uterus and mammary gland
• Transport of nutrients from the dam to the fetal compartment

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Relaxin/insulin-like family peptides

Commonly denoted by – RLNs

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Source of RLNs

• Placenta – Horse, cat, dog, rabbit and camel
• Carpus luteum – Pig and rodents

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RLNs functions

Function of RLNs are different in various species

• Decidualization
• Immunomodulation
• Quiescence of the myometrium
• Maternal circulatory adaptations of pregnancy
• Stimulation of angiogenesis

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• uterine and vaginal growth
• Development of the mammary gland and/or nipples

During prepartal period

• Relaxation of the pubic ligament
• Preparation of the vaginal canal for

parturition.

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Endocrinology of pregnancy in mare

A different species to deal with

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Maintenance of progesterone concentration during pregnancy

Early stage of pregnancy, Primary corpus luteum secrets progesterone followed by secondary carpora lutea

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Post day 150 matured placenta takes up secretion of progesterone sufficient for physiological need of pregnancy, phenomena is termed as luteo-placental shift

Courtesy - Kritika’s drawing

Estrogen during pregnancy

Plasma estrogen concentration remains low during first trimester, gradually increases to peak between 9^th to 11^th month, thereafter declines near foaling

Endocrinology of pregnancy in mare

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Thanks!

Any questions?

You can find me at:

• alok9alright@gmail.com

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Dr Alok Kumar

Assistant Professor cum jr. Scientist

Veterinary Gynaecology and Obstetrics

Bihar Veterinary College, BASU. Patna