Progesterone (P4)




Introduction

Source: Placenta (not the main source in all species during pregnancy e.g., goat, cat, dog, and camelid), CL (main source in all species).
Sex steroids: Includes Progesterone, E2, and testosterone.

Steroidogenesis

These hormones are produced by the process of steroidogenesis from cholesterol (27-C). Cholesterol is converted into Pregnenolone (21-C), then Pregnenolone is converted into Progesterone (21-C), Then Progesterone is converted into testosterone (19-C), then testosterone is converted into E2 (18-C).
Steroids hormones have 4 benzene rings. All the above-mentioned hormones have 4 (a, b, c, and d) rings known as Cyclo-pentane-perhydro-phenanthrene.
Cyclo-pentane-perhydro-phenanthrene is the common structure of all above-mentioned hormones.
Progestogens: Progesterone is a part of group named progestogens or progestagens.
Progestin: Synthetic P4 is known as Progestin.
Androgen: Testosterone is a part of a group named androgens.
Estrogen: E2 is a part of a group named estrogen. Other members of this group include E1 and E3.
All these are sex steroids (P4, T, and E2). 

Functions of P4

In female

  • It is responsible for the maintenance of pregnancy by
  1. Forming a mucus plug known as cervical seal or seal of pregnancy.
  2. Close the cervix.
  3. Decrease the local immunity of the uterus (it prevents fetal rejection).
  4. Causes the growth of the endometrium (uterus)
  • When the level of P4 is high in the blood, it decreases GnRH, FSH, and LH.
  • It suppresses estrus behavior.
  • It is responsible for the formation of estradiol (E2) receptors on the brain. This formation phenomenon is known as the priming of the brain for the action of E2 by P4.
  • It is responsible for the growth of mammary glands (growth of alveoli).
  • It has some maternal behavior.
  • Uterine milk is produced by P4.

In male

 Source: No major source
  • It plays role in sperm capacitation.
  • It plays role in spermiogenesis.

Clinical uses of P4

  1. It is responsible for pregnancy maintenance.
  2. In any species, if abortion happens at a specific time, measure the blood level of P4. Then in next conceivement starts P4 supplementation before that time.
  3. We use it if abortion starts/fetus, uterus or placenta is infected (placentitis). In the case of ruminants, let the abortion happens.
  4. In mare, if pus comes from the uterus, it indicates the start of abortion. If the fetus is alive, then give P4 and other treatments for the prevention of abortion.
  5. It is used to suppress estrus in mares especially racing mares. (administer by inoculation or orally).
  6. It can be fed to beef/feedlot heifers for fattening but only in females.

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